Published papers

Schooling is a collective behavior that relies on a fish's ability to sense and respond to the other fish around it. Previous work has identified ‘rules’ of schooling – attraction to neighbors that are far away, repulsion from neighbors that are too close and alignment with neighbors at the correct distance – but we do not understand well how these rules emerge from the sensory physiology and behavior of individual fish. In particular, fish use both vision and their lateral lines to sense each other, but it is unclear how much they rely on information from these sensory modalities to coordinate schooling behavior. To address this question, we studied how the schooling of giant danios (Devario aequipinnatus) changes when they are unable to see or use their lateral lines. We found that giant danios were able to school without their lateral lines but did not school in darkness. Surprisingly, giant danios in darkness had the same attraction properties as fish in light when they were in close proximity, indicating that they could sense nearby fish with their lateral lines. However, they were not attracted to more distant fish, suggesting that long-distance attraction through vision is important for maintaining a cohesive school. These results help us expand our understanding of the roles that vision and the lateral line play in the schooling of some fish species.

Locomotion is thermally sensitive in ectotherms and therefore it is typically expressed differently among thermally heterogenous environments. Locomotion is a complex function, and whereas physiological and behavioral traits that influence locomotor performance may respond to thermal variation throughout life, other contributing traits, like body shape, may have more restricted responses. How morphology affects locomotor performance under variable temperature conditions is unknown. Here, we investigated 3 genetically distinct strains of zebrafish, Danio rerio (AB, WIK, and Tu) with a shared multi-generational history at 28 °C. After rearing fish at 28 °C, we measured prolonged swimming speed (Ucrit) at each of 6 temperatures (between 16 °C and 34 °C). Speed was strongly positively correlated among temperatures, resulting in most among individual variation being temperature-independent (i.e., fish were relatively fast or slow across all temperatures). However, we also detected significant variation along 2 axes reflecting temperature-dependent variation. Although strains differed in mean swimming performance, within strain (among-individual) patterns of speed variation were markedly consistent. Body shape and size explained significant variation among individuals in both temperature-independent and temperature-dependent axes of swimming speed variation. Notably, morphological traits that were most strongly associated with temperature-independent performance variation (i.e., faster–slower) differed from those associated with temperature-dependent (i.e., hotter–colder) variation. Further, there were significant differences among strains in both the direction and strength of association for specific morphological traits. Our results suggest that thermally heterogenous environments could have complex effects on the evolution of traits that contribute to whole organism performance traits.

Seawater hypoxia is increasing globally and can drive declines in organismal performance across a wide range of marine taxa. However, the effects of hypoxia on early life stages (e.g., larvae and juveniles) are largely unknown, and it is unclear how evolutionary and life histories may influence these outcomes. Here, we addressed this question by comparing hypoxia responses across early life stages of three cnidarian species representing a range of life histories: the reef-building coral Galaxea fascicularis, a broadcast spawner with horizontal transmission of endosymbiotic algae (family Symbiodiniaceae); the reef-building coral Porites astreoides, a brooder with vertical endosymbiont transmission; and the estuarine sea anemone Nematostella vectensis, a non-symbiotic broadcast spawner. Transient exposure of larvae to hypoxia (dissolved oxygen < 2 mg L−1 for 6 h) led to decreased larval swimming and growth for all three species, which resulted in impaired settlement for the corals. Coral-specific responses also included larval swelling, depressed respiration rates, and decreases in symbiont densities and function. These results indicate both immediate and latent negative effects of hypoxia on cnidarian physiology and coral–algal mutualisms specifically. In addition, G. fascicularis and P. astreoides were sensitized to heat stress following hypoxia exposure, suggesting that the combinatorial nature of climate stressors will lead to declining performance for corals. However, sensitization to heat stress was not observed in N. vectensis exposed to hypoxia, suggesting that this species may be more resilient to combined stressors. Overall, these results emphasize the importance of reducing anthropogenic carbon emissions to limit further ocean deoxygenation and warming.

The characteristics of infected animals, including their odour, appearance, behaviour and sound, greatly differ from those of uninfected conspecifics. These differences can serve as cues to recognize and avoid infected individuals and minimize the risk of infection. Avoidance of infected conspecifics is a risk-sensitive behaviour that can be influenced by various factors, including sensory cues, which are poorly understood in fish. We investigated the ability of two populations of wild-caught pumpkinseed sunfish, Lepomis gibbosus, to distinguish between conspecifics infected with parasitic worms and uninfected individuals in two-choice experiments using visual and chemical cues separately. One population was from a lake without parasites (parasite-naïve), whereas the second population originated from a lake with a high prevalence of trematode and cestode worms (parasite-experienced). Both populations preferred to be with conspecifics, regardless of their infection level, over being alone when given visual cues but avoided conspecifics and preferred to be alone when given chemical cues, suggesting that visual and chemical cues are not redundant. Fish from neither population showed a preference between infected and uninfected conspecifics when given visual cues. However, there was a large interindividual variation in preference for chemical cues: some fish preferred uninfected conspecifics, whereas others preferred infected fish. On average, naïve fish avoided infected conspecifics, whereas experienced fish did not show any preferences, suggesting that fish from lakes with high prevalence of infection are habituated to infection cues. We suggest that pumpkinseeds use chemical rather than visual cues to discriminate between infected and uninfected conspecifics during shoaling decisions. Our study highlighted the importance of considering different sensory cues as well as environmental parasite abundance when studying avoidance and shoaling behaviours, especially considering the growing impacts of global changes on the sensory landscape and parasite abundance in freshwater ecosystems.

The effects of turbidity and sedimentation stress on early life stages of corals are poorly understood, particularly in Atlantic species. Dredging operations, beach nourishment, and other coastal construction activities can increase sedimentation and turbidity in nearby coral reef habitats and have the potential to negatively affect coral larval development and metamorphosis, reducing sexual reproduction success. In this study, we investigated the performance of larvae of the threatened Caribbean coral species Orbicella faveolata exposed to suspended sediments collected from a reef site in southeast Florida recently impacted by dredging (Port of Miami), and compared it to the performance of larvae exposed to sediments collected from the offshore, natal reef of the parent colonies. In a laboratory experiment, we tested whether low and high doses of each of these sediment types affected the survival, settlement, and respiration of coral larvae compared to a no-sediment control treatment. In addition, we analyzed the sediments used in the experiments with 16S rRNA gene amplicon sequencing to assess differences in the microbial communities present in the Port versus Reef sediments, and their potential impact on coral performance. Overall, only O. faveolata larvae exposed to the high-dose Port sediment treatment had significantly lower survival rates compared to the control treatment, suggesting an initial tolerance to elevated suspended sediments. However, significantly lower settlement rates were observed in both Port treatments (low- and high-dose) compared to the control treatment one week after exposure, suggesting strong latent effects. Sediments collected near the Port also contained different microbial communities than Reef sediments, and higher relative abundances of the bacteria Desulfobacterales, which has been associated with coral disease. We hypothesize that differences in microbial communities between the two sediments may be a contributing factor in explaining the observed differences in larval performance. Together, these results suggest that the settlement success and survival of O. faveolata larvae are more readily compromised by encountering port inlet sediments compared to reef sediments, with potentially important consequences for the recruitment success of this species in affected areas.

The evolutionary consequence of changes to physical activity upon skeletal muscle physiology remains unexplored. Using the Mexican cavefish, we find that loss of moderate-to-vigorous swimming following cave colonization results in broad shifts in skeletal muscle investment—away from muscle mass and instead toward fat and sugar accumulation—ultimately decreasing muscle fiber twitch kinetics. Surprisingly though, cavefish possess marked muscular endurance, reaching maximal swimming speeds rivaling their river-dwelling counterpart. Multi-omic analysis revealed carbohydrate metabolic reprogramming as a contributing component, most notably elevated abundance and phosphorylation of the enzyme phosphoglucomutase-1—a likely consequence of cave-specific hypoxia. These findings emphasize the impact multiple selective pressures have on skeletal muscle physiology, providing insight into the extremes of skeletal muscle plasticity under diverse environmental conditions.

Adult zebrafish have an innate ability to recover from severe spinal cord injury. Here, we report a comprehensive single nuclear RNA sequencing atlas that spans 6 weeks of regeneration. We identify cooperative roles for adult neurogenesis and neuronal plasticity during spinal cord repair. Neurogenesis of glutamatergic and GABAergic neurons restores the excitatory/inhibitory balance after injury. In addition, a transient population of injury-responsive neurons (iNeurons) show elevated plasticity 1 week post-injury. We found iNeurons are injury-surviving neurons that acquire a neuroblast-like gene expression signature after injury. CRISPR/Cas9 mutagenesis showed iNeurons are required for functional recovery and employ vesicular trafficking as an essential mechanism that underlies neuronal plasticity. This study provides a comprehensive resource of the cells and mechanisms that direct spinal cord regeneration and establishes zebrafish as a model of plasticity-driven neural repair.

Anthropogenic impacts can lead to increased temperatures in freshwater environments through thermal effluent and climate change. Thermal preference of aquatic organisms can be modulated by abiotic and biotic factors including environmental temperature. Whether increased temperature during embryogenesis can lead to long-term alterations in thermal preference has not been explicitly tested in native freshwater species. Lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish were incubated at natural and elevated temperatures until hatching, following which, all groups were moved to common garden conditions (15°C) during the post-hatching stage. Temperature preference was determined at 8 months (Lake whitefish only) and 12 months of age (both species) using a shuttle box system. Round whitefish preferred a cooler temperature when incubated at 2 and 6°C compared with 0.5°C. Lake whitefish had similar temperature preferences regardless of age, weight and incubation temperature. These results reveal that temperature preference in freshwater fish can be programmed during early development, and that round whitefish may be more sensitive to incubation temperature. This study highlights the effects that small increases in temperature caused by anthropogenic impacts may have on cold-adapted freshwater fish.

The extraordinary breath-hold diving capacity of crocodilians has been ascribed to a unique mode of allosterically regulating hemoglobin (Hb)-oxygenation in circulating red blood cells. We investigated the origin and mechanistic basis of this novel biochemical phenomenon by performing directed mutagenesis experiments on resurrected ancestral Hbs. Comparisons of Hb function between the common ancestor of archosaurs (the group that includes crocodilians and birds) and the last common ancestor of modern crocodilians revealed that regulation of Hb-O2 affinity via allosteric binding of bicarbonate ions represents a croc-specific innovation that evolved in combination with the loss of allosteric regulation by ATP binding. Mutagenesis experiments revealed that evolution of the novel allosteric function in crocodilians and the concomitant loss of ancestral function were not mechanistically coupled and were caused by different sets of substitutions. The gain of bicarbonate sensitivity in crocodilian Hb involved the direct effect of few amino acid substitutions at key sites in combination with indirect effects of numerous other substitutions at structurally disparate sites. Such indirect interaction effects suggest that evolution of the novel protein function was conditional on neutral mutations that produced no adaptive benefit when they first arose but that contributed to a permissive background for subsequent function-altering mutations at other sites. Due to the context dependence of causative substitutions, the unique allosteric properties of crocodilian Hb cannot be easily transplanted into divergent homologs of other species.

Understanding the resilience of ectotherms to high temperatures is essential because of the influence of climate change on aquatic ecosystems. The ability of species to acclimate to high temperatures may determine whether populations can persist in their native ranges. We examined physiological and molecular responses of juvenile brook trout (Salvelinus fontinalis) to six acclimation temperatures (5, 10, 15, 20, 23 and 25°C) that span the thermal distribution of the species to predict acclimation limits. Brook trout exhibited an upregulation of stress-related mRNA transcripts (heat shock protein 90-beta, heat shock cognate 71 kDa protein, glutathione peroxidase 1) and downregulation of transcription factors and osmoregulation-related transcripts (nuclear protein 1, Na+/K+/2Cl− co-transporter-1-a) at temperatures ≥20°C. We then examined the effects of acclimation temperature on metabolic rate (MR) and physiological parameters in fish exposed to an acute exhaustive exercise and air exposure stress. Fish acclimated to temperatures ≥20°C exhibited elevated plasma cortisol and glucose, and muscle lactate after exposure to the acute stress. Fish exhibited longer MR recovery times at 15 and 20°C compared with the 5 and 10°C groups; however, cortisol levels remained elevated at temperatures ≥20°C after 24 h. Oxygen consumption in fish acclimated to 23°C recovered quickest after exposure to acute stress. Standard MR was highest and factorial aerobic scope was lowest for fish held at temperatures ≥20°C. Our findings demonstrate how molecular and physiological responses predict acclimation limits in a freshwater fish as the brook trout in the present study had a limited ability to acclimate to temperatures beyond 20°C.

The expansion of hydropower infrastructure has increased the prevalence of total dissolved gas (TDG) supersaturation, posing significant threats to aquatic organisms. However, the impacts of TDG on immune function and energy metabolism across fish life stages remain insufficiently characterized. This study evaluated TDG effects on Danio rerio and Schizothorax davidi by integrating development, hatching, survival, locomotion and transcriptomic analyses across embryos and juveniles. Exposure to 130 % TDG significantly reduced embryonic survival and hatching rates in both species, with larvae displaying gas bubble trauma (GBT), growth inhibition, and elevated heart rates. Transcriptomic data revealed species-specific responses: Danio rerio larvae exhibited activation of Toll-like receptor-mediated innate immunity and suppressed ATP synthase gene expression, indicating energy metabolism impairment, whereas Schizothorax davidi showed complement system dysregulation and compromised protein homeostasis. Acute lethality tests indicated greater TDG sensitivity in Schizothorax davidi than Danio rerio. Both species experienced impaired swimming capacity and reduced metabolic performance, with distinct molecular adaptation strategies observed in gill tissues. Danio rerio prioritized energy allocation to antigen processing, while Schizothorax davidi relied on low-energy innate pathways. These findings highlight species- and stage-specific mechanistic disruptions induced by TDG supersaturation. The results provide crucial insights for ecological risk assessment and inform conservation strategies for aquatic species in regulated river systems.

During hydraulic fracturing, wastewaters - termed flowback and produced water (FPW) - are created as a by-product during hydrocarbon extraction. Given the large volumes of FPW that a single well can produce, and the history of FPW release to surface water bodies, it is imperative to understand the hazards that hydraulic fracturing and FPW pose to aquatic biota. Using rainbow trout embryos as model organisms, we investigated impacts to cardio-respiratory system development and function following acute (48 h) and sub-chronic (28-day) FPW exposure by examining occurrences of developmental deformities, rates of embryonic respiration (MO2), and changes in expression of critical cardiac-specific genes. FPW-exposed embryos had significantly increased rates of pericardial edema, yolk-sac edema, and tail/trunk curvatures at hatch. Furthermore, when exposed at three days post-fertilization (dpf), acute 5% FPW exposures significantly increased embryonic MO2 through development until 15 dpf, where a switch to significantly reduced MO2 rates was subsequently recorded. A similar trend was observed during sub-chronic 1% FPW exposures. Interestingly, at certain specific developmental timepoints, previous salinity exposure seemed to affect embryonic MO2; a result not previously observed. Following acute FPW exposures, embryonic genes for cardiac development and function were significantly altered, although at termination of sub-chronic exposures, significant changes to these same genes were not found. Together, our evidence of induced developmental deformities, modified embryonic MO2, and altered cardiac transcript expression suggest that cardio-respiratory tissues are toxicologically targeted following FPW exposure in developing rainbow trout. These results may be helpful to regulatory bodies when developing hazard identification and risk management protocols concerning hydraulic fracturing activities.

Many studies have investigated how nanoplastics (NPs) exposure mediates nerve and intestinal toxicity through a dysregulated brain-gut axis interaction, but there are few studies aimed at alleviating those effects. To determine whether and how vitamin D can impact that toxicity, fish were supplemented with a vitamin D-low diet and vitamin D-high diet. Transmission electron microscopy (TEM) showed that polystyrene nanoplastics (PS-NPs) accumulated in zebrafish brain and intestine, resulting in brain blood–brain barrier basement membrane damage and the vacuolization of intestinal goblet cells and mitochondria. A high concentration of vitamin D reduced the accumulation of PS-NPs in zebrafish brain tissues by 20% and intestinal tissues by 58.8% and 52.2%, respectively, and alleviated the pathological damage induced by PS-NPs. Adequate vitamin D significantly increased the content of serotonin (5-HT) and reduced the anxiety-like behavior of zebrafish caused by PS-NPs exposure. Virus metagenome showed that PS-NPs exposure affected the composition and abundance of zebrafish intestinal viruses. Differentially expressed viruses in the vitamin D-low and vitamin D-high group affected the secretion of brain neurotransmitters in zebrafish. Virus AF191073 was negatively correlated with neurotransmitter 5-HT, whereas KT319643 was positively correlated with malondialdehyde (MDA) content and the expression of cytochrome 1a1 (cyp1a1) and cytochrome 1b1 (cyp1b1) in the intestine. This suggests that AF191073 and KT319643 may be key viruses that mediate the vitamin D reduction in neurotoxicity and immunotoxicity induced by PS-NPs. Vitamin D can alleviate neurotoxicity and immunotoxicity induced by PS-NPs exposure by directionally altering the gut virome. These findings highlight the potential of vitamin D to alleviate the brain-gut-virome disorder caused by PS-NPs exposure and suggest potential therapeutic strategies to reduce the risk of NPs toxicity in aquaculture, that is, adding adequate vitamin D to diet.

Energy efficiency is a key component of movement strategy for many species. In fish, optimal swimming speed (Uopt) is the speed at which the mass-specific energetic cost to move a given distance is minimised. However, additional factors may influence an individual's preferred swimming speed (Upref). Activities requiring consistent sensory inputs, such as food finding, may require slower swimming speeds than Uopt. Further, although the majority of fish display some form of social behaviour, the influence of social interactions on Upref remains unclear. It is unlikely that all fish within a group will have the same Upref, and fish may therefore compromise individual Upref to swim with a conspecific. This study measured the Uopt, Upref and Upref in the presence of a conspecific (Upair) of pile perch, Phanerodon vacca, a non-migratory coastal marine generalist. Uopt was significantly higher than, and was not correlated with, Upref. Fish therefore chose to swim at speeds below their energetic optimum, possibly because slower swimming allows for greater awareness of surroundings. Mean Upair was significantly lower than the Upref of the faster fish in each pair but did not differ significantly from the Upref of the slower fish. Therefore, faster fish appear to slow their speed to remain with a slower conspecific. Our study suggests that environmental factors, including social surroundings, may be more important than energetic efficiency for determining swim speed in P. vacca. Further studies of fish species from various habitats will be necessary to elucidate the environmental and energetic factors underpinning Upref.

Artificial light at night (ALAN) is a pervasive anthropogenic pollutant, increasing in intensity and scope. While its impacts on biological and ecological processes are well documented among terrestrial taxa, marine organisms have received less attention, though a quarter of the world’s coastlines are affected by artificial light at night. Furthermore, the intergenerational effects of artificial light at night have never been documented in the wild. We conducted a field manipulation experiment in the lagoon of Mo’orea, French Polynesia, using LED (Light-Emitting Diode) lights to test artificial light at night’s effects on adult life-history and offspring fitness of the coral reef anemonefish Amphiprion chrysopterus. Exposing adults and embryos to LEDs, we found artificial light at night enhanced adult growth but did not alter measured reproductive traits, including fecundity. We observed reduced parental reproductive hormone levels with downstream consequences for offspring. Hatching success was unchanged, but offspring showed reduced embryonic heart rate and yolk sac size, and drastically diminished larval escape responses and swimming performance. This comprehensive study is the first in a wild organism to demonstrate combined intergenerational and direct negative effects of artificial light at night, highlighting limited compensatory capacity. These impacts could impair larval recruitment and hinder population replenishment in reef fish. This research underscores urgent need for conservation and management to address artificial lighting impacts.

Corals are under siege by both local and global threats, creating a worldwide reef crisis. Cryopreservation is an important intervention measure and a vital component of the modern coral conservation toolkit, but preservation techniques are currently limited to sensitive reproductive materials that can only be obtained a few nights per year during spawning. Here, we report the successful cryopreservation and revival of cm-scale coral fragments via mL-scale isochoric vitrification. We demonstrate coral viability at 24 h post-thaw using a calibrated oxygen-uptake respirometry technique, and further show that the method can be applied in a passive, electronics-free configuration. Finally, we detail a complete prototype coral cryopreservation pipeline, which provides a platform for essential next steps in modulating post-thaw stress and initiating long-term growth. These findings pave the way towards an approach that can be rapidly deployed around the world to secure the biological genetic diversity of our vanishing coral reefs.

Adult zebrafish are capable of anatomical and functional recovery following severe spinal cord injury. Axon growth, glial bridging and adult neurogenesis are hallmarks of cellular regeneration during spinal cord repair. However, the correlation between these cellular regenerative processes and functional recovery remains to be elucidated. Whereas the majority of established functional regeneration metrics measure swim capacity, we hypothesize that gait quality is more directly related to neurological health. Here, we performed a longitudinal swim tracking study for 60 individual zebrafish spanning 8 weeks of spinal cord regeneration. Multiple swim parameters as well as axonal and glial bridging were integrated. We established rostral compensation as a new gait quality metric that highly correlates with functional recovery. Tensor component analysis of longitudinal data supports a correspondence between functional recovery trajectories and neurological outcomes. Moreover, our studies predicted and validated that a subset of functional regeneration parameters measured 1 to 2 weeks post-injury is sufficient to predict the regenerative outcomes of individual animals at 8 weeks post-injury. Our findings established new functional regeneration parameters and generated a comprehensive correlative database between various functional and cellular regeneration outputs.

Fish protection screens are increasingly being considered as management tools to prevent significant numbers of fish being extracted from Australian rivers at water diversions. Australian design standards specify an approach velocity (the perpendicular flow 8cm in front of the screen) of 0.1 m.s−1. This value was based on studies on juvenile fish, but the extent that it protects larval fish is understudied. The swimming of three ontogenetic stages of Golden perch larvae (protolarvae, postflexion and metalarvae) was observed in front of a screen in a variable speed swimming flume. Approach velocity and water temperature were varied, and the likelihood of impingement and the time for impingement to occur was measured. Swimming behaviours employed by fish to avoid impingement were also quantified. Protolarvae were the most susceptible, with almost 100% impingement at all tested velocities. Impingement became less likely as larvae increased in age. However, at velocities above 0.10 m.s−1 impingement likelihood increased for all stages. The results indicate that if an approach velocity of 0.10 m.s−1 is adhered to, that a critical time of 10 s is available in which larvae may be protected. Larvae implemented key behaviours to avoid impingement, which changed as they developed morphologically. Protolarvae displayed use of hydraulic refuging behaviours, whilst postflexion and metalarvae used a burst and coast strategy. Those that did not implement these behaviours became impinged. Current Australian specifications for fish protection screen design can therefore facilitate the protection of larval Golden perch. Protection improves significantly as larvae develop beyond the protolarval stage.

Ultraviolet (UV) filters are compounds utilized in many manufacturing processes and personal care products such as sunscreen to protect against UV-radiation. These highly lipophilic compounds are emerging contaminants of concern in aquatic environments due to their previously observed potential to bioaccumulate and exert toxic effects in marine ecosystems. Currently, research into the toxic effects of UV filter contamination of freshwater ecosystems is lacking, thus the present study sought to model the effects of acute and chronic developmental exposures to UV filters avobenzone, oxybenzone and octocrylene as well as a mixture of these substances in the freshwater invertebrate, Daphnia magna, at environmentally realistic concentrations. Median 48-hour effect and lethal concentrations were determined to be in the low mg/L range, with the exception of octocrylene causing 50% immobilization near environmental concentrations. 48-hour acute developmental exposures proved to behaviourally impair daphnid phototactic response; however, recovery was observed following a 19-day post-exposure period. Although no physiological disruptions were detected in acutely exposed daphnids, delayed mortality was observed up to seven days post-exposure at 200 μg/L of avobenzone and octocrylene. 21-day chronic exposure to 7.5 μg/L octocrylene yielded complete mortality within 7 days, while sublethal chronic exposure to avobenzone increased Daphnia reproductive output and decreased metabolic rate. 2 μg/L oxybenzone induced a 25% increase in metabolic rate of adult daphnids, and otherwise caused no toxic effects at this dose. These data indicate that UV filters can exert toxic effects in freshwater invertebrates, therefore further study is required. It is clear that the most well-studied UV filter, oxybenzone, may not be the most toxic to Daphnia, as both avobenzone and octocrylene induced behavioural and physiological disruption at environmentally realistic concentrations.

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-quinone) is an environmental transformation product of the widely used rubber tire antioxidant, 6PPD. Found in stormwater runoff, 6PPD-quinone has been reported to cause acute lethality at ≤1 μg/L in salmonids like coho salmon, rainbow trout, and brook trout. Conversely, other species such as Arctic char and brown trout are insensitive, even when exposed to significantly greater concentrations (3.8–50 μg/L). Sensitive species exhibit symptoms such as gasping, spiraling, increased ventilation, and loss of equilibrium, suggesting a possible impact on cardiorespiratory physiology. This study investigated sublethal 6PPD-quinone toxicities, focusing on cardiovascular and metabolic effects in two salmonids of varying sensitivity: a sensitive species, rainbow trout (Oncorhynchus mykiss) and a tolerant species, Arctic char (Salvelinus alpinus). Fish were exposed to measured concentrations of 0.59 or 7.15 μg/L 6PPD-quinone, respectively, in respirometry chambers for 48 h to assess temporal changes in resting oxygen consumption compared to unexposed controls. Following exposure, cardiac ultrasound and electrocardiography characterized cardiac function in vivo, while blood gas analysis examined blood composition changes. In both species, changes in resting oxygen consumption were observed. In rainbow trout only, a decrease in end systolic volume and an increase in passive ventricular filling, cardiac output, and PR interval length were observed, indicating cardiac stimulation. Cardiorespiratory symptoms observed following rainbow trout exposure might partly be driven by a significant increase in methemoglobin, resulting in an impaired ability to oxygenate tissues. This study is the first to examine the effects of 6PPD-quinone exposure on the cardiorespiratory system of salmonid fishes and provides information invaluable to a better understanding of the mechanism of 6PPD-quinone toxicity.

Aging is accompanied by profound changes in energy metabolism, yet the underlying drivers and modulators of these shifts remain incompletely understood. Here, we investigated how life‐history evolution shapes metabolic aging and pharmacological responsiveness by leveraging Drosophila melanogaster lines divergently selected for reproductive timing. We measured organismal oxygen consumption rate and performed untargeted metabolomics in young and old flies of both sexes from long‐lived “O” lines (selected for female late‐life reproduction) and unselected “B” control lines. Males and females from the O lines maintained stable metabolic rates and largely preserved metabolite profiles with age, whereas B line flies showed age‐related increases in oxygen consumption, citrate accumulation, and elevated levels of medium‐ and long‐chain fatty acids, hallmarks of mitochondrial inefficiency and impaired lipid oxidation. Aged B flies also displayed elevated S‐adenosylmethionine, reduced sarcosine, and diminished heme levels, indicating dysregulation of one‐carbon metabolism and impaired heme biosynthesis. Furthermore, Vitamin B6 metabolites, pyridoxamine, pyridoxal, and 4‐pyridoxate, increased with aging only in B line females. Motivated by evidence implicating the renin‐angiotensin system in metabolic aging, we treated flies with the angiotensin‐converting enzyme (ACE) inhibitor lisinopril. Lisinopril prevented the age‐related rise in metabolic rate in B line females, aligning their metabolic phenotype with that of O line flies. This suggests that ACE inhibition may buffer against age‐associated increases in metabolic rate and contribute to enhanced metabolic stability. Our results show that selection for delayed reproduction and increased lifespan modifies age‐related metabolic trajectories and modulates physiological responses to pharmacological intervention.

Evidence suggests that angiotensin-converting enzyme inhibitors (ACEIs) may increase metabolic rate by promoting thermogenesis, potentially through enhanced fat oxidation and improved insulin. More research is, however, needed to understand this intricate process. In this study, we used 22 lines from the Drosophila Genetic Reference Panel to assess the metabolic rate of virgin female and male flies that were either fed a standard medium or received lisinopril for one week or five weeks. We demonstrated that lisinopril affects the whole-body metabolic rate in Drosophila melanogaster in a genotype-dependent manner. However, the effects of genotypes are highly context-dependent, being influenced by sex and age. Our findings also suggest that lisinopril may increase the Drosophila metabolic rate via the accumulation of a bradykinin-like peptide, which, in turn, enhances cold tolerance by upregulating Ucp4b and Ucp4c genes. Finally, we showed that knocking down Ance, the ortholog of mammalian ACE in Malpighian/renal tubules and the nervous system, leads to opposite changes in metabolic rate, and that the effect of lisinopril depends on Ance in these systems, but in a sex- and age-specific manner. In conclusion, our results regarding D. melanogaster support existing evidence of a connection between ACEI drugs and metabolic rate while offering new insights into this relationship.

Aquatic organisms are exposed to low concentrations of neuro-active chemicals, many of them acting also as neuroendocrine disruptors that can be hazardous during earlier embryonic stages. The present study aims to assess how exposure early in live to environmental low concentrations of two selective serotonin reuptake inhibitors (SSRIs), fluoxetine and sertraline, and tributyltin (TBT) affected cognitive, metabolic and cardiac responses in the model aquatic crustacean Daphnia magna. To that end, newly brooded females were exposed for an entire reproductive cycle (3-4 days) and the response of collected juveniles in the first, second and third consecutive broods, which were exposed, respectively, as embryos, provisioned and un-provisioned egg stages, was monitored. Pre-exposure to the selected SSRIs during embryonic and egg developmental stages altered the swimming behaviour of D. magna juveniles to light in a similar way reported elsewhere by serotonergic compounds while TBT altered cognition disrupting multiple neurological signalling routes. The studied compounds also altered body size, the amount of storage lipids in lipid droplets, heart rate, oxygen consumption rates and the transcription of related serotonergic, dopaminergic and lipid metabolic genes in new-born individuals, mostly pre-exposed during their embryonic and provisioning egg stages. The obtained cognitive, cardiac and metabolic defects in juveniles developed from exposed sensitive pre-natal stages align with the "Developmental Origins of Health and Disease (DoHAD)" paradigm.

Aquatic insects cope with hypoxia and anoxia using a variety of behavioral and physiological responses. Most stoneflies (Plecoptera) occur in highly oxygenated surface waters, but some species live underground in alluvial aquifers containing heterogeneous oxygen concentrations. Aquifer stoneflies appear to be supported by methane-derived food resources, which they may exploit using anoxia-resistant behaviors. We documented dissolved oxygen dynamics and collected stoneflies over five years in floodplain wells of the Flathead River, Montana. Hypoxia regularly occurred in two wells, and nymphs of Paraperla frontalis were collected during hypoxic periods. We measured mass-specific metabolic rates (MSMR) at different oxygen concentrations (12, 8, 6, 4, 2, 0.5 mg/L, and during recovery) for 111 stonefly nymphs to determine whether aquifer and benthic taxa differed in hypoxia tolerance. Metabolic rates of aquifer taxa were similar across oxygen concentrations spanning 12 to 2 mg/L (P>0.437), but rates of benthic taxa dropped significantly with declining oxygen (P<0.0001; 2.9× lower at 2 vs. 12 mg/L). Aquifer taxa tolerated short-term repeated exposure to extreme hypoxia surprisingly well (100% survival), but repeated longer-term (> 12 hours) exposures resulted in lower survival (38-91%) and lower metabolic rates during recovery. Our work suggests that aquifer stoneflies have evolved a remarkable set of behavioral and physiological adaptations that allow them to exploit the unique food resources available in hypoxic zones. These adaptations help explain how large-bodied consumers might thrive in the underground aquifers of diverse and productive river floodplains.

Being composed of small cells may carry energetic costs related to maintaining ionic gradients across cell membranes as well as benefits related to diffusive oxygen uptake. Here, we test the hypothesis that these costs and benefits of cell size in ectotherms are temperature dependent. To study the consequences of cell size for whole-organism metabolic rate, we compared diploid and triploid zebrafish larvae differing in cell size. A fully factorial design was applied combining three different rearing and test temperatures that allowed us to distinguish acute from acclimated thermal effects. Individual oxygen consumption rates of diploid and triploid larvae across declining levels of oxygen availability were measured. We found that both acute and acclimated thermal effects affected the metabolic response. In comparison with triploids, diploids responded more strongly to acute temperatures, especially when reared at the highest temperature. These observations support the hypothesis that animals composed of smaller cells (i.e. diploids) are less vulnerable to oxygen limitation in warm aquatic habitats. Furthermore, we found slightly improved hypoxia tolerance in diploids. By contrast, warm-reared triploids had higher metabolic rates when they were tested at acute cold temperature, suggesting that being composed of larger cells may provide metabolic advantages in the cold. We offer two mechanisms as a potential explanation of this result, related to homeoviscous adaptation of membrane function and the mitigation of developmental noise. Our results suggest that being composed of larger cells provides metabolic advantages in cold water, while being composed of smaller cells provides metabolic advantages in warm water.

Aging is accompanied by increased susceptibility to infections including with viral pathogens resulting in higher morbidity and mortality among the elderly. Significant changes in host metabolism can take place following virus infection. Efficient immune responses are energetically costly, and viruses divert host molecular resources to promote their own replication. Virus-induced metabolic reprogramming could impact infection outcomes, however, how this is affected by aging and impacts organismal survival remains poorly understood. RNA virus infection of Drosophila melanogaster with Flock House virus (FHV) is an effective model to study antiviral responses with age, where older flies die faster than younger flies due to impaired disease tolerance. Using this aged host-virus model, we conducted longitudinal, single-fly respirometry studies to determine if metabolism impacts infection outcomes. Analysis using linear mixed models on Oxygen Consumption Rate (OCR) following the first 72-hours post-infection showed that FHV modulates respiration, but age has no significant effect on OCR. However, the longitudinal assessment revealed that OCR in young flies progressively and significantly decreases, while OCR in aged flies remains constant throughout the three days of the experiment. Furthermore, we found that the OCR signature at 24-hours varied in response to both experimental treatment and survival status. FHV-injected flies that died prior to 48- or 72-hours measurements had a lower OCR compared to survivors at 48-hours. Our findings suggest the hostâs metabolic profile could influence the outcome of viral infections.

The hydrophobic surface of plastics adsorbs hydrophobic persistent organic pollutants (POP) such as Perfluorooctanoic acid (PFOA). The potential for hydrophobic nanoparticles such as titanium dioxide (TiO 2 ) to associate with PFOA and alter accumulation rates has not been investigated. Nanoparticles form ecocorona by adsorption of multiple constituents in water, but few studies have examined if this results in differences in the rate of PFOA accumulation in freshwater animals. We demonstrate the PFOA associates with the hydrophobic surfaces of nano-sized TiO 2 particles and this increases the rate of uptake of PFOA into Daphnia magna. Accumulation of PFOA in daphnia was measurement over multiple concentrations, flux times and particle sizes using a radiotracer-based method ( 14 C-labelled PFOA). Our results show that TiO 2 NPs have a high sorption capacity for PFOA and PFOA sorption decreased aggregation of TiO 2 as evidenced by a decrease in average hydrodynamic diameter, decreased zeta potential and increased polydispersity index. Uptake of PFOA at 10 μg/L was found to be 45 % higher in the presence of 500 μg/L of 5 nm TiO 2 compared to control PFOA alone uptake. Potentiation of PFOA uptake using 25 nm TiO 2 NPs was 25 % higher than control PFOA alone. PFOA alone (0.5 mg/L) reduced metabolic oxygen consumption (MO 2 ) in daphnia by 52 %, but exposure to (100 mg/L) 5 nm TiO 2 NPs sorbed with (0.5 mg/L) PFOA decreased metabolic oxygen consumption (MO 2 ) by ~88 %. These findings show that TiO 2 nanoparticles act as vectors for hydrophobic organic pollutant accumulation and significantly potentiate PFOA accumulation and toxicity in aquatic organisms.

In this study, the behaviour of Daphnia magna was studied under equipotent and sub-lethal concentrations of two pesticides congeners: chlorpyrifos (CPF; 5 ng L-1 to 50 ng L-1) and chlorpyrifos-methyl (CPF-m; 30 ng L-1 to 300 ng L-1) with aims to assess and compare the behavioural swimming responses (BSRs) of the cladocerans elicited by both compounds at different concentrations and exposure times. A video tracking analysis after 24 h and 48 h of exposure allowed us to evaluate different behavioural responses (distance moved, average velocity, active time, and average acceleration). The results indicate that BSRs are sensitive indicators of sub-lethal stress. Highly concentration- and time-response changes for both compounds were observed during the experiments. In particular, in the first 24 h of exposure, both compounds elicited a similar decreasing trend in swimming behaviour, in which CPF induced the highest decline. Further, hypoactivity was associated with the narcotic effects of both compounds. Conversely, after 48 h of exposure, we observed an increasing tendency in the swimming parameters, particularly at the highest tested concentrations. However, the compounds did not exhibit the same trend. Rather, CPF-m induced high variations from the control groups. This reversal trend could be due to the activation of compensatory mechanisms, such as feeding, searching, or avoidance behaviours. These results suggest that BSRs are measurable active responses of organisms, which are controlled by time.

Mitochondrial replacement therapy (MRT) presents a promising preventative measure to combat mitochondrial diseases. However, the long-term consequences of disrupting mitonuclear coevolution at both the molecular and organismal levels remain understudied. Data on sex-specific effects are also lacking despite predictions that males may be especially vulnerable to mitochondrial replacement. To address this, we used backcrossed lines of the copepod Tigriopus californicus to produce offspring with nuclear genotype contributions from two populations and a mitochondrial genotype from a third, separate, population. When compared to hybrid controls with mitochondrial genotypes that matched the maternal nuclear genotype but not the paternal, these “three-parent offspring” did not significantly differ in lifespan or routine metabolic rate. While these organismal-level traits showed no effect, molecular metrics of mitochondrial health revealed consequences of mitochondrial replacement. Oxidative DNA damage, measured by 8-hydroxy-2’-deoxyguanosine content, was higher in three-parent offspring, and mitochondrial DNA content was lower than in hybrid controls. While differences between sexes were present in some traits, sex did not interact with mitochondrial replacement for any of these metrics. Although these results could be due either to donor mitochondrial DNA matching neither of the nuclear parents, or to deficits in the donor mitochondrial DNA itself, they highlight the importance of considering molecular level consequences of mitochondrial replacement that may be masked at the organismal level when evaluating the health impacts of this treatment.

The success and impact of invasive non-native species depend on how they cope with local abiotic conditions, especially in comparison to co-occurring native taxa. In aquatic systems, salinity serves as a key environmental filter, mediating the establishment of invasive species and influencing biotic interactions. However, the mechanistic basis behind these context-dependent responses remains poorly understood. In this study, we examined interspecific differences in metabolic rate, movement behaviour, and their relationship between the worldwide invasive Gambusia holbrooki and a threatened Spanish endemic fish Aphanius iberus across an experimentally-manipulated salinity gradient. Using intermittent-flow respirometry and automated tracking of movement patterns, we compared aerobic metabolic traits and movement behaviours under various salinities. Toothcarp maintained a stable aerobic scope across salinity treatments, whereas invasive mosquitofish exhibited a markedly lower aerobic scope with higher salinity, primarily due to a decline in maximum metabolic rate. This stress response was not linked to increased osmoregulatory costs, as baseline metabolism decreased. Behavioural tests demonstrated consistent species differences in routine locomotion, with mosquitofish showing more exploratory behaviour and toothcarp showing more stop-go behaviour and remaining more stationary overall. Notably, in toothcarps, we found a negative link between standard metabolic rate and space use, suggesting that individuals with higher baseline metabolism may be constrained in their movement. Conversely, in mosquitofish, although salinity affected metabolic capacities, this effect was not reflected in their movement, indicating a weak relationship between metabolism and behaviour, likely supported by trait flexibility. By integrating metabolic traits with behavioural data, our results reveal mechanisms underlying invasive species responses and strengthen predictions of their performance relative to native fishes under changing conditions, such as salinity in inland waters. This highlights the importance of trait-based approaches for predicting responses to abiotic stressors and for evaluating the ecological impacts of invasive taxa.

In recent decades, rising industrial demand for palladium (Pd), driven by its unique properties and affordability compared to other noble metals, has increased its environmental release into aquatic systems. This highlights the need to assess its effects on organisms, given the lack of standardized toxicity studies and regulations for this element. This study examines the acute and chronic impacts of Pd exposure on D. magna. Acute lethality was assessed over 48 h at measured Pd concentrations ranging from 2 to 110 μg/L, yielding an LC 50 of 52 ± 2 μg/L and an LC 10 of 33 ± 3 μg/L. The impact of natural organic matter from the Suwannee River on Pd lethality and bioaccumulation was also examined. No mortality occurred at DOC concentrations of 1, 2, 5, and 8 mg C/L, in contrast with the results obtained at 0.8 mg C/L, which resulted in an LC 50 of 74 ± 1 μg/L. Pd bioaccumulation decreased significantly with increasing DOC concentrations compared to controls. After 15 days of chronic exposure, offspring viability significantly declined, with an EC 50 of 1 ± 0.1 μg/L, alongside reductions in total broods per D. magna (EC 50: 7 ± 2 μg/L). Parental dry weight also decreased significantly, though the timing of the first brood and weight‐normalized oxygen consumption rates remained unaffected across treatments. Parental survival was notably affected, with an LC 50 value of 14 ± 2 μg/L. These results emphasize Pd's potential for both lethal and sublethal effects, highlighting the need for environmental standards to protect aquatic life. This study examines acute and chronic impacts of Pd exposure on Daphnia magna. Acute lethality yielded an LC 50 of 52 ± 2 μg/L and an LC 10 of 33 ± 3 μg/L. Pd toxicity and bioaccumulation decreased with increasing dissolved organic carbon concentrations. Chronic exposure led to a decline in offspring viability and total brood size. These results emphasize Pd's potential for lethal and sublethal effects, highlighting the need for environmental standards to protect aquatic life.

The majority of fish swim by aerobic muscular force, and so there has been considerable interest in the metabolic basis for swimming. Most of this work has measured whole-body oxygen consumption as a metabolic proxy, without any quantification of the actual energy that is produced at the cellular level. In this study we explored links between organism level metabolic rate (both standard (SMR) and maximal (MMR)), mitochondrial function - the rates of oxygen consumption associated with oxidative phosphorylation (OXPHOS) and offsetting proton leak (i.e., OXPHOS coupling efficiency

Potential ecotoxicity of the solar chlor-photo-Fenton (SCPF) process as a novel approach for wastewater reclamation has been investigated in relation to reuse for crop irrigation. Several secondary effluents from wastewater treatment plants across different geolocations were treated by applying the process with low reagent concentrations of 0.1 mM of ferric nitrilotriacetate (Fe 3+ -NTA), 0.73 mM of hydrogen peroxide, at different chlorine doses ranging from 0.13 to 0.40 mM. Chlorination, using comparable chlorine concentrations, and the solar photo-Fenton process were evaluated in parallel to compare with SCPF. A UVB-LED system was also used to perform the SCPF treatment, demonstrating its adaptability to both solar and artificial light-driven applications. Potential environmental toxicity was assessed using a battery of bioassays, including bacterial toxicity and genotoxicity, phytotoxicity in algae and plants, and toxicity toward mixed microbial communities (microrespirometry). Water treated with SCPF exhibited minimal bacterial and algal toxicity (<13 %), low phytotoxicity as assessed by plant germination (35 % at high chlorine concentration) and shoot/root elongation (22 % and -30 %), low toxicity toward mixed microbial communities (<30 %), and low apparent levels of genotoxicity. In comparison, chlorination yielded higher ecotoxic responses across the bioassays, suggesting that SCPF may mitigate these adverse effects. Although Fe 3+ -NTA dissolution showed toxicity its ecotoxic impact was markedly reduced at the operational concentration of 0.1 mM used in SCPF. These results indicate that chlor-photo-Fenton can produce treated water with low apparent ecotoxicity, supporting its potential as an environmentally friendly and scalable solution for wastewater treatment and reuse.

Triploid Atlantic salmon are sterile and used in aquaculture to prevent escapees from breeding in the wild. Meanwhile, triploids suffer poor animal welfare in the latter marine growth phase. Previous experiments have mainly tested smaller fish, and physiological differences between triploids and diploids tended to be subtle or non-existing. We therefore hypothesized that triploidy first becomes a disadvantage at larger body sizes where scaling constraints become more magnified in triploids owing to them having larger cells with lower surface to volume ratios. We measured metabolic rates, stress responses, hypoxia tolerance, and critical thermal maximum in big (≈3 kg) triploid and diploid Atlantic salmon. Additionally, we assessed gill histology metrics. Big triploids had higher standard metabolic rates, lower aerobic scopes, and reduced tolerances to hypoxia and thermal stress. Oxygen extraction coefficients were overall lower in triploids, suggesting reduced efficiency in gill oxygen uptake. This was further supported by lower lamellar densities which indicate less gill surface area. In conclusion, big triploid Atlantic salmon were more vulnerable to environmental extremes driven by oxygen supply limitation and higher basal maintenance costs. This provides a mechanistic explanation for why triploids become prone to animal welfare issues in the latter growth phase of marine aquaculture.

Copepods are the dominant crustacean group in groundwater, where they perform valuable ecosystem services related to carbon recycling. The life-history traits of stygobitic (groundwater-obligate dweller) copepods, however, have only been casually studied in the past. In addition, next to nothing is known about the responses of stygobitic copepods to climate change. In this study, we investigated the life-history traits and respiratory metabolism of a species of harpacticoid copepods, Moraria sp., endemic to the Corchia Cave in the Apuan Alps (Italy). We collected the specimens of Moraria sp. from the dripping waters of the cave and observed their development, survival, and reproduction rates in the laboratory for one year. We also evaluated the acclimation ability of adult females of Moraria sp. by measuring their oxygen consumption in a temperature range from 8 °C (average annual temperature of the dripping water in the Stalactites Gallery of the Corchia Cave) to 12.5 °C (maximum temperature of the dripping water of the cave expected according to climate change scenarios in 2100). Our results indicate that Moraria sp. Is a stenothermal species showing remarkable stygobitic traits (long life span, low metabolic rates). We noted that the metabolism of this species is significantly affected by small (+1.5 °C) thermal changes. Our results showed no metabolic compensation occurring in this species over two weeks of exposure to temperatures higher than 8 °C. The outcomes of this study suggest that Moraria sp. May not be able to tolerate thermal changes brought on by climate change.

Swimming in fish arises from tightly integrated neural, muscular, skeletal, and hydrodynamic processes that are difficult to capture in compact, transferable models for robotics. An interpretable system identification (SySID) is presented that bidirectionally maps between electromyography (EMG) and kinematics in freely swimming koi and further tests its generalization to a robotic fish. Synchronized EMG and kinematic are collected across laminar, Kármán vortex, and reverse Kármán vortex flows spanning 0.146–0.274 m s −1. A linear autoregressive with exogenous input (ARX) model architecture is chosen to capture both feedforward (EMG to kinematics) and feedback (kinematics to EMG) pathways, enabling the extraction of key system parameters, such as natural frequency, damping ratio, and input–output delays. Cross‐individual validation demonstrates robust performance and identifies the best‐performing fish‐trained model, which is then evaluated for cross‐domain transfer by replacing EMG input with processed pulse width modulation actuation signals from a robotic fish. Despite differences in mechanics and actuation physics, predictions closely match measured trajectories (mean R 2 = 0.86 ± 0.13), substantially outperforming a deep neural network (97.8% higher percentage fit index) trained on the same biological datasets. These findings show that compact, interpretable SySID models enable accurate bio‐to‐robot transfer without robot‐specific retraining, grounding robotic motion models directly in biological function rather than imitation.

The reproductive process in Octopus maya was analyzed to establish the amount of reactive oxygen species that the embryos inherit from females, during yolk synthesis. At the same time, respiratory metabolism, ROS production, and the expression of some genes of the antioxidant system were monitored to understand the ability of embryos to neutralize maternal ROS and those produced during development. The results indicate that carbonylated proteins and peroxidized lipids (LPO) were transferred from females to the embryos, presumably derived from the metabolic processes carried out during yolk synthesis in the ovary. Along with ROS, females also transferred to embryos glutathione (GSH), a key element of the antioxidant defense system, thus facilitating the neutralization of inherited ROS and those produced during development. Embryos are capable of neutralizing ROS thanks to the early expression of genes such as catalase (CAT) and superoxide dismutase (SOD), which give rise to the synthesis of enzymes when the circulatory system is activated. Also, it was observed that the levels of the routine metabolic rate of embryos are almost as high as those of the maximum activity metabolism, which leads, on the one hand, to the elevated production of ROS and suggests that, at this stage of the life cycle in octopuses, energy production is maximum and is physically limited by the biological properties inherent to the structure of embryonic life (oxygen transfer through the chorion, gill surface, pumping capacity, etc.). Due to its role in regulating vascularization, a high expression of HIf-1A during organogenesis suggests that circulatory system development has begun in this phase of embryo development. The results indicate that the routine metabolic rate and the ability of O. maya embryos to neutralize the ROS are probably the maximum possible. Under such circumstances, embryos cannot generate more energy to combat the free radicals produced by their metabolism, even when environmental factors such as high temperatures or contaminants could demand excess energy.

Objective Cultured catfish are subjected to cold temperatures during winter, as aquaculture ponds are relatively shallow (<1.5 m) and experience seasonal thermal fluctuations. Cold temperatures reduce metabolic processes; however, little is known about comparative differences in metabolic rates, swimming performance, and blood metabolites among principal types of cultured catfish. Therefore, the objective of this study was to address this knowledge gap for catfish types used in the U.S. aquaculture industry. Methods Standard metabolic rate, maximum metabolic rate, metabolic scope, critical swimming speed (Ucrit), and blood metabolites were analyzed at 10°C and 20°C in juvenile Channel Catfish Ictalurus punctatus, Blue Catfish I. furcatus, and hybrid catfish (Channel Catfish × Blue Catfish). Results It was hypothesized that hybrid catfish would have greater metabolic and swimming performance than Channel and Blue catfishes across experimental temperatures due to heterosis. However, metabolic scope and Ucrit did not vary among fish types, but Ucrit was reduced among all fish types at 10°C. Lactate and glucose concentrations were higher and blood pH was lower in fatigued catfish, with Channel Catfish generally differing in blood metabolites from Blue and hybrid catfishes. Conclusions Results indicate that prolonged exposure to cold temperatures limits metabolic processes and swimming capacity, ultimately requiring catfish to allocate energetic resources to maintenance metabolic requirements. Although no distinct comparative advantage was found for any of the catfish types at low temperature, long-term health and survival likely relate to energy stores accrued prior to and during exposure to cold temperatures. These findings provide useful comparative metrics to direct future efforts into investigating the physiological and environmental mechanisms affecting the catfish aquaculture industry.

Inflammatory muscle loss results from excessive inflammatory responses, causing muscle damage and weakness. In the current investigation, we evaluated the protective effects of diphlorethohydroxycarmalol (DPHC) against tumor necrosis factor-alpha (TNF-α)-induced skeletal muscle inflammation and muscle loss and elucidated the underlying mechanisms. Furthermore, the effect of DPHC on swimming performance was confirmed under TNF-α-induced inflammatory muscle loss-conditioned zebrafish by assessing the swimming number, distance moved, time spent swimming, frequency of swimming zebrafishes in an upstream swim track (Zone A). In vivo behavioral endurance test results indicated that TNF-α treatment significantly decreased the number of swimming zebrafish and swimming distance in Zone A compared with the Control. Meanwhile, the DPHC treatment significantly increased the number of swimming zebrafish and swimming distance in Zone A compared to TNF-α-induced zebrafish. These findings indicate that DPHC treatment effectively improved the swimming performance of TNF-α-induced zebrafish. In an additional study, TNF-α significantly induced inflammatory muscle loss by upregulating nuclear factor kappa light chain enhancer of activated B cells (NF-κB) mitogen activated protein kinase (MAPK) associated proteins and MuRF-1 in the skeletal muscle tissues of TNF-α-induced zebrafish. However, DPHC administration significantly counteracted TNF-α-induced inflammation and muscle loss by downregulating NF-Κb and MAPK-associated proteins, as well as the muscle degradation-related proteins MuRF-1 and MAFbx, in the skeletal muscle tissues of TNF-α-induced zebrafish. In summary, our research findings demonstrated that DPHC from Ishige okamurae could be used for the development of nutraceuticals or functional foods targeting inflammatory muscle loss.

Stress significantly impacts fish welfare, and for a comprehensive evaluation, welfare assessment requires an integrative approach. The objective of this study is to gain insight into the physiological and behavioural responses of European sea bass subjected to swimming and crowding stress tests through biologging. Individuals implanted with biologgers were subjected to swim tunnel and crowding tests, measuring locomotion, oxygen consumption, heart rate, acceleration and QRS-wave amplitude. During swimming stress tests, oxygen consumption correlated positively with heart rate (R2 = 0.56, p < 0.001) and acceleration (R2 = 0.76, p < 0.001). Acceleration values recorded by biologgers were strongly correlated with head and tail beat frequency (R2 = 0.69 and R2 = 0.70 respectively; p < 0.001), validating heart rate and acceleration as reliable proxies for energy expenditure in sea bass. During the crowding challenge, heart rate increased progressively with each stressing event, while QRS-wave amplitude and acceleration peaked with stress but decreased in-between stressors. The assessment of physiological and behavioural responses of sea bass to swimming and crowding stress tests with biologgers allows the characterization of four welfare states, and therefore, highlights the potential of biologging for fish stress response and welfare monitoring.

Harpacticoid copepods are key components of the meiofauna in nearly all benthic ecosystems, commonly characterized by a low availability of dissolved oxygen (DO). Harpacticoids exhibit a functional loss of Hypoxia Inducible Factor (HIF), and their ability to tolerate and respond to hypoxic conditions has been studied in the tidal-pool genus Tigriopus, but not in harpacticoids inhabiting other ecosystems. To improve our understanding of the metabolic pathways used by harpacticoid copepods to survive in low-oxygen environments, we measured the metabolic rate and established the critical oxygen pressure (Pcrit) in Amphiascoides atopus using flow-through respirometry along a DO gradient. Our results indicate that A. atopus switched from oxyregulating to oxyconforming behavior at a Pcrit of 10.5 kPa. Below a DO concentration of 5.9 kPa, the metabolic rate of A. atopus was undetectable in 72 % of the cases, indicating a probable switch to anaerobic metabolism. Additionally, we performed a survival assay at experimental DO concentrations of 20.8 kPa,7.8 kPa, and 3.1 kPa, and anoxia at DO levels <0.92 kPa. Survival rate after 96 h was 100 % under the two hypoxic conditions and 25 % under anoxia. Finally, we compared the temperature-dependent metabolic rates between harpacticoids (w/o functional HIF) and calanoids (with functional HIF). The differences between the two groups were mainly driven by temperature, as studies in harpacticoids have generally been conducted at higher temperatures, as in the present study.

Due to their renowned regenerative capacity, adult zebrafish are a premier vertebrate model to interrogate mechanisms of innate spinal cord regeneration. Following complete transection to their spinal cord, zebrafish extend glial and axonal bridges across severed tissue, regenerate neurons proximal to the lesion, and regain swim capacity within 8 weeks of injury. Here, we describe methods to perform complete spinal cord transections and to assess functional and cellular recovery during regeneration. For spinal cord injury, a complete transection is performed 4 mm caudal to the brainstem. Swim endurance is quantified as a central readout of functional spinal cord repair. For swim endurance, zebrafish are subjected to a constantly increasing water current velocity until exhaustion, and time at exhaustion is reported. To assess cellular regeneration, histological examination is performed to analyze the extents of glial and axonal bridging across the lesion.

Understanding how macroalgal forests will respond to environmental change is critical for predicting future impacts on coastal ecosystems. Although measures of adult macroalgae physiological responses to environmental stress are advancing, measures of early life‐stage physiology are rare, in part due to the methodological difficulties associated with their small size. Here we tested a novel, high‐throughput method (rate of oxygen consumption and production; V̇O2 via a sensor dish reader microplate system to rapidly measure physiological rates of the early life stages of three habitat‐forming macroalgae, the kelp Ecklonia radiata and the fucoids Hormosira banksii and Phyllospora comosa. We measured the rate of O2 consumption (respiration) and O2 production (net primary production) to then calculate gross primary production (GPP) under temperatures representing their natural thermal range. The V̇O2 microplate system was suitable for rapidly measuring physiological rates over a temperature gradient to establish thermal performance curves for all species. The V̇O2 microplate system proved efficient for measures of early life stages of macroalgae ranging in size from approximately 50 μm up to 150 mm. This method has the potential for measuring responses of early life stages across a range of environmental factors, species, populations, and developmental stages, vastly increasing the speed, precision, and efficacy of macroalgal physiological measures under future ocean change scenarios.

This individual-based study reveals sex-specific differences in stress responses of the copepod Calanus finmarchicus to oxidative stress, with males showing higher sensitivity but no significant different metabolic strategies compared with females. It also identifies the antagonistic and synergistic effects of heat and paraquat-induced oxidative stress on antioxidant gene expression, and a potential maximum threshold for superoxide dismutase and catalase fold change in females.

The changes in water flow caused by hydropower projects and river diversions have had a profound impact on aquatic ecosystems, especially due to artificial structures such as dams and bridge piers. This study investigates the swimming behavior differences between single and dual fish in the wake region behind a D-shaped obstacle, using Percocypris pingi as the experimental species. The results show that single fish efficiently utilize vortex energy through the Kármán gait, improving swimming efficiency, while the dual-fish group failed to maintain a stable Kármán gait, resulting in irregular swimming trajectories. However, the dual-fish group optimized wake utilization by maintaining a fore–aft linear alignment, improving swimming efficiency and resisting vortices. The conclusion indicates that mutual interference in group swimming affects swimming efficiency, with fish adjusting their swimming patterns to adapt to complex hydrodynamic conditions. By altering swimming formations, fish schools can adapt to the flow environment, offering new insights into the swimming behavior of fish and providing theoretical support for ecological conservation and hydropower project design.

Chronic hypoxia exposure of fish can cause remodelling of the gills as well as increases to haematocrit and haemoglobin binding affinity. There is less known, however, about how chronic hypoxia affects the structure and function of the heart. In the current study, zebrafish were exposed to moderate hypoxia for 7 weeks and then ultrasound was used to characterize cardiac function. We found that cardiac output of the hypoxia-acclimated fish was greater than that of the control fish during an acute hypoxia exposure. This difference was due, at least in part, to the higher cardiac stroke volume. Histological measurements demonstrated an increase in the cross-sectional area of the ventricle of hypoxia-exposed fish and this was supported by higher end diastolic area measurements made using ultrasound. These changes to the heart occurred in conjunction with an increase in haematocrit and the respiratory surface area of the gills, as well as an improved capacity of the fish to respond to a more severe acute hypoxia challenge. We also found an increase in the expression of the gene transcripts for hif-1αa and vegfaa at 24 h, 3 days and 8 days of hypoxia exposure, suggesting a rapid and consistent response. Our results suggest that, unlike normoxia-acclimated fish which demonstrate a decrease in cardiac output with acute hypoxia exposure, zebrafish acclimated to hypoxia maintain cardiac output when acutely exposed to hypoxia.

The principle of the 3Rs-Reduction, Refinement, and Replacement-encourages minimizing animal use, improving experimental design, and developing alternative models for toxicology testing. Among such models, planaria (aquatic flatworms) have gained increasing attention in pharmacology, regenerative medicine, and toxicology because of their simple anatomy, high environmental sensitivity, exceptional regenerative ability, and ease of laboratory maintenance. In this study, we examined the effects of benzalkonium chloride (BAC)-a commonly used pharmaceutical excipient with antimicrobial and permeability-enhancing properties, as well as a known environmental toxicant-on the locomotor activity of Schmidtea mediterranea using both manual assessment and Lolitrack video-tracking software. Six concentrations of BAC (5-1000 μg/mL) and a negative control were tested. Both approaches showed an overall reduction in locomotor activity over time, though manual analysis indicated a transient stimulation at lower concentrations. The software-based method demonstrated greater reliability, precision, and objectivity, making it preferable for toxicity evaluation in planaria.

In aquatic environments, muscle activity in free-swimming fishes not only propels body undulations to generate thrust but also serves as proprioceptive sensors for detecting surrounding fluid dynamics. Testing the proprioceptive function of the muscle is challenging owing to its deep integration with swimming activity. To address this, we introduce an experimental platform that records up to 12-channel electromyography (EMG) signals synchronized with detailed kinematics in koi and carp. We first apply various neural networks to map densely collected EMG signals to synchronized video-based body kinematics, thereby validating our EMG collection system. We then compare EMG data from fishes swimming in various laminar flows and within Kármán vortices. Our results show that the phase of muscle activity consistently precedes body kinematics in various laminar flows. While within Kármán vortices, we observe a mixed phase relationship, where muscle activity sometimes leads and at other times lags behind body kinematics. This suggests that fishes may use muscle proprioceptive sensing when interacting with complex flows, such as nearby vortices. Our research not only introduces novel methods for biological EMG studies but also offers insights that could influence the design of bio-inspired underwater sensory systems.

Sea trout, Salmo trutta, display a wide range of migratory behaviours, and one aspect of variation comes from freshwater migration distance. The overall aim of this study was to determine if offspring of long‐ and short‐distance migrants exhibited phenotypic differences relating to parental migration distance. For that purpose, we conducted several behavioural tests (dyadic contest, boldness scoring and open field test) and morphological analysis (relative pectoral‐fin length) in multiple freshwater systems across the distribution range of the target species in Europe. It was expected that offspring of long‐distance migrants would be more active, bold and dominant than those of short‐distance migrants and would have longer pectoral fins relative to body length. Additionally, we investigated if boldness varied in relation to latitude. We showed that offspring of long‐distance migrants were more dominant in two cases and more active in one case than those of short‐distance migrants; however, there was no difference in swimming distance or velocity. Boldness and relative pectoral‐fin length were significantly related to site of origin; however, the direction of this relationship differed between systems. Generally, we detected a decrease in boldness with declining latitude. In summary, we have detected variation among juveniles related to location within a stream; however, the drivers and processes behind these are likely more complex than purely parental migratory strategy. Our results can inform suitable management and conservation efforts directed to anadromous Salmo trutta. For example, habitat restoration and removal of migration barriers can increase the possible range of migration distances helping maintain the phenotypic diversity of offspring.

Climate change is shifting the aerobic capacity of aquatic ectotherms, affecting their ability to move efficiently through their environment. Rising temperatures also alter host–parasite interactions, yet how these stressors interact to impact locomotion remains unclear. This is especially relevant for infections that disrupt streamlining and fin function, with implications for wild fish populations, aquaculture, and fisheries. Pumpkinseed sunfish ( Lepomis gibbosus (Linnaeus, 1758)), a popular recreational fishing species, are naturally co-infected with trematodes, forming rigid cysts on fins and body, and cestode tapeworms, infecting the liver and digestive tract. We tested whether pumpkinseed swimming performance is affected by drag from cysts by measuring critical swimming speed ( U crit ) and aerobic metabolic traits in naturally infected fish and fish treated to remove cestodes. Individuals with more cysts had lower U crit, maximum metabolic rate (MMR) and aerobic scope, likely due to increased drag. Next, we acclimated wild-caught, co-infected fish to 20, 25, and 30 °C and measured U crit and MMR. Warmer temperatures increased both metrics, and internal parasites were related to reduced MMR and U crit. Overall, infections can impair swimming by increasing drag and through physiological effects, but warming does not appear to exacerbate these effects in species not living near their thermal limits.

Recently, a large family of French-Canadians was found to possess above-average strength and muscle hypertrophy that segregated with a single variant in the gene encoding Dendritic Cell-specific Six Transmembrane domain containing protein 2 (DCST2). To investigate the potential role DCST2 has in muscle cell biology we used the CRISPR/Cas9 mutagenic system and generated a 2-nucleotide deletion in exon 3 of zebrafish dcst2 resulting in a frameshift mutation. Homozygous carriers of the mutation displayed reduced transcriptional expression of dcst2 suggesting that our mutation disrupted gene expression. Homozygous mutant dcst2 zebrafish developed normally to adulthood and displayed no differences in motor function using a free-swim and swim tunnel assays. Furthermore, histological examination of muscle cells revealed no differences in slow-twitch or fast-twitch muscle cell cross-sectional area in our mutants. We did observe that male dcst2−/− zebrafish were infertile. The data collected here, suggest that dcst2 does not play a role in zebrafish muscle cell biology.

The transfer of information between individuals is fundamental to living systems and requires comprehensive research in various species. Weakly electric fish, Gnathonemus petersii, provides a unique model organism for such investigations due to its advanced electrocommunication via electric organ discharges (EODs). As separating EODs from multiple individuals remains challenging, we developed an unsupervised approach for EOD separation in two free-swimming individuals. Using continuous wavelet transform, t-distributed Stochastic Neighbor Embedding, and hierarchical clustering, we achieved accurate discrimination of EODs without the necessity of any training data. This approach overcomes the supervised algorithms based on previously published methods in accuracy and computational efficiency, simplifies experimental procedures, and supports animal well-being by reducing the number of required measurements. We applied our separation approach in a dyadic fish model, where ketamine was used to induce schizophrenia-like behavior in one fish. We confirmed the ketamine-induced alteration of the intrinsic relationship between locomotion and EOD signaling. Moreover, while ketamine-induced changes in locomotion were socially transferred, correlated changes in EOD signaling were not observed between dyad members, which may be interpreted as a communication deficit. Additionally, we introduced two techniques for EOD sonification, facilitating exploratory analysis of EOD sequences. These advancements lay the groundwork for future studies of EOD-based communication, highlighting the potential of Gnathonemus petersii in neuroethological, psychopharmacological, and translational research.

Crayfish (Procambarus clarkii) aquaculture is threatened by abrupt temperature decreases caused by climatic phenomena, such as cold waves and seasonal fluctuations. In this study, crayfish were exposed to an abrupt temperature change from 17 °C to 7 °C for 24 h to investigate the effects of acute low-temperatures on respiratory metabolism, antioxidants, and metabolomics. The results showed that acute low-temperatures significantly reduced the activities of pyruvate kinase, lactate dehydrogenase, and succinate dehydrogenase in the gills and hemolymph, associated with decreases in anaerobic and aerobic respiratory capacities, and significant decreases in oxygen consumption, ammonia excretion, and maximum metabolic rates. Antioxidant enzymes in the hepatopancreas and hemolymph initially increased then decreased within 24 h. Metabolomics revealed that glycerophospholipid metabolism and glycosylphosphatidylinositol anchor biosynthesis pathways responded to acute low-temperatures, with glycerophospholipids being the most significantly differentially expressed metabolites. These results supported the hypothesis that crayfish exhibit lower metabolic activity at low temperatures. Our data provide mechanistic insight into the biological changes induced by acute low-temperature and may provide insight into culture of P. clarkii in cold waters.

Objective Flavobacterium columnare is a common pathogen of Chinook Salmon Oncorhynchus tshawytscha in the Klamath River. Elevated water temperatures invoke congregation behavior within thermal refugia and are associated with columnaris disease. A flowing-water F. columnare challenge system was compared with the standard static-bath challenge as an initial step in simulating a riverine exposure. Methods Juvenile Chinook Salmon were exposed to 103 CFU/mL F. columnare for 20 h either in an aerated static bath or within a recirculation swim chamber set at one body length per second. Fish were held at a constant 20°C or exposed to short-term temperature fluctuations to a maximum of 24°C prior to the challenge. Mucus and gill samples were collected at the end of the 20-h challenge and from fish held up to 96 h postchallenge. Samples were assayed for detection of F. columnare by quantitative PCR and conventional plate culture method. Results In static-bath challenge groups, F. columnare was detected in asymptomatic (38%) and moribund Chinook Salmon (29%). In contrast, F. columnare was detected in only one asymptomatic (4%) and one moribund (4%) Chinook Salmon in the flowing-water challenge groups. Prechallenge temperature conditions had no effect on infection. Other yellow-pigmented bacteria were isolated from the Chinook Salmon (particularly static-bath challenge) but were not associated with morbidity or amplified in the F. columnare quantitative PCR. Conclusions Low transmission of F. columnare occurred among juvenile Chinook Salmon under flowing-water conditions simulating a thermal refugia during early summer (20°C, flow of one body length per second, 20-h exposure to 103 CFU/mL). The flowing-water system is sufficient to examine the environmental factors (velocity, temperature, host density, duration, and bacterial concentration of exposure) of riverine exposures on F. columnare transmission to juvenile Chinook Salmon.

Hatchery-raised lake sturgeon (Acipenser fulvescens) are essential to the restoration of this species, but deviation from optimal juvenile growth conditions may limit post-stocking survival. This study investigated the effects of temperature for lake sturgeon raised at 15 °C, 18 °C, and 21 °C. Survival, growth, and synthesis and storage of metabolic energy reserves were measured weekly for 6 weeks following the onset of exogenous feeding. No significant differences in survival, total length, body mass, or SGR were observed based on rearing temperature. Whole-body lipid concentrations were stable over 6 weeks of growth, while mass-specific protein concentrations were significantly increased in all treatments starting at week 3, suggesting the prioritization of lean muscle production in early life at all tested temperatures. Furthermore, total protein accounted for a greater proportion of body mass in fish exposed to lower temperatures. Finally, persistent effects of rearing temperature were examined in stocking-size juveniles by measuring standard metabolic rate following acute transfer from 20 °C to each of the initial rearing temperatures. Metabolic rate increased with temperature, with no differences between rearing groups at each of the measured temperatures. However, fish reared at 18 °C demonstrated improved plasticity within the measured temperature range compared to lake sturgeon that experienced low (15 °C) or high (21 °C) temperatures in their early life. These results indicate that temperature plays a role in balancing the trade-off between rapid growth and nutritional condition of juvenile lake sturgeon, and thermal plasticity later in life, which may influence recruitment to depleted populations.

Synopsis Over 97% of ray-finned fish produce free-swimming larvae. With survival rates of less than 0.01% and radically different morphologies from adults, fish larvae play a crucial role in adapting to environmental changes and dispersing fish populations. Despite over a century of research, a critical gap remains in quantifying the energetic strategies of developing fish to determine how species from different thermal environments self-regulate in response to chronic and acute temperature changes and, the energetic costs associated with allostatic adjustments, referred to as allostatic load (RAL). This study examines the metabolic differences in yolk-sac larvae and their capacity to adjust to energetically adjust to chronic and acute temperature change. We studied the yolk-sac stages of two species: (1) zebrafish (Danio rerio, a tropical eurythermal freshwater fish) and (2) Atlantic cod (Gadus morhua, a cold-temperate stenothermal marine fish), under control (C) conditions (28°C for zebrafish and 5°C for Atlantic cod) and compared responses to larvae raised at chronic higher temperatures (31°C for zebrafish and 10°C for Atlantic cod) and exposed to acute temperature change for 1 h in a respirometer (3°C, zebrafish and 5°C, Atlantic cod) during the first week of larval life. Generally, both species exhibited higher metabolic rates and greater energetic-related changes in response to chronic stressors than to acute stressors compared to C conditions. While an acute increase in temperature resulted in some metabolic compensation, acute decrease in temperature led to what appeared to be metabolic dysregulation. Both species demonstrated higher variability in response to acute decreases in temperature compared to other treatments. Overall, the range of metabolic responsiveness was greater in Atlantic cod than in zebrafish, suggesting that stenothermal Atlantic cod have less resilience to changes in temperature than eurythermal zebrafish, at least at the yolk-sac stage and, during the first week of larval life when the yolk limits energy supply.

Aeration is important for wastewater treatment. A significant amount of energy is used for the aeration process, sometimes up to 80 % of the total energy used at the wastewater treatment plant. Small sub-micrometer gas bubbles (“nanobubbles”) have been suggested as an alternative method for full or supplementary aeration to ensure an efficient process. This study investigates the aeration efficiency of a membrane-based nanobubble generator. The aim is to understand the role of nanobubbles in enhancing the aeration transfer efficiency, and to investigate whether nanobubbles can act as an oxygen reservoir, releasing oxygen into the liquid phase when the concentration falls below saturation. Data confirmed that the nanobubble generator enhances aeration efficiency compared with conventional methods. The gas content within the generated nanobubbles was examined, revealing negligible gas content within the nanobubbles themselves. These results suggest that the observed increase in the standard oxygen transfer efficiency (SOTE) was primarily attributable to the turbulence of liquid flow at the membrane surface and to the rapid transfer of oxygen from the formed bubbles to the liquid, rather than to significant oxygen storage in the nanobubbles themselves. The SOTE of clean water increased with the liquid flow rate and was 20 % at a flow rate of 10 L/min and 54 % at 20 L/min. Aeration happened quickly and the nanobubbles did not release a significant amount of oxygen after the generation process.

Quaternary ammonium compounds (QACs) such as benzalkonium compounds (BACs) are heavily used as biocides and are thus present in raw wastewater. BACs with dodecyl-, tetradecyl-, and hexadecyl groups as well as didecyl-dimethylammonium chloride (DDAC-10) were detected in all tested WWTPs with concentrations of 1728-3318; 1072-1830; 40-68 and 117-168 ng/L for DDAC-10, BAC-12, BAC-14 and BAC-16, respectively, dissolved in wastewater influent. The concentrations in the particulate phase of the wastewater were 20,000-300,000 times higher. Removals in the tested WWTPs exceeded 99%. Sorption constants to secondary and primary sludge (pK D ’s) ranged from 0.32 to 6.3. The biodegradation half-lives for DDAC-10, BAC-12, BAC-14, and BAC-16 were 31, 49, 13, and 68 h, respectively, even though they are strongly sorbing to sludge. Nine metabolites of BAC-12 were identified in the sludge incubation experiments, and five in the WWTP effluents, confirming the relevance of the biodegradation of QACs. Overall, the removal (from the water phase) is controlled by quick sorption, while the overall fate of QACs is controlled by biodegradation, as QACs are cycled in the WWTPs together with the sludge.

The mechanisms linking purine metabolism disorders to skeletal muscle pathology are unclear. This study constructed a CRISPR/Cas9-mediated zebrafish atic knockout model and a siRNA-interfered C2C12 myoblast cell model. We revealed a novel mechanism by which ATIC (5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase) deletion drove the atrophy of skeletal muscle through the downregulation of the oxidative phosphorylation of mitochondria (OXPHOS) pathway. It was found that atic/Atic knockout/knockdown led to the interruption of purine de novo synthesis, abnormal 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) accumulation, and blockage of inosine monophosphate (IMP) synthesis, which in turn triggered mitochondrial structural damage, dysfunction of complex I-V function, and a burst of reactive oxygen species (ROS), and ultimately triggered muscle atrophy through activation of the ubiquitin-proteasome system. The progressive aerobic intervention revealed that 8 weeks of training significantly restored skeletal muscle function in zebrafish atic-/- mutants, and the mechanism was related to the enhancement of mitochondrial biogenesis, up-regulation of the core complex expression of the OXPHOS pathway, and the improvement of ROS scavenging ability. These findings reveal that ATIC deficiency disrupts mitochondrial function through purine metabolism dysregulation, linking aberrant AICAR accumulation to OXPHOS impairment, which provides a theoretical basis for the early warning of muscular toxicity of targeted purine metabolizing drugs and lays a molecular foundation for the exercise rehabilitation strategy of metabolic myopathies.

Recently, concerns about the toxicity of microplastics (MPs) pollution have attracted significant attention. However, the influence of hydrodynamics on MPs bioaccumulation in fish, and the associated risks, remains poorly understood. Therefore, this study addressed this critical knowledge gap by examining how water velocity, individual and in combination with MPs, impacts brain in juvenile grass carp (Ctenopharyngodon idella). Fish were exposed for seven days (28 h total, with 2-h sessions twice daily) to 5 µm polystyrene MPs (PS-MPs) at an environmentally relevant concentration of 1000 µg/L across eight groups: control, low (LV), medium (MV), and high (HV) water velocity, MPs-only, and three combined treatments (MPs + each velocity level). Fish exposed to the MPs + HV group illustrated the highest accumulation of PS-MPs with a concentration of 33.94 ± 1.00 × 10 3 μg/kg (p < 0.05) and exhibited more brain damage, including hemorrhage, edema, and tissue rupture. Furthermore, this group demonstrated significantly increased superoxide dismutase (SOD) and lipid peroxidation (LPO) activities, along with significant reduction in acetylcholinesterase (AChE) activity (p < 0.05), providing clear evidence of oxidative stress and neurotoxicity. Transcriptomic analysis showed a significant variation in gene expression with associated key pathways such as DNA repair, RNA transport, FoxO signaling, and MAPK signaling, indicating active cellular responses to genetic damage. Overall, this study highlighted the critical role of hydrodynamics in MPs bioaccumulation in fish and the compounded risks of MPs and water velocity, emphasizing the crucial need for monitoring of MPs pollution in dynamic aquatic environments, particularly in riverine systems.

The inference of metabolic rate from behavioural measurements is an open question in fish biology. Here, we put forward a predictive model of zebrafish ( Danio rerio ) metabolic rate in still water from mouth opening and pectoral‐fin beating. Our analysis revisits experimental results published in this journal, reprocessed to include information about the pectoral‐fin beating. Using Cobb–Douglas function, we identify a positive (negative) correlation between metabolic rate and mouth opening amplitude (pectoral‐fin amplitude), pointing at the interplay between buccal pumping and pectoral‐fin stabilization.

Understanding marine species' metabolic responses to short- and long-term temperature variation is critical for predicting the resilience of communities and ecosystems at local and global scales. This study investigated the effect of temperature on the routine metabolic rate (RMR) across the zoea and megalopa stages of two brachyuran species, Hymenosoma orbiculare and Pinnotheres sp. Respirometry results under temperatures ranging from 11 to 25 °C revealed stage- and species-specific metabolic responses. In H. orbiculare, RMR in the megalopa life stage increased steeply and significantly at 22 °C, whereas the zoea life stage showed no significant change across the temperature range tested. For Pinnotheres sp., the megalopa life stage also exhibited significant RMR increases above 19 °C, while the zoea life stage showed stable RMR. These results demonstrate that megalopae, particularly H. orbiculare, are more metabolically sensitive to acute warming, operating closer to their physiological limits, while zoeae maintain relative stability, but may be constrained by limited plasticity under sustained warming. Species-level comparisons indicate that H. orbiculare, with its higher and more variable RMR, is more vulnerable than Pinnotheres sp., whose larval stages maintain comparatively stable metabolism. This study highlights the importance of understanding life-stage- and species-specific thermal responses to better predict larval survival, recruitment, and resilience under future climate warming.

This article presents a novel vision-based artificial lateral line (ALL) sensor, FlowSight, enhancing the perception capabilities of underwater robots. Through an autonomous vision system, FlowSight allows for simultaneous sensing the speed and direction of local water flow without relying on external auxiliary equipment. Inspired by the lateral line neuromast of fish, a flexible bionic tentacle is designed to sense water flow. Deformation and motion characteristics of the tentacle are modeled and analyzed using bidirectional fluid-structure interaction (FSI) simulation. Upon contact with water flow, the tentacle converts water flow information into elastic deformation information, which is captured and processed into an image sequence by the autonomous vision system. Subsequently, a water flow perception method based on deep neural networks is proposed to estimate the flow speed and direction from the captured image sequence. The perception network is trained and tested using data collected from practical experiments conducted in a controllable swim tunnel. Finally, the FlowSight sensor is integrated into the bionic underwater robot RoboDact, and a closed-loop motion control experiment based on water flow perception is conducted. Experiments conducted in the swim tunnel and water pool demonstrate the feasibility and effectiveness of FlowSight sensor and the water flow perception method.

Operational rules of the hydropower plant and hydrological conditions can lead to significant fluctuations of water levels downstream the dam and affect the efficiency of fishway entrance. Designing a fishway with two entrances to accommodate the fluctuations in downstream water levels can help fish successful upstream migration. This study aims at identifying the operating modes and optimal flow conditions of fishway with two entrances considering of fish swimming performance and hydraulics conditions at fishway entrances. Hence, fish swimming tests related to four endemic species including Schizothorax oconnori, Schizothorax waltoni, Ptychobarbus dipogon and Schizopygopsis younghusbandi in XH River to identify five behavioral zones (non-rheotactic, induction, preference, burst, and barrier zone) of fish by coupling of hydrodynamic conditions under seven different dam operational scenarios. It is found that the induction zone (0.1–0.4 m/s) and preference zone (0.4–1.3 m/s) for four endemic fish species, the potential migration routes of fish and potential management rules of two entrances have been proposed. The results suggested that #1 entrance of fishway can be operated in scenarios A2, and #2 entrance of fishway can be operated in scenarios A1 and B2, while both two entrances of the fishway needed to be operated in scenarios B1, B3 and C. This study highlights the importance reference for regulating fishway with two entrances at the investigated case study in the Tibetan Himalaya, and proposes a methodology of the fishway entrances for other high-altitude hydropower stations to improve fishway efficiency.

Muscle atrophy, characterized by declines in muscle mass and functionality, currently lacks effective therapeutic options, highlighting an urgent need for further research. This research aimed to elucidate the protective effects of Trifuhalol A (TFA), a phlorotannin derived from Agarum cribrosum, against dexamethasone (Dexa)-induced muscle atrophy in zebrafish and C2C12 cells. TFA enhanced differentiation of myoblasts and myotube formation by upregulating MyHC, myogenin, MyoD, p-Akt, and p-mTOR, as well as activation of key downstream effectors of the mTOR pathway, enhancing protein synthesis. It also inhibited key markers associated with muscle atrophy, such as FoxO3a, MuRF-1, and MAFbx. In vivo, TFA treatment prevented the Dexa-induced reduction in myofiber diameter and cross-sectional area (CSA). Zebrafish exploratory behavior tests revealed that TFA improved swimming patterns and food-tracking velocity, indicating improved swimming performance and responsiveness. In conclusion, TFA mitigates Dexa-triggered muscle atrophy, and these effects are associated with improvements in muscle morphology and swimming performance. While the underlying mechanisms remain to be fully elucidated, the observed effects may involve modulation of the Akt/mTOR/FoxO3a signaling pathway. These findings suggest that TFA holds promise as a potential functional ingredient for supporting muscle health and mitigating muscle atrophy.

Objective Freshwater systems have undergone major changes relative to their hydrologic profile, thermal regime, habitat, and connectivity due to anthropogenic causes. Migratory species are particularly susceptible to such changes given the distances that they travel and the diversity of habitats occupied through their life history. Because of this, it is becoming increasingly important to understand freshwater species’ behavior and physiology to help facilitate their up- and downstream passage past physical and hydrological barriers. Here, we use a combination of approaches, including an enzyme assay that measures the reduction of oxygen in the mitochondria to evaluate the potential thermal tolerance of juvenile (<1 year old) Paddlefish Polyodon spathula acclimated at three temperatures (12, 20, and 25°C). We also used critical swimming speed trials to determine the swimming capacity and respiration rate of juvenile Paddlefish that were acclimated to those three temperatures. Methods We collected skeletal muscle samples from three areas of each fish (dorsal epaxial white skeletal muscle, abdominal white hypaxial skeletal muscle, and a combination of epaxial and hypaxial skeletal muscle tissue [mix of white and red fibers] from the caudal peduncle) to determine whether the estimated enzymatic thermal tolerance was different across tissue types for potential future application to field-collected adult Paddlefish. Results The temperatures at peak enzymatic activity differed across tissue these collection sites (range: 23.12–35.55°C), suggesting that tissue collection site should be carefully considered. Critical swimming speed did not vary significantly across acclimation temperatures (mean ± SE = 40.4 ± 3.03 at 12°C, 59.18 ± 7.08 at 20°C, and 50.13 ± 11.56 at 25°C). Although respiration rate increased with swimming speed, there were no significant differences in maximum metabolic rate across acclimation temperatures during critical swimming trials. Conclusions These data contribute to filling our knowledge gaps concerning the metabolic demands, swimming behavior, and thermal sensitivity of juvenile Paddlefish and suggest that nonlethal approaches may be possible.

Our results indicate that regular exposure to challenging natural conditions activates mechanisms involved in hypoxia resistance in Aplysia californica. This experience is passed to the next generation, fading in the absence of exposure for at least two generations. Gene expression and physiological responses varied significantly between resistant and sensitive sea hares under normoxic and hypoxic conditions, displaying clear evidence of preconditioning in core hypoxia response pathways like HIF.

Environments with fluctuating oxygen are intense challenges for organisms both on land and in the water. Aquatic organisms can be exposed to especially stressful bouts of hypoxia that come on rapidly and to extreme levels. The copepod Tigriopus californicus inhabits supralittoral rocky pools and appears tolerant of hypoxia levels considered lethal for other aquatic organisms despite lacking molecular components typically used by animals to detect and respond to low environmental oxygen. Here, we quantified the natural regime of dissolved oxygen (DO) pools inhabited by T. californicus via deployment of continuous oxygen sensors in copepod pools in Oregon, USA. Using wild-derived cultures from northern (Oregon) and southern (Californian) populations, we exposed copepods to hypoxia and anoxia and assayed loss of equilibrium (LOE) and survival. We also quantified respiratory regulation via critical oxygen tension, oxygen supply capacity, and regulation index. The pools underwent extreme daily cycles of DO, and near anoxia often persisted for up to 6 h. Respiratory statistics indicated individuals could regulate oxygen consumption even near anoxia, predicting a species with hypoxia tolerance ranking high among aquatic taxa. Copepods survived hypoxia below 0.3 mg O 2 l -1 for up to 72 h with some individuals not showing any LOE. Survival was high following even 6 and 15 h exposure to anoxia. We observed sex and population differences in lethality and LOE, with southern populations exhibiting higher resilience. Intraspecific variation in tolerance makes this system a candidate for future studies to investigate alternative molecular and physiological pathways of hypoxia response.

Fishes navigating complex aquatic environments rely on various sensory systems, primarily the lateral line system and vision, to guide their movements. One interesting example is the Mexican blind cavefish (Astyanax mexicanus). This fish relies on the lateral line system as it navigates through the environment without the aid of sight. It is unclear, however, how they might navigate through a novel environment when the lateral line is not functional. In this study, we used high-speed videography to quantify whether naïve blind cavefish alter locomotor behavior, navigation patterns, and the use of body and fins to explore a novel environment with obstacles when the lateral line is ablated. Blind cavefish with an intact lateral line demonstrated deliberate slower exploratory movements and navigated around obstacles with fewer touching events. Conversely, fish with ablated lateral line exhibited increased speed to potentially improve flow sensing. Fish with an ablated lateral line also touched obstacles more often, suggesting a reliance on fin and snout mechanoreception for navigation. These results show the blind cavefish have compensatory sensory mechanisms to navigate novel environments when their major sensory system is not functioning.

We investigated the combined effects of marine heatwaves (MHWs) and nano-titanium dioxide (nano-TiO2) on the physiological fitness of the mussel Mytilus coruscus. The experimental design included multiple concentrations of nano-TiO2 (0, 25, and 250 µg/L) under both ambient temperature (22 °C) and simulated marine heatwave (28 °C) conditions. Results demonstrated that both MHWs and nano-TiO2 exposure significantly increased gonadal tissue damage, reduced shell strength, and altered the expression of genes related to lipid metabolism (SCD) and biomineralization (CALM, CA, CHS), thereby compromising physiological functions in both gonadal and mantle tissues. Additionally, mitochondrial activity was impaired and DNA damage was enhanced in both tissues. The combined exposure to MHWs and high concentrations of nano-TiO2 exacerbated these effects, suggesting that MHWs amplify the toxicity of nano-TiO2. Noteworthy was the distinct difference in mitochondrial activity between gonadal and mantle tissues, indicating tissue-specific metabolic responses under multifactorial stress. These findings highlight the vulnerability of bivalves to multiple environmental stressors and emphasize the need for integrated biomarker approaches in ecological risk assessment within rapidly changing marine environments.

Tralopyril has emerged as a promising alternative to the banned tributyltin in marine antifouling applications. However, its ecological risks remain underestimated. Through an integrated approach combining behavioral phenotyping, transcriptomics, and whole-genome bisulfite sequencing (WGBS), we demonstrate that tralopyril (0, 1, 10 µg/L) disrupts marine medaka (Oryzias melastigma) development via two interrelated mechanisms: (1) Epigenetic dysregulation: Aberrant CG methylation in key regulatory genes (casr, cacna2d2, dnai1, alox15b, etc.) was associated with developmental toxicity, altering gene expression profiles critical for normal growth. (2) Ferroptosis activation: Tralopyril exposure triggered iron overload and fth1 dysregulation, while mitochondrial uncoupling (ucp2) exacerbated oxidative stress, contributing to cellular damage. Notably, epigenetic alterations, such as methylation changes in alox15b, can influence the ferroptosis pathway by regulating genes involved in iron metabolism and oxidative stress. This, in turn, amplified toxic effects and contributed to multiorgan damage. These alterations led to defects such as cardiac remodeling, skeletal malformations, and neuromuscular dysfunction, ultimately resulting in locomotor decline. Inhibitor rescue experiments identified critical molecular targets of tralopyril's toxic effects and demonstrated cross-regulation between ucp2 expression and the ferroptosis pathway. These findings elucidate the key molecular mechanisms underlying tralopyril-induced developmental abnormalities and behavioral impairments, emphasizing the synergistic effects of mitochondrial dysfunction and ferroptosis. Overall, this study expands the understanding of mitochondrial function and ferroptosis in environmental toxicology and provides a scientific basis for ecological risk assessment and mitigation strategies for environmental pollutants.

Long-term declines in salmonid populations observed in California Central Valley have prompted efforts to enhance the understanding of how environmental stressors impact sensitive species. Bifenthrin, a current-use insecticide, has been consistently detected throughout the Sacramento-San Joaquin River Delta (Delta) and has been linked to detrimental effects in salmon. Traditionally, aqueous concentration is used in toxicological studies to evaluate the effects of pesticides on aquatic organisms, which assumes that concentration of the toxicant in water is a valid surrogate for dose. The critical body residue approach was established as an improved technique for assessing toxicity of hydrophobic contaminants, but there is a lack of data to support the application of this method in assessing risk of contaminant exposure in the environment. The current study creates a response spectrum model (RSM) demonstrating the relationship between internal residue and effects observed in Chinook Salmon from laboratory-based exposures. To develop the RSM, a series of behavioral and physiological endpoints were measured using bifenthrin-dosed Chinook Salmon to use with previously generated sublethal and mortality data for incorporation in the model. The most sensitive endpoints were locomotion and shoaling behavior, followed by anxiety, growth, swim performance, upper thermal sensitivity, olfactory response, and lethality. The RSM endpoints were compared to bifenthrin residues in field-collected juvenile Chinook Salmon collected in 2019–2020 as part of our earlier studies. We found bifenthrin tissue residues were at similar levels to the most sensitive endpoints featured in the RSM, suggesting that bifenthrin exposure in the field could cause behavioral effects to salmon as they out-migrate through the Delta. The developed RSM is a tool that could be used by water quality managers to evaluate the extent to which bifenthrin exposure may impact behavior and performance in juvenile salmon, providing a field-based verification of its effects on outmigration.

The endangered anadromous naked carp Gymnocypris przewalskii is a rare fish species found in Qinghai Lake, China. Studying the swimming abilities of naked carp is crucial for enhancing the design of passageways for these unique fish. Two regression models were employed to assess the influence of salinity, water temperature, body size, and gender on induced flow velocity (Uind), critical swimming speed (Ucrit), burst swimming speed (Uburst), and endurance in naked carp. The findings pointed toward the fact that larger fish under-performed smaller fish for (Uind), (Ucrit), (Uburst), and endurance. Male fish generally attained higher (Uind), (Ucrit), (Uburst), and endurance than female fish. Naked carp in saltwater demonstrated a higher level of (Uind), (Ucrit), and (Uburst) than freshwater. The velocity limit of the pool-and-weir fishway should be lower than the fastest flow speed fish can swim against over a specific distance. The endurance model can estimate the maximum swimming distance at various flow velocity barriers. Observed results can guide design and operation criteria of pool-and-weir fishways for native naked carp.

Climate change accelerates coral reef decline and jeopardizes recruitment essential for ecosystem recovery. Adult corals rely on a vital nutritional exchange with their symbiotic algae (Symbiodiniaceae), but the dynamics of reliance from fertilization to recruitment are understudied. We investigated the physiological, metabolomic, and transcriptomic changes across 13 developmental stages of Montipora capitata, a coral in Hawai?i that inherits symbionts from parent to egg. We found that embryonic development depends on maternally provisioned mRNAs and lipids, with a rapid shift to symbiont-derived nutrition in late developmental stages. Symbiont density and photosynthesis peak in swimming larvae to fuel pelagic dispersal. By contrast, respiratory demand increases significantly during metamorphosis and settlement, reflecting this energy-intensive morphological reorganization. Symbiont proliferation is driven by symbiont ammonium assimilation in larval stages with little evidence of nitrogen metabolism in the coral host. As development progresses, the host enhances nitrogen sequestration, regulating symbiont populations, and ensuring the transfer of fixed carbon to support metamorphosis, with both metabolomic and transcriptomic indicators of increased carbohydrate availability. Although algal symbiont community composition remained stable, bacterial communities shifted with ontogeny, associated with holobiont metabolic reorganization. Our study reveals extensive metabolic changes during development with increasing reliance on symbiont nutrition. Metamorphosis and settlement emerge as critical periods of energetic vulnerability to projected climate scenarios that destabilize symbiosis. This highly detailed characterization of symbiotic nutritional exchange during sensitive early life stages provides essential knowledge for understanding and forecasting the function of nutritional symbioses and, specifically, coral survival and recruitment in a future of climate change.

The white abalone, Haliotis sorenseni, is an endangered marine gastropod that has shown no signs of population recovery despite fishery closure and protective status. To better understand the energetic demands, hypoxia tolerance, and critical habitat of this species, we measured oxygen consumption rates over a size range of captive-reared H. sorenseni at different environmental oxygen concentrations and temperatures in comparison to the more common red abalone, H. rufescens. We found that H. sorenseni has a relatively low metabolic rate that likely contributes to generally slow growth that can hamper recovery efforts. We also discovered that both H. sorenseni and H. rufescens appear to partially conform to ambient oxygen conditions by lowering their metabolism to deal with increasing hypoxia while still retaining an aerobic scope until reaching a critical oxygen concentration (Pcrit), at which point they become oxylimited. For species exhibiting such relationships, determining the P90, P75, P50, and P25 (dissolved oxygen value at which oxygen consumption is 90 %, 75 %, 50 %, and 25 % of resting metabolic rate), as well as the Pcrit and oxygen supply capacity, can provide useful metrics to compare hypoxia sensitivities among species and individuals. Variability in these metrics suggest potential fitness differences for H. sorenseni individuals spawned and raised in captivity for restoration outplanting. Higher temperatures also led to an increase in P90, P75, P50, P25, and Pcrit and decrease in factorial aerobic scope for H. sorenseni, revealing the potential compounding effects of high temperature and low oxygen. Our results thus provide a suite of physiological metrics on which to test the health and fitness of captive-reared abalone and can help inform selection of appropriate outplanting sites for endangered H. sorenseni.

Animals may respond to threats from climate change through plastic physiological changes (i.e., acclimation), adaptive evolution (i.e., genetic change), or moving to new habitats that match their climatic niche. Organisms from volcanic habitats are underexplored but may serve as models for physiological and evolutionary responses to warming temperatures. Here, we examined how different genetic lineages of the Hawaiian anchialine shrimp Halocaridina rubra respond to temperature, including animals from noticeably warm habitats created during eruptions of Kilauea in 2018. We find that thermal limits are elevated in animals from newer, warm habitats, but decrease to match those of animals from older, cooler habitats after being maintained at room temperature. Laboratory experiments further suggest thermal limits are mainly shaped by acclimation. In contrast, metabolic rates show almost no acclimation responses to temperature, with rates largely explained by test, not acclimation temperatures. There was little difference in thermal acclimation of metabolic rates among animals from different genetic lineages. However, metabolic rates at room temperature were different among shrimps from different genetic lineages, suggesting genetic variation for aerobic metabolism could be a target of selection during climate change. We find that shrimp from newer, warm habitats can live at or near their critical thermal maximum, suggesting some anchialine species may be able to deal with increased temperatures from climate change by being pre-adapted to colonize warm habitats associated with volcanism. We also highlight the potential impacts of climate change on anchialine habitats and suitable experimental designs for categorizing and quantifying thermal acclimation of biological rates.

Despite extensive research in the last two decades, exploring the potential mechanisms underlying the sensitivity and resistance of marine organisms to ocean acidification is still imperative. Species interactions can play a role in these mechanisms, but the extent to which they modulate organismal responses to ocean acidification remains largely unknown. Here, we investigated how ocean acidification (pH 7.7) affects energy homeostasis and fitness of mussels (Mytilus coruscus) by assessing their physiological responses, intestinal microbiome and nutritional quality of their food (microalgae). Under ocean acidification, the mussels had reduced feeding rates by 34 % and reduced activities of digestive enzymes (pepsin by 39 %, trypsin by 28 % and lipase by 53 %) due to direct exposure to acidified seawater and increased phenol content of microalgae. Richness and diversity of intestinal microbiome (OTU, Chao1 index and Shannon index) were also lowered by ocean acidification, which can undermine nutrient absorption. On the other hand, energy expenditure of mussels increased by 53 % under ocean acidification, which was associated with the upregulation of antioxidant defence (SOD, CAT and GPx activities). Consequently, energy reserves in mussels decreased by 28 %, which were underpinned by the reduction in protein, carbohydrate and lipid contents. Overall, we demonstrate that ocean acidification could disrupt herbivore-algae and host-microbe interactions, thereby lowering the energy balance and impairing the health of marine organisms. This can have ramifications on the population and energy dynamics of marine communities in the acidifying ocean.

Muscular biopsy is a non-lethal muscle sampling technique allowing for the fish to be returned to its natural environment or its tank after sampling. This technique offers the opportunity for the scientific community and fish farmers to carry out assays on very small muscle samples (between 1 and 40 mg) such as heavy metal, trace elements, lipid composition or muscle energetic metabolism to evaluate, for instance, the health of the fish. The aim of the present study was to determine if a red muscle biopsy affects rainbow trout (Oncorhynchus mykiss) survival and their physiological performances (swimming and hypoxia resistances). Each group, fish that had a biopsy (n = 30) or fish that did not (n = 30), was subsequently tested for either a hypoxia resistance test (HRT) or a swimming resistance test (SRT). HRT and SRT were conducted 7- and 10-days post-surgery (dps), respectively. Biopsy had no effect on hypoxia resistance and on swimming parameters (sustained and critical swimming speeds, tail beat frequency, routine and maximal oxygen consumptions). Even if no significant effect was observed between control and biopsy groups on morphometric parameters (body weight variation and condition factors), all the trout lost weight which can be explained by a post-surgery trauma such as human manipulation stress or a local inflammation. More specifically, body weight variation was significantly more important in the 7-dps group compared to the 10-dps group which had the opportunity to eat three more days compared to the 7-dps group. Corroborated with a principal component analysis, we showed that a red muscle biopsy is a good approach as it had no effect on whole-animal performance 7- and 10-dps and it had no effect their survival.

Objective
Mutations in TARDBP (encoding TDP-43) are associated with the neurodegenerative disease amyotrophic lateral sclerosis (ALS) and include familial missense mutations where there are a lack of models and mechanisms examining how they are pathogenic.

Methods
In this study, we developed 2 tardbp (Tdp-43) knock-in (KI) zebrafish mutant models encoding the analogous A382T and G348C variants and investigated their degenerative phenotypes.

Results
We show that both models display reduced survival as well as an age-dependent motor phenotype that manifests at 1.5 years. Both variants in either the heterozygous or homozygous state did not impact protein expression levels of Tdp-43 in the central nervous system. However, homozygous G347C zebrafish displayed reduced expression levels of the tardbp transcript. We observed muscle cell atrophy starting at 1 year of age and loss of large spinal cord motor neurons in both KI models in older fish (2.35–3 years of age). We did not observe Tdp-43 aggregates. However, we did observe increased cytoplasmic Tdp-43 localization in spinal cord motor neurons in A379T zebrafish. At 1 year of age, whole spinal cord RNA-sequencing revealed an upregulation of neuroinflammatory transcripts in both models, as well as the selective downregulation of transcripts involved with synaptic function in G347C zebrafish, including syn2a, syn2b, syt2a, and stxbp1a.

Interpretation
These novel models of common TDP-43 disease variants provide a unique opportunity to further our understanding of neurodegeneration in vivo and demonstrate that mutations in the same protein and domain can manifest with different phenotypes.

Ocean warming and marine heatwaves are predicted to have adverse impacts on marine organisms. Yet, knowledge of the molecular mechanisms that underpin successful or failed acclimation to increasing temperatures remains incomplete. We conducted an aquaria-based study of early-life stage clownfish comprising of six thermal regimes, measuring the metabolic, and multi-tissue transcriptional response of Amphiprion ocellaris using seven tissues. Sampling at 31°C increased metabolic rates in fish reared at 28°C; however, these effects were reduced with increasing developmental rearing at 31°C. Transcriptomic analysis revealed multi-tissue reprogramming of metabolic processes at +3°C, particularly in the liver-pancreas axis. Importantly, chronic larval-juvenile exposure to +3°C induced the acclimation of metabolic rates and caused the upregulation of oxidative phosphorylation (liver) and the downregulation of insulin secretion (pancreas). These results indicate that temperature increase will drive tissue-wide metabolic reprogramming in fish, with changes in key energetic pathways underpinning fish's ability to acclimate to warming.

Marine heatwaves (MHWs), coral bleaching, and chronic local stressors such as eutrophication are accelerating regime shifts from coral‐ to algae‐dominated reefs, increasingly favoring the proliferation of invasive, fast‐growing, and often more grazing‐resistant turf and macroalgae. A central tenet of global reef management strategies is that herbivorous fishes can sustain critical top‐down control of algal proliferation as oceans warm. Here, we challenge this tenet by experimentally evaluating, under controlled laboratory conditions, whether herbivorous coral reef fishes across three key functional groups—browser ( Naso lituratus ), grazer ( Acanthurus triostegus ), and scraper ( Chlorurus spilurus )—can maintain effective algal control across present‐day (24.0°C–27.5°C) temperatures and into projected MHWs (31°C). We assessed (1) whether individuals evacuated thermally stressed conditions, effectively abandoning algal control, and (2) for those that remained, whether they could meet elevated energetic demands by foraging ad libitum on a mixture of Caulerpa spp.—a rapidly spreading and archetypal group of invasive algae in the Indo‐Pacific. All species gained body mass while foraging exclusively on these algae during winter and summer (~0.18%–0.62% per day). However, despite remaining in thermally stressed conditions and maintaining stable foraging rates, all species experienced consistent body mass declines (~0.41%–1.62% per day) under MHW exposure. This precipitous decline in body mass was driven by ~54%–60% increases in basal energetic demands without corresponding increases in food intake. Survival estimates based on body mass loss ranged from ~20–81 days, which is substantially shorter than the projected ~126–152‐day average duration of future MHWs. Our findings reveal that while short‐term algal control may persist during thermal stress, prolonged exposure appears to erode herbivore physiological condition, effectively undermining top‐down control of some algal types. Consequently, as ocean warming intensifies, herbivore protection strategies may become increasingly less effective at staving off algae proliferation and dominance in threatened reef ecosystems.

Total dissolved gas supersaturation (TDGS), commonly resulting from dam discharge, poses significant threats to fish survival by inducing gas bubble trauma (GBT) in downstream populations. Understanding the sensitivity of fish to TDGS during developmental stages is critical for evaluating survival risks during flood seasons. This study investigated the adverse effects of TDGS on three life stages-eggs, larvae, and juveniles-of the endemic fish Schizothorax prenanti (S. prenanti) in the upper Yangtze River. After hatching in 120 % and 130 % TDG levels, both eggs and larvae exhibited severe GBT symptoms with survival rates declining to 70 % and 77 % respectively, compared to 88 % in the control group. Hatching rates also dropped significantly to 66 % and 59 %, compared to 84 % in the control group. Larvae exhibited a marked reduction in body length at TDG levels above 120 %, while heart rates increased significantly at TDGS levels above 110 %. Juveniles subjected to 120 % and 130 % TDGS showed extensive GBT symptoms, with median lethal times of 92 and 35 h, respectively. After 35 h of exposure, juveniles in the 130 % TDGS group showed significant reductions in active metabolic rate (AMR), standard metabolic rate (SMR), and factorial aerobic scope (F-AS), while critical swimming speed (U crit ) and burst swimming speed (U burst ) remained unchanged compared to the control group. In terms of S. prenanti exposed to 130 % TDGS, U crit and U burst significantly declined when survival rate dropped to 25 %, while AMR, SMR, and F-AS exhibited significant changes prior to mortality occurred. Moreover, AMR, SMR, and F-AS in juveniles were more vulnerable to TDGS than U crit and U burst. These findings enhance the understanding of TDGS-induced stress on developing fish and support the development of ecological management strategies for TDG during flood seasons.

The thermal dependence of metabolism has attracted much attention because metabolism is linked to many ecological properties, from individuals to ecosystems. The rate at which physiological traits change is an important factor to account for when assessing thermal plasticity since the time of exposure might allow organisms to compensate for the effect of temperature on performance. Here, we studied short‐ and long‐term thermal plasticity of metabolic rate and its scaling with body mass of Alpine charr ( Salvelinus umbla ). To do so, we raised juveniles from Lake Geneva at 4.5°C and 8.5°C, measured their routine metabolic rate at their incubation temperature (long exposure, > 6 months), and individuals raised at 4.5°C were also tested at 8.5°C (short exposure, < 24 h). The metabolic rate of Alpine charr increased with temperature, as theoretically expected. We found no effects of duration of exposure on metabolic rate or its scaling with body mass. Despite a long‐term exposure to higher temperature, individuals did not adjust their metabolic rate as compared to individuals exposed to a rapid increase in temperature, questioning the capacity of Alpine charr to compensate for temperature increase through their metabolic rate. Therefore, our data reveal no compensation mechanisms of Alpine charr to counterbalance the acute effect of temperature. Further studies will be required to fully understand the adaptive potential of Alpine charr in the context of global change.

Thermal studies on fish can help us to understand their robustness to warming climates. Most experiments are performed on smaller individuals and may not represent larger life-stages owing to physiological scaling effects, particularly with regards to thermal tolerance and respiratory capacities. In this study, respirometry experiments were performed on big Atlantic salmon (Salmo salar) (≈4 kg) following 3-weeks acclimation to seawater of 9 °C or 19 °C. Additionally, gill and heart morphology traits were assessed. At 9 °C metabolic rates resembled earlier work on smaller fish. However, at 19 °C following stress exposure, 81 % died unexpectedly within ≈6 h while surviving fish struggled to recover a baseline metabolic rate. Most noteworthy was that maximum metabolic rates remained similar across temperature whereas smaller Atlantic salmon previously were found to increase their maximum metabolic rates until near-lethal temperatures. As standard metabolic rates also inevitably increases with temperature, aerobic scopes become reduced at 19 °C. Meanwhile lamellar density was unaffected, indicating similar gill surface areas. However, acclimation to 19 °C reduced ventricle roundness and symmetry, while bulbus width to ventricle width ratios increased. These changes presumably reflect adaptive responses to more metabolically demanding environments. Yet the fish appeared unable to supply sufficient oxygen at 19 °C during stress, which we attribute to physiological scaling constraints. Big Atlantic salmon were therefore more susceptible to stress-induced mortality at elevated temperatures, indicating reduced thermal tolerance relative to smaller individuals. This highlights the need to include larger fish in experiments as the underlying basis for thermal tolerance changes across large differences in body size.

Predation pressure plays an important role in shaping animal behaviour and physiology, driving prey species to evolve stronger escape strategies. Swimming performance is a key trait for many aquatic organisms to evade predation. It is therefore intuitive that increased predation pressure should select for faster swimming abilities when outswimming predators is a viable option for prey. However, experimental evidence allowing for a causal link between predation and the evolution of swimming performance is currently lacking. Here, we used artificial selection lines of guppies (Poecilia reticulata) based on predation survival to test the evolutionary relationship between predation pressure and swimming speed. We used a swim tunnel with incremental increase in water flow to test critical swimming speed. Our results show that predation-line females, but not males, outperformed those of the control-lines in critical swimming speed. We also found that in predation-line females the variance in critical swimming speed was reduced in comparison with control-line females, which is congruent with directional selection against slow swimming genotypes. This study provides experimental evidence for the evolutionary role of predation pressure in enhancing swimming performance and shaping behavioural adaptations in prey species.

Washing of road tunnels is essential for removing accumulated pollutants such as tyre wear particles, brake dust, exhaust residues, and road debris to ensure visibility and safe driving. Tunnel washing generates large volumes of contaminated runoff known as untreated tunnel wash runoff (UTWR). Some countries filter UTWR through a sedimentation process before release to reduce contamination, generating what is known as treated tunnel wash runoff (TWR). This study investigates the potential environmental impact of diluted UTWR (25 %) and TWR (50 %) by evaluating their toxicity in fish and comparing the effect to tyre-particle leachate (TPL, 2 g/L). UTWR was collected during tunnel cleaning, and TWR was collected after 14 days of filtration through sand sediments, from the Bodø tunnel in Norway. Zebrafish larvae, used as a fish model, exposed to contaminated runoff exhibited increased mortality, impaired growth, developmental anomalies, altered swimming behaviour, and changes in gene expression. Both UTWR and TWR exposure induced significant toxicity in zebrafish larvae, though the toxicity caused by TWR was notably lower than that of UTWR. This study shows that current filtration methods of tunnel wash water reduce the levels of most pollutants, however, more research is needed on how tunnel wash-water runoff affect aquatic ecosystems.

Under global warming, understanding the evolutionary adaptation of ectotherms resting metabolic rate (RMR) is critical for predicting long‐term populations' response to temperature increases. While several studies have evaluated metabolic rate evolution under different thermal context, most focused on space‐for‐time substitutions rather than assessment of populations' adaptation over time. Here, applying the method of resurrection ecology, we used sediment cores as an archive of populations' evolution and hatched ephippia from different sediment layers to examine the metabolic evolution of modern vs. ancient Daphnia longispina populations. Focusing on an oligotrophic subalpine lake, for which temperature has been monitored for almost a century, we were able to link population response to historical thermal contexts. We demonstrate that modern (2021) clonal lines exhibit a 60% higher RMR than ancient ones (1997) when measured at 20°C. The higher RMR correlated with reduced juvenile growth rates at 20°C but increased survival rates at high temperatures, with a higher thermal limit 2°C higher in modern populations. These findings reflect a trade‐off favoring survival over growth under warming and likely result from increased oxygen uptake capacities, which provide an advantage at high temperatures but constrain individual energy budgets at non‐stressful temperatures. Overall, this study suggests that survival at extreme weather events, such as heatwaves, may play an important role in shaping the RMR adaptation of Daphnia and, more generally, zooplankton populations.

Bioavailable nitrogen governs ocean productivity and carbon fixation by regulating phytoplankton growth and community composition. Nitrogen input primarily results from fixation, while denitrification and anammox remove bioavailable nitrogen in oxygen‐depleted conditions. Traditionally considered limited to highly suboxic (i.e., <5 μM) waters, recent studies suggest that fixed‐nitrogen removal processes may extend beyond, elevating global nitrogen loss estimates. This study directly quantifies fixed‐nitrogen loss across oxygen gradients (from 140 to 32 μM) along the Estuary and Gulf of St. Lawrence using N cycle tracers (,, and ). Notably, we observe significant production when ambient concentrations fall below a threshold value of 58.9 ± 1.1 μM, including potential water column fixed‐nitrogen removal processes above suboxia. We hypothesis that ambient deoxygenation eases the formation of suboxic microareas in suspended organic matter. Benthic production remains unaffected under intensifying water column deoxygenation from 50 down to 32 μM, but the contribution of produced through nitrification in the sediment to denitrification diminishes as deoxygenation intensifies. Combined, water column and benthic fixed‐nitrogen removal processes drive anomalies and strong deficiency in bottom waters. Additionally, the observed threshold also triggers production. Overall, our study highlights the profound impact of coastal ocean deoxygenation on nitrogen cycling, suggesting unexpected shifts even at ambient oxygen concentrations traditionally considered well above suboxic conditions. This study explores processes that influence the availability of nitrogen, a limiting key nutrient for algal production and the biological carbon pump in the ocean. It focusses on nitrogen loss mechanisms which remove bioavailable nitrogen under barely detectable oxygen levels. Contrary to previous assumptions limiting these mechanisms to very low oxygen levels, this research suggests, in natural conditions, that nitrogen loss mechanisms can potentially occur in environments with higher ambient oxygen levels, challenging our understanding of nitrogen cycling. This study uses multiple nitrogen cycle tracers coupled with sediment core incubations to quantify nitrogen loss in the Estuary and Gulf of St. Lawrence. The findings include substantial bioavailable nitrogen loss and nitrous oxide production in the hypoxic water column as well as strong nitrate deficiency. This nitrogen loss can have broad implications and impact the growth and productivity of algae at the ocean surface. These insights will help to better predict the role of the ocean in the context of climate change. Key Points Fixed‐N is possibly removed in suboxic (<5 μM) microzones on suspended organic matter at bulk of 32–59 μM in the St. Lawrence Estuary Benthic and possibly water column fixed‐N removal processes drive a strong deficiency in bottom waters of the St. Lawrence Estuary Significant net production of was observed in bottom waters of the St. Lawrence Estuary when ambient fell below 59 μM

African turquoise killifish (Nothobranchius furzeri) is the shortest-lived vertebrate that can be bred in captivity, making it an ideal model organism for aging studies. However, whether the animal can be used for studying cardiac aging and whether cellular senescence contribute to this ageing process remain unclear. Here, we conducted a longitudinal study on the GRZ strain, aiming to identify phenotypic and functional markers for cardiac aging. We found that cardiac ageing in GRZ fish can be measured by comparing fish at 16 weeks to 8 weeks of age, using systemic markers such as body/fin coloration, body weight, BMI, cardiac ageing markers such as EF, E/A ratio, and swimming capacity, and cellular senescence markers such as SA-β-gal staining, p15/p16, γ-H2A.X, and SASP markers. Senolytic treatment with D (Dasatinib) and Q (Quercetin) from 12 to 16 weeks mitigated senescence and decelerated cardiac ageing. Together, our findings established GRZ as a useful vertebrate model for studying cardiac ageing and related cardiac senescence.

In marine benthic environments, oxygen availability is highly variable across temporal and spatial scales. Such variability generates heterogeneous microhabitats in which organisms experience marked changes from saturated (i.e. normoxic) to anoxic conditions. For sessile colonial species, fine spatial differences in oxygen availability can trigger intra-colony phenotypic differences, influencing the overall colony performance/fitness. Here, we assessed the extent to which intra-colony differences in oxygen regimens influence biological characteristics in adult and larval stages of the colonial bryozoan Bugula neritina. For this, we measured the critical sensitivity to low oxygen for upper and lower zones of adult colonies and their larvae. We also measured larval swimming–exploring behaviour and settlement under hypoxia and normoxia. Although the results show similar intra-colony tolerances in the adults, differences were found in their larvae. While the lower zones of the colonies showed higher tolerant larvae, the upper zones had larvae with higher sensitivity and a tendency to avoid low-oxygen microhabitats. These larvae settle more quickly and in greater numbers compared with their lower-zone counterparts. Our results suggest that intra-colony differences in sensitivity to low-oxygen conditions (particularly during larval stages) can be important regulators of ecological processes (e.g. recruitment) and the resilience of benthic colonial species in deoxygenated oceans.

Isogenic (clonal) fish lines are useful experimental models to study effects of environment versus genetics on phenotypic traits, as they can be maintained for generations without change, providing advantages over outbred groups prone to generational change and higher variation. Here we performed experiments on isogenic Atlantic salmon groups that were either heterozygous diploid, homozygous diploid, triploid, or heterozygous diploid incubated at 4 °C instead of 8 °C. We measured metabolic rates, stress response, and hypoxia tolerance to assess whole-animal performance traits. Then we measured the morphology of hearts and otoliths since both are known to be influenced by environmental history. Isogenic, ploidy, and zygosity statuses were confirmed from microsatellite markers. Embryonic development is affected by temperature, hence the 4 °C incubation group was tested 9 months later when it had reached an equivalent size as the other groups. Curiously, a bimodal size distribution emerged in this group. Physiological traits were similar between groups apart from higher standard metabolic rates in the 4 °C incubated fish. Each group had distinct heart morphologies where fish with a slower growth history resembled wild-phenotypes while homozygous fish had the most deviating hearts. Proportions of vaterite deposition in otoliths showed high individual variation and did not differ between groups. Lower coefficients of variation within groups were found when compared to outbred fish, but this was not consistent for all traits assessed. As such, substantial phenotypic variation in physiology and morphology was still observed in isogenic Atlantic salmon, which can be ascribed to random environmental factors.

Objective We investigated whether physical enrichment can be used at the captive-rearing stage to promote a more natural phenotype and better prepare juvenile Lake Sturgeon for the variability of the natural environment upon release. Methods We exposed age-0 Lake Sturgeon to different types of physical enrichment for 6 months. We used four treatments: a nonenriched (control) tank, a tank with gravel substrate, a tank with vertical structures, and a tank with both gravel substrate and vertical structures. We tracked the survivorship, growth, and body condition of each fish throughout the experiment and analyzed their dorsal color pattern prior to and following 5 months of enrichment exposure. At the end of the experiment (6 months), we measured several physiological parameters, including metabolic rate, plasma cortisol, and critical thermal maximum. Results We observed mortalities in all the enriched tanks but not in the nonenriched tank. Growth rate and body condition varied considerably between enrichment treatments across time. The fish that were reared with structures alone displayed a lower routine metabolic rate and higher aerobic scope than those in all the other treatment groups. We did not observe any effects of enrichment on the critical thermal maximum or the baseline or stress-induced cortisol levels in these fish. Conclusions We recommend that hatchery managers add structures that allow for sheltering and resting behaviors to the rearing environment of age-0 Lake Sturgeon for a few months prior to release. Our study highlights the value of physical enrichment for improving the welfare of captive-reared fish, which could translate to higher rates of postrelease survival and success for reintroduced age-0 Lake Sturgeon.

Groundwater ecosystems play a pivotal role in global biodiversity and ecosystem functioning, yet they face increasing pressures from climate change. The amphipod genus Niphargus, a dominant taxon in European groundwater habitats, has shown evidence of broad thermal adaptability that challenges prevailing theories on narrow thermal niches in groundwater species. This study investigated the locomotory behaviour of Niphargus longicaudatus (Costa, 1851), a stygobitic amphipod, under habitat temperature (9 °C) and preferred temperature (15 °C) using 3D tracking techniques. Individuals at 15 °C displayed significantly higher average swimming speed, increased vertical occupancy, and greater trajectory tortuosity compared to those at 9 °C, despite spending a similar amount of time in movement. These behavioural shifts suggest metabolic adjustments enabling enhanced resource exploration at warmer temperatures. The findings are contextualized within the evolutionary history of the amphipod genus Niphargus, shaped by past climatic, geological and hydrological conditions, which may have selected for eurythermal traits in some lineages. These adaptations highlight potential to exploit habitats across a broad temperature range, not necessarily providing an advantage to N.longicaudatus due to the complex effects of climate change on groundwater ecosystems. This work underscores the importance of integrating behavioural, metabolic, and paleoclimatic perspectives in understanding the impacts of climate change on subterranean biodiversity and distribution.

Variation in rates of oxygen uptake (Mo 2 ) among individuals within a species is widespread and observed during both rest and activity. Such variation is expected to be important in animal physiology, ecology, and evolution, yet the mechanistic bases for this variation are incompletely understood. In the present study, we asked whether interindividual variation in Mo 2 at rest (standard Mo 2) and during an incremental swim test (peak swimming Mo 2 [peak Mo 2,swim ]) in Gulf killifish ( Fundulus grandis ) is related to variation in mitochondrial Mo 2 in five tissues: heart, oxidative skeletal muscle, glycolytic skeletal muscle, liver, and brain. After accounting for the effects of body mass, Mo 2,standard was positively related to liver mass and its maximum capacity for oxygen flux by the electron transport system (ETS). Peak Mo 2,swim was positively related to ETS respiration by heart ventricle and mitochondrial respiration required to offset the dissipation of the proton gradient in the absence of ATP synthesis (LEAK) by glycolytic skeletal muscle. The relationship between peak Mo 2,swim and glycolytic muscle LEAK respiration prompted us to examine the relationship between the aerobic cost of transport and mitochondrial phosphorylation efficiency in glycolytic skeletal muscle. We found that individuals with a lower phosphorylation efficiency consumed more oxygen to travel a given distance (i.e., had a higher aerobic cost of transport). This result supports the idea that LEAK respiration represents an energetic cost during activity, which might be partially offset if higher LEAK results in less reactive oxygen species formation.

The establishment of laboratory-based species has facilitated the standardization of biological research methods; however, the stable culturing conditions of laboratories are dissimilar to the dynamic conditions of natural environments, potentially influencing fundamentally different research outcomes between laboratory and wild populations. This study sought to compare the toxicity of ultraviolet filters (UVFs) avobenzone, octocrylene, and oxybenzone to laboratory and wild populations of Daphnia pulex, while also testing the effects of culturing both populations in either laboratory or lake water in 48 hr and 21 day toxicity tests. Both daphnid populations demonstrated poor performance when cultured in nonancestral waters for three generations (i.e., laboratory Daphnia in lake water or wild Daphnia in laboratory water), including 25% decreased reproduction in control treatments and ≥ 50% mortality to most UVF treatments. Toxicity varied in each population cultured in ancestral waters; laboratory D. pulex were more sensitive to 30.7 μg/L of avobenzone and 18.8 μg/L of oxybenzone (> 25% greater mortality, ≥ 20% decreased reproduction vs. wild daphnids), whereas wild D. pulex were more sensitive to 25.6 μg/L of octocrylene (30% decreased mortality, 44% decreased reproduction vs. laboratory daphnids). These results demonstrate that Daphnia populations can deviate after decades of isolation, highlighting the challenges of relating laboratory-generated data to field results. In addition, culture water greatly affected daphnid performance during experimentation, potentially leading to misinterpreted results when studying wild organisms. This research highlights the importance of understanding how laboratory and wild organisms can differ, so that research modeling environmental outcomes can be applied in an appropriate context.

Under phosphorus (P) deficiency, Lupinus albus develops cluster roots that allow efficient P acquisition, while L. angustifolius without cluster roots also grows well. Both species are non‐mycorrhizal. We quantitatively examined the carbon budgets to investigate the different strategies of these species. Biomass allocation, respiratory rates, protein amounts and carboxylate exudation rates were examined in hydroponically‐grown plants treated with low (1 μM; P1) or high (100 μM; P100) P. At P1, L. albus formed cluster roots, and L. angustifolius increased biomass allocation to the roots. The respiratory rates of the roots were faster in L. albus than in L. angustifolius. The protein amounts of the non‐phosphorylating alternative oxidase and uncoupling protein were greater in the cluster roots of L. albus at P1 than in the roots at P100, but similar between the P treatments in L. angustifolius roots. At P1, L. albus exuded carboxylates at a faster rate than L. angustifolius. The carbon budgets at P1 were surprisingly similar between the two species, which is attributed to the contrasting root growth and development strategies. L. albus developed cluster roots with rapid respiratory and carboxylate exudation rates, while L. angustifolius developed a larger root system with slow respiratory and exudation rates. Under phosphorus deficiency, Lupinus albus developed cluster roots with fast respiratory and carboxylate exudation rates, while L. angustifolius developed a large root system with slow respiratory and exudation rates. These contrasting traits resulted in similar whole‐plant carbon budgets.

Global temperature increases are predicted to have pronounced negative effects on the metabolic performance of both terrestrial and aquatic organisms. These metabolic effects may be even more pronounced in intertidal organisms that are subject to multiple, abruptly changing abiotic stressors in the land-sea transition zone. Of the available studies targeting the intertidal environment, emphasis has largely been on water-breathing model organisms and this selective focus resulted in limited reliable forecasts on the impact of global warming on primarily air-breathing intertidal species. We investigated the thermal sensitivity of six phylogenetically related fiddler crab species that occupy different microhabitats on intertidal shores from south America and east Asia to test how bimodal-breathing intertidal ectotherms cope with thermal stress. We examined the metabolic physiology and thermal limits of the crabs by measuring their cardiac function and oxygen consumption along a thermal gradient. Their specific thermal microhabitat was also appraised. We found that subtropical fiddler crab species inhabiting vegetated microhabitats have lower upper lethal temperatures and therefore greater thermal sensitivity in comparison to their tropical counterparts. Additionally, females exhibited higher oxygen consumption and lower lethal temperatures in comparison to males. Our results contradict previous predictions that species from higher latitudes that experience greater temperature variability have broader latitudinal distributions, greater phenotypic plasticity and lower thermal sensitivity. Furthermore, the higher thermal sensitivity demonstrated by female fiddler crabs with respect to males strongly suggests a role of both gametogenesis and physiological dimorphism on the thermal performance of tropical and subtropical intertidal organisms. These observations ultimately, advocates for further studies on sex-biased and development-biased thermal sensitivity before drawing any generalizations based on a single sex or life stage.

Unlike adult mammals, zebrafish regenerate spinal cord tissue and recover locomotor ability after a paralyzing injury. Here, we find that ependymal cells in zebrafish spinal cords produce the neurogenic factor Hb-egfa upon transection injury. Animals with hb-egfa mutations display defective swim capacity, axon crossing, and tissue bridging after spinal cord transection, associated with disrupted indicators of neuron production. Local recombinant human HB-EGF delivery alters ependymal cell cycling and tissue bridging, enhancing functional regeneration. Epigenetic profiling reveals a tissue regeneration enhancer element (TREE) linked to hb-egfa that directs gene expression in spinal cord injuries. Systemically delivered recombinant AAVs containing this zebrafish TREE target gene expression to crush injuries of neonatal, but not adult, murine spinal cords. Moreover, enhancer-based HB-EGF delivery by AAV administration improves axon densities after crush injury in neonatal cords. Our results identify Hb-egf as a neurogenic factor necessary for innate spinal cord regeneration and suggest strategies to improve spinal cord repair in mammals. Zebrafish can regenerate after paralyzing spine injuries and regain locomotor ability, unlike mammals. Here authors show that the neurogenic factor Hb-egf promotes spinal cord regeneration in zebrafish and is regulated by an enhancer that can similarly direct expression in the pro-regenerative setting of neonatal mice.

Spinal cord injury (SCI) is one of the most frequent causes of disability, accompanied by motor and postural impairments, as well as autonomic and behavioural disorders. Since the beginning of the last century, researchers have been developing and refining experimental models of SCI to study pathogenesis and find therapies. Since the beginning of the 20th century, quite a wide range of methods have been developed for contusion and compression injury, complete and partial transection of the spinal cord, and many others. The choice of model subject in such studies was not limited to mammals, but also included amphibians, lampreys, and even fish. Many functional tests have been proposed to assess functional recovery after injury in laboratory animals, ranging from simple rating scales to locomotion kinematics or recording of spinal neuronal activity. This review describes existing models of SCI in most animal species used in neurobiology. Their key characteristics are discussed, which determine the choice of model and model animals depending on the experimental tasks. Each experimental model of SCI has its own advantages and disadvantages determined by species-specific features of spinal cord anatomy and physiology, the speed of recovery from injury, and the ratio of the necrosis zone to the penumbra. The applicability and availability of the proposed methods for assessing the speed and completeness of recovery is also an important factor.

Skeletal muscle function and quality are strong indicators of metabolic health. Here, we present a protocol for skeletal muscle phenotyping in zebrafish. We describe steps to evaluate spontaneous locomotion, measure oxygen consumption during incremental exercise, and analyze cross-sectional area of skeletal muscle cells in adult zebrafish. This protocol has potential applications to assess zebrafish muscle quality and function in studies of metabolic diseases, aging, and skeletal muscle health. For complete details on the use and execution of this protocol, please refer to Grepper and Tabasso et al. 1.

Triploidy is an effective tool for producing sterile fishes but often results in impaired performance in commercial aquaculture. In light of this, our study compared the physiological response to exhaustive exercise in juvenile diploid and triploid Arctic charr Salvelinus alpinus, a polar species with great potential for aquaculture. A standard ramping swimming protocol revealed no significant difference in critical swimming velocity ( U crit ) between ploidies. There was also no effect of ploidy on post‐ U crit blood glucose, lactate or haematocrit. However, triploids had a significantly higher frequency of erythrocyte nuclear segmentation. Independent of ploidy, there was also a significant positive correlation between blood lactate levels and U crit. We conclude that triploidy does not impair the response to exhaustive exercise in juvenile S. alpinus.

Invasive bigheaded carps (Hypophthalmichthys molitrix and H. nobilis) have caused substantial ecological and economic damage throughout the Mississippi River Basin and expanded their range threatening the Laurentian Great Lakes. Broadband acoustic deterrents have shown promise in repelling carp and are currently being assessed in navigational lock chambers on the Mississippi River. These nonphysical deterrents permit vessel navigation while reducing carp passage. However, no single deterrent is 100% effective and fish may habituate to the sound after repeated playback. Carp exhibit aversive behaviors to carbon dioxide, which suggests combining these two stimuli into one deterrent system could extend the effective duration of sound and reduce the frequency of carbon dioxide (CO2) application. We conditioned bigheaded carps to associate broadband sound from outboard boat motors (0.06–5 kHz, ~150 dB re. 1 μPa) with CO2 application (~35,000 ppm) in small (80 L) and large (3475 L) two-choice shuttle tanks. We compared negative phonotaxis responses over one to four weeks between fish conditioned with sound and CO2, sound and air, or sound alone. Similar CO2 avoidance thresholds were found across tank sizes and species. Conditioning treatment did not affect time to leave the sound chamber, confirming sound alone remains a deterrent for all fish. Carp conditioned with CO2 took longer to return to the sound chamber than control treatments. Control fish were closer to the speaker during playback than during the pre-sound period, while fish conditioned with CO2 were not significantly closer. Conditioning paradigms may extend the effective duration of nonphysical deterrents for bigheaded carps. Conditioning with CO2 may also increase proactive flight-responses over reactive freeze-responses. Findings could be applied to increase nonphysical barrier effectiveness at locks along the Mississippi River and help protect the Laurentian Great Lakes from invasion.

Di-2-ethylhexyl phthalate (DEHP), a widely used plasticiser, is a pervasive environmental contaminant with potential detrimental effects on aquatic organisms. The objective of this study was to provide an integrative analysis of how DEHP alters energy balance, temporal homeostasis and fish welfare - interrelated aspects critical to animal survival - to address critical gaps in our understanding of its toxicological effects. Goldfish (Carassius auratus) were chronically (14 days) treated with DEHP. Energy balance was assessed through locomotor activity, metabolic rate, feed intake, and growth indices. Daily of locomotor and metabolic rate rhythms were examined to explore potential circadian disruptions. Anxiety-like behaviours were also examined to assess welfare. DEHP decreased feed intake and food-anticipatory activity (FAA), suggesting an anorexigenic effect, which may have been mediated by increased expression of anorexigenic genes in the hypothalamus and liver, along with decreased expression of orexigenic npy (neuropeptide Y) gene in the hypothalamus. Growth parameters remained unchanged, probably due to compensatory reductions in energy expenditure, as indicated by decreased locomotor activity and metabolic rate. Daily rhythms in these two parameters were preserved, suggesting no disruption in temporal homeostasis. DEHP increased hepatic expression of peroxisome proliferator-activated receptor (PPAR)-related genes, suggesting that PPARs activation is a potential mode of action for DEHP in fish. Anxiety levels were elevated, as evidenced by increased thigmotaxis and scototaxis in behavioural tests, which may be mediated by changes in hypothalamic neuropeptides. These findings highlight the adverse effects of DEHP on energy regulation and animal welfare, providing novel insights into its broader physiological consequences in fish.

Deterrent technologies are one component of preventing the spread of invasive fishes to protect aquatic ecosystems from biodiversity loss. Curtains of bubbles can act as a non-physical barrier to deter fish movements, but will not stop all species in all situations. Modifications to bubble curtains that decrease fish movements would help protect aquatic ecosystems. The current study sought to quantify whether adding carbon dioxide gas (CO2) to a bubble curtain would enhance its efficacy to block fish. For this, a choice tank was outfitted with bubble curtains infused with either compressed air alone, or with two different concentrations of CO2 [30 or 100 mg/L]. Passage rates and position of common carp (Cyprinus carpio, an invasive Cyprinid) and black bullhead (Ameiurus melas, a native Ictalurid) exposed to these treatments were compared. Common carp were less likely to pass a bubble curtain when CO2 gas was used relative to the use of compressed air alone, and only 30 mg/L CO2 was needed to reduce passage. Black bullhead passages were not influenced by the bubble curtain, even with the addition of CO2. However, black bullhead, were found 30% further upstream of the curtain when CO2 was used relative to the control and air alone treatments, demonstrating avoidance of CO2. This study shows that CO2 added to a bubble curtain will enhance its ability to block passage of invasive fish.

Parental care can increase the fitness of parents through increased offspring survival but can also reduce reproductive output by limiting time and energy allocated to additional mating opportunities. The evolutionary origin of parental care is often associated with shifts in life‐history traits (e.g., high investment in few, large offspring, slow offspring growth), but little is known about whether the evolutionary loss of care is associated with reciprocal shifts in the same life‐history traits. Here, we capitalize on the divergence of parental care between ecotypes of three‐spined stickleback ( Gasterosteus aculeatus ) to test for associations between parental care and life‐history traits. While males from most stickleback populations provide care, an unusual “white” ecotype has recently lost paternal care. We found support for the hypothesis that the evolutionary loss of paternal care is associated with shifts in female life‐history traits; relative to females of the ecotype with paternal care, females of the white ecotype that lack paternal care produced clutches with a similar overall mass and a greater number of smaller eggs, despite their smaller body size, suggesting lower per‐offspring investment. We did not detect an ecotypic difference in embryonic development rate, metabolic rate, or offspring age at hatching, contrary to the ‘safe harbor hypothesis’. These results support the theory that behavioral traits such as parental care co‐evolve with other life‐history traits and highlight opportunities for future study of the underlying causal mechanisms.

Ocean acidification, a major consequence of climate change, poses significant threats to marine organisms, particularly when combined with other environmental stressors such as chemical pollution. This study investigated the physiological responses of Trochus niloticus to a 28-day exposure of ocean acidification and/or sulfamethoxazole, a commonly detected antibiotic in the South China Sea. Exposure to either acidification or sulfamethoxazole individually triggered adaptive responses through immune activation, antioxidant reactions, and metabolic adjustments. However, concurrent exposure resulted in significant adverse effects, including compromised immunity, oxidative damage, and disrupted energy budget. These findings provide new insights into how ocean acidification interacts with antibiotic pollution to synergistically impact marine gastropods, suggesting that multiple stressors may pose greater threats to T. niloticus populations than single stressors alone.

As more physiologists start to incorporate animal behavior into their experiments, especially in the olfactory behavior research field, some considerations are often overlooked, partly due to the inherited way that physiological experiments are traditionally designed and performed. Here we highlight some of these subtle but important considerations and make a case for why these might affect the results collected from behavioral assays. Our aim is to provide useful suggestions for increased standardization of methods so they can be more easily replicated among different experiments and laboratories. We have focused on areas that are less likely to be mentioned in the materials and methods section of a manuscript such as starvation, preliminary experiments, appropriate sample sizes and considerations when choosing an odorant for an assay. Additionally, we are strongly cautioning against the use of alarm cue to generate behavioral responses due to its highly unstable chemical properties/potency. Instead, we suggest using pure chemicals (made up of one known molecule) such as amino acids, bile acids, or polyamines that are commercially available and easier to make up in known concentrations. Lastly, we strongly suggest using environmentally relevant concentrations of these odorants. We believe these guidelines will help standardize these assays and improve replication of experiments within and between laboratories.

Temperature fluctuations challenge ectothermic species, particularly tropical fish dependent on external temperatures for physiological regulation. However, the molecular mechanisms through which low-temperature stress impacts immune responses in these species, especially in relation to chromatin accessibility and epigenetic regulation, remain poorly understood. In this study, we investigate chromatin and transcriptional changes in the head kidney and thymus tissues of Nile tilapia (Oreochromis niloticus), a tropical fish of significant economic importance, under cold stress. By analyzing cis-regulatory elements in open chromatin regions and their associated transcription factors (TFs), we construct a comprehensive transcriptional regulatory network (TRN) governing immune responses, including DNA damage-induced apoptosis. Our analysis identifies 119 TFs within the TRN, with Stat1 emerging as a central hub exhibiting distinct binding dynamics under cold stress, as revealed by footprint analysis. Overexpression of Stat1 in immune cells leads to apoptosis and increases the expression of apoptosis-related genes, many of which contain Stat1-binding sites in their regulatory regions, emphasizing its critical role in immune cell survival during cold stress. These results provide insights into the transcriptional and epigenetic regulation of immune responses to cold stress in tilapia and highlight Stat1 as a promising target for enhancing cold tolerance in tropical fish species.

The importance of energy budgets in understanding the ecology, conservation and production of crayfishes has long been recognized. Standard metabolic rate (SMR) estimates the minimum metabolic rate required for basic maintenance of an organism while at rest, and is a critical parameter for investigating energy balance and metabolism. Estimating SMR involves quantifying oxygen uptake under specific conditions. Standard methodology for estimating SMR has been described and evaluated for fishes, but not thoroughly investigated for crayfishes. We adapted a recommended protocol developed for fishes in order to determine appropriate methodologies for measuring SMR in crayfishes. Study animals consisted of 18 individuals of Procambarus clarkii (Girard, 1852) collected in Alabama, USA. Respiration rates were measured using an optical respirometry system (Loligo Systems®; Viborg, Denmark) and intermittent respirometry techniques. Crayfish respiration stabilized the morning after initiation of the trial indicating that a 12 h overnight period was sufficient to acclimate crayfish to respirometry chambers. After 12 h of daylight, respiration of acclimated crayfish typically exhibited a short spike when lights were turned off, indicating data collected within ~2 h following a light change should be excluded from the dataset used to calculate SMR. When calculating SMR, a quantile approach was typically more appropriate than the mean of the lowest normal distribution approach. SMR calculated during the day was only marginally higher than SMR calculated during the night, indicating that SMR can be estimated during either period if shelters are provided in the respiration chambers. Due to the wide diversity of crayfish species and ranges, our recommendations may not be appropriate for every crayfish species or subpopulation. The recommendations can serve, however, as a valuable starting point and the described methodology provides a standardized approach for determining appropriate protocols to measure SMR of crayfish species of interest.

The carbon isotopic compositions of otolith can be used to retrospectively estimate fish field metabolic rates (FMR) and are advantageous for practical applications, particularly for small-sized fish whose metabolic rates are challenging to measure in the field. Based on the proportional contribution of metabolism-derived carbon to otolith carbon, this study validated an approach for juveniles of the anadromous fish species, chum salmon Oncorhynchus keta, by integrating respirometry experiments and stable isotope ratio mass spectrometry (SIA). The isotopic results showed that the compositions of otolith carbon isotope (d13Cotolith) values were negatively correlated with body mass, aligning with the mass-specific allometric theory. The ratio of metabolism-derived carbon in otoliths (Cresp) was calculated based on the carbon isotope compositions of the otolith, dissolved inorganic carbon in water (DIC), and diet. The results indicated that up to nearly 50 % of the carbon in juvenile chum salmon otoliths was metabolism-origin. Further, temperature gradient experiments showed that the Cresp values increased until around a temperature of 15? and fell significantly at 20?, suggesting that the factorial FMR was restricted at temperatures exceeding the optimal temperature for metabolism (Topt). Thus, the relationship between metabolic rate and Cresp was validated within the temperature range of 9–15?. Nonetheless, as a cool-water species, wild chum salmon rarely experience water masses above 15?. Therefore, our results were feasible to estimate the FMR of juvenile chum salmon in the wild and could be used for reconstructing their metabolic histories, thereby providing insights into the metabolic strategies associated with migration traits.

This study focuses on selecting the most appropriate turbulence model for simulating fish swimming behavior in river confluences. To achieve this, three numerical models—k-ε, k-ω, and large eddy simulation—were compared by running simulations under identical flow conditions and evaluating the results against biological experimental data. Among the models, the k-ω model demonstrated the smallest relative error, consistently within 5% of the experimental results, confirming its superior accuracy and reliability for this application. The k-ω model's ability to capture boundary layer turbulence and near-wall flow dynamics proved essential for studying fish swimming in complex turbulent environments. Simulations revealed that both the flow velocity ratio between the main stream and tributary and the confluence angle are critical factors influencing the flow structure. At higher flow velocity ratios (R = 1/3 and 3/1) or large confluence angles (α ≥ 90°), turbulence intensity increased, leading to more complex vortex formations that significantly impacted fish swimming speed. When the flow velocity ratio (R) is 1/3, the fish can achieve a maximum swimming speed of 2.75 L/s, which is significantly higher than the swimming speed of 1.18 L/s observed when R is 3/1. Additionally, fish closer to the center of the flow field experienced greater turbulence, resulting in higher energy expenditure. The findings provide crucial insights into the hydrodynamic mechanisms driving fish swimming behavior in dynamic aquatic environments.

Little is known about the non-thermal climate change factors (hypoxia and acidification) in the context of freshwater invasions. It is supposed that invasive Ponto-Caspian gobies have relatively wide environmental tolerance ranges due to their evolution in the highly variable environment of local limans and estuaries. Thus, we assumed that they better tolerate reduced oxygen and pH levels in invaded areas of Central and Western Europe compared to native species. Using a laboratory respirometry assay, we compared the effect of short-term progressive hypoxia and acidification on routine metabolic rate (RMR) of the invasive racer goby Babka gymnotrachelus and monkey goby Neogobius fluviatilis and their native counterparts sharing similar ecological niches (European bullhead Cottus gobio and gudgeon Gobio gobio, respectively). The natives displayed a lower hypoxia tolerance compared to the gobies (as changes in their RMR appeared at higher oxygen concentrations), whereas the monkey goby, but not the racer goby, appeared more tolerant to reduced pH than its native competitor. Thus, hypoxia tolerance seems to be a key feature shaping the invasive potential of the monkey and racer goby in benthic fish communities. However, the invasion success of the racer goby may be attenuated by progressing water acidification.

Coastal seawater hypoxia is increasing in temperate estuaries under global climate change, yet it is unknown how low oxygen conditions affect most estuarine species. We found that hypoxia has increased since the 1990s in an estuary hosting the sea anemone Nematostella vectensis (Jacques Cousteau National Estuarine Research Reserve, New Jersey, USA). Adult N. vectensis bred from anemones collected in this estuary exposed to three consecutive nights of hypoxia (dissolved oxygen = 0.5–1.5 mg L −1 for ~12 h night −1 ) during gametogenesis displayed decreased aerobic respiration rates and biomass, indicating metabolic disruption. Physiological declines were correlated with changes in the expression of genes related to oxygen‐dependent metabolic processes, many of which are targets of hypoxia‐inducible factor 1α (HIF1α), demonstrating the activity of this transcription factor for the first time in this early‐diverging metazoan. The upregulation of genes involved in the unfolded protein response and endoplasmic reticulum and Golgi apparatus homeostasis suggested that misfolded proteins contributed to disrupted physiology. Notably, these responses were more pronounced in females, demonstrating sex‐specific sensitivity that was also observed in reproductive outcomes, with declines in female but not male fecundity following hypoxia exposure. However, sperm from exposed males had higher mitochondrial membrane potential, indicating altered spermatogenesis. Further, crosses performed with gametes from hypoxia‐exposed adults yielded strikingly low developmental success (~2%), yet larvae that did develop displayed similar respiration rates and accelerated settlement compared to controls. Overall, hypoxia depressed fitness in N. vectensis by over 95%, suggesting that even stress‐tolerant estuarine species may be threatened by coastal deoxygenation.

The degree of tolerance to adverse conditions ultimately shapes a species' vulnerability to environmental changes. Some studies have reported limited thermal tolerance due to hypoxia in fish employing aquatic respiration. However, there is a lack of information regarding the effects of hypoxia on thermal tolerance in fish exhibiting bimodal respiration. A set of Amazonian fish species has adaptations to breathe air when oxygen in water is not enough to fulfil demand. Additionally, loricariid species within this group possess stomach adaptations for air breathing. The Loricariidae family exhibits varying stomach types and observed morphological differences could influence their ability to obtain oxygen from the air. This ability may, in turn, have consequences for the thermal tolerance of these species. Our objective was to assess the effects of hypoxia on thermal tolerance, along with the physiological (whole-animal metabolic rates and mitochondrial respiration) and behavioural mechanisms involved, in two facultative air-breathing species: Pterygoplichthys pardalis and Ancistrus dolichopterus. These species showcase morphological distinctions in their stomachs, with the former having a higher capacity to obtain oxygen from the air. Thermal tolerance in P. pardalis remained unaffected by dissolved oxygen in the water when air access was available but decreased when access to the water surface was restricted, specifically in hypoxic conditions. Conversely, the thermal tolerance of A. dolichopterus decreased below the critical oxygen partial pressure (Pcrit), even with access to air, highlighting their limited ability to obtain oxygen through their adapted stomach. Our results underscore that air breathing enhances thermal tolerance, but this effect is prominent only in species with a higher capacity for air breathing.

Upper thermal tolerance may be limited by convective oxygen transport in fish, but the mechanisms constraining heart function remain elusive. The activation of anaerobic metabolism imposes an osmotic stress on cardiomyocytes at high temperatures that must be countered to prevent swelling and cardiac dysfunction. We tested the hypothesis that cardiac taurine efflux is required to counter the osmotic impact of anaerobic end product accumulation in brook char, Salvelinus fontinalis. Fish were fed a diet enriched in β-alanine, a competitive inhibitor of the taurine transporter, to induce taurine deficiency and inhibit transporter function. In vivo, stroke volume increased by 60% and cardiac output doubled in control fish during a 2°C h−1 thermal ramp. Stroke volume was temperature insensitive in taurine-deficient (TD) fish, so cardiac output was 30% lower at high temperatures. The thermal sensitivity of aerobic metabolism did not differ, and lactate accumulated to a similar degree in the two diet treatment groups, indicating that taurine deficiency does not impact energy metabolism. Heart taurine efflux was absent and ventricular muscle osmolality was 40 mOsmol kg−1 higher in TD brook char following thermal stress. Swelling and decreased ventricular compliance likely impair diastolic filling to constrain stroke volume in TD fish. The adrenaline sensitivity of cardiac contractility and the regulation of intracellular pH in the brain and liver were also impacted in TD brook char. Taurine efflux appears necessary to counteract the hydrodynamic impact of activating anaerobic metabolism and this process may limit heart function under acute thermal stress.

Quantifying the energy costs of various activities is critical to understand key aspects of animal behavior and ecology. Currently, calorimetry is the most widely used method to measure those costs in laboratory studies, whereas field studies use the doubly labeled water method, heart rate and dynamic body acceleration (DBA). However, these methods are limited or even biased because of restricted space for movement, low temporal resolution and/or the need for logger attachment or implantation. Measuring energy costs of behaviors is difficult, especially in small, highly mobile animals. Here, using a damselfish, Chromis viridis, we demonstrate that DBA, obtained from marker-less, automatic video tracking and 3D reconstruction, can effectively estimate oxygen consumption rate. We show that our video-based DBA method can be used to estimate metabolic costs of various activities, such as locomotion and feeding, on an individual basis.

Heavy crude oil, like bitumen, is used globally for plastics, petrochemicals and road surfacing. Canada's oil sands are the world's third largest crude oil reserve, and diluted bitumen (dilbit) is transported across North America primarily via pipeline and rail. Two environmentally-relevant concentrations of dilbit were used with a suite of toxicological endpoints to determine if a 3 °C increase in ambient temperature (Ta) water modulated the effects of dilbit to coho salmon (Oncorhynchus kisutch) when exposed from fertilization to swim-up. The 10–20 % increase in mortality and 25 % reduction in hypoxia tolerance with dilbit exposure was magnified by 18 % and 40 %, respectively, in warmer water. Consequences of dilbit exposure persisted after 6 weeks of additional rearing in clean Ta water but were greatest in fish exposed to dilbit at elevated temperature: additional 20 % mortality and 30 % decrease in mass relative to controls, and a residual 20 % reduction in hypoxia tolerance not seen with dilbit exposure alone. Relatively lower induction of the Phase I biotransformation enzyme cyp1a and greater tissue PAC content in warm-exposed coho suggests reduced PAC metabolism as a mechanism for the observed potentiation. Thus, seasonal fluctuations and baseline increases in water temperature from climate change can exacerbate the adverse effects of oil spills on developing fish.

Swimming ability is critical for navigating complex benthic habitats, yet the biomechanical strategies demersal sharks employ to modulate body and fin movements across varying speeds remain largely unexplored. This study examines speed‐dependent kinematic patterns in the small‐spotted catshark ( Scyliorhinus canicula ), a benthic species with limited endurance for sustained swimming. Using high‐speed videography in a flow tank, we quantified adjustments in tail beat frequency, body angle, wave speed and curvature across a range of speeds (0.5–6 body lengths per second). Our results reveal that S. canicula exhibits distinct kinematic shifts as speed increases, adopting a more streamlined posture and increasing tail beat frequency to accommodate higher flow rates. Principal component analysis identified swimming speed as the primary factor influencing kinematic variation, with higher speeds necessitating more consistent body alignment and tail movement. Strouhal numbers within the optimal range for propulsive efficiency (0.2–0.4) at intermediate speeds (1–2 BL s −1 ) suggest that S. canicula maximizes energetic efficiency within this range, although further research is required to elucidate the metabolic implications. This study establishes a foundational framework for understanding the biomechanics of steady swimming in a demersal shark, providing insights into the ecological and evolutionary pressures shaping locomotor adaptations in benthic species.

Ectotherms, such as fish, are highly dependent on the stability of their environment to regulate body temperature, performance, and metabolism. Increasing temperatures cause behavioural changes in fish which can be observed and used as indices for determining upper thermal limits. The thermal agitation temperature (T ag ) is a recent, and ecologically significant, sublethal index for the upper thermal limit. Previous studies have described thermal agitation as the endpoint, prior to the critical thermal maximum (CT max ), where fish start exhibiting apparent refuge-seeking and thermal avoidance behaviour. It is an assumption that fish are seeking thermal refuge at T ag, but evidence for this is lacking. Therefore, this study aimed to validate this assumption by using zebrafish (Danio rerio) and providing them with thermal refuge while increasing their environment's temperature past T ag. The behavioural responses of D. rerio were observed and their spatial movements were tracked using the animal-tracking software, AnimalTA. The analysis from this study indicated that refuge is sought out prior to T ag and distance between shoal members increases after T ag, indicating D. rerio may trade-off the protective value of a shoal to search for thermal refuge. Our study demonstrates that with refuge available, D. rerio can surpass T ag until refuge itself exceeds T ag, validating that agitation is refuge-seeking behaviour, but a mechanism of last resort. This insight improves our understanding of fish responses to thermal stress and emphasizes the value of using T ag as a sublethal metric alongside CT max in thermal tolerance studies, with potential applications in ecology and conservation contexts.

Anthropogenic noise pollution is increasingly acknowledged as a major threat to marine ecosystems, especially for sound-sensitive species, such as the large yellow croaker (Larimichthys crocea). While the effects of underwater noise on fish behavior and physiology have been well-documented, its influence on oxygen metabolism across varying temperatures remains poorly understood. This study examines the impact of boat noise on the oxygen consumption rate (OCR) of juvenile large yellow croakers at different temperatures, a key factor in their metabolic activity. The underwater noise generated by a fishing boat spans a broad frequency range, with a peak spectrum level of 130 dB re 1 µPa at low frequencies between 100 and 200 Hz. Our findings reveal that boat noise significantly elevates the OCR of juvenile fish, with mass-specific OCR increasing by 65.0%, 35.3%, and 28.9% at 18 °C, 25 °C, and 30 °C, respectively. Similarly, individual OCR rose by 60.7%, 35.3%, and 17.1% at these temperatures. These results demonstrate that boat noise triggers a stress response in fish, resulting in heightened metabolic demands across different seasonal conditions. Notably, the impact of boat noise on respiratory metabolism is most significant at lower temperatures. In aquatic environments with stable oxygen levels, the noise-induced rise in oxygen consumption could lead to hypoxia and provoke maladaptive behavioral changes in fish.

In aquaculture, analyzing the swimming behavior of micropterus salmoides using multi-object tracking technology is a crucial non-contact method for obtaining data and assessing vitality. However, existing approaches suffer from high false detection and target loss rates due to issues like occlusion between individuals and their variable body shapes. Therefore, this paper proposes a novel multi-object tracking model (Yolo-AWD + CBT) for accurate and real-time tracking of micropterus salmoides swimming behavior. Our method improves upon the Yolov8n backbone network feature extraction module by incorporating an Adaptive Weight Downsampling (AWD) module to address the loss of feature information during downsampling in the original network. To tackle the challenge of variable body shapes during swimming, we replace the original loss function with XIOU, enhancing the network's ability to localize targets. For the tracking algorithm, we introduce trajectory confidence information into ByteTrack, thus improving the tracking accuracy of micropterus salmoides during swimming. Experimental results on object detection and multi-object tracking datasets demonstrate that our proposed model (Yolo-AWD + CBT) achieves a 1.07 % and 5.4 % improvement in P and (AP50:95). In terms of tracking performance, compared to the original model, HOTA increases by 6.25 %, MOTA by 3.15 %, and IDsw decreases by 58.33 %, resulting in swimming behavior data errors within the range of -7 % to +3 %. These results indicate that our proposed multi-object tracking method can effectively track multiple targets in various scenarios and accurately capture micropterus salmoides swimming behavior data, providing technical support for non-contact vitality analysis.

Genome size is an important correlate of many biological features including body size, metabolic rate, and developmental rate and can vary due to a variety of mechanisms, including incorporation of repetitive elements, duplication events, or reduction due to selective constraints. Our ability to understand the causes of genome size variation is hampered by limited sampling of many nonmodel taxa, including monogonont rotifers. Here, we used high-throughput Nanopore sequencing and flow cytometry to estimate genome sizes of nine species of monogonont rotifers representing seven families, including three representatives of Superorder Gnesiotrocha. We annotated the genomes and classified the repetitive elements. We also compared genome size with two biological features: body size and metabolic rate. Body sizes were obtained from the literature and our estimates. Oxygen consumption was used as a proxy for metabolic rate and was determined using a respirometer. We obtained similar genome size estimates from genome assemblies and flow cytometry, which were positively correlated with body size and size-specific respiration rate. Importantly, we determined that genome size variation is not due to increased numbers of repetitive elements or large regions of duplication. Instead, we observed higher numbers of predicted proteins as genome size increased, but currently many have no known function. Our results substantially expand the taxonomic scope of available genomes for Rotifera and provide opportunities for addressing genetic mechanisms underlying evolutionary and ecological processes in the phylum.

Forecasts indicate that rising temperatures towards the future and the expansion of dead zones will change environmental suitability for fish early stages. Therefore, we assessed the chronic effects of warming (26 °C), hypoxia (<2-2.5 mg L -1 ) or their combination on mortality rate, growth, behaviour, energy metabolism and oxidative stress using Atherina presbyter larvae as a model species. There were no differences between the treatments in terms of mortality rate. The combination of warming and hypoxia induced faster loss of body mass (+22.7%). Warming, hypoxia or their combination enhanced boldness (+14.7-25.4%), but decreased exploration (-95%-121%), increased the time in frozen state (+60.6-80.5%) and depleted swimming speed (-45.6-50.5%). Moreover, routine metabolic rate was depleted under hypoxia or under the combination of warming and hypoxia (-56.6 and 57.2%, respectively). Under hypoxia, increased catalase activity (+56.3%) indicates some level of antioxidant defence capacity, although increased DNA damage (+25.2%) has also been observed. Larvae also exhibited a great capacity to maintain the anaerobic metabolism stable in all situations, but the aerobic metabolism is enhanced (+19.3%) when exposed to the combination of both stressors. The integrative approach showed that changes in most target responses can be explained physiologically by oxidative stress responses. Increased oxidative damages (lipid peroxidation and DNA damage) and increased interaction between antioxidant enzymes (superoxide dismutase and catalase) are associated to increased time in frozen state and decreased swimming activity, growth rates and boldness. Under all stressful situations, larvae reduced energy-consuming behaviours (e.g. depleted exploration and swimming activity) likely to stabilize or compensate for the aerobic and anaerobic metabolisms. Despite being an active small pelagic fish, we concluded that the sensitive larval phase exhibited complex coping strategies to physiologically acclimate under thermal and hypoxic stress via behavioural responses.

By linking gene regulation to swimming performance under different water flow conditions, the study could reveal how the fish adapt to their environments, providing insights into evolutionary biology and ecology. The current study observed significant variations in swimming performance under various water flow velocities and examined the associated gene regulation. Grass carp were subjected to controlled water velocities to measure the critical swimming speed ( U crit ), which showed that the swimming performance was increased based on body length; however, a reduction in swimming performance was observed as the water flow increased ( p < 0.05). Additionally, brain samples were collected for transcriptomic analysis, which revealed that differentially expressed genes (DEGs) were functionally annotated revealing key pathways associated with changed behavior patterns. The Enrichment analysis showed significant variation in all groups including behavior ( p < 0.05***), skeletal system development ( p < 0.05***), hormone activity ( p < 0.05***), muscle contraction ( p < 0.05**), locomotion ( p < 0.05*), and swim bladder development ( p < 0.05*) were found the major regulators of behavior in grass carp under water velocities. Moreover, some genes were identified and found significantly different for enzymes and hormones, which could play a potential role during swimming performance such as gene‐ca7 ( p < 0.005***). The current study provides evidence of the neurogenetic mechanism underlying the changed swimming activity of grass carp under water velocity, which could have important implications for understanding the impact of hydrodynamics and the fish.

Early rearing environment affects performance later in life. In Atlantic salmon (Salmo salar) aquaculture intensive smolt production has been linked to deviating cardiac morphology and increased mortality risks following stressful events during the marine production phase. To investigate the effects of early growth environment on later life-stages, two smolt groups were produced; a fast-growing group reared at 13 °C under continuous light and a slow-growing group reared at 6 °C under a natural photoperiod. The two groups were smoltified and transferred to 9 °C seawater at the same time and at similar sizes, although the slow smolts were ≈ 1000 day degrees older. Respirometry and swim tunnel experiments were performed to assess physiological performances along with morphological analyses of the hearts. We hypothesized that the slower growth trajectory would allow for the development of heart morphology more resembling that of wild salmon and that this should translate into improved physiological performance. Fast-growing smolt had more misaligned and enlarged bulbi as well as asymmetric ventricles compared to slow-growing smolt. However, contrary to our hypothesis, we did not find clear evidence for impaired physiological performance in fast-growing fish. That is, neither standard nor maximum metabolic rates, absolute critical swimming speed, stress recovery, or haematological parameters at fatigue differed between treatments. Mortality risks associated with deviating cardiac morphology first tend to occur in larger sized fish than investigated here. We therefore conclude that while early rearing environment clearly modulates cardiac morphology, recently seawater adapted Atlantic salmon do not yet show signs of compromised functionality associated with cardiac morphological differences at the whole-animal level. Future research should aim to incorporate larger sized fish in physiological experiments for a more appropriate representation of the latter production phase in Atlantic salmon aquaculture and its associated fish welfare problems.

Air-breathing fish risk losing aerially sourced oxygen to ambient hypoxic water since oxygenated blood from the air-breathing organ returns through the heart to the branchial basket before distribution. This loss is thought to help drive the evolutionary reduction in gill size with the advent of air-breathing. In many teleost fish, gill size is known to be highly plastic by modulation of their anatomic diffusion factor (ADF) with inter-lamellar cell mass (ILCM). In the anoxia-tolerant crucian carp, ILCM recedes with hypoxia but regrows in anoxia. The air-breathing teleost Chitala ornata has been shown to increase gill ADF from normoxic to mildly hypoxic water by reducing ILCM. Here, we test the hypothesis that ADF is modulated to minimize oxygen loss in severe aquatic hypoxia by measuring ADF, gas-exchange, and by using computed tomography scans to reveal possible trans-branchial shunt vessels. Contrary to our hypothesis, ADF does not modulate to prevent oxygen loss and despite no evident trans-branchial shunting, C. ornata loses only 3% of its aerially sourced O 2 while still excreting 79% of its CO 2 production to the severely hypoxic water. We propose this is achieved by ventilatory control and by compensating the minor oxygen loss by extra aerial O 2 uptake.

Inspired from discussions around human dietetics and behavioral traits, the study presumed that bold fish may have better long chain polyunsaturated fatty acids (LC-PUFA) accumulation strengths than shy fish, when subjected to a common food. Using Eurasian perch (Perca fluviatilis) model similar in age and sexually immature, it was investigated whether any statistically significant difference in the LC-PUFA accumulation from food to liver or brain between size-matched bold and shy individuals exist. Results suggest an enhanced accumulation of LC-PUFAs such as arachidonic acid (ARA, 20:4n-6), eicosatrienoic acid (ETA, 20:3n-3), eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) happen from feed (p < 0.05) to either liver or brain. However, we found no statistically significant difference (p > 0.05) in overall fatty acids profile or LC-PUFA of liver or brain between bold and shy individuals, neither any differences in potential eicosanoid actions (as mediated by LC-PUFAs ARA: EPA ratio) in their brain or liver, when fed a common feed/ lipid source. As such the original presumption was rejected. The bold and shy Eurasian perch are similar in their capabilities to selectively incorporate or endogenously fortify LC-PUFA content. The study concludes that the endogenous pool or stoichiometry of LC-PUFAs seem unrelated to boldness or shyness in fish. The managerial implication of the findings is to better link the behavioral traits in aquaculture or fish ethology to nutrition and physiology.

Winter is a critical period for largemouth bass (Micropterus nigricans) with winter severity and duration limiting their population growth at northern latitudes. Unfortunately, we have an incomplete understanding of their winter behaviour and energy use in the wild. More winter-focused research is needed to better understand their annual energy budget, improve bioenergetics models, and establish baselines to assess the impacts of climate warming; however, winter research is challenging due to ice cover. Implantable tags show promise for winter-focused research as they can be deployed prior to ice formation. Here, using swim tunnel respirometry, we calibrated heart rate and acceleration biologgers to enable estimations of metabolic rate (ṀO 2 ) and swimming speed in free-swimming largemouth bass across a range of winter-relevant temperatures. In addition, we assessed their aerobic and swim performance. Calculated group thermal sensitivities of most performance metrics indicated the passive physicochemical effects of temperature, suggesting little compensation in the cold; however, resting metabolic rate and critical swimming speed showed partial compensation. We found strong relationships between acceleration and swimming speed, as well as between ṀO 2 and heart rate, acceleration, or swimming speed. Jackknife validations indicated that these modeled relationships accurately estimate swimming speed and ṀO 2 from biologger recordings. However, there were relatively few reliable heart rate recordings to model the ṀO 2 relationship. Recordings of heart rate were high-quality during holding but dropped during experimentation, potentially due to interference from aerobic muscles during swimming. The models informed by acceleration or swimming speed appear to be best suited for field applications.

A fundamental requirement for all animals is to sense and respond to changes in environmental O2 availability. Low O2 (hypoxia) typically stimulates breathing, a universal and critical response termed the hypoxic ventilatory response (HVR). In this study, we test the hypothesis that taste-signaling pathways are used for O2 sensing and activation of the HVR. We show that Merkel-like cells (MLCs), which are part of the taste-bud complex, function as O2 chemoreceptor cells in larval zebrafish and that transduction of the O2 signal uses taste-signaling pathways. Specifically, MLCs responded to hypoxia in vivo with an increase in Ca2+ activity that can drive the HVR. In addition, MLCs transmit O2 signals to afferent cranial nerves IX and X (nIX/X), which project into the area postrema within the hindbrain and synapse with interneurons that are in contact with vagal motor neurons. Hypoxia or chemo-activation of nIX/X caused Ca2+ activity to increase within the area postrema and elicited hyperventilation. The results provide the first demonstration of an O2 signaling pathway that commences with the activation of taste receptors (MLCs) to yield a critical physiological reflex, the HVR.

We use the sentinel mangrove crab, Minuca rapax, as a model to investigate the effects of metallic settleable particulate matter (SePM) on wetland. Multiple levels of energetic responses, including (i) metabolic rate and energy budget, (ii) oxidative stress, and (iii) behavioral response by righting time, were assessed as well as the metal and metalloid content in crabs exposed to 0, 0.1 and 1 g.L -1 of SePM, under emerged and submerged conditions over five days, simulating the rigors of the intertidal habitat. Al, Fe, Mn, Cr, and Y exhibited a concentration-dependent increase. Metal concentrations were higher in submerged crabs due to the continuous ingestion of SePM and direct exposure through gills. Exposure concentration up to 1 g.L -1 decreased metabolic rate and enzymatic activities, reduced assimilation efficiency and energy for maintenance, and induces a slower response to righting time, probably by metal effects on nervous system and energy deficits. In conclusion, SePM exposure affects the redox status and physiology of M. rapax depending on he submersion regime and SePM concentration. The disruption to the energy budget and the lethargic behavior in M. rapax exposed to SePM implies potential ecological alterations in the mangrove ecosystem with unknown consequences for the local population.

Red drum, Sciaenops ocellatus, are a marine teleost native to the Gulf of Mexico that routinely experiences periods of low oxygen (hypoxia). Recent work has demonstrated this species has the capacity to improve aerobic performance in hypoxia through respiratory acclimation. However, it remains unknown how hypoxia acclimation impacts anaerobic metabolism in red drum, and the consequences of exhaustive exercise and recovery. Juvenile fish were acclimated to normoxia (n = 15, DO 90.4 ± 6.42 %) or hypoxia (n = 15, DO 33.6 ± 7.2 %) for 8 days then sampled at three time points: at rest, after exercise, and after a 3 h recovery period. The resting time point was used to characterize the acclimated phenotype, while the remaining time points demonstrate how this phenotype responds to exhaustive exercise. Whole blood, red muscle, white muscle, and heart tissues were sampled for metabolites and enzyme activity. The resting phenotype was characterized by lower pH e and changes to skeletal muscle ATP. Exhaustive exercise increased muscle lactate, and decreased phosphocreatine and ATP with no effect of acclimation. Interestingly, hypoxia-acclimated fish had higher pH e and pH i than control in all exercise time points. Red muscle ATP was lower in hypoxia-acclimated fish versus control at each sample period. Moreover, acclimated fish increased lactate dehydrogenase activity in the red muscle. Hypoxia acclimation increased white muscle ATP and hexokinase activity, a glycolytic enzyme. In a gait-transition swim test, hypoxia-acclimated fish recruited anaerobic-powered burst swimming at lower speeds in normoxia compared to control fish. These data suggest that acclimation increases reliance on anaerobic metabolism, and does not benefit recovery from exhaustive exercise.

Microplastics (MPs), as a ubiquitous environmental contaminant in marine and freshwater systems, produced a significant influence on the physiological characteristics of aquatic organisms, and inevitably posed unknown effects on their swimming capacity. Herein, we evaluated the MPs accumulation in potamodromous fish, Ctenopharyngodon idellus, and their potential effects on oxidative stress, neurotoxicity, gut microbial diversity, and swimming capability through a toxic-control experiment. Juvenile fish were exposed to 5 µm polystyrene-MPs (PS-MPs) for 6 days at concentrations of 0.1, 1, and 10 mg/L. Exposure to PS-MPs resulted in significant inhibition of acetylcholinesterase (AChE) in the brain of fish, with significant increases in superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels at 1 and 10 mg/L exposures. Meanwhile, MPs altered grass carp gut microbiota and reduced the Shannon diversity index. In addition, MPs significantly increased induced swimming speed by observing the flow rate at which grass carp happened to produce a reverse current behavioral response. The 1 and 10 mg/L of MPs treatments can significantly reduce the critical swimming speed of grass carp, meaning that the completion of the life history of grass carp may be delayed. Furthermore, there were significant correlations between biomarkers and indicators of swimming capacity. Therefore, the present study suggests that MPs produced a negative effect on the physiological properties of fish, reducing the swimming capacity of migratory fish.

The widespread and severe drop in dissolved oxygen concentration in the open ocean and coastal waters has attracted much attention, but assessments of the impacts of environmental hypoxia on aquatic organisms have focused primarily on responses to current exposure. Past stress exposure might also affect the performance of aquatic organisms through carryover effects, and whether these effects scale from positive to negative based on exposure degree is unknown. We investigated the carryover effects of varying embryonic hypoxia levels (mediate hypoxia: 3.0-3.1 mg O2/L; severe hypoxia: 2.0-2.1 mg O2/L) on the fitness traits of adult Pacific abalone (Haliotis discus hannai), including growth, hypoxia tolerance, oxygen consumption, ammonia excretion rate, and biochemical responses to acute hypoxia. Moderate embryonic hypoxia exposure significantly improved the hypoxia tolerance of adult Pacific abalone without sacrificing growth and survival. Adult abalone exposed to embryonic hypoxia exhibited physiological plasticity, including decreased oxygen consumption rates under environmental stress, increased basal methylation levels, and a more active response to acute hypoxia, which might support their higher hypoxia tolerance. Thus, moderate oxygen declines in early life have persistent effects on the fitness of abalone even two years later, further affecting population dynamics. The results suggested that incorporating the carryover effects of embryonic hypoxia exposure into genetic breeding programs would be an important step toward rapidly improving the hypoxia tolerance of aquatic animals. The study also inspires the protection of endangered wild animals and other vulnerable species under global climate change.

Digestion can make up a substantial proportion of animal energy budgets, yet our understanding of how it varies with sex, body mass and ration size is limited. A warming climate may have consequences for animal growth and feeding dynamics that will differentially impact individuals in their ability to efficiently acquire and assimilate meals. Many species, such as walleye (Sander vitreus), exhibit sexual size dimorphism (SSD), whereby one sex is larger than the other, suggesting sex differences in energy acquisition and/or expenditure. Here, we present the first thorough estimates of specific dynamic action (SDA) in adult walleye using intermittent-flow respirometry. We fed male (n=14) and female (n=9) walleye two ration sizes, 2% and 4% of individual body mass, over a range of temperatures from 2 to 20°C. SDA was shorter in duration and reached higher peak rates of oxygen consumption with increasing temperature. Peak SDA increased with ration size and decreased with body mass. The proportion of digestible energy lost to SDA (i.e. the SDA coefficient) was consistent at 6% and was unrelated to temperature, body mass, sex or ration size. Our findings suggest that sex has a negligible role in shaping SDA, nor is SDA a contributor to SSD for this species. Standard and maximum metabolic rates were similar between sexes but maximum metabolic rate decreased drastically with body mass. Large fish, which are important for population growth because of reproductive hyperallometry, may therefore face a bioenergetic disadvantage and struggle most to perform optimally in future, warmer waters.

Nano-titanium dioxide (nano-TiO2) is a ubiquitous contaminant in the marine environment that accumulates in sediments and biological tissues. Coupled with global warming, these challenges can enhance the deleterious properties of nano-TiO2, leading to compounded pollution effects on marine life and ecosystems. This study investigated the effects of nano-TiO2 and increased temperatures on the Japanese swimming crab's gut microbiota and digestive system, Charybdis japonica, through different scenarios. We employed three exposure scenarios: direct exposure (DE) of the crabs to warming and nano-TiO2, indirect exposure (IE) through consumption of mussels Mytilus coruscus subjected to the same conditions, and combined exposure (CE), where crabs were directly exposed to warming and nano-TiO2 while consuming affected mussels. Additionally, a control group was established, comprising Japanese crab C. japonica and thick-shelled mussel M. coruscus that were reared under standard temperature (22 °C, the average annual temperature in the region where the mussels and crabs were sampled) and 0 mg L−1 nano-TiO2 concentration conditions. The findings indicated that warming and nano-TiO2 disrupted the crabs' ATP production, digestive responses, and body chemical composition, leading to intestinal flora dysfunction. Notably, nano-TiO2 exerted a stronger impact on the crabs' digestive enzymes and intestinal flora than warming alone; however, the concurrent presence of warming and nano-TiO2, especially under the direct exposure (DE) conditions, generally exacerbated the negative effects of nano-TiO2. This research provides valuable insights into the implications of nano-TiO2 and elevated temperature on the digestive responses of marine crabs.

This study aimed to investigate the impact of acute velocity stress on the exercise physiology of mandarin fish (Siniperca chuatsi). Initially, the relative critical swimming speed (U’crit) was estimated to be around 4.87 body lengths per second (bl/s), while the relative burst swimming speed (U’burst) reached approximately 8.60 bl/s. Then, the results showed that as the flow velocity increased, the oxygen consumption rate (MO2) of mandarin fish gradually elevated, while the cost of transport (COT) displayed a decreasing trend. Subsequently, four groups were established for the experiment, including control group (0 %Ucrit), low flow velocity (20 %Ucrit), medium flow velocity (50 %Ucrit) and high flow velocity (80 %Ucrit). The results showed that with the increase of flow velocity, the content of muscle glycogen decreased gradually and the content of muscle lactate increased significantly. Furthermore, the results of serum myocardial enzymes and antioxidant enzymes showed that the levels of creatine kinase (CK), total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) exhibited an initial increase followed by a decrease. During the examination of the gills, the highest level of Na+-K+-ATPase was reached at 80 %Ucrit, while the content of malondialdehyde (MDA) was significantly reduced. Additionally, transcriptomic sequencing was conducted on 0 %Ucrit and 80 %Ucrit groups, resulting in the identification of 101 upregulated genes and 116 downregulated genes. KEGG enrichment analysis revealed that the differentially expressed genes (DEGs) were significantly enriched in lipid metabolism and signal transduction. Finally, it was observed that the MAPK signaling pathway within the signaling transduction pathway exhibited the highest number of annotated DEGs. In general, it can be inferred that mandarin fish may regulate lipid peroxidation levels, and MAPK signaling pathway as an adaptive response to mitigate the effects induced by acute velocity stress. The above research is of great significance for improving the farming method of mandarin fish.

The wide use of nano-titanium dioxide (nano-TiO2) and its ubiquitous emission into aquatic environments are threatening environmental health. Ambient temperature can affect the aggregation state of nano-TiO2 in seawater, thus influencing the intake and physiological effects on marine species. We studied the physiological effects of mixed nano-TiO2 (a mixture of anatase and rutile crystals with an average particle size of 25 nm, P25) on mussels. Subsequently, we investigated the oxidative stress, immunotoxicity, neurotoxicity, and detoxification in Mytilus coruscus exposed to two different crystal structures of nano-TiO2 (anatase and rutile) at 100 µg/L concentration under marine heatwaves (MHWs, 28 °C). MHWs and nano-TiO2 exposure induced neurotoxicity and immune damage and caused dysregulation of redox balance in the gills. Moreover, MHWs exposure disturbed the glutathione system and detoxification function of mussels, resulting in enhanced toxicity of nano-TiO2 under co-exposure. Anatase exposure significantly impaired the antioxidant system and downregulated the relative expression of antioxidant-related genes (Nrf2 and Bcl-2), HSP-90, and immune parameters under MHWs, while producing higher ROS levels compared to rutile. Based on integrated biomarker response (IBR), mussels co-exposed to anatase and MHW showed the highest value (19.29). However, there was no significant difference in bioaccumulation of titanium between anatase (6.07 ± 0.47 µg/g) and rutile (5.3 ± 0.44 µg/g) exposures under MHWs. These results indicate that MHWs would elevate the potential hazard of nanoparticles to marine organisms.

Global climate change is a major trigger of unexpected temperature fluctuations. The impacts of marine heatwaves (MHWs) and nano-titanium dioxide (nano-TiO2) on marine organisms have been extensively investigated. However, the potential mechanisms underlying their interactive effects on physiological processes and metabolism remain poorly understood, especially regarding periodic MHWs in real-world conditions. In this study, the effects of nano-TiO2 (at concentrations of 0, 25, and 250 µg/L) and periodic MHWs on the condition index (CI) and underlying metabolic mechanisms were investigated in mussels (Mytilus coruscus). The results showed that mussels try to upregulate their respiration rate (RR) to enhance aerobic metabolism (indicated by elevated succinate dehydrogenase) under short-term nano-TiO2 exposure. However, even at ambient concentration (25 µg/L), prolonged nano-TiO2 exposure inhibited ingestion ability (decreased clearance rate) and glycolysis (inhibited pyruvate kinase, hexokinase, and phosphofructokinase activities), which led to an insufficient energy supply (decreased triglyceride, albumin, and ATP contents). Repeated thermal scenarios caused more severe physiological damage, demonstrating that mussels are fragile to periodic MHWs. MHWs decreased the zeta potential of the nano-TiO2 particles but increased the hydrodynamic diameter. Additionally, exposure to nano-TiO2 and periodic MHWs further affected aerobic respiration (inhibited lactate dehydrogenase and succinate dehydrogenase activities), metabolism (decreased RR, activities of respiratory metabolism-related enzymes, and expressions of PEPCK, PPAR?, and ACO), and overall health condition (decreased ATP and CI). These findings indicate that the combined stress of these two stressors exerts more detrimental impact on the physiological performance and energy metabolism of mussels, and periodic MHWs exacerbate the toxicological effects of ambient concentration nano-TiO2. Given the potential worsening of nanoparticle pollution and the increase in extreme heat events in the future, the well-being of mussels in the marine environment may face further threats.

The Yarlung Zangbo River is a river with abundant hydropower resources but fragile biodiversity in China. As an important benchmark for both research and ecological management, there is still a lack of knowledge about the swimming ability of fishes in the Yarlung Zangbo River. The induced flow velocity ( U ind ), critical swimming speed ( U crit ), and burst swimming speed ( U burst ) of five Schizothoracinae species were tested in this study. Relative swimming ability related to body length and body shape was calculated. The results indicated that the average absolute swimming speeds ( U ind‐a, U crit‐a, and U burst‐a ) of all the experimental fish were 10.20 ± 0.01, 57.58 ± 3.28, and 69.54 ± 2.94 cm/s, respectively, and the corresponding relative U ind, U crit, and U burst related to body length ( U ind‐l, U crit‐l, U burst‐l ) were 1.15 ± 0.07, 5.04 ± 0.26, and 7.23 ± 0.28 BL/s, respectively. Moreover, relative U ind, U crit, and U burst related to body shape ( U ind‐s, U crit‐s, and U burst‐s ) were 0.80 ± 0.13, 2.49 ± 0.51, and 4.32 ± 0.57 cm −2 /s, respectively. No significantly differences in relative swimming speeds existed among five species. Only Oxygymnocypris stewartii was significantly weaker in U burst‐s than Schizothorax o'connori. The body shape showed a stronger relationship with swimming speed than the body length did. Schizothoracinae fish in the Yarlung Zangbo River basin are less sensitive to the water flow and performed weaker U crit and U burst compared to those in the Yangtze River basin, indicating that Schizothoracinae fish in the Yarlung Zangbo River may be more susceptible to threats from environmental changes. The paper enriched the research on the swimming ability of Schizothoracinae fishes and provided efficient data for the fish conservation in the Yarlung Zangbo River.

Coastal marine environments are characterized by daily, seasonal and long-term changes in both O2 and CO2, driven by local biotic and abiotic factors. The neuroepithelial cells (NECs) of fish are thought to be the putative chemoreceptors for sensing oxygen and CO2, and, thus, NECs play a key role in detecting these environmental changes. However, the role of NECs as chemosensors in marine fish remains largely understudied. In this study, the NECs of marine threespine sticklebacks (Gasterosteus aculeatus) were characterized using immunohistochemistry. We then determined if there were changes in NEC size and density, and in gill morphology in response to either mild (10 kPa) or moderate (6.8 kPa) hypoxia and two levels of elevated CO2 (1,500 and 3,000 µatm). We found that the NECs of stickleback contained synaptic vesicles and were innervated, and were 50–300% larger and 2 to 4 times more abundant than in other similar sized freshwater fishes. NEC size and density were largely unaffected by exposure to hypoxia, but there was a 50% decrease in interlamellar cell mass (ILCM) in response to mild and moderate hypoxia. NECs increased in size, but not abundance in response to elevated CO2. Moreover, fish exposed to moderate or elevated CO2 had 53–78% larger ILCMs compared to control fish. Our results demonstrated that adult marine sticklebacks have NECs that can respond to environmentally relevant pCO2 and likely hypoxia, which highlights the importance of NECs in marine fishes under the heterogeneity of environmental conditions in coastal areas.

Stress strongly influences the physiology and behavior of animals, and leads into a pathological condition and disease. NMDA receptors (NMDARs) play a crucial role in the modulation of neural activity. To understand the role of NMDARs in fish stress response, we used NMDARs agonist aspartate to test the functional role of its input on the Dahlgren cell population in the caudal neurosecretory system (CNSS) of the olive flounder. In addition, the effect of the NMDARs antagonist D‐AP5 on the expression of genes of the main secretory products of the CNSS after stress was investigated by using qPCR technology and the effect of the NMDARs antagonist D‐AP5 on post‐stress behavior was explored by behavioral methods. Ex vivo electrophysiological experiments showed that the NMDARs agonist aspartate enhanced the firing frequency of Dahlgren cells. Additionally, aspartate treatment increased the incidence of cells exhibiting bursting firing pattern, this result is corroborated by the observed upregulation in the expression of ion channels and major hormone genes in the CNSS. Furthermore, the excitatory influence of aspartate was effectively counteracted by NMDARs antagonist D‐AP5. Interestingly, NMDARs antagonist D‐AP5 treatment also significantly decreased the plasma cortisol levels and the expression of CRH, UI, and UII in CNSS after acute stress. Treatment with D‐AP5 effectively attenuated the stress response, as evidenced by alterations in respiratory metabolism, sand‐burying behavior, swimming distance, simulated capture, and escape response. In conclusion, modulation of Dahlgren cell excitability in the CNSS by NMDARs contributes to the regulation of the stress response, NMDARs antagonist D‐AP5 can effectively suppress stress response in flounder by regulating the stress hormone expression and secretion. Clinical Trial Registration Project code SHOU‐DW‐2022‐032.

The chorion is the first protective barrier set to prevent numerous pollutants from damaging the developing embryo. However, depending on their size, some nanoplastics (NPs) can pass through this barrier and reach the embryo, while all microplastics (MPs) remain on the outside. This study brings a straight approach to compare MPs and NPs, and assess their direct and indirect effects on zebrafish embryos and larvae. Zebrafish eggs were exposed before 2 h post fertilization (hpf) to polystyrene MPs (5 µm) and NPs (250 nm) at a concentration of 1000 µg/L until 96 hpf. Physiotoxicity and neurotoxicity were assessed prior and post-hatching through several biomarkers. Response to hypoxia (upregulation of hif-1aa and hif-1ab) were found in embryos exposed to MPs, and partly found in those exposed to NPs. Embryos exposed to NPs showed significant tachycardia, reduced O2 consumption and increased apoptosis in the eyes, whereas MPs affected the expressions of all genes related to the neurodevelopment of embryos (elavl3, pax2a, pax6a, act1b). Post-hatching, physiological responses were muted. MPs and NPs exposures ended by evaluating larval behaviours during dark-and-light cycles. Both sizes of plastic particles negatively affected the visual motor response (VMR) and vibrational startle response (VSR). Thigmotaxis levels were significantly increased by NPs whereas MPs showed anxiolytic properties. This study shows that both MPs and NPs affect the physiology and neurodevelopment of zebrafish at different levels, before and after hatching.

New evidence regarding the risks that microplastics (MP) ingestion pose to human and wildlife health are being revealed with progress made in ecotoxicological research. However, comprehensive and realistic approaches that evaluate multiple physiological responses simultaneously are still scarce despite their relevance to understand whole-organism effects. To address this information gap, we performed an experiment to assess the effects of MP on freshwater fish physiology from the molecular to the organismal level. Using a model species of global commercial importance (Cyprinus carpio) and MP type (recycling industry fragments), size (range between 125-1000 µm), and two concentrations of environmental relevance (0.75 and 8.25 µg/L). Experimental design included 5 blocks containing 3 treatment levels each one: control, low, and high MP concentration, with 6 fish each aquarium (5 blocks x 3 treatments x 6 fish per aquarium = 90 fish). Our results suggest that, under the experimental conditions applied, MP exposure did not cause adverse effects at the morphological (variation in size of gut), metabolic (variation of standard metabolic rate), or ecological (growth performance) levels. Nonetheless, we observed an increased frequency of micronucleated cells with increasing MP concentration (df = 42, t-value = 3.68, p-value < 0.001), showing the potential genotoxicity of MP, which can clearly harm fish health in long-term. Thus, despite being a highly resistant species, exposure to MP may generate negative effects in juvenile C. carpio at cellular or subcellular levels. Our findings highlight that the manifestation of MP effects may vary over time, emphasizing the need for future studies to consider longer exposure durations in experimental designs.

The antiepileptic drug carbamazepine (CBZ) has been widely detected in freshwater, yet its toxic actions in fish at multiple endpoints and the subsequent recovery patterns of the impacted are less discussed. This study investigated the bioaccumulation, physiological and behavioral changes of crucian carp (Carassius carassius) following CBZ exposure (G1 = 6.15 µg/L, G2 = 61.5 µg/L, G3 = 615 µg/L, G4 = 6150 µg/L) and subsequent recovery. Our results showed that CBZ was more likely to accumulate in the liver and brain than in the gills. A concentration-dependent phenomenon was observed; however, the residual CBZ decreased to similar levels after recovery. The behavioral indicators (i.e. feeding, social and spontaneous swimming) were significantly inhibited after 7-days of CBZ exposure, and only recovered at low concentration treatment (G1) after 7-days recovery in CBZ-free water. The acetylcholinesterase (AChE) activity in the brain and superoxide dismutase (SOD) activity in the liver and gills were induced after CBZ exposure and returned to normal levels after 7-days of recovery. In contrast, the inhibition of catalase (CAT) activity caused by CBZ exposure persisted in the high concentration treatment (G4) after recovery. Furthermore, correlation analysis indicated that changes in feeding behavior were closely related to the variation of CBZ concentrations in tissues, and the persistence of abnormal swimming and social behavior was closely related to gill CAT activity. These findings contribute to explore the toxic mechanisms of CBZ and highlight the recovery process and connections between various endpoints.

Nano-TiO2 is inevitably released into aquatic environment with increasing of nanotechnology industries. Study pointed that different individuality showed divergent behavioral and physiological response when facing environmental stress. However, the effects of nano-TiO2 on tolerance of bivalves with different individualities remain unknown. In the study, clams were divided into two types of individuality - proactive and reactive by post-stress recovery method. It turned out that proactive individuals had quicker shell opening level, stronger burrowing behavior, faster feeding recovery, higher standard metabolic rate and more rapid ammonia excretion ability than reactive individuals after exposed to air. Then, the survival rate, hemocytes response and oxidase activity of classified clams were evaluated after nano-TiO2 exposure. Results showed that after 30 d exposure, proactive individuals accelerated burrowing behavior with higher survival rate. Moreover, proactive clams had better adaptability and less hemocytes response and oxidative damage than reactive clams. The study highlights the individualities of marine shell fish determine individual capacity to adapt to environmental changes, play important roles in aquaculture and coastal ecosystem health.

Mutations in the nuclear-encoded mitochondrial gene CHCHD10 have been observed in patients with a spectrum of diseases that include amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). To investigate the pathogenic nature of disease-associated variants of CHCHD10 we generated a zebrafish knock-in (KI) model expressing the orthologous ALS-associated CHCHD10 P80L variant (zebrafish: Chchd10 P83L ). Larval chchd10 P83L/P83L fish displayed reduced Chchd10 protein expression levels, motor impairment, reduced survival and abnormal neuromuscular junctions (NMJ). These deficits were not accompanied by changes in transcripts involved in the integrated stress response (ISR), phenocopying previous findings in our knockout (chchd10 -/- ). Adult, 11-month old chchd10 P83L/P83L zebrafish, displayed smaller slow- and fast-twitch muscle cell cross-sectional areas compared to wild type zebrafish muscle cells. Motoneurons in the spinal cord of chchd10 P83L/P83L zebrafish displayed similar cross-sectional areas to that of wild type motor neurons and significantly fewer motor neurons were observed when compared to chchd2 -/- adult spinal cords. Bulk RNA sequencing using whole spinal cords of 7-month old fish revealed transcriptional changes associated with neuroinflammation, apoptosis, amino acid metabolism and mt-DNA inflammatory response in our chchd10 P83L/P83L model. The findings presented here, suggest that the CHCHD10 P80L variant confers an ALS-like phenotype when expressed in zebrafish.

Agri-chemicals such as fungicides are applied in natural settings and hence are exposed to the environment's ultraviolet (UV) light. Recently, many fungicides in commerce are being modified as nano-enabled formulations to increase agricultural productivity and reduce potential off-target effects. The present study investigated the impacts of sunlight-grade UV emission on the effects of either conventional or nano-enabled azoxystrobin (Az or nAz, respectively), a commonly applied agricultural fungicide, on Daphnia magna. Daphnids were exposed to increasing concentrations of Az or nAz under either full-spectrum (Vis) or full-spectrum Vis + UV (Vis + UV) lighting regimes to evaluate LC 50 s. Az LC 50 was calculated at 268.8 and 234.2 μg/L in Vis or Vis + UV, respectively, while LC 50 for nAz was 485.6 and 431.0 μg/L under Vis or Vis + UV light, respectively. Daphnids were exposed to 10% LC 50 of either Az or nAz under Vis or Vis + UV lighting regime for 48 h or 21 d (acute and chronic, respectively). By 48 h, both Az and nAz reduced O 2 consumption and increased TBARS. Heart rate was increased in Az-exposed daphnids but not in nAz groups. Neither of the two chemicals impacted thoracic limb activity. In 21 d exposures, Az significantly reduced biomass production and fecundity, but nAz groups were not significantly different from controls. The results of the present study demonstrate that conventional Az is more toxic to D. magna at lethal and sub-lethal levels in acute and chronic exposures, and sunlight strength UV can potentiate both acute and chronic effects of Az and nAz on D. magna.

In connection with the expansion of alien gobies in European waters, a question arises whether this process can be enhanced or inhibited by global warming. The gobies are of Ponto‐Caspian origin, where the climate is warmer than in invaded European areas. Therefore, they are likely to cope physiologically with climate warming better than native species. Our aim was to identify differences in metabolic traits under elevated summer temperature between the invasive gobies and their native counterparts. Using a laboratory respirometer, we compared the effect of elevated summer temperature (25 vs. 17°C) on the metabolic responses of fish in two species pairs consisting of an invasive goby versus its native counterpart from the same ecological guild: the invasive racer goby Babka gymnotrachelus versus native European bullhead Cottus gobio, and the invasive monkey goby Neogobius fluviatilis versus native gudgeon Gobio gobio. The paired species share functional traits, including morphological characteristics, despite belonging to different fish families. After 4 weeks of acclimation, standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS = MMR–SMR) of the fish were determined. We found that SMR increased under elevated temperature irrespective of species, yet it was always lower in the gobies than in natives. The MMR of the racer goby was lower than that of the bullhead across all temperatures, whereas no differences in MMR were found between the gudgeon and monkey goby. On the one hand, the elevated temperature did not affect the AS of the racer goby and bullhead. However, the AS of the racer goby was consistently lower than that of the bullhead across all temperatures. On the other, elevated temperature caused a decrease in AS in both the monkey goby and gudgeon. However, this temperature‐induced change in AS was higher in the gudgeon than in the monkey goby. In terms of AS, the invaders did not always outperform the natives at higher temperatures. However, the invaders had lower living costs by maintaining a lower SMR. These results suggest that invasion by gobies may be facilitated by global warming, which is likely to increase their occurrence and effect on local fish communities in freshwater temperate systems.

Growing impacts of climate change necessitate predicting species’ vulnerability to altered ecosystems. Assessing vulnerability requires understanding how species’ physiology, life history, and ecology vary among populations and can be altered by behavioral, plastic, and evolutionary adaptations. To examine intraspecific variation in sensitivity to climate change, we measured metabolic responses to acute and chronic temperature exposures in three rearing pond populations of walleye ( Sander vitreus), a cool-water-adapted fish species threatened by climate change. We show significant differences among rearing pond populations in response to increasing temperatures which may originate from broodstock, developmental plasticity, and acclimation. Our results indicate northern walleye may be more tolerant of acute and chronic exposure to higher temperatures by being able to maintain a higher aerobic scope than more southern populations. Furthermore, even over small geographic distances, populations can have significantly different physiological responses to environmental stressors. Quantifying variation in population-specific metabolic responses can inform predictions of growth, reproduction, and fitness across a species range and clarify the importance of within-species diversity in determining vulnerability to environmental stressors.

In aquaculture, exposure to stressors results in heightened neuroendocrine responses, increasing metabolic activities and reducing growth to offset additional stressor-related energetic costs for allostasis. Supplementation with probiotics increases metabolic expenditures from elevated fish digestion and upregulated immune systems, but effects of the probiotics concentrations on energy budgets remains unknown. This study used respirometry to determine the effects of five different probiotic concentrations: T0 control (0 × 1011 CFU/g), T1 (5 × 1011 CFU/g), T2 (10 × 1011 CFU/g), T3 (15 × 1011 CFU/g), and T4 (20 × 1011 CFU/g) of a dietary single-strain probiotic (Lactobacillus rhamnosus IMC 501) on feed consumption, and the proportion of feed intake energy (C) allocated to growth (G), and routine metabolic rates (Rr), in the energy budgets of early juvenile (1-3 g wet weight) Mozambique tilapia (Oreochromis mossambicus), weekly over a 28-day experimental period. Two-factor ANOVA analyses revealed that the amount of feed intake energy (C) increased in probiotic treatments over controls. Allocation of feed energy for growth (G) differed among treatments, but not with time, but for routine metabolic activities (Rr), allocation of feed energy differed among treatments and over time. Increases of somatic tissue (TTW) was highest in the T2 treatment (intermediate concentration), while Rr was highest in the T3 and T4 (highest concentration) treatments, but only after 14–21 days of supplementation. Within energy budgets, the highest proportion of feed energy was allocated to growth in all treatments (G; mean ± SE, 43.0 ± 3.1 %), followed by routine metabolic activities (Rr; mean ± SE, 26.12 ± 2.1 %). Overall, the mean net mass-specific cost of growth (cr) (mgO2l-1 g-1) was highest, and the net growth efficiency (% KN) was lowest, in the T3 and T4 treatments indicating that higher probiotic concentrations were related to higher allostatic loads (AL) compared to lower probiotic treatments (T1, T2). Overall, our results revealed that the proportion of C allocated to G and Rr varied differently with probiotic concentration, was tightly related to gut bacteria metabolic expenditures, and highlighted the importance of carefully evaluating the probiotic concentrations for optimization of growth performance in Mozambique tilapia aquaculture.'

Parasitism is increasingly seen as an ecological factor contributing to behavioural variation among individuals. Yet, the causal direction of the relationship between animal personality and parasites remains unclear. We measured behavioural traits (i.e. exploration, activity, boldness) in pumpkinseed sunfish, Lepomis gibbosus, before and after an experimental infection using cages in a lake where sunfish were naturally exposed to trematode and cestode infection for 1 month. Despite our initial assumptions (i.e. that all individuals would have the same risk of infection within a cage), we found that initial behavioural traits strongly influenced infection susceptibility: initially bolder and less active fish acquired a higher density of trematode and cestode parasites during the infection period. Following infection, fish body condition decreased with increasing cestode density, suggesting that infection is costly to hosts. Body condition was positively correlated with distance moved, a measure of activity, regardless of individual infection status. The repeatability of exploration and activity behaviour and the strength of the activity–exploration correlation (i.e. behavioural syndrome) were reduced following parasite exposure. Distance moved and trematode density were negatively correlated, suggesting that this infection decreases host activity levels. Since trematodes have a complex life cycle with piscivorous birds as a final host, a decrease in activity following infection may make infected fish more susceptible to bird predation, benefiting the parasite. Our results highlight the close links between behaviour and parasitism. We propose that two mechanisms may simultaneously operate: initial host behaviour influences their risk of infection, and infection introduces variation in the behavioural traits of infected hosts.

Ocean warming is increasing organismal oxygen demand, yet at the same time the ocean’s oxygen supply is decreasing. For a patch of habitat to remain viable, there must be a minimum level of environmental oxygen available for an organism to fuel its metabolic demand—quantified as its critical oxygen partial pressure ( p O 2crit ). The temperature-dependence of p O 2crit sets an absolute lower boundary on aerobically viable ocean space for a species, yet whether certain life stages or geographically distant populations differ in their temperature-dependent hypoxia tolerance remains largely unknown. To address these questions, we used the purple sea urchin Strongylocentrotus purpuratus as a model species and measured p O 2crit for 3 populations of adult urchins (Clallam Bay, WA [n = 39], Monterey Bay, CA [91], San Diego, CA [34]) spanning 5-22°C and for key embryonic and larval developmental phases (blastula [n = 11], gastrula [21], prism [31], early-pluteus [21], late-pluteus [14], settled [12]) at temperatures of 10-19°C. We found that temperature-dependent hypoxia tolerance is consistent among adult populations exposed to different temperature and oxygen regimes, despite variable basal oxygen demands, suggesting differential capacity to provision oxygen. Moreover, we did not detect evidence for a hypoxia tolerance bottleneck for any developmental phase. Earlier larval phases are associated with higher hypoxia tolerance and greater temperature sensitivity, while this pattern shifts towards lower hypoxia tolerance and reduced temperature sensitivity as larvae develop. Our results indicate that, at least for S. purpuratus, models quantifying aerobically viable habitat based on p O 2crit -temperature relationships from a single adult population will conservatively estimate viable habitat.

A multitude of anthropogenic stressors impact biological communities and ecosystem processes in urban streams. Prominent among them are salinization, increased temperature, and altered flow regimes, all of which can affect microbial decomposer communities and litter decomposition, a fundamental ecosystem process in streams. Impairments caused by these stressors individually or in combination and recovery of communities and ecosystem processes after release from these stressors are not well understood. To improve our understanding of multiple stressors impacts we performed an outdoor stream mesocosm experiment with 64 experimental units to assess the response of microbial litter decomposers and decomposition. The three stressors we applied in a full-factorial design were increased salinity (NaCl addition, 0.53 mS cm -1 above ambient), elevated temperature (3.5 °C above ambient), and reduced flow velocity (3.5 vs 14.2 cm s -1 ). After two weeks of stressor exposure (first sampling) and two subsequent weeks of recovery (second sampling), we determined leaf-associated microbial respiration, fungal biomass, and the sporulation activity and community composition of aquatic hyphomycetes in addition to decomposition rates of black alder (Alnus glutinosa) leaves confined in fine-mesh litter bags. Microbial colonization of the litter was accompanied by significant mass loss in all mesocosms. However, there was little indication that mass loss, microbial respiration, fungal biomass, sporulation rate or community composition of aquatic hyphomycetes was strongly affected by either single stressors or their interactions. Two exceptions were temperature effects on sporulation and decomposition rate. Similarly, no notable differences among mesocosms were observed after the recovery phase. These results suggest that microbial decomposers and leaf litter decomposition are either barely impaired by exposure to the tested stressors at the levels applied in our experiment, or that communities in restored urban streams are well adapted to cope with these stressor levels.

Coloniality may grant colony members an energetic advantage in the form of lower individual respiration rates as colony size increases. If this occurs it should be apparent as negative allometric scaling of respiration with colony size, and colonial organisms should have scaling factors <1. However, colonial members from phylum Rotifera have yet to be examined. To test if colonial rotifers possess allometric scaling relationships between respiration rate and colony size, we measured respiration rates for four solitary and three colonial rotifer species; from these respiration rates we estimated scaling factors. We found mixed evidence for allometric scaling of respiration rate in colonial rotifers. Both rotifers with allometric scaling of respiration rate, Conochilus hippocrepis and Lacinularia flosculosa, have extensive mucilaginous coverings. These coverings may represent an investment of colony members into a shared structure, lowering individual metabolic costs and thus respiratory needs. Additionally, we determined which traits are associated with allometric scaling of respiration. We compiled known scaling factors for animal phyla from a wide phylogenetic spectrum with colonial representatives and conducted a hierarchical mixed regression that included attributes of colonies. Allometric scaling was found for two of the three colonial species measured. Traits associated with allometric scaling in colonial animals included colony shape, the presence of shared extrazooidal structures, and planktonic lifestyle. There are many other colonial rotifers and animal taxa for which allometric scaling factors have yet to be estimated, knowing these may enlighten our understanding of the benefits of coloniality in animals.

Organic ultraviolet filters (UVFs) are known to contaminate many aquatic ecosystems, with much environmental contamination attributed to the use of UVF-containing skin care products such as sunscreens during aquatic recreation. Most studies addressing the impact of sunscreen contamination have focused on the effects of UVFs under the assumption that they are the primary contaminants of concern from sunscreen pollution; however, the extent to which the toxicity of UVFs is representative of the environmental impacts of the whole sunscreen mixture is unknown. To address this knowledge gap, this study compared the mixture toxicity of five off-the-shelf sunscreen spray products containing the UVFs avobenzone, homosalate, octisalate, octocrylene and oxybenzone to the toxicity of each UVF in isolation to the freshwater invertebrate Daphnia magna. It was found that sunscreen toxicity was not proportional to their total UVF content, as the sunscreen containing the fewest UVFs was approximately equivalent to the sunscreen with the most UVFs, causing ≥90 % mortality and inhibiting all daphnid reproduction over 21 d exposures. Sunscreen toxicity was typically lower than expected when compared to the toxicity of each individual UVF within the mixture, as some sunscreens causing ≤20 % mortality contained octocrylene and/or oxybenzone at concentrations exceeding those which caused 90 % mortality during exposure to the UVF alone. Despite sunscreens causing large impairments in reproduction, growth and metabolism, poor correlations existed between the severity of most sublethal endpoints with respect to the measured UVF content of each sunscreen. Overall, these results indicate that potential antagonistic relationships between sunscreen ingredients can greatly reduce the toxicity of UVFs, creating more uncertainty regarding the level of threat that UVFs pose to the environment as a result of sunscreen contamination.

How do fish respond to an intralipid infusion (a soybean-derived emulsion used for parenteral nutrition of human patients)? In rainbow trout, intralipid administration triples the rate of lipid mobilization (lipolysis) and reduces hepatic glucose production by 36%. These changes in substrate fluxes allow fish to decrease their reliance on amino acids and carbohydrates by substituting them with fatty acids as metabolic fuels.

We recently showed that Crh‐Crhr1 signalling is essential for acute stress‐related locomotor activity in zebrafish larvae. However, the possibility that Crhr1 activation may also initiate the acute metabolic demands for stress coping was unexplored. Here, we tested the hypothesis that Crhr1 signalling is essential for the thermal stressor‐induced increases in the acute metabolic rate, a key response for coping with the enhanced energy demands during stress. We tested this by using a wildtype (WT) and a ubiquitous Crhr1 knockout (crhr1 −/− ) zebrafish and subjecting them to an acute thermal stressor (TS: +5°C above ambient for 60 min). The TS induced the heat shock proteins response in both genotypes, but the elevated cortisol response observed in the WT was absent in the crhr1 −/− mutant. The TS also increased the locomotor activity and the metabolic rate in the WT fish, but this response was inhibited in the crhr1 −/− mutants. To test if this was due to a lack of TS‐induced cortisol elevation in the crhr1 −/− mutant, we mimicked the response in the WT fish by treating them with metyrapone, an 11β‐hydroxylase inhibitor. While metyrapone inhibited the TS‐induced cortisol elevation in the WT, it did not affect the metabolic rate. The lack of Crhr1 also reduced the swimming performance, and the lower U crit in the mutants corresponded with alterations in muscle energy metabolism. Together, our results indicate that Crh‐Crhr1 signalling, independent of downstream cortisol action, is essential for the TS‐induced acute hyperlocomotor activity and the associated increases in the metabolic demand for stress coping.

Bioenergetic modelling is valuable for addressing many questions in animal ecology. However, applying these models to wild animals is limited by challenges with collecting in situ energetics data. Accelerometers have emerged as a popular tool to estimate field metabolic rates. We conducted laboratory experiments using a swim tunnel respirometer on wild (n=28) and hatchery-origin (n=19) walleye (Sander vitreus) to calibrate acoustic accelerometer transmitters (InnovaSea V13A and V16AT) for estimating metabolic rate (ṀO2). Walleye (0.36-3.06 kg) underwent ramp-Ucrit swim trials (n=70) amongst temperatures (5-21°C). Using mixed-effects models, we analyzed critical swimming speed (Ucrit), swimming speed, tailbeat frequency, and ṀO2 as functions of body mass, acceleration, sex, and water temperature. ṀO2 decreased with body mass and increased with higher swimming speeds, acceleration values, and water temperatures. Notably, ṀO2 increased more rapidly with acceleration at higher temperatures. No mass-specific sex differences were observed across measured parameters, and there were no differences in Ucrit or ṀO2 between control and tagged fish. These findings support the use of accelerometers to generate field estimates of energy expenditure in wild walleye.

Sustained exercise in aquaculture is known to improve the health and growth of finfish. Implementing exercise regimes has become an increasing focus in aquaculture practice. This study examined the relationship between the preferred swimming speed (Upref) and the optimal swimming speed (Uopt) in rainbow trout (Oncorhynchus mykiss) under non-migratory conditions typical of aquaculture environments. Using a circular raceway, rainbow trout were allowed to swim voluntarily to determine Upref. Uopt was measured using a forced-swimming test in a swim tunnel respirometer. Experiments were conducted at three temperatures (10 °C, 15 °C, and 20 °C). The results revealed a significant difference between Upref (1.18 ± 0.14, 1.17 ± 0.19, and 1.24 ± 0.15 BL s−1, respectively) and Uopt (1.4 ± 0.19, 1.5 ± 0.15, and 1.6 ± 0.24 BL s−1, respectively) across all temperatures. Aerobic scope was greatest at 15 °C (3.8), consistent with the species’ thermal range. Notably, swimming at Upref required 18–22% less energy than Uopt, suggesting that Upref is more suitable for aquaculture systems. This study introduces a minimally invasive and stress-free method for determining Upref and provides insights that can optimize flow regimes in aquaculture tanks, improving both energy efficiency and fish welfare.

Changes in the environment promote variations in fish physiological responses. Genetic variation also plays a role in physiological variation. To explore the role of genetics in physiological variation, we assessed variation of cardiac function (heart rate, stroke volume, and cardiac output), oxygen consumption, yolk conversion efficiency, and cost of development in embryonic and larval AB wild-type and NHGRI-1 zebrafish (low heterozygosity line backcrossed from AB wild-type) exposed to different temperature and oxygen regimes. Fish were exposed from fertilization to 7 days post-fertilization (dpf) to control conditions (28 °C, 21% O2) or to low temperature (23 °C, 21% O2), high temperature (33 °C, 21% O2), moderate hypoxia (28 °C, 13% O2), or severe hypoxia (28 °C, 10% O2). We hypothesized that (1) assessed physiological variables will respond similarly in both fish lines and (2) data variability in the low heterozygosity NHGRI-1 zebrafish will be lower than in AB zebrafish. Cardiac function decreased at lower temperature and in hypoxia in both AB and NHGRI-1 zebrafish. Oxygen consumption was increased by higher temperature and hypoxia in AB fish and by severe hypoxia in NHGRI-1 fish. Yolk conversion efficiency was decreased by lower temperature and hypoxia in AB fish and increased by higher temperature and decreased by hypoxia in NHGRI-1 fish. Cost of development was higher mainly in hypoxia-treated fish. Supporting our hypothesis that genetics contributes to physiological variation, NHGRI-1 zebrafish data showed significantly lower coefficients of variation in 84% of assessed endpoints. We conclude that (1) there is a strong genetic component to physiological variation in fishes and (2) low heterozygosity NHGRI-1 zebrafish are useful models for reducing the ‘noise’ from genetic backgrounds in physiological research in fish, which may aid interpretation of experimental results and facilitate reproducibility.

Assessing how at-risk species respond to co-occurring stressors is critical for predicting climate change vulnerability. In this study, we characterized how young-of-the-year White Sturgeon (Acipenser transmontanus) cope with warming and low oxygen (hypoxia) and investigated whether prior exposure to one stressor may improve the tolerance to a subsequent stressor through “cross-tolerance”. Fish were acclimated to five temperatures within their natural range (14-22°C) for one month prior to assessment of thermal tolerance (critical thermal maxima, CTmax) and hypoxia tolerance (incipient lethal oxygen saturation, ILOS; tested at 20°C). White Sturgeon showed a high capacity for thermal acclimation, linearly increasing thermal tolerance with increasing acclimation temperature (slope = 0.55, adjusted R2 = 0.79), and an overall acclimation response ratio (ARR) of 0.58, from 14°C (CTmax = 29.4 ± 0.2°C, mean ± S.E.M.) to 22°C (CTmax = 34.1 ± 0.2°C). Acute warming most negatively impacted hypoxia tolerance in 14°C-acclimated fish (ILOS = 15.79 ± 0.74% air saturation), but prior acclimation to 20°C conferred the greatest hypoxia tolerance at this temperature (ILOS = 2.60 ± 1.74% air saturation). Interestingly, individuals that had been previously tested for thermal tolerance had lower hypoxia tolerance than naïve fish that had no prior testing. This was particularly apparent for hypoxia-tolerant 20°C-acclimated fish, whereas naïve fish persisted the entire 15-h duration of the hypoxia trial and did not lose equilibrium at air saturation levels below 20%. Warm-acclimated fish demonstrated significantly smaller relative ventricular mass, indicating potential changes to tissue oxygen delivery, but no other changes to red blood cell characteristics and somatic indices. These data suggest young-of-the-year White Sturgeon are resilient to warming and hypoxia, but the order in which these stressors are experienced and whether exposures are acute or chronic may have important effects on phenotype.

High dam discharge can lead to total dissolved gas (TDG) supersaturation in downstream rivers, causing fish to suffer from bubble trauma and even mortality. Focusing on the Datengxia hydropower station in the Xijiang River basin, we conducted in-situ experiments to explore the tolerance patterns of economic fish species, including Ctenopharyngodon idella, Hypophthalmichthys molitrix, and Cirrhinus molitorella, under the influence of TDG supersaturation at different compensation depths. Moreover, the development and recovery patterns of bubble trauma and the swimming ability of fish exposed to TDG supersaturated water were investigated. In-situ experiments showed that TDG supersaturation ranged from 112.2 % to 125.2 %, averaging 118.3 % at the experiment site. The results revealed that compensation depth is favorable in fish avoidance of TDG supersaturation. The survival rate of the experimental fish at the surface was lower than for those at the 0-3 m water depth. The survival rates of Ctenopharyngodon idella, Hypophthalmichthys molitrix, and Cirrhinus molitorella at the surface were only 30 %, 47.5 %, and 70 %, respectively, while at the 0-3 m water depth, the survival rates were 97.5 %, 87.5 %, and 87.5 %, respectively. Additionally, the survival rate of fish was related to their preferred water depth. The bubble trauma scores of the experimental fish in TDG supersaturated water significantly increased with exposure time and significantly decreased after recovery in freshwater. The relative and absolute critical swimming speed (U crit ) of Ctenopharyngodon idella ranged from 10.91 to 12.98 BL/s and 83.3-102.9 cm/s respectively, and there were no significant changes in the U crit with increasing TDG supersaturation exposure.

Understanding the fates of organisms and ecosystems under global change requires consideration of the organisms’ rapid adaptation potential. In the Arctic, the recent temperature increase strongly impacts freshwater ecosystems which are important sentinels for climate change. However, a mechanistic understanding on the adaptive capacity of their key zooplankton grazers, among them polyploid, obligate parthenogenetic Daphnia, is lacking. Theory suggests low adaptation potential of asexual animals, yet examples exist of asexuals persisting through marked environmental changes. Here, we studied asexual Daphnia pulicaria from a meromictic lake in South-West Greenland. Its oxycline hosts purple sulphur bacteria (PSB), a potential food source for Daphnia. We tested two key phenotypic traits: (1) thermal tolerance as a response to rapid regional warming and (2) hypoxia tolerance tied to grazing of PSB in the hypoxic/anoxic transition zone. We resurrected Daphnia from dormant eggs representing a historical subpopulation from 2011, sampled modern subpopulation representatives in 2022 and measured phenotypic variation of thermal (time to immobilization -Timm) and hypoxia tolerance (respiration rate and critical oxygen limit -Pcrit) in clonal lineages of both subpopulations. Whole genome sequencing of the tested clonal lineages identified three closely related genetic clusters, one with clones from both subpopulations and two unique to each subpopulation. We observed significantly lower Timm and Pcrit and a trend for higher respiration rates in the modern subpopulation, indicating a lower tolerance to both high temperature and hypoxia in comparison to the historical subpopulation. As these two traits share common physiological mechanisms, the observed phenotypic divergence might be driven by a relaxed selection pressure on hypoxia tolerance linked to variation in PSB abundance. Our results, while contrary to our expectation of higher thermal tolerance of the modern subpopulation, provide evidence for phenotypic change within a decade in this asexual Daphnia population.

Across the globe, there are millions of in‐stream structures that fragment the world's river networks, acting as barriers that can impede the movements of fish. Designing effective solutions to accommodate fish communities requires information about the swimming abilities and behaviours of all species. This should account for different swimming modes, abilities, behaviours, and niches. We investigated the swimming speeds of nine migratory New Zealand species to assess both inter‐ and intraspecies variation. We then calculated maximum traversable speeds for culverts of a given length, based on the endurance abilities of our lowest performing species ( Galaxias maculatus ). Our findings reveal significant inter‐ and intraspecies variation in swimming speeds. Among the species studied, Galaxias brevipinnis, Galaxias argenteus, and Galaxias postvectis were the strongest swimmers. In contrast, Galaxias maculatus was one of the weakest swimmers. Body length positively correlated with U max indicating that fish passage barriers select against the weakest swimming species, as well as smaller individuals within a species. Maximum water speeds in a culvert must be lower than 0.3 m s −1, the previously assumed standard rule‐of‐thumb for New Zealand, to provide adequate passage for a high proportion of a weak‐swimming indicator species ( Galaxias maculatus ). Synthesis and applications. Previous maximum traversable water speeds for fish passage designs have been based on average swimming ability, but this approach only enables fish that are better than the average swimmers of their species to overcome barriers. This study highlights the importance of evidence‐based designs for successful fish passage solutions to account for the ability of all fish. By considering differences between and within species, rather than assuming a ‘one‐size‐fits‐all’ approach we can develop more effective passage solutions that better preserve fish communities.

Pathogens play a key role in individual function and the dynamics of wild populations, but the link between pathogens and individual performance has rarely been investigated in the wild. Migrating salmonids offer an ideal study system to investigate how infection with pathogens affects performance given that climate change and fish farming portend increasing prevalence of pathogens in wild populations. To test for effects of pathogen burden on the performance of a migrating salmonid, we paired data from individual brown trout tagged with acoustic accelerometer transmitters and gill biopsies to investigate how pathogen infection affected whole animal activity during the spawning migration. Generalised additive models fitted to the acceleration data revealed individual and temporal variation in acceleration as expected, but also provided a significant effect of relative infection burden on acceleration. However, when linking this pathogen‐specific effect to a relevant bioenergetic change, it was evident that the effect had little impact on the exercise‐related oxygen consumption at the individual level, especially in cases where fish were not exerting high exercise activity. The results are a powerful example of how pairing non‐lethal biopsies with individual tracking technologies can be used to assess how pathogens impact fish in situ.

As Arctic sea temperatures rise and sea ice declines, boreal species are becoming more abundant in these waters. Generally, both inter- and intra-species variations show larger body sizes at higher latitudes and in colder climates. Continued Arctic amplification may lead to shifts in the size and composition of marine plankton, with cascading effects throughout the ecosystem. This study examines the metabolic rates of three common zooplankton species, Calanus finmarchicus, C. glacialis, and Metridia longa, across different temperatures (0°C, 3°C, and 6°C) to understand these dynamics. Results showed a distinct decrease in aerobic scope with rising temperatures for all three copepod species, indicating potential fitness reductions in warmer waters. Larger copepods exhibited higher aerobic scopes than smaller ones at all temperatures; however, this advantage diminished at 6°C, suggesting that smaller body sizes may confer metabolic benefits at higher temperatures. Conversely, larger sizes are favored in colder waters. These findings help explain the increase of smaller boreal species in warming Arctic seas and why colder Arctic conditions favor larger individuals.

Understanding how interactive environmental challenges affect marine species is critical to long‐term ecological and economic stability under global change. Marine calcifiers are thought to be vulnerable to ocean acidification (OA; elevated p CO 2 ); active dissolution of aragonite (Ω ar ) is associated with disrupted development, survivorship, and gene expression in bivalve larvae, resulting in an early life‐stage bottleneck. Dynamic carbonate chemistry in coastal systems emphasizes the importance of multiple stressors, e.g., warming and low salinity events may change organismal responses relative to OA alone. We exposed Eastern oyster larvae ( Crassostrea virginica ) to a full‐factorial experimental design using two temperatures (23°C and 27°C), salinities (17 and 27), and p CO 2 levels (~700 μatm and 1850 μatm p CO 2 ), resulting in Ω ar conditions 0.3–1.7. Ω ar reduced by low salinity, elevated p CO 2, and low temperature, each slowed early development and reduced survival. Low salinity × elevated p CO 2 was linked to severe Ω ar undersaturation (< 0.5) that suppressed expression of bicarbonate transport, biomineralization and augmented expression for ciliary locomotion, proteostasis, and histone modifiers. In isolation and under moderate Ω ar intensity (0.5 < Ω ar < 1), larvae increased transcription for osmoregulatory activity and endocytosis under low salinity, and suppressed transcription for iron metabolism under elevated p CO 2. Although shell growth and survival were affected by Ω ar undersaturation, gene expression patterns of D‐stage oyster larvae and oyster juveniles suggests tolerance to dynamic estuarine environments. Genes and expression patterns that confer survival of postmetamorphosed oysters can improve our understanding of environmental‐organismal interactions and improve breeding programs enabling sustainable production.

Urbanization is a widespread threat to freshwater ecosystems. After rainfall, urban streams often experience unnaturally fast water flows and acute increases in suspended sediment due to the high degree of adjacent impervious land surface. Suspended sediments may negatively affect fishes by impairing respiration, and reduced water clarity may also affect social behaviours such as schooling that are dependent on visual cues. Given these two mechanisms of harm, suspended sediments may therefore exacerbate the difficulty of swimming at high water velocities. We tested this idea using imperilled Redside Dace ( Clinostomus elongatus) to examine the consequences of suspended sediment on swimming performance and schooling behaviour. Using individual fish, we assayed swimming performance (standard critical swim speed test) and tail beat frequency and amplitude under a range of ecologically relevant sediment concentrations. Next, we measured the impact of sediment on the cohesion and polarization of schools. Swimming performance of individual fish was not affected by suspended sediment levels we examined. School polarization was positively correlated with water flow overall and at the fastest flows we tested; schools were more polarized when exposed to sediment. School cohesion decreased with increasing flows and was unaffected by the suspended sediment levels we examined. Our results collectively suggest that swimming performance of Redside Dace may be resilient to ecologically relevant acute suspended sediment exposure.

High phenotypic diversity should provide populations with resilience to environmental change by increasing their capacity to respond to changing conditions. The aim of this study was to identify whether there is consistency in individual behaviours on a reactive-proactive axis in European barbel Barbus barbus ("barbel"), a riverine and aggregatory fish that expresses individual differences in its behaviours in nature. This was tested using three sequential experiments in ex-situ conditions that required individuals to leave a shelter and then explore new habitats (‘open-field test’), respond to social stimuli (‘mirror-image stimulation test’) and forage (‘foraging behaviour test’; assessing exploratory traits). Each suite of experiments was replicated three times per individual (46 hours minimum time between replicates). There was high variability in behaviours both within and among individuals. The most repeatable behaviours were latency to exit the shelter, active time in the shelter, and the number of food items consumed. Principal component scores did, however, indicate a range of consistent behavioural phenotypes across the individuals, distributing them along a reactive-proactive axis in which most of individuals were more reactive phenotypes (shyer, less exploratory, less social). These results suggest that within controlled conditions, there is considerable phenotypic diversity among individuals in their behaviours, suggesting their populations will have some adaptive capacity to environmental change.

This study explores the metabolic response and carbon budget of two cyclopoid copepod species, Diacyclops belgicus Kiefer, 1936 (a stygobitic, groundwater-adapted species) and Diacyclops crassicaudis crassicaudis (Sars G.O., 1863) (a stygophilic, predominantly surface-associated species). We measured oxygen consumption rates (OCRs), carbon requirements (CRs), ingestion (I) rates, and egestion (E) rates at 14 °C and 17 °C, representing current and predicted future conditions in the collection habitats of the two species. Diacyclops belgicus displayed OCRs (28.15 and 18.32 µL O2/mg DW × h at 14 and 17 °C, respectively) and carbon budget (CR: 0.14 and 0.10 µg C/mg × d at 14 and 17 °C) lower than those of D. crassicaudis crassicaudis (OCR: 55.67 and 47.93 µL O2/mg DW × h at 14 and 17 °C; CR: 0.3 and 0.27 µg C/mg × d at 14 and 17 °C). However, D. belgicus exhibited metabolic rates and carbon requirements comparable to those of other epigean species, challenging the assumption that low metabolic rates are universal among stygobitic species. Temperature variations did not significantly affect the metabolic responses and carbon requirements of the two species, suggesting that they may cope with moderate temperature increases.

Type 2 diabetes mellitus (T2DM) is a common metabolic disease that is frequently accompanied by multiple complications, including diabetic myopathy, a muscle disorder that is mainly manifested as decreased muscle function and reduced muscle mass. Diabetic myopathy is a relatively common complication among patients with diabetes that is mainly attributed to mitochondrial dysfunction. Therefore, we investigated the mechanisms underlying diabetic myopathy development, focusing on the role of microRNAs (miRs). Zebrafish were fed a high-sugar diet for 8 weeks and immersed in a glucose solution to establish a model of T2DM. Notably, the fish exhibited impaired blood glucose homeostasis, increased lipid accumulation in the skeletal muscles, and decreased insulin levels in the skeletal muscle. Additionally, we observed various symptoms of diabetic myopathy, including a decreased cross-sectional area of skeletal muscle fibers, increased skeletal muscle fibrosis, a significant decline in exercise capacity, and a significant decrease in mitochondrial respiratory function. Mechanistically, bioinformatic analysis combined with various molecular analyses showed that the miR-139-5p/NAMPT pathway was involved in long-term high-glucose-induced mitochondrial dysfunction in the skeletal muscle, leading to diabetic myopathy. Conclusively, this study provides a basis for the development of novel strategies for the prevention and treatment of diabetic myopathy.

Sea lamprey (Petromyzon marinus) are an invasive species in the Laurentian Great Lakes, where parasitism by blood-feeding juvenile lampreys greatly reduced populations of economically and culturally important native fishes in the early-mid 1900s. To control sea lamprey populations, the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is added to streams infested with larval sea lamprey. Sea lamprey have a lower capacity to detoxify TFM than most non-target fishes, making it a highly effective pesticide. TFM decreases ATP production by disrupting oxidative phosphorylation in the mitochondria, leading to an increase in mitochondrial oxygen consumption. However, little is known about how TFM affects whole animal oxygen consumption in sea lamprey and other fishes. To test the hypothesis that TFM has dose-dependent effects on larval sea lamprey metabolic rate, we measured the mass-specific oxygen consumption rates (?O2) of larval sea lamprey using intermittent-flow respirometry during TFM exposure. Exposure to increasing concentrations of TFM led to stepwise increases in ?O2 in larval sea lamprey, resulting in death after ?O2 reached levels equivalent to their known maximum metabolic rates. Similar measurements of ?O2 could be used to determine the relative TFM sensitivity of non-target species to better assess the potential impacts of TFM on resident fisheries.

The primary function of spermatozoa is to fertilize the oocyte, which depends on their motility and is directly associated with their metabolic state. The oxygen consumption rate (OCR) of spermatozoa reflects the respiratory capacity of sperm mitochondria under various physiological conditions and is an essential marker of sperm quality. We determined the OCR of common carp (Cyprinus carpio) sperm using two respirometry methods: the conventionally used polarographic method with a Clark-type electrode and fluorometric assay with an Oxo Dish optochemical oxygen sensor. The latter was used for the first time to evaluate spermatozoa oxygen consumption in various metabolic states (under different treatments) at different dilution rates. These two methods were compared using Bland–Altman analysis, and the applicability of the optochemical oxygen sensor for evaluating carp sperm oxygen consumption was discussed. Sperm motility and progressive velocity parameters were also assessed to evaluate the effect of sperm respiration under different metabolic states and dilution rates and preincubation period on the physiological status of spermatozoa. The comparison of these respirometry methods clearly shows that while the polarographic method allows immediate measurement of oxygen levels after adding a sperm sample, the optochemical oxygen sensor has a priority in the amount of data obtained due to simultaneous measurements of several samples (e.g., different males, different fish species, repetitions of the same sample or various experimental conditions), even at a later time after adding sperm to the measuring chamber. However, the compared methods are complementary, and the proposed methodology can be applied to other fish species.

Fish in the wild often contend with complex flows that are produced by natural and artificial structures. Research into fish interactions with turbulence often investigates metrics such as turbulent kinetic energy (TKE) or fish positional location, with less focus on the specific interactions between vortex organization and body swimming kinematics. Here, we compared the swimming kinematics of rainbow trout (Oncorhynchus mykiss) holding station in flows produced by two different 3×5 cylinder arrays. We systematically utilized computational fluid dynamics to identify one array that produced a Kármán vortex street with high vortex periodicity (KVS array) and another that produced low periodicity, similar to a parallel vortex street (PVS array), both validated with particle image velocimetry. The only difference in swimming kinematics between cylinder arrays was an increased tail beat amplitude in the KVS array. In both cylinder arrays, the tail beat frequency decreased and snout amplitude increased compared with the freestream. The center of mass amplitude was greater in the PVS array than in only the freestream, however, suggesting some buffeting of the body by the fluid. Notably, we did not observe Kármán gaiting in the KVS array as in previous studies. We hypothesize that this is because (1) vorticity was dissipated in the region where fish held station or (2) vortices were in-line rather than staggered. These results are the first to quantify the kinematics and behavior of fishes swimming in the wake of multiple cylinder arrays, which has important implications for biomechanics, fluid dynamics and fisheries management.

Scyphozoan jellyfish, known for their evolutionary position and ecological significance, are thought to exhibit relatively notable resilience to ocean acidification. However, knowledge regarding the molecular mechanisms underlying the scyphozoan jellyfish response to acidified seawater conditions is currently lacking. In this study, two independent experiments were conducted to determine the physiological and molecular responses of moon jellyfish (Aurelia coerulea) polyps to within- and trans-generational exposure to two reduced pH treatments (pH 7.8 and pH 7.6). The results revealed that the asexual reproduction of A. coerulea polyps significantly declined under acute exposure to pH 7.6 compared with that of polyps at ambient pH conditions. Transcriptomics revealed a notable upregulation of genes involved in immunity and cytoskeleton components. In contrast, genes associated with metabolism were downregulated in response to reduced pH treatments after 6 weeks of within-generational acidified conditions. However, reduced pH treatments had no significant influence on the asexual reproduction of A. coerulea polyps after exposure to acidified conditions over a total of five generations, suggesting that A. coerulea polyps may acclimate to low pH levels. Transcriptomics revealed distinct gene expression profiles between within- and trans-generational exposure groups to two reduced pH treatments. The offspring polyps of A. coerulea subjected to trans-generational acidified conditions exhibited both upregulated and downregulated expression of genes associated with metabolism. These physiological and transcriptomic characteristics of A. coerulea polyps in response to elevated CO2 levels suggest that polyps produced asexually under acidified conditions may be resilient to such conditions in the future.

To assess the relationship among various measures of thermal tolerance and performance suggested for use in fish, we determined the critical thermal maximum (CTmax), critical swimming speed (Ucrit), maximum thermal tolerance while swimming [CTSmax] and realistic aerobic scope (ASR) of juvenile schoolmaster snapper (Lutjanus apodus). Their CTSmax (37.5±0.1°C) was only slightly lower than their CTmax (38.9±0.1°C) and this is probably because their maximum metabolic rate (MMR) and ASR during the former test were ∼42 and 65% higher, respectively. Furthermore, we did not observe a transition to unsteady (i.e. anaerobically fueled) swimming in the CTSmax test as we did in the Ucrit protocol. These data strongly suggest that thermal tolerance tests on fishes whose lifestyle involves schooling or sustained activity should be performed at ecologically relevant swimming speeds. Our results do not support the hypothesis that failure during a CTSmax test is due to a fish's inability to meet its tissue oxygen demands.

Captive breeding and stocking are commonly employed strategies for enhancing fisheries and conserving endangered fish species. However, hatchery-raised fish often exhibit reduced performance in the wild, displaying alterations in physiological, morphological, and behavioral traits. We tested for differences in swimming capacity and metabolic traits between wild and hatchery-reared individuals of the Spanish toothcarp (Aphanius iberus) from 2 different populations. Furthermore, we experimentally tested if these changes translated into fitness differences after their stocking into the wild. There were significant differences in swimming capacity and metabolic traits between wild and hatchery-reared individuals and also between the 2 populations. Captive-bred individuals displayed consistently lower metabolic rates than wild individuals from the same population (30–76% lower). Critical swimming speed rather differed between the 2 populations. Sex-specific differences were observed in maximum and standard metabolic rates, with wild individuals and females generally exhibiting higher values but with some exceptions. During a 3-month experiment, survival rates did not significantly differ between wild and captive-bred fish. Captive-bred individuals started smaller but exhibited rapid growth during the experiment. Initially, larger captive-bred fish had lower body conditions than their wild counterparts, but these differences progressively diminished. In summary, captive-bred individuals of this fish species showed lower metabolic rates, although the differences with wild individuals slightly depended on sex and size.

Declining body size in fishes and other aquatic ectotherms associated with anthropogenic climate warming has significant implications for future fisheries yields, stock assessments and aquatic ecosystem stability. One proposed mechanism seeking to explain such body-size reductions, known as the gill oxygen limitation (GOL) hypothesis, has recently been used to model future impacts of climate warming on fisheries but has not been robustly empirically tested. We used brook trout (Salvelinus fontinalis), a fast-growing, cold-water salmonid species of broad economic, conservation and ecological value, to examine the GOL hypothesis in a long-term experiment quantifying effects of temperature on growth, resting metabolic rate (RMR), maximum metabolic rate (MMR) and gill surface area (GSA). Despite significantly reduced growth and body size at an elevated temperature, allometric slopes of GSA were not significantly different than 1.0 and were above those for RMR and MMR at both temperature treatments (15°C and 20°C), contrary to GOL expectations. We also found that the effect of temperature on RMR was time-dependent, contradicting the prediction that heightened temperatures increase metabolic rates and reinforcing the importance of longer-term exposures (e.g. >6 months) to fully understand the influence of acclimation on temperature–metabolic rate relationships. Our results indicate that although oxygen limitation may be important in some aspects of temperature–body size relationships and constraints on metabolic supply may contribute to reduced growth in some cases, it is unlikely that GOL is a universal mechanism explaining temperature–body size relationships in aquatic ectotherms. We suggest future research focus on alternative mechanisms underlying temperature–body size relationships, and that projections of climate change impacts on fisheries yields using models based on GOL assumptions be interpreted with caution.

Although hypoxia is a serious environmental concern for marine ecosystems globally, its biological effects on the benthic biota remain mostly unclear for some endangered species. To provide an deep understanding of the possible effects of hypoxia on the tri-spine horseshoe crab Tachypleus tridentatus, the cellular energy allocation (CEA) approach was utilized to examine the cellular responses and adaption potential of horseshoe crabs. We examined the energetic responses of T. tridentatus under low dissolved oxygen level (2 mg O2/L). The horseshoe crabs first experienced 14 days of hypoxic stress, and then recovered in a normal dissolved oxygen environment for 7 days. On the 7th and 14th day of hypoxic exposure, the levels of available energy, electron transport system activity, protein, lipids, and carbohydrates were decreased in T. tridentatus (p < 0.05). All measured parameters in the hypoxic group partially or completely recovered after seven days of re-oxygenation, reaching a level that was significantly up-regulated (p < 0.05) compared with the 14th day and non-significantly different from the 0th day exposure (p ? 0.05). In conclusion, hypoxic stress has adverse effects on the energy balance of juvenile T. tridentatus, but these adverse effects can be alleviated in a short recovery period. As a result, our findings provide novel perspectives on the physiology of T. tridentatus under hypoxia acclimation, which is essential information for establishing ideal conditions for the cultivation of this endangered species.

An important goal of environmental and comparative physiology research is to identify species or populations that may be susceptible to environmental change such as heat wave events that are predicted to become more frequent and intense in the future. This study tested the hypothesis that fishes inhabiting alkaline lakes face significant physiological challenges, which results in reduced thermal tolerance. Brook stickleback (Culaea inconstans) were collected from an alkaline lake (pH 9.3) in Alberta, Canada and held under neutral conditions in the laboratory. Subsequently, fish were acutely exposed (4 d) to neutral (pH 7) or alkaline (pH 9.5) waters at 10 or 25°C. Exposure to alkaline water reduced critical thermal maximum (CTmax) in stickleback by approximately 1°C, but thermal acclimation capacity (“thermal plasticity”) was unaffected by alkaline exposure. Alkaline conditions resulted in physiological disturbances characteristic of exposure to high pH including elevated whole-body ammonia and lactate concentrations. Acute warming to CTmax in alkaline-exposed fish resulted in reductions in whole-body sodium and chloride concentrations. In addition, alkaline exposure compromised recovery from exercise at elevated temperatures. Overall, these results suggest that the physiological disturbances observed in response to alkaline exposure may render fish more susceptible to acute warming, reducing thermal tolerance.

Ocean warming is a prevailing threat to marine ectotherms. Recently the “plastic floors, concrete ceilings” hypothesis was proposed, which suggests that a warmed fish will acclimate to higher temperatures by reducing standard metabolic rate (SMR) while keeping maximum metabolic rate (MMR) stable, therefore improving aerobic scope (AS). Here we evaluated this hypothesis on red drum (Sciaenops ocellatus) while incorporating measures of hypoxia vulnerability (critical oxygen threshold; Pcrit) and mitochondrial performance. Fish were subjected to a 12-week acclimation to 20 °C or 28 °C. Respirometry was performed every 4 weeks to obtain metabolic rate and Pcrit; mitochondrial respirometry was performed on liver and heart samples at the end of the acclimation. 28 °C fish had a significantly higher SMR, MMR, and Pcrit than 20 °C controls at time 0, but SMR declined by 36.2 % over the 12-week acclimation. No change in SMR was observed in the control treatment. Contrary to expectations, SMR suppression did not improve AS relative to time 0 owing to a progressive decline in MMR over acclimation time. Pcrit decreased by 27.2 % in the warm-acclimated fishes, which resulted in temperature treatments having statistically similar values by 12-weeks. No differences in mitochondrial traits were observed in the heart – despite a ?8 °C assay temperature – while liver respiratory and coupling control ratios were significantly improved, suggesting that mitochondrial plasticity may contribute to the reduced SMR with warming. Overall, this work suggests that warming induced metabolic suppression offsets the deleterious consequences of high oxygen demand on hypoxia vulnerability, and in so doing greatly expands the theoretical range of metabolically available habitats for red drum.

With the wide use of nanomaterials in daily life, nano-titanium dioxide (nano-TiO2) presents potential ecological risks to marine ecosystems, which can be exacerbated by ocean warming (OW). However, most previous studies have only centered around waterborne exposure, while there is a scarcity of studies concentrating on the impact of trophic transfer exposure on organisms. We investigated the differences in toxic effects of 100 µg/L nano-TiO2 on mussels via two pathways (waterborne and foodborne) under normal (24 °C) and warming (28 °C) conditions. Single nano-TiO2 exposure (waterborne and foodborne) elevated the superoxide dismutase (SOD) and catalase (CAT) activities as well as the content of glutathione (GSH), indicating activated antioxidatant response in the intestine. However, depressed antioxidant enzymes and accumulated peroxide products (LPO and protein carbonyl content, PCC) demonstrated that warming in combination with nano-TiO2 broke the prooxidant-antioxidant homeostasis of mussels. Our findings also indicated that nano-TiO2 and high temperature exhibited adverse impacts on amylase (AMS), trypsin (PS), and trehalase (THL). Additionally, activated immune function (lysozyme) comes at the cost of energy expenditure of protein (decreased protein concentration). The hydrodynamic diameter of nano-TiO2 at 24 °C (1693–2261 nm) was lower than that at 28 °C (2666–3086 nm). Bioaccumulation results (range from 0.022 to 0.432 µg/g) suggested that foodborne induced higher Ti contents in intestine than waterborne. In general, the combined effects of nano-TiO2 and warming demonstrated a more pronounced extent of interactive effects and severe damage to antioxidant, digestive, and immune parameters in mussel intestine. The toxicological impact of nano-TiO2 was intensified through trophic transfer. The toxic effects of nano-TiO2 are non-negligible and can be exerted together through both water- and foodborne exposure routes, which deserves further investigation.

Microplastics (MPs) pollution's impact on the marine ecosystem is widely recognized. This study compared the effects of polyethylene (PE) and polyethylene terephthalate (PET) on two bivalve species, Ruditapes philippinarum (clam) and Chlamys farreri (scallop), at two particle concentrations (10 and 1000 µg/L). MPs were found in the digestive glands and gills of both species. Although clearance rates showed no significant changes, exposure to different MPs caused oxidative stress, energy disruption, and lipid metabolism disorders in both clam and scallop. Histopathological damage was observed in gills and digestive glands. IBR values indicated increasing toxicity with concentration, with PET being more toxic than PE. WOE model suggested increasing hazard with concentration, highlighting higher PET toxicity on clam digestive glands. In contrast, PE hazard increased in gills, showing different species responses. R. philippinarum exhibited higher sensitivity to MPs than C. farreri, providing insights for assessing ecological risk under realistic conditions and stress conditions.

Multiple studies have shown that exposure to moderate water currents (exercise training) can improve growth and physiological performance of hatchery-reared fish. Proactive implementation of sustained aerobic swimming training can be particularly beneficial for improving post-release performance of fish in stock enhancement- or ‘ranching’ programs. Black seabream Acanthopagrus schlegelii is an important species in aquaculture and stock enhancement in the East China Sea. For juveniles of this species, we assess the impacts of exercise training at various flow rates on the morphology, growth performance, swimming ability, body composition and locomotors metabolism. A group of sibling juvenile fish (initial mass: 13.72 ± 0.29 g) underwent daily exercise training for 12 h (9:00–21:00) over 30 days at four different water velocities (0, 1, 2, or 4 body lengths per second, BL/s). All the trained fish exhibited a significant decrease in their respiratory metabolic rate during the test of swimming ability. Fish from the 2 BL/s training group exhibited a significantly increased burst swimming speed compared to the other groups. Fish from 1 BL/s training group showed elevated hexokinase activities in the white muscle and citrate synthase activities in the liver compared to the 0 BL/s group. Citrate synthase activities in the white muscle of fish from the 2 BL/s training group were elevated, along with citrate synthase activities in the liver, as compared to 0 BL/s. The fish in the 4 BL/s training group showed a tendency for increased crude protein content and a corresponding decrease in crude lipid content. Morphological analysis revealed that fish in the 4 BL/s group exhibited larger dorsal fins and more streamlined body profiles, compared to 0 BL/s. Activities of white muscle citrate synthase as well as liver hexokinase activity were higher in the 4 BL/s group, while lactate content activity in the white muscle were lower compared to 0 BL/s. These findings underscore the effectiveness of training at 2 BL/s, offering a promising strategy to enhance the performance of juvenile black seabream for stocking initiatives.

Despite the growing use of hybrid catfish (Ictalurus punctatus × I. furcatus) in the aquaculture industry, few studies have compared their physiological performance with more commonly reared channel catfish (I. punctatus) and their other parent stock, blue catfish (I. furcatus). An understanding of metabolic scope and swimming performance, particularly in elevated water temperatures, is important because these metrics directly relate to the overall performance or fitness of an organism. Therefore, metabolic scope, the difference between standard metabolic rate (SMR) and maximum metabolic rate (MMR), and swimming performance in channel, blue, and hybrid catfish were compared using intermittent and swim-flume respirometry coupled with Ucrit protocols at moderate (23 °C) and high (33 °C) temperatures. It was hypothesized hybrid catfish would have larger metabolic scope and greater swimming performance than channel and blue catfish due to heterosis from hybridization. Hybrid catfish SMR did not differ from blue catfish, while hybrid catfish had higher MMR, larger metabolic scope, and better swimming performance than channel and blue catfish. These results indicate hybrid catfish outperform channel and blue catfish, in terms of swimming performance, presumably due to larger metabolic scope over moderate to high temperatures.

Oxygen is essential to fuel aerobic metabolism. Some species evolved mechanisms to tolerate periods of severe hypoxia and even anoxia in their environment. Among them, goldfish (Carassius auratus) are unique, in that they do not enter a comatose state under severely hypoxic conditions. There is thus significant interest in the field of comparative physiology to uncover the mechanistic basis underlying hypoxia tolerance in goldfish, with a particular focus on the brain. Taking advantage of the recently published and annotated goldfish genome, we profile the transcriptomic response of the goldfish brain under normoxic (21 kPa oxygen saturation) and, following gradual reduction, constant hypoxic conditions after 1 and 4 weeks (2.1 kPa oxygen saturation). In addition to analyzing differentially expressed protein-coding genes and enriched pathways, we also profile differentially expressed microRNAs (miRs). Using in silico approaches, we identify possible miR-mRNA relationships. Differentially expressed transcripts compared to normoxia were either common to both timepoints of hypoxia exposure (n = 174 mRNAs; n = 6 miRs), or exclusive to 1-week (n = 441 mRNAs; n = 23 miRs) or 4-week hypoxia exposure (n = 491 mRNAs; n = 34 miRs). Under chronic hypoxia, an increasing number of transcripts, including those of paralogous genes, was downregulated over time, suggesting a decrease in transcription. GO-terms related to the vascular system, oxidative stress, stress signalling, oxidoreductase activity, nucleotide- and intermediary metabolism, and mRNA posttranscriptional regulation were found to be enriched under chronic hypoxia. Known ‘hypoxamiRs’, such as miR-210-3p/5p, and miRs such as miR-29b-3p likely contribute to posttranscriptional regulation of these pathways under chronic hypoxia in the goldfish brain.

In recent years, carbon nanotubes (CNTs) have become one of the most promising materials for the technology industry. However, due to the extensive usage of these materials, they may be released into the environment, and cause toxicities to the organism. Here, their acute toxicities in zebrafish embryos and larvae were evaluated by using various assessments that may provide us with a novel perspective on their effects on aquatic animals. Before conducting the toxicity assessments, the CNTs were characterized as multiwall carbon nanotubes (MWCNTs) functionalized with hydroxyl and carboxyl groups, which improved their solubility and dispersibility. Based on the results, abnormalities in zebrafish behaviors were observed in the exposed groups, indicated by a reduction in tail coiling frequency and alterations in the locomotion as the response toward photo and vibration stimuli that might be due to the disruption in the neuromodulatory system and the formation of reactive oxygen species (ROS) by MWCNTs. Next, based on the respiratory rate assay, exposed larvae consumed more oxygen, which may be due to the injuries in the larval gill by the MWCNTs. Finally, even though no irregularity was observed in the exposed larval cardiac rhythm, abnormalities were shown in their cardiac physiology and blood flow with significant downregulation in several cardiac development-related gene expressions. To sum up, although the following studies are necessary to understand the exact mechanism of their toxicity, the current study demonstrated the environmental implications of MWCNTs in particularly low concentrations and short-term exposure, especially to aquatic organisms.

Respiratory plasticity is a beneficial response to chronic hypoxia in fish. Red drum, a teleost that commonly experiences hypoxia in the Gulf of Mexico, have shown respiratory plasticity following sublethal hypoxia exposure as juveniles, but implications of hypoxia exposure during development are unknown. We exposed red drum embryos to hypoxia (40% air saturation) or normoxia (100% air saturation) for 3 days post fertilization (dpf). This time frame encompasses hatch and exogenous feeding. At 3 dpf, there was no difference in survival or changes in size. After the 3-day hypoxia exposure, all larvae were moved and reared in common normoxic conditions. Fish were reared for ∼3 months and effects of the developmental hypoxia exposure on swim performance and whole-animal aerobic metabolism were measured. We used a cross design wherein fish from normoxia (N=24) were exercised in swim tunnels in both hypoxia (40%, n=12) and normoxia (100%, n=12) conditions, and likewise for hypoxia-exposed fish (n=10 in each group). Oxygen consumption, critical swim speed (Ucrit), critical oxygen threshold (Pcrit) and mitochondrial respiration were measured. Hypoxia-exposed fish had higher aerobic scope, maximum metabolic rate, and higher liver mitochondrial efficiency relative to control fish in normoxia. Interestingly, hypoxia-exposed fish showed increased hypoxia sensitivity (higher Pcrit) and recruited burst swimming at lower swim speeds relative to control fish. These data provide evidence that early hypoxia exposure leads to a complex response in later life.

Background
The iono- and osmoregulatory capacities of marine teleosts, such as European sea bass (Dicentrarchus labrax) are expected to be challenged by high carbon dioxide exposure, and the adverse effects of elevated CO2 could be amplified when such fish migrate into less buffered hypo-osmotic estuarine environments. Therefore, the effects of increased CO2 on the physiological responses of European sea bass (Dicentrarchus labrax) acclimated to 32 ppt, 10 ppt and 2.5 ppt were investigated.

Methods
Following acclimation to different salinities for two weeks, fish were exposed to present-day (400 µatm) and future (1000 µatm) atmospheric CO2 for 1, 3, 7 and 21 days. Blood pH, plasma ions (Na+, K+, Cl-), branchial mRNA expression of ion transporters such as Na+/K+–ATPase (NKA), Na+/K+/2Cl– co-transporters (NKCC) and ammonia transporters (e.g. Rhesus glycoproteins Rhbg, Rhcg1 and Rhcg2) were examined to understand the iono- and osmoregulatory consequences of elevated CO2.

Results
A transient but significant increase in the blood pH of exposed fish acclimated at 10 ppt (day 1) and 2.5 ppt (day 21) was observed possibly due to an overshoot of the blood HCO3− accumulation while a significant reduction of blood pH was observed after 21 days at 2.5ppt. However, no change was seen at 32 ppt. Generally, Na + concentration of control fish was relatively higher at 10 ppt and lower at 2.5 ppt compared to 32 ppt control group at all sampling periods. Additionally, NKA was upregulated in gill of juvenile sea bass when acclimated to lower salinities compared to 32 ppt control group. CO2 exposure generally downregulated NKA mRNA expression at 32ppt (day 1), 10 ppt (days 3, 7 and 21) and 2.5ppt (days 1 and 7) and also a significant reduction of NKCC mRNA level of the exposed fish acclimated at 32 ppt (1–3 days) and 10 ppt (7–21 days) was observed. Furthermore, Rhesus glycoproteins were generally upregulated in the fish acclimated at lower salinities indicating a higher dependance on gill ammonia excretion. Increased CO2 led to a reduced expression of Rhbg and may therefore reduce ammonia excretion rate.

Conclusion
Juvenile sea bass were relatively successful in keeping acid base balance under an ocean acidification scenario. However, this came at a cost for ionoregulation with reduced NKA, NKCC and Rhbg expression rates as a consequence.

Lamin A/C gene (LMNA) mutations contribute to severe striated muscle laminopathies, affecting cardiac and skeletal muscles, with limited treatment options. In this study, we delve into the investigations of five distinct LMNA mutations, including three novel variants and two pathogenic variants identified in patients with muscular laminopathy. Our approach employs zebrafish models to comprehensively study these variants. Transgenic zebrafish expressing wild-type LMNA and each mutation undergo extensive morphological profiling, swimming behavior assessments, muscle endurance evaluations, heartbeat measurement, and histopathological analysis of skeletal muscles. Additionally, these models serve as platform for focused drug screening. We explore the transcriptomic landscape through qPCR and RNAseq to unveil altered gene expression profiles in muscle tissues. Larvae of LMNA(L35P), LMNA(E358K), and LMNA(R453W) transgenic fish exhibit reduced swim speed compared to LMNA(WT) measured by DanioVision. All LMNA transgenic adult fish exhibit reduced swim speed compared to LMNA(WT) in T-maze. Moreover, all LMNA transgenic adult fish, except LMNA(E358K), display weaker muscle endurance than LMNA(WT) measured by swimming tunnel. Histochemical staining reveals decreased fiber size in all LMNA mutations transgenic fish, excluding LMNA(WT) fish. Interestingly, LMNA(A539V) and LMNA(E358K) exhibited elevated heartbeats. We recognize potential limitations with transgene overexpression and conducted association calculations to explore its effects on zebrafish phenotypes. Our results suggest lamin A/C overexpression may not directly impact mutant phenotypes, such as impaired swim speed, increased heart rates, or decreased muscle fiber diameter. Utilizing LMNA zebrafish models for drug screening, we identify l-carnitine treatment rescuing muscle endurance in LMNA(L35P) and creatine treatment reversing muscle endurance in LMNA(R453W) zebrafish models. Creatine activates AMPK and mTOR pathways, improving muscle endurance and swim speed in LMNA(R453W) fish. Transcriptomic profiling reveals upstream regulators and affected genes contributing to motor dysfunction, cardiac anomalies, and ion flux dysregulation in LMNA mutant transgenic fish. These findings faithfully mimic clinical manifestations of muscular laminopathies, including dysmorphism, early mortality, decreased fiber size, and muscle dysfunction in zebrafish. Furthermore, our drug screening results suggest l-carnitine and creatine treatments as potential rescuers of muscle endurance in LMNA(L35P) and LMNA(R453W) zebrafish models. Our study offers valuable insights into the future development of potential treatments for LMNA-related muscular laminopathy.

Anthropogenic structures in freshwater systems pose a significant threat by fragmenting habitats. Effective fish passage solutions must consider how environmental changes introduce variability into swimming performance. As temperature is considered the most important external factor influencing fish physiology, it is especially important to consider its effects on fish swimming performance. Even minor alterations in water properties, such as temperature and velocity, can profoundly affect fish metabolic demands, foraging behaviours, fitness and, consequently, swimming performance and passage success. In this study, we investigated the impact of varying water temperatures on the critical swimming speeds of four migratory New Zealand species. Our findings revealed a significant reduction in critical swimming speeds at higher water temperatures (26°C) compared to lower ones (8 and 15°C) for three out of four species (Galaxias maculatus, Galaxias brevipinnis and Gobiomorphus cotidianus). In contrast, Galaxias fasciatus exhibited no significant temperature-related changes in swimming performance, suggesting species-specific responses to temperature. The cold temperature treatment did not impact swimming performance for any of the studied species. As high water temperatures significantly reduce fish swimming performance, it is important to ensure that fish passage solutions are designed to accommodate a range of temperature changes, including spatial and temporal changes, ranging from diel to decadal fluctuations. Our research underscores the importance of incorporating temperature effects into fish passage models for habitat restoration, connectivity initiatives, and freshwater fish conservation. The influence of temperature on fish swimming performance can alter migration patterns and population dynamics, highlighting the need for adaptive conservation strategies. To ensure the resilience of freshwater ecosystems it is important to account for the impact of temperature on fish swimming performance, particularly in the context of a changing climate.

Aim To identify the physiological role of the acid‐base sensing enzyme, soluble adenylyl cyclase (sAC), in red blood cells (RBC) of the model teleost fish, rainbow trout. Methods We used: (i) super‐resolution microscopy to determine the subcellular location of sAC protein; (ii) live‐cell imaging of RBC intracellular pH (pH i ) with specific sAC inhibition (KH7 or LRE1) to determine its role in cellular acid‐base regulation; (iii) spectrophotometric measurements of haemoglobin–oxygen (Hb‐O 2 ) binding in steady‐state conditions; and (iv) during simulated arterial‐venous transit, to determine the role of sAC in systemic O 2 transport. Results Distinct pools of sAC protein were detected in the RBC cytoplasm, at the plasma membrane and within the nucleus. Inhibition of sAC decreased the setpoint for RBC pH i regulation by ~0.25 pH units compared to controls, and slowed the rates of RBC pH i recovery after an acid‐base disturbance. RBC pH i recovery was entirely through the anion exchanger (AE) that was in part regulated by HCO 3 − ‐dependent sAC signaling. Inhibition of sAC decreased Hb‐O 2 affinity during a respiratory acidosis compared to controls and reduced the cooperativity of O 2 binding. During in vitro simulations of arterial‐venous transit, sAC inhibition decreased the amount of O 2 that is unloaded by ~11%. Conclusion sAC represents a novel acid‐base sensor in the RBCs of rainbow trout, where it participates in the modulation of RBC pH i and blood O 2 transport though the regulation of AE activity. If substantiated in other species, these findings may have broad implications for our understanding of cardiovascular physiology in vertebrates.

Giant clams obtain their nutrition from both filter-feeding and photosynthates produced by symbiotic zooxanthellae within their mantle tissue. The symbiotic partnerships between giant clam and zooxanthellae are critical for the health and survival of giant clams. Therefore, light/dark alternation plays a crucial role in influencing the growth performance and physiological change of the giant clam-zooxanthellae symbiosis in natural ecosystems. In this study, the rhythms of mantle surface area, physiological metabolic activity, and oxidative stress in the boring giant clam, Tridacna crocea, caused by two different light-dark cycles (7:00–19:00 light-on and 9:00–21:00 light-on, respectively) were investigated. The relative mantle surface area, net calcification rate and gross primary production significantly increased with the increase in light time, and the highest values were observed after 4–7 h of light exposure. The values of symbiosis Y (II) sharply increased when giant clams were transferred from dark to light conditions, and then slightly decreased to a low level until the next light/dark cycle. Dynamic changes of zooxanthellae density in the outer mantle were observed with two-peak values noted at 4 h after light-on and -off, respectively. The absorption of ammonium-nitrogen (negative values of ammonia metabolic rate) was observed when giant clams were exposed to light, and the rate reached its highest value after 10 h of light exposure. Rhythmic changes of oxidative stress related enzymes and antioxidant molecule were also detected in the inner and outer mantles. In detail, the highest values of SOD activity were observed around light-on time in both the inner and outer mantles, while the tendency of CAT activity was not the same in the inner and outer mantles; the GSH contents in the inner mantle were significantly higher than that in the outer mantle, and their values significantly increased with light exposure; the MDA concentrations from 5:00 to 14:00 were almost the same in both the inner and outer mantles, which were significantly higher than those at other sampling points. The rhythms of these detected behaviors and physiological responses were almost delayed with the delay of photocycle. This provides experimental support for the hypothesis that some behaviors and physiological responses of giant clams exhibit 24-h rhythms, which are affected by changes of light/dark alternation.

The relationship between behavioral thermoregulation and physiological recovery following exhaustive exercise is not well understood. Behavioral thermoregulation could be beneficial for exercise recovery; for example, selection of cooler temperatures could reduce maintenance metabolic cost to preserve aerobic scope for recovery cost, or selection of warmer temperatures could accelerate recovery of exercise metabolites. While post-exercise behavioral thermoregulation has been observed in lizards and frogs, little is known about its importance in fish. We examined the influence of post-exercise recovery temperature on metabolic rate, thermal preference, and metabolite concentrations in juvenile brook char (Salvelinus fontinalis). Fish were acclimated to and exercised at 15 °C, then recovered at either 15 °C or 10 °C while their metabolic rate was measured via respirometry. Metabolite concentrations were measured in fish after exercise at 15 °C and recovery under one of three thermal treatments (to simulate various behavioral thermoregulation scenarios): (i) 6 h recovery at 15 °C, (ii) 6 h recovery at 10 °C, or (iii) 3 h recovery at 10 °C followed by 3 h recovery at 15 °C. Thermal preference was quantified using a static temperature preference system (15 °C vs. 10 °C). Metabolic rates returned to resting faster at 10 °C compared with 15 °C, although at 10 °C there was a tradeoff of delayed metabolite recovery. Specifically, post-exercise plasma osmolality, plasma lactate, and muscle lactate remained elevated for the entire period in fish recovering at 10 °C, whereas these parameters returned to resting levels by 6 h in fish from the other two recovery groups. Regardless, fish did not exhibit clear behavioral thermoregulation (i.e., fish overall did not consistently prefer one temperature) to prioritize either physiological recovery process. The advantage of metabolic rate recovery at cooler temperatures may balance against the advantage of metabolite recovery at warmer temperatures, lessening the usefulness of behavioral thermoregulation as a post-exercise recovery strategy in fish.

The maximum rate at which fish can take up oxygen from their environment to fuel aerobic metabolism is an important feature of their physiology and ecology. Methods to quantify maximum oxygen uptake rate ( Ṁ O 2 ), therefore, should reliably and reproducibly estimate the highest possible Ṁ O 2 by an individual or species under a given set of conditions (peak Ṁ O 2 ). This study determined peak Ṁ O 2 and its repeatability in Gulf killifish, Fundulus grandis, subjected to three methods to elevate metabolism: swimming at increasing water speeds, during recovery after an exhaustive chase, and after ingestion of a large meal. Estimates of peak Ṁ O 2 during swimming and after an exhaustive chase were repeatable across two trials, whereas peak Ṁ O 2 after feeding was not. Peak Ṁ O 2 determined by the three methods was significantly different from one another, being highest during swimming, lowest after an exhaustive chase, and intermediate after feeding. In addition, peak Ṁ O 2 during recovery from an exhaustive chase depended on the length of time of recovery: in nearly 60% of the trials, values within the first hour of the chase were lower than those measured later. A novel and important finding was that an individual's peak Ṁ O 2 was not repeatable when compared across methods. Therefore, the peak Ṁ O 2 estimated for a group of fish, as well as the ranking of individual Ṁ O 2 within that group, depends on the method used to elevate aerobic metabolism.

The maximum rate at which fish can take up oxygen from their environment to fuel aerobic metabolism is an important feature of their physiology and ecology. Methods to quantify maximum oxygen uptake rate ( Ṁ O 2 ), therefore, should reliably and reproducibly estimate the highest possible Ṁ O 2 by an individual or species under a given set of conditions (peak Ṁ O 2 ). This study determined peak Ṁ O 2 and its repeatability in Gulf killifish, Fundulus grandis, subjected to three methods to elevate metabolism: swimming at increasing water speeds, during recovery after an exhaustive chase, and after ingestion of a large meal. Estimates of peak Ṁ O 2 during swimming and after an exhaustive chase were repeatable across two trials, whereas peak Ṁ O 2 after feeding was not. Peak Ṁ O 2 determined by the three methods was significantly different from one another, being highest during swimming, lowest after an exhaustive chase, and intermediate after feeding. In addition, peak Ṁ O 2 during recovery from an exhaustive chase depended on the length of time of recovery: in nearly 60% of the trials, values within the first hour of the chase were lower than those measured later. A novel and important finding was that an individual's peak Ṁ O 2 was not repeatable when compared across methods. Therefore, the peak Ṁ O 2 estimated for a group of fish, as well as the ranking of individual Ṁ O 2 within that group, depends on the method used to elevate aerobic metabolism.

Animals routinely encounter environmental (e.g., high temperatures and hypoxia) as well as physiological perturbations (e.g., exercise and digestion) that may threaten homeostasis. However, comparing the relative threat or “disruptiveness” imposed by different stressors is difficult, as stressors vary in their mechanisms, effects, and timescales. We exploited the fact that several acute stressors can induce the loss of equilibrium (LOE) in fish to (i) compare the metabolic recovery profiles of three environmentally relevant stressors and (ii) test the concept that LOE could be used as a physiological calibration for the intensity of different stressors. We focused on Etheostoma caeruleum, a species that routinely copes with environmental fluctuations in temperature and oxygen and that relies on burst swimming to relocate and avoid predators, as our model. Using stop‐flow (intermittent) respirometry, we tracked the oxygen consumption rate (MO 2 ) as E. caeruleum recovered from LOE induced by hypoxia (PO 2 at LOE), warming (critical thermal maximum, CT max ), or exhaustive exercise. Regardless of the stressor used, E. caeruleum recovered rapidly, returning to routine MO 2 within ~3 h. Fish recovering from hypoxia and warming had similar maximum MO 2, aerobic scopes, recovery time, and total excess post‐hypoxia or post‐warming oxygen consumption. Though exhaustive exercise induced a greater maximum MO 2 and corresponding higher aerobic scope than warming or hypoxia, its recovery profile was otherwise similar to the other stressors, suggesting that “calibration” to a physiological state such as LOE may be a viable conceptual approach for investigators interested in questions related to multiple stressors, cross tolerance, and how animals cope with challenges to homeostasis.

Heatwaves are becoming more frequent and intensified with climate change. Freshwater ecosystems are among the most threatened, within which, differing responses between cool- and warmwater species to heatwaves can lead to fundamental changes in communities. Physiological experiments can identify potential mechanisms underlying the impacts of such heatwaves on fish communities. In the current study, we quantified the oxygen consumption rate, aerobic scope and swimming performance of cool- and warmwater fish species following the simulation of short-term heatwaves currently occurring in streams in the Midwestern United States. The coolwater predator walleye (Sander vitreus) showed clear thermal disadvantages relative to the warmwater predator largemouth bass (Micropterus salmoides), based on a high metabolic cost during the heatwave, low metabolic activity when encountering prey, and reduced swimming performance following the heatwave. Largemouth bass also showed a thermal advantage relative to the warmwater prey fathead minnow (Pimephales promelas) related to swimming performance and energetic costs, highlighting differing thermal responses between predators and prey. This study demonstrates the importance of considering short-term extreme thermal events in the response of aquatic communities to climate stressors.

Behavioural, physiological and biochemical mechanisms constitute the adaptive capacities that allow marine ectotherms to explore the environment beyond their thermal optimal. Limitations to the efficiency of these mechanisms define the transition from moderate to severe thermal stress, and serve to characterise the thermoregulatory response in the zone of thermal tolerance. We selected a tropical population of Hippocampus erectus to describe the timing of the physiological and biochemical mechanisms in response to the following increments in water temperature: (i) 4°C abrupt (26–30°C in <5 min); (ii) 7°C abrupt (26–33°C); (iii) 4°C gradual (1°C every 3 h) and (iv) 7°C gradual (1.5°C every 3 h). The routine metabolic rate ( Rrout ) of juvenile H. erectus was measured immediately before and after 0.5, 12 and 28 h of being exposed to each thermal treatment. Samples of muscle and abdominal organs were taken to quantify indicators of aerobic and anaerobic metabolism and antioxidant enzymes and oxidative stress at each moment throughout exposure. Results showed a full thermoregulatory response within 0.5 h: Rrout increased in direct correspondence with both the magnitude and rate of thermal increase; peroxidised lipids rapidly accumulated before the antioxidant defence was activated and early lactate concentrations suggested an immediate, yet temporary, reduction in aerobic scope. After 12 h, Rrout had decreased in sea horses exposed to 30°C, but not to 33°C, where Rrout continued high until the end of trials. Within 28 h of thermal exposure, all metabolite and antioxidant defence indicators had been restored to control levels (26°C). These findings testify to the outstanding thermal plasticity of H. erectus and explain their adjustment to rapid fluctuations in ambient temperature. Such features, however, do not protect this tropical population from the deleterious effects of chronic exposure to temperatures that have been predicted for the future.

Global warming can either promote or constrain the invasive potential of alien species. In ectotherm invaders that exhibit a complex life cycle, success is inherently dependent on the capacity of each developmental stage to cope with environmental change. This is particularly relevant for invasive anurans, which disperse on land while requiring water for reproduction. However, it remains unknown how the different life stages respond in terms of energy expenditure under different climate change scenarios. We here quantified the oxygen uptake of frogs at rest (a proxy of the standard metabolic rate) in the aquatic phase (at the tadpole and climax, i.e. during metamorphosis, stages) and in the terrestrial phase (metamorphosed stage) at three environmental temperatures. To do so, we used marsh frogs (Pelophylax ridibundus), an amphibian with the largest invasive range within the palearctic realm and for which their adaptation to global warming might be key to their invasion success. Beyond an increase of metabolic rate with temperature, our data show variation in thermal adaptation across life stages and a higher metabolic cost during metamorphosis. These results suggest that the cost to shift habitat and face changes in temperature may be a constraint on the invasive potential of species with a complex life cycle which may be particularly vulnerable during metamorphosis.

The yellowtail kingfish is a highly active and fast-growing marine fish with promising potential for aquaculture. In this study, essential insights were gained into the energy economy of this species by heart rate and acceleration logging during a swim-fitness test and a subsequent stress challenge test. Oxygen consumption values of the 600–800 g fish, when swimming in the range of 0.2 up to 1 m·s−1, were high—between 550 and 800 mg·kg−1·h−1—and the heart rate values—up to 228 bpm—were even among the highest ever measured for fishes. When swimming at these increasing speeds, their heart rate increased from 126 up to 162 bpm, and acceleration increased from 11 up to 26 milli-g. When exposed to four sequential steps of increasing stress load, the decreasing peaks of acceleration (baseline values of 12 to peaks of 26, 19 and 15 milli-g) indicated anticipatory behavior, but the heart rate increases (110 up to 138–144 bpm) remained similar. During the fourth step, when fish were also chased, peaking values of 186 bpm and 44 milli-g were measured. Oxygen consumption and heart rate increased with swimming speed and was well reflected by increases in tail beat and head width frequencies. Only when swimming steadily near the optimal swimming speed were these parameters strongly correlated.

Nanoplastics (NPs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs) are ubiquitous aquatic pollutants. The coexistence of these pollutants in the environment emphasises the need to study their combined toxicity. NPs can cross biological membranes and act as vectors for other pollutants, whereas PCBs are known for their ability to bioaccumulate and biomagnify. The present work aimed to study the combined toxicity of polystyrene NPs and PCB-153 using physiological (development, heart rate, respiration), behavioural (swimming behaviour) and molecular (transcriptome) endpoints in zebrafish larvae. The results show that exposure to NPs, PCB and their mixture significantly affected the development and respiration in zebrafish larvae. Larvae co-exposed to NPs and PCB exhibited significant hyperlocomotion, whereas no such effect was observed after exposure to NPs or PCB alone. The transcriptomic results revealed that NPs exposure significantly affected several pathways associated with DNA compaction and nucleosome assembly, whereas PCB exposure significantly affected critical neurogenic pathways. In contrast, co-exposure to NPs and PCB generated multi-faceted toxicity and suppressed neurobehavioural, immune-related and detoxification pathways. The study highlights the complex interplay between NPs and PCBs, and documents how the two toxicants in combination give a stronger effect than the single toxicants alone. Understanding the mixture toxicity of these two pollutants is important to assess the environmental risks and developing effective management strategies, ultimately safeguarding ecosystems and human health.

Many aquatic networks are fragmented by road crossing structures; remediating these barriers to allow fish passage is critical to restoring connectivity. Maximizing connectivity requires effective barrier identification and prioritization, but many barrier prioritization efforts do not consider swimming capabilities of target species. Given the many potential barriers within watersheds, inventory efforts integrating species-specific swimming speeds into rapid assessment protocols may allow for more accurate barrier removal prioritization. In this study, we demonstrate an approach for integrating fish swimming speeds into rapid barrier assessment and illustrate its utility via two case studies. We measured critical swimming speeds (Ucrit) of two stream-resident fish species with very different swimming modes: Yoknapatawpha Darter (Etheostoma faulkneri), an at-risk species whose current distribution is restricted to highly degraded habitat, and Bluehead Chub (Nocomis leptocephalus), an important host species for the federally endangered Carolina Heelsplitter mussel (Lasmigona decorata). We assessed potential barriers for Yoknapatawpha Darters in the Mississippi-Yocona River watershed, and Bluehead Chubs in the Stevens Creek watershed, South Carolina, USA. We integrated Ucrit into the Southeast Aquatic Resources Partnership (SARP) barrier assessment protocol by estimating the proportion of individuals per species swimming at least as fast as the current through the assessed structures. Integrating Ucrit estimates into the SARP protocol considerably increased barrier severity estimates and rankings only for Yoknapatawpha Darters in the Yocona River watershed. These results indicate the importance of including species-specific swimming abilities in rapid barrier assessments and the importance of species-watershed contexts in estimating where swimming speed information might be most important. Our method has broad application for those working to identify barriers more realistically to improve species-specific fish passage. This work represents a next step in improving rapid barrier assessments and could be improved by investigating how results change with different measurements of swimming abilities and structure characteristics.

Animals often experience changes in their environment that can be perceived as stressful. Previous evidence indicates that different individuals may have distinct stress responses. The role of serotonin (5-HT) in stress adaptation is well established, but its relationship with different defense strategies and the persistence of physiological and behavioral responses in different individuals during repeated acute stress remain unclear. In this study, using olive flounder (Paralichthys olivaceus) as a model, we analyzed the relationship between boldness and neurotransmitter 5-HT activity. We found that 5-HT suppression with 5-HT synthesis inhibitor p-chlorophenylalanine (pCPA) and 5-HT receptor subtype 1A (5-HT1A) antagonist WAY-100635 increased their oxygen consumption rates and the boldness of shy individuals. We determined the metabolic and behavioral changes in bold and shy individuals to repeated acute stress. The results suggest that bold individuals switch on passive “energy-saving” personality by changing their defense behavior from “fight-flight” to “freeze-hide” during a threat encounter, which manifests high behavioral plasticity. Both behavioral types decreased their spontaneous activity levels, which were also strengthened by limiting metabolic rate. Interestingly, treatment with pCPA and WAY-100635 before stress procedure attenuated stress and increased the boldness across diverse behavioral types. This study provides the initial empirical evidence of how perception of stress impacts both individual defense behavior and personality in this species. These findings can enhance our comprehension of individual variability and behavioral plasticity in animals, thereby improving our ability to develop effective adaptive management strategies.

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure, and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite the fact that the phenotype being essential for organism ecology and evolution. In this study, we tested the effects of heat shocks during the embryonic period on the phenotype of Arctic charr ( Salvelinus alpinus ). We repeatedly quantified multiple phenotypic traits, including morphology, development, and behavior, over a period of 4 months, from hatching to juvenile stage in individuals that had experienced heat shocks (+ 5°C on 24 h, seven times) during their embryonic stage and those that had not. We found that heat shocks led to smaller body size at hatching and a lower sociability. Interestingly, these effects weakened throughout the development of individuals and even reversed in the case of body size. We also found an accelerated growth rate and a higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long‐lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and the unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity.

Coastal habitats are exposed to increasing pressure of nanopollutants commonly combined with warming due to the seasonal temperature cycles and global climate change. To investigate the toxicological effects of TiO2 nanoparticles (TiO2 NPs) and elevated temperature on the intestinal health of the mussels (Mytilus coruscus), the mussels were exposed to 0.1 mg/L TiO2 NPs with different crystal structures for 14 days at 20 °C and 28 °C, respectively. Compared to 20 °C, the agglomeration of TiO2 NPs was more serious at 28 °C. Exposure to TiO2 NPs led to elevated mortality of M. coruscus and modified the intestinal microbial community as shown by 16S rRNA sequence analysis. Exposure to TiO2 NPs changed the relative abundance of Bacteroidetes, Proteobacteria and Firmicutes. The relative abundances of putative mutualistic symbionts Tenericutes and Fusobacteria increased in the gut of M. coruscus exposed to anatase, which have contributed to the lower mortality in this group. LEfSe showed the combined stress of warming and TiO2 NPs increased the risk of M. coruscus being infected with potential pathogenic bacteria. This study emphasizes the toxicity differences between crystal structures of TiO2 NPs, and will provides an important reference for analyzing the physiological and ecological effects of nanomaterial pollution on bivalves under the background of global climate change.

Attempting to differentiate phenotypic variation caused by environmentally-induced alterations in gene expression from that caused by actual allelic differences can be experimentally difficult. Environmental variables must be carefully controlled and then interindividual genetic differences ruled out as sources of phenotypic variation. We investigated phenotypic variability of cardiorespiratory physiology as well as biometric traits in the parthenogenetically-reproducing marbled crayfish Procambarus virginalis Lyko, 2017, all offspring being genetically identical clones. Populations of P. virginalis were reared from eggs tank-bred at four different temperatures (16, 19, 22 and 25 °C) or two different oxygen levels (9.5 and 20 kPa). Then, at Stage 3 and 4 juvenile stages, physiological (heart rate, oxygen consumption) and morphological (carapace length, body mass) variables were measured. Heart rate and oxygen consumption measured at 23 °C showed only small effects of rearing temperature in Stage 3 juveniles, with larger effects evident in older, Stage 4 juveniles. Additionally, coefficients of variation were calculated to compare our data to previously published data on P. virginalis as well as sexually-reproducing crayfish. Comparison revealed that carapace length, body mass and heart rate (but not oxygen consumption) indeed showed lower, yet notable coefficients of variation in clonal crayfish. Yet, despite being genetically identical, significant variation in their morphology and physiology in response to different rearing conditions nonetheless occurred in marbled crayfish. This suggests that epigenetically induced phenotypic variation might play a significant role in asexual but also sexually reproducing species.

Carnivorous reptiles exhibit an intense metabolic increment during digestion, which is accompanied by several cardiovascular adjustments responsible for meeting the physiological demands of the gastrointestinal system. Postprandial tachycardia, a well-documented phenomenon in these animals, is mediated by the withdrawal of vagal tone associated with the chronotropic effects of non-adrenergic and non-cholinergic (NANC) factors. However, herbivorous reptiles exhibit a modest metabolic increment during digestion and there is no information about postprandial cardiovascular adjustments. Considering the significant impact of feeding characteristics on physiological responses, we investigated cardiovascular and metabolic responses, as well as the neurohumoral mechanisms of cardiac control, in the herbivorous lizard Iguana iguana during digestion. We measured oxygen consumption rate (O2), heart rate (fH), mean arterial blood pressure (MAP), myocardial activity, cardiac autonomic tone, fH/MAP variability and baroreflex efficiency in both fasting and digesting animals before and after parasympathetic blockade with atropine followed by double autonomic blockade with atropine and propranolol. Our results revealed that the peak of O2 in iguanas was reached 24 h after feeding, accompanied by an increase in myocardial activity and a subtle tachycardia mediated exclusively by a reduction in cardiac parasympathetic activity. This represents the first reported case of postprandial tachycardia in digesting reptiles without the involvement of NANC factors. Furthermore, this withdrawal of vagal stimulation during digestion may reduce the regulatory range for short-term fH adjustments, subsequently intensifying the blood pressure variability as a consequence of limiting baroreflex efficiency.

Many animals moving through fluids exhibit highly coordinated group movement that is thought to reduce the cost of locomotion. However, direct energetic measurements demonstrating the energy-saving benefits of fluid-mediated collective movements remain elusive. By characterizing both aerobic and anaerobic metabolic energy contributions in schools of giant danio ( Devario aequipinnatus ), we discovered that fish schools have a concave upward shaped metabolism–speed curve, with a minimum metabolic cost at ~1 body length s -1. We demonstrate that fish schools reduce total energy expenditure (TEE) per tail beat by up to 56% compared to solitary fish. When reaching their maximum sustained swimming speed, fish swimming in schools had a 44% higher maximum aerobic performance and used 65% less non-aerobic energy compared to solitary individuals, which lowered the TEE and total cost of transport by up to 53%, near the lowest recorded for any aquatic organism. Fish in schools also recovered from exercise 43% faster than solitary fish. The non-aerobic energetic savings that occur when fish in schools actively swim at high speed can considerably improve both peak and repeated performance which is likely to be beneficial for evading predators. These energetic savings may underlie the prevalence of coordinated group locomotion in fishes.

During swimming, many fishes use pectoral fins for propulsion and, in the process, move substantial amounts of water rearward. However, the effect that this upstream wake has on the caudal fin remains largely unexplored. By coordinating motions of the caudal fin with the pectoral fins, fishes have the potential to create constructive flow interactions which may act to partially recapture the upstream energy lost in the pectoral fin wake. Using experimentally derived velocity and pressure fields for the silver mojarra ( Eucinostomus argenteus ), we show that pectoral–caudal fin (PCF) coordination enables the circulation and interception of pectoral fin wake vortices by the caudal fin. This acts to transfer energy to the caudal fin and enhance its hydrodynamic efficiency at swimming speeds where this behaviour occurs. We also find that mojarras commonly use PCF coordination in nature. The results offer new insights into the evolutionary drivers and behavioural plasticity of fish swimming as well as for developing more capable bioinspired underwater vehicles.

Freshwater ecosystems are undergoing rapid thermal shifts, making it increasingly important to understand species-specific responses to these changes. Traditional techniques for determining a species’ thermal tolerance are often lethal and time consuming. Using the enzyme activity associated with the electron transport system (ETS; hereafter referred to as enzyme assay) may provide a non-lethal, rapid, and efficient alternative to traditional techniques for some species. We used largemouth bass Micropterus salmoides (Lacepede, 1802) to test the efficacy of using an enzyme assay to determine thermal tolerance and respiratory exploitation in response to variable acclimation temperatures. Three tissue types were dissected from fish acclimated to 20, 25, or 30 °C and used in ETS assays at temperatures ranging from 7.5 to 40 °C. While there were significant differences among tissue types and acclimation temperatures, maximal enzyme activity occurred from 25.23 to 31.91 °C. Fish lost equilibrium at 39–42 °C in traditional CT max trials, significantly higher than the upper optimum range determined via enzyme assays. The ratio of enzyme activity to measured whole organism respiration rate decreased with increasing water temperature, with the largest changes occurring at the upper optimum thermal range determined by enzyme assays. Our results indicate that ETS analysis may prove useful for obtaining biologically relevant thermal tolerances.

Overharvesting is a serious threat to many fish populations. High mortality and directional selection on body size can cause evolutionary change in exploited populations via selection for a specific phenotype and a potential reduction in phenotypic diversity. Whether the loss of phenotypic diversity that accompanies directional selection impairs response to environmental stress is not known. To address this question, we exposed three zebrafish selection lines to thermal stress. Two lines had experienced directional selection for (1) large and (2) small body size, and one was (3) subject to random removal of individuals with respect to body size (i.e. line with no directional selection). Selection lines were exposed to three temperatures (elevated, 34°C; ambient, 28°C; low, 22°C) to determine the response to an environmental stressor (thermal stress). We assessed differences among selection lines in their life history (growth and reproduction), physiological traits (metabolic rate and critical thermal max) and behaviour (activity and feeding behaviour) when reared at different temperatures. Lines experiencing directional selection (i.e. size selected) showed reduced growth rate and a shift in average phenotype in response to lower or elevated thermal stress compared with fish from the random‐selected line. Our data indicate that populations exposed to directional selection can have a more limited capacity to respond to thermal stress compared with fish that experience a comparable reduction in population size (but without directional selection). Future studies should aim to understand the impacts of environmental stressors on natural fish stocks.

Sustained swimming induces beneficial effects on growth and energy metabolism in some fish species. However, the absence of a standardized exercise regimen that guarantees an optimal response to physical activity is due to the anatomical, behavioral, and physiological differences among species, and the different conditions of tests applied, which are especially notable for the early stages of cultured species. The objective of this study was to assess the growth and metabolic responses of European sea bass submitted to continuous and moderate exercise exposure, selecting a practical swimming speed from swimming tests of groups of five fingerlings. The exercise-effects trial was carried out with 600 sea bass fingerlings (3–5 g body weight) distributed in two groups (control: voluntary swimming; exercised: under sustained swimming at 1.5 body lengths·s−1). After 6 weeks, growth parameters and proximal composition of both muscles were not altered by sustained swimming, but an increased synthetic capacity (increased RNA/DNA ratio) and more efficient use of proteins (decreased ΔN15) were observed in white muscle. The gene expression of mitochondrial proteins in white and red muscle was not affected by exercise, except for ucp3, which increased. The increase of UCP3 and Cox4 protein expression, as well as the higher COX/CS ratio of enzyme activity in white muscle, pointed out an enhanced oxidative capacity in this tissue during sustained swimming. In the protein expression of red muscle, only CS increased. All these metabolic adaptations to sustained exercise were also reflected in an enhanced maximum metabolic rate (MMR) with higher aerobic scope (AMS) of exercised fish in comparison to the non-trained fish, during a swimming test. These results demonstrated that moderate sustained swimming applied to sea bass fingerlings can improve the physical fitness of individuals through the enhancement of their aerobic capacities.

By living and moving in groups, fish can gain many benefits, such as heightened predator detection, greater hunting efficiency, more accurate environmental sensing, and energy saving. Although the benefits of hydrodynamic interactions in schooling fish have drawn growing interest in fields such as biology, physics, and engineering, and multiple hypotheses for how such benefits may arise have been proposed, it is still largely unknown which mechanisms fish employ to obtain hydrodynamic benefits, such as increased thrust or improved movement efficiency. One main bottleneck has been the difficulty in collecting detailed sensory information, corresponding locomotory responses, and hydrodynamic information from real schooling fish.

In variable environments, repeatable phenotypic differences between individuals provide the variation required for natural selection. The pace-of-life syndrome (POLS) provides a conceptual framework linking individual physiology and life histories to behaviour, where rapidly growing individuals demonstrate higher rates of resting or “standard” metabolic rate (SMR). If differences in SMR are consistent between fast- and slow-growing individuals, these differences may be important to capture in bioenergetic relationships used to describe their growth, energy acquisition, and allocation. We compared growth rates and SMR between a domesticated and wild strain of rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) using intermittent flow respirometry. Though mass-scaling exponents were similar between strains, mass-scaling coefficients of SMR for fast-growing rainbow trout were 1.25 times higher than those for slower growing fish. These observed differences in mass-scaling coefficients between fast- and slow-growing rainbow trout were consistent with data extracted from several other studies. Bioenergetic estimates of consumption for domestic strain fish increased as the difference in SMR and wild strain fish increased, and increased as activity level increased. Our results indicate patterns of SMR consistent with POLS, and suggest that strain-specific SMR equations may be important for applications to active populations (i.e., field observations).

Reef fishes in the California Current Ecosystem have evolved in habitats affected by seasonally variable, episodic upwelling of high pCO2 (acidified, low pH) and low dissolved oxygen (deoxygenated) water, which suggests that these fishes might exhibit resilience to ocean acidification (OA) and deoxygenation. Yet, how the fitness of these fish are affected by natural variability in pH and DO over short time scales remains poorly understood, as do the effects of longer-term trends in pH and DO driven by climate change. We conducted a complementary suite of experiments to study the effects of acidification and deoxygenation on the critical swimming speed (Ucrit) of juvenile copper (Sebastes caurinus) and black (S. melanops) rockfish collected from nearshore habitats in an ocean acidification “hotspot” off Northern California. We consistently observed that Ucrit declined more strongly in response to deoxygenation than to acidification, at least under ranges of these stressors consistent with current conditions and plausible future scenarios, and that reduction in swimming performance reflected additive rather than synergistic responses to concurrent exposure. Reductions in swimming performance manifested quickly–on the scale of hours–in response to exposure to elevated pCO2/reduced DO, yet are reversible: swimming performance of juvenile rockfish recovers within a matter of days, and perhaps much more quickly, after acidified/deoxygenated conditions have subsided. Insights from this study address potential effects of variability in upwelling intensity at event and seasonal scales for nearshore rockfishes and contribute to our understanding of fish responses to future ocean conditions driven by ongoing climate change.

Tacrolimus (FK506) is a common immunosuppressant that is used in organ transplantation. However, despite its importance in medical applications, it is prone to adverse side effects. While some studies have demonstrated its toxicities to humans and various animal models, very few studies have addressed this issue in aquatic organisms, especially zebrafish. Here, we assessed the adverse effects of acute and chronic exposure to tacrolimus in relatively low doses in zebrafish in both larval and adult stages, respectively. Based on the results, although tacrolimus did not cause any cardiotoxicity and respiratory toxicity toward zebrafish larvae, it affected their locomotor activity performance in light–dark locomotion tests. Meanwhile, tacrolimus was also found to slightly affect the behavior performance, shoaling formation, circadian rhythm locomotor activity, and color preference of adult zebrafish in a dose-dependent manner. In addition, alterations in the cognitive performance of the fish were also displayed by the treated fish, indicated by a loss of short-term memory. To help elucidate the toxicity mechanism of tacrolimus, molecular docking was conducted to calculate the strength of the binding interaction between tacrolimus to human FKBP12. The results showed a relatively normal binding affinity, indicating that this interaction might only partly contribute to the observed alterations. Nevertheless, the current research could help clinicians and researchers to further understand the toxicology of tacrolimus, especially to zebrafish, thus highlighting the importance of considering the toxicity of tacrolimus prior to its usage.

In a recent mechanistic study, octopamine was shown to promote proton transport over the branchial epithelium in green crabs, Carcinus maenas. Here, we follow up on this finding by investigating the involvement of octopamine in an environmental and physiological context that challenges acid-base homeostasis, the response to short-term high pCO2 exposure (400 Pa) in a brackish water environment. We show that hyperregulating green crabs experienced a respiratory acidosis as early as 6 h of exposure to hypercapnia, with a rise in hemolymph pCO2 accompanied by a simultaneous drop of hemolymph pH. The slightly delayed increase in hemolymph HCO3- observed after 24 h helped to restore hemolymph pH to initial values by 48 h. Circulating levels of the biogenic amine octopamine were significantly higher in short-term high pCO2 exposed crabs compared to control crabs after 48 h. Whole animal metabolic rates, intracellular levels of octopamine and cAMP, as well as branchial mitochondrial enzyme activities for complex I + III and citrate synthase were unchanged in posterior gill #7 after 48 h of hypercapnia. However, application of octopamine in gill respirometry experiments suppressed branchial metabolic rate in posterior gills of short-term high pCO2 exposed animals. Furthermore, branchial enzyme activity of cytochrome C oxidase decreased in high pCO2 exposed crabs after 48 h. Our results indicate that hyperregulating green crabs are capable of quickly counteracting a hypercapnia-induced respiratory acidosis. The role of octopamine in the acclimation of green crabs to short-term hypercapnia seems to entail the alteration of branchial metabolic pathways, possibly targeting mitochondrial cytochrome C in the gill. Our findings help advancing our current limited understanding of endocrine components in hypercapnia acclimation.

Understanding how metabolic costs change in relation to increasing temperature under future climate changes is important to predict how ectotherms will be affected across the globe. In fish, whole body respiration is traditionally used to estimate aerobic performance via an organism’s minimum and maximum oxygen consumption rates. However, mitochondria play a crucial role in the aerobic cascade and may be a useful surrogate of aerobic performance. To test whether whole body oxygen consumption and mitochondrial capacity are correlated, we estimated whole body metabolic and mitochondrial respiration rates (using permeabilized red muscle fibres) in brook trout ( Salvelinus fontinalis (Mitchill, 1814)) at 10, 15, and 20 °C. Standard metabolic rate increased with acclimation temperature, while maximum rates were less sensitive. All mitochondrial respiration rates increased with acclimation temperature, suggesting that red muscle mitochondrial preparations may correlate to the minimal metabolic demands in this species. When expressed as relative rates of electron flow, the red muscle fibres showed no effect of temperature on mitochondrial coupling efficiency. However, there was a pattern of declining capacity to augment respiration via complex II with increasing temperature with a concomitant increase in the capacity of the phosphorylating system relative to maximal rates of mitochondrial electron flow.

Microdosing ketamine is a novel antidepressant for treatment‐resistant depression. Traditional antidepressants, like selective serotonin reuptake inhibitors (SSRIs), inhibit serotonin reuptake, but it is not clear if ketamine shows a similar mechanism. Here, we tested the effects of feeding ketamine and SSRIs to Drosophila melanogaster larvae, which has a similar serotonin system to mammals and is a good model to track depressive behaviors, such as locomotion and feeding. Fast‐scan cyclic voltammetry (FSCV) was used to measure optogenetically stimulated serotonin changes, and locomotion tracking software and blue dye feeding to monitor behavior. We fed larvae various doses (1–100 mM) of antidepressants for 24 h and found that 1 mM ketamine did not affect serotonin, but increased locomotion and feeding. Low doses (≤10 mM) of escitalopram and fluoxetine inhibited dSERT and also increased feeding and locomotion behaviors. At 100 mM, ketamine inhibited dSERT and increased serotonin concentrations, but decreased locomotion and feeding because of its anesthetic properties. Since microdosing ketamine causes behavioral effects, we further investigated behavioral changes with a SERT16 mutant and low doses of other NMDA receptor antagonists and 5‐HT 1A and 2 agonists. Feeding and locomotion changes were similar to ketamine in the mutant, and we found NMDA receptor antagonism increased feeding, while serotonin receptor agonism increased locomotion, which could explain these effects with ketamine. Ultimately, this work shows that Drosophila is a good model to discern antidepressant mechanisms, and that ketamine does not work on dSERT like SSRIs, but effects behavior with other mechanisms that should be investigated further. image

To ensure optimal feed intake, growth, and general fish health in aquaculture sea cages, interactions between drivers that affect oxygen conditions need to be understood. The main drivers are oxygen consumption and water exchange, caused by flow through the cage. Swimming energetics in rainbow trout (Oncorhynchus mykiss) in normoxia and hypoxia at 10, 15, and 20 °C were determined. Using the determinations, a conceptual model of oxygen conditions within sea cages was created. By applying the model to a case study, results show that with a temperature increase of 10 °C, oxygen concentration will decrease three times faster. To maintain optimal oxygen concentration within the cage, the flow velocity must be increased by a factor of 3.7. The model is highly relevant for current farms since the model predictions can explain why and when suboptimal conditions occur within the cages. Using the same method, the model can be used to estimate the suitability of potential new aquaculture sites.

Alcoholic myopathy is caused by chronic consumption of alcohol (ethanol) and is characterized by weakness and atrophy of skeletal muscle. Regular exercise is one of the important ways to prevent or alleviate skeletal muscle myopathy. However, the beneficial effects and the exact mechanisms underlying regular exercise on alcohol myopathy remain unclear. In this study, a model of alcoholic myopathy was established using zebrafish soaked in 0.5% ethanol. Additionally, these zebrafish were intervened to swim for 8 weeks at an exercise intensity of 30% of the absolute critical swimming speed (Ucrit), aiming to explore the beneficial effects and underlying mechanisms of regular exercise on alcoholic myopathy. This study found that regular exercise inhibited protein degradation, improved locomotion ability, and increased muscle fiber cross-sectional area (CSA) in ethanol-treated zebrafish. In addition, regular exercise increases the functional activity of mitochondrial respiratory chain (MRC) complexes and upregulates the expression levels of MRC complexes. Regular exercise can also improve oxidative stress and mitochondrial dynamics in zebrafish skeletal muscle induced by ethanol. Additionally, regular exercise can activate mitochondrial biogenesis and inhibit mitochondrial unfolded protein response (UPRmt). Together, our results suggest regular exercise is an effective intervention strategy to improve mitochondrial homeostasis to attenuate alcoholic myopathy.

A fundamental issue in the metabolic field is whether it is possible to understand underlying mechanisms that characterize individual variation. Whole-animal performance relies on mitochondrial function as it produces energy for cellular processes. However, our lack of longitudinal measures to evaluate how mitochondrial function can change within and among individuals and with environmental context makes it difficult to assess individual variation in mitochondrial traits. The aims of this study were to test the repeatability of muscle mitochondrial metabolism by performing two biopsies of red muscle, and to evaluate the effects of biopsies on whole-animal performance in goldfish Carassius auratus. Our results show that basal mitochondrial respiration and net phosphorylation efficiency are repeatable at 14-day intervals. We also show that swimming performance (optimal cost of transport and critical swimming speed) was repeatable in biopsied fish, whereas the repeatability of individual oxygen consumption (standard and maximal metabolic rates) seemed unstable over time. However, we noted that the means of individual and mitochondrial traits did not change over time in biopsied fish. This study shows that muscle biopsies allow the measurement of mitochondrial metabolism without sacrificing animals and that two muscle biopsies 14 days apart affect the intraspecific variation in fish performance without affecting average performance of individuals. This article is part of the theme issue ‘The evolutionary significance of variation in metabolic rates’.

Metabolic rates are linked to key life-history traits that are thought to set the pace of life and affect fitness, yet the role that parents may have in shaping the metabolism of their offspring to enhance survival remains unclear. Here, we investigated the effect of temperature (24°C or 30°C) and feeding frequency experienced by parent zebrafish ( Danio rerio ) on offspring phenotypes and early survival at different developmental temperatures (24°C or 30°C). We found that embryo size was larger, but survival lower, in offspring from the parental low food treatment. Parents exposed to the warmer temperature and lower food treatment also produced offspring with lower standard metabolic rates—aligning with selection on embryo metabolic rates. Lower metabolic rates were correlated with reduced developmental and growth rates, suggesting selection for a slow pace of life. Our results show that intergenerational phenotypic plasticity on offspring size and metabolic rate can be adaptive when parent and offspring temperatures are matched: the direction of selection on embryo size and metabolism aligned with intergenerational plasticity towards lower metabolism at higher temperatures, particularly in offspring from low-condition parents. These findings provide evidence for adaptive parental effects, but only when parental and offspring environments match.

Across diverse taxa, sublethal exposure to abiotic stressors early in life can lead to benefits such as increased stress tolerance upon repeat exposure. This phenomenon, known as hormetic priming, is largely unexplored in early life stages of marine invertebrates, which are increasingly threatened by anthropogenic climate change. To investigate this phenomenon, larvae of the sea anemone and model marine invertebrate Nematostella vectensis were exposed to control (18 °C) or elevated (24 °C, 30 °C, 35 °C, or 39 °C) temperatures for 1 h at 3 days post-fertilization (DPF), followed by return to control temperatures (18 °C). The animals were then assessed for growth, development, metabolic rates, and heat tolerance at 4, 7, and 11 DPF. Priming at intermediately elevated temperatures (24 °C, 30 °C, or 35 °C) augmented growth and development compared to controls or priming at 39 °C. Indeed, priming at 39 °C hampered developmental progression, with around 40% of larvae still in the planula stage at 11 DPF, in contrast to 0% for all other groups. Total protein content, a proxy for biomass, and respiration rates were not significantly affected by priming, suggesting metabolic resilience. Heat tolerance was quantified with acute heat stress exposures, and was significantly higher for animals primed at intermediate temperatures (24 °C, 30 °C, or 35 °C) compared to controls or those primed at 39 °C at all time points. To investigate a possible molecular mechanism for the observed changes in heat tolerance, the expression of heat shock protein 70 (HSP70) was quantified at 11 DPF. Expression of HSP70 significantly increased with increasing priming temperature, with the presence of a doublet band for larvae primed at 39 °C, suggesting persistent negative effects of priming on protein homeostasis. Interestingly, primed larvae in a second cohort cultured to 6 weeks post-fertilization continued to display hormetic growth responses, whereas benefits for heat tolerance were lost; in contrast, negative effects of short-term exposure to extreme heat stress (39 °C) persisted. These results demonstrate that some dose-dependent effects of priming waned over time while others persisted, resulting in heterogeneity in organismal performance across ontogeny following priming. Overall, these findings suggest that heat priming may augment the climate resilience of marine invertebrate early life stages via the modulation of key developmental and physiological phenotypes, while also affirming the need to limit further anthropogenic ocean warming.

Spring conditions, especially in temperate regions, may fluctuate abruptly and drastically. Environmental variability can expose organisms to temperatures outside of their optimal thermal ranges. For ectotherms, sudden changes in temperature may cause short- and long-term physiological effects, including changes in respiration, morphology, and reproduction. Exposure to variable temperatures during active development, which is likely to occur for insects developing in spring, can cause detrimental effects. Using the alfalfa leafcutting bee, Megachile rotundata, we aimed to determine if oxygen consumption could be measured using a new system and to test the hypothesis that female and male M. rotundata have a thermal performance curve with a wide optimal range. Oxygen consumption of M. rotundata pupae was measured across a large range of temperatures (6–48°C) using an optical oxygen sensor in a closed respirometry system. Absolute and mass-specific metabolic rates were calculated and compared between bees that were extracted from their brood cells and those remaining in the brood cell to determine whether pupae could be accurately measured inside their brood cells. The metabolic response to temperature was non-linear, which is an assumption of a thermal performance curve; however, the predicted negative slope at higher temperatures was not observed. Despite sexual dimorphism in body mass, sex differences only occurred in mass-specific metabolic rates. Higher metabolic rates in males may be attributed to faster development times, which could explain why there were no differences in absolute metabolic rate measurements. Understanding the physiological and ecological effects of thermal environmental variability on M. rotundata will help to better predict their response to climate change.

How two-chambered hearts in basal vertebrates have evolved from single-chamber hearts found in ancestral chordates remains unclear. Here, we show that the teleost sinus venosus (SV) is a chamber-like vessel comprised of an outer layer of smooth muscle cells. We find that in adult zebrafish nr2f1a mutants, which lack atria, the SV comes to physically resemble the thicker bulbus arteriosus (BA) at the arterial pole of the heart through an adaptive, hypertensive response involving smooth muscle proliferation due to aberrant hemodynamic flow. Single cell transcriptomics show that smooth muscle and endothelial cell populations within the adapting SV also take on arterial signatures. Bulk transcriptomics of the blood sinuses flanking the tunicate heart reinforce a model of greater equivalency in ancestral chordate BA and SV precursors. Our data simultaneously reveal that secondary complications from congenital heart defects can develop in adult zebrafish similar to those in humans and that the foundation of equivalency between flanking auxiliary vessels may remain latent within basal vertebrate hearts. Nr2fs are conserved transcription factors that regulate atrial chamber and venous development. Here, the authors use adult zebrafish nr2f1a mutants to investigate compensatory remodeling of the inflow tract and hypotheses of cardiac evolution.

Phenotypes that allow animals to detect, weather, and predict changes efficiently are essential for survival in fluctuating environments. Some phenotypes may remain specialized to suit an environment perfectly, while others become more plastic or generalized, shifting flexibly to match current context or adopting a form that can utilize a wide range of contexts. Here, we tested the differences in behavior, morphology, sensory and metabolic physiology between wild zebrafish (Danio rerio) in highly variable fast-flowing rivers and still-water sites. We found that river zebrafish moved at higher velocities than did still-water fish, had lower oxygen demands, and responded less vigorously to small changes in flow rate, as we might expect for fish that are well-suited to high-flow environments. River zebrafish also had less streamlined bodies and were more behaviorally plastic than were still-water zebrafish, both features that may make them better-suited to a transitional lifestyle. Our results suggest that zebrafish use distinct sensory mechanisms and metabolic physiology to reduce energetic costs of living in fast-flowing water while relying on morphology and behavior to create flexible solutions to a challenging habitat. Insights on animals’ reliance on traits with different outcomes provide a framework to better understand their survival in future environmental fluctuations.

Fenpropathrin, a pyrethroid insecticide, has been widely used for many years in agricultural fields. It works by disturbing the voltage-gated sodium channel, leading to paralysis and the death of the target animal. While past studies have focused on neurodegeneration following fenpropathrin poisoning in humans, relatively few pieces of research have examined its effect on other peripheral organs. This study successfully investigated the potential toxicity of fenpropathrin on the cardiovascular system using zebrafish as an animal model. Zebrafish larvae exposed to varying doses of fenpropathrin underwent an evaluation of cardiac physiology by measuring the heart rate, stroke volume, cardiac output, and shortening fraction. The blood flow velocity and the dorsal aorta diameter were also measured to assess the impact of fenpropathrin exposure on the vascular system. Furthermore, molecular docking was performed to evaluate the pesticide binding affinity to various proteins associated with the cardiovascular system, revealing the potential mechanism of the fenpropathrin cardiotoxic effect. The findings demonstrated a significant dose-dependent increase in the heart rate stroke volume, cardiac output, shortening fraction, and ejection fraction of zebrafish larvae after 24 h of acute treatment with fenpropathrin. Additionally, zebrafish treated at a concentration of 1 ppm exhibited significantly larger blood vessels in diameter and an increased blood flow velocity compared to the control group. According to molecular docking, fenpropathrin showed a high affinity for various voltage-gated sodium channels like scn1lab, cacna1sb, and clcn3. Finally, from the results, we found that fenpropathrin caused cardiomegaly, which may have been induced by the voltage-gated sodium channel disruption. This study highlights the significant disruption of fenpropathrin in the cardiovascular system and emphasizes the need for further research on the health implications of this pesticide.

Recent advances in bio-sensing technologies open for new possibilities to monitor and safeguard the welfare of fishes in aquaculture. Yet before taken into practice, the applicability of all novel biosensors must be validated, and the breadth of their potential uses must be investigated. Here, we investigated how ECG and accelerometry-derived parameters measured using bio-loggers, such as heart rate, acceleration and variance of acceleration, relate to O2 consumption rate (MO2) and blood borne indicators of stress and tissue damage to determine how biologgers may be used to estimate stress and welfare. To do this, we instrumented 13 fish with a biologger and an intravascular catheter and subjected them to a swimming protocol followed by a stress protocol throughout which the physiological parameters were measured and analyzed a posteriori. Additionally, based on the empirical data obtained, we calculated the mathematical relationships between the bio-logger data and the other parameters and tested the relationship between the calculated parameters using the linear regression algorithms and the measured parameters. Our results show that acceleration is a good proxy for swimming activity as it is closely related to tail beat frequency. In addition, we show that heart rate, acceleration and variance of acceleration all can be used as predictors for metabolic rate. Accelerometry based data, especially variance of acceleration, significantly explain some of the variation in venous partial pressure of O2, blood lactate and plasma cortisol concentration. Variance of acceleration also significantly explains some of the variation in pH and mean corpuscular hemoglobin concentration. These relationships are explained by variance of acceleration being a good indicator of the onset of burst-swimming activity, which is often followed by acid-base imbalances and release of catecholamines. The results herein indicate that bio-logger data can be used to extrapolate a range of stress-related physiological events when these are accompanied by increases in activity and highlight the great potential of biosensors for monitoring fish welfare.

Teleost fish have evolved various adaptations that allow them to tolerate cold water conditions. However, the underlying mechanism of this adaptation is poorly understood in Tibetan Plateau fish. RNA-seq combined with liquid chromatography‒mass spectrometry (LC‒MS/MS) metabolomics was used to investigate the physiological responses of a Tibetan Plateau-specific teleost, Gymnocypris przewalskii, under cold conditions. The 8-month G. przewalskii juvenile fish were exposed to cold (4 ℃, cold acclimation, CA) and warm (17 ℃, normal temperature, NT) temperature water for 15 days. Then, the transcript profiles of eight tissues, including the brain, gill, heart, intestine, hepatopancreas, kidney, muscle, and skin, were evaluated by transcriptome sequencing. The metabolites of the intestine, hepatopancreas, and muscle were identified by LC‒MS/MS. A total of 5,745 differentially expressed genes (DEGs) were obtained in the CA group. The key DEGs were annotated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. The DEGs from the eight tissues were significantly enriched in spliceosome pathways, indicating that activated alternative splicing is a critical biological process that occurs in the tissues to help fish cope with cold stress. Additionally, 82, 97, and 66 differentially expressed metabolites were identified in the intestine, hepatopancreas, and muscle, respectively. Glutathione metabolism was the only overlapping significant pathway between the transcriptome and metabolome analyses in these three tissues, indicating that an activated antioxidative process was triggered during cold stress. In combination with the multitissue transcriptome and metabolome, we established a physiology-gene‒metabolite interaction network related to energy metabolism during cold stress and found that gluconeogenesis and long-chain fatty acid metabolism played critical roles in glucose homeostasis and energy supply.

Fish adapt to changing environments by maintaining homeostasis or making energy trade-offs that impact fitness. We investigated the effect of Zn on the fitness and physiology of Barbus meridionalis, a native cyprinid fish species, under two exposure scenarios. The Osor stream's mine-effluent reach represented long-term (chronic) exposure, while the upstream reach served as a control/acute exposure. Acute exposure involved exposing B. meridionalis to 1mg/L Zn for 96 h in the laboratory. We examined physiological traits (Standard metabolic rate SMR, Maximum metabolic rate MMR, Absolute Aerobic scope AAS, Critical swimming capacity Ucrit) and antioxidant system, AS (Superoxide dismutase, SOD; Catalase, CAT; Glutathione peroxidase, GPX; Glutathione-S-transferase, GST; Glutathione, GSH; Thiobarbaturic acid reactive substances, TBARS) biomarkers. The results indicated that Zn had no significant effect on osmoregulatory cost (SMR) in either exposure scenario but impaired energetically costly exercise (low MMR). AAS reduction in both exposure groups suggested compromised energy allocation for life-history traits, evidenced by decreased locomotor performance (Ucrit) after acute exposure. Tissue-specific and time-dependent responses were observed for AS biomarkers. The fish exhibited ineffective control of oxidative damage, as evidenced by high TBARS levels in the liver and gills, despite increased CAT and GSH in the liver under acute conditions. Our findings demonstrate differential responses at the subcellular level between the two exposure scenarios, while trait-based endpoints followed a similar pattern. This highlights the utility of a trait-based approach as a supplementary endpoint in biomonitoring studies, which provides insights into impacts on individual fitness and population demography.

The gills of most teleost fishes lack plasma-accessible carbonic anhydrase (paCA) that could participate in CO2 excretion. We tested the prevailing hypothesis that paCA would interfere with red blood cell (RBC) intracellular pH regulation by β-adrenergic sodium-proton exchangers (β-NHE) that protect pH-sensitive haemoglobin–oxygen (Hb–O2) binding during an acidosis. In an open system that mimics the gills, β-NHE activity increased Hb–O2 saturation during a respiratory acidosis in the presence or absence of paCA, whereas the effect was abolished by NHE inhibition. However, in a closed system that mimics the tissue capillaries, paCA disrupted the protective effects of β-NHE activity on Hb–O2 binding. The gills are an open system, where CO2 generated by paCA can diffuse out and is not available to acidifying the RBCs. Therefore, branchial paCA in teleosts may not interfere with RBC pH regulation by β-NHEs, and other explanations for the evolutionary loss of the enzyme must be considered.

All freshwater organisms are challenged to control their internal balance of water and ions in strongly hypotonic environments. We compared the influence of external salinity on the oxygen consumption rates (ṀO2) of three species of freshwater insects, one snail and two crustaceans. Consistent with available literature, we found a clear decrease in ṀO2 with increasing salinity in the snail Elimia sp. and crustaceans Hyalella azteca and Gammarus pulex (r5=−0.90, P=0.03). However, we show here for the first time that metabolic rate was unchanged by salinity in the aquatic insects, whereas ion transport rates were positively correlated with higher salinities. In contrast, when we examined the ionic influx rates in the freshwater snail and crustaceans, we found that Ca uptake rates were highest under the most dilute conditions, while Na uptake rates increased with salinity. In G. pulex exposed to a serially diluted ion matrix, Ca uptake rates were positively associated with ṀO2 (r5=−0.93, P=0.02). This positive association between Ca uptake rate and ṀO2 was also observed when conductivity was held constant but Ca concentration was manipulated (1.7–17.3 mg Ca l−1) (r5=0.94, P=0.05). This finding potentially implicates the cost of calcium uptake as a driver of increased metabolic rate under dilute conditions in organisms with calcified exoskeletons and suggests major phyletic differences in osmoregulatory physiology. Freshwater insects may be energetically challenged by higher salinities, while lower salinities may be more challenging for other freshwater taxa.

Anthropologic activities caused frequent eutrophication in coastal and estuarine waters, resulting in diel-cycling hypoxia. Given global climate change, extreme weather events often occur, thus salinity fluctuation frequently breaks out in these waters. This study aimed to evaluate the combined effects of salinity and hypoxia on intestinal microbiota and digestive enzymes of Crassostrea hongkongensis. Specifically, we sequenced 16 S rRNA of intestinal microbiota and measured the digestive enzymes trypsin (TRS), lipase (LPS) and amylase (AMY) in oysters exposed for 28 days to three salinities (10, 25 and 35) and two dissolved oxygen conditions, normoxia (6 mg/L) and hypoxia (6 mg/L for 12 h, 2 mg/L for 12 h). Oysters in normoxia and salinity of 25 were treated as control. After 28-day exposure, for microbial components, Fusobacteriota, Firmicutes, Bacteroidota, Proteobacteria and Actinobacteriota comprised the majority for all experimental groups. Compared with the control group, the diversity and structure of intestinal microbiota tended to change in all treated groups. The species richness in C. hongkongensis intestine also changed. It was the most significant that high salinity increased Proteobacteria proportion while low salinity and hypoxia increased Fusobacteriota but decreased Proteobacteria, respectively. Additionally, Actinobacteriota was sensitive and changed under environmental stressor (P < 0.01). The prediction results on intestinal microbiota showed that, all functions of oysters were up-regulated to distinct degrees under low/high salinity with hypoxia. According to the KEGG prediction, cellular processes were more active and energy metabolism upregulated, indicating the adaptation of C. hongkongensis to environmental change. Periodical hypoxia and low/high salinity had complex effect on the digestive enzymes, in which the activity of TRS and LPS decreased while AMY increased. High/low salinity and periodical hypoxia can change the secretion of digestive enzymes and influence intestinal microbial diversity and species richness of C. hongkongensis, deducing the chronic adverse effects on the digestive physiology in long-term exposure.

Despite their potential vulnerability to oil spills, little is known about the physiological effects of petroleum exposure and spill responses in cold-water marine animal larvae. We investigated the effects of physically dispersed (water-accommodated fraction, WAF) and chemically dispersed (chemically enhanced WAF, CEWAF; using Slickgone EW) conventional heavy crude oil on the routine metabolic rate and heart rate of stage I larval American lobster (Homarus americanus). We found no effects of 24-h exposure to sublethal concentrations of crude oil WAF or CEWAF at 12 °C. We then investigated the effect of sublethal concentrations of WAFs at three environmentally relevant temperatures (9, 12, 15 °C). The highest WAF concentration increased metabolic rate at 9 °C, whereas it decreased heart rate and increased mortality at 15 °C. Overall, metabolic and cardiac function of American lobster larvae is relatively resilient to conventional heavy crude oil and Slickgone EW exposure, but responses to WAF may be temperature-dependent.

One of the hallmarks of invasive species is their propensity to spread. Removing an invasive species after establishment is virtually impossible, and so considerable effort is invested in preventing the range expansion of invaders. Silver carp were discovered in the Mississippi River in 1981 and have spread throughout the basin. Despite their propensity to expand, the ‘leading edge’ in the Illinois River has stalled south of Chicago, and has remained stable for a decade. Studies have suggested that pollutants in the Chicago Area Waterway System (CAWS) may be contributing to the lack of upstream movement, but this hypothesis has not been tested. This study used a laboratory setting to quantify the role of pollutants in deterring upstream movement of silver carp within the CAWS. For this, water was collected from the CAWS near the upstream edge of the distribution and transported to a fish culture facility. Silver carp and one native species were exposed to CAWS water, and activity, behavior, avoidance and metabolic rates were quantified. Results showed that silver carp experience an elevated metabolic cost in CAWS water, along with reductions in swimming behavior. Together, results suggest a role for components of CAWS water at deterring range expansion.

In this study, Atlantic salmon were: (i) implanted with heart rate (fH) data storage tags (DSTs), pharmacologically stimulated to maximum fH, and warmed at 10°C h−1 (i.e. tested using a ‘rapid screening protocol’); (ii) fitted with Doppler® flow probes, recovered in respirometers and given a critical thermal maximum (CTmax) test at 2°C h−1; and (iii) implanted with fH DSTs, recovered in a tank with conspecifics for 4 weeks, and had their CTmax determined at 2°C h−1. Fish in respirometers and those free-swimming were also exposed to a stepwise decrease in water oxygen level (100% to 30% air saturation) to determine the oxygen level at which bradycardia occurred. Resting fH was much lower in free-swimming fish than in those in respirometers (∼49 versus 69 beats min−1) and this was reflected in their scope for fH (∼104 versus 71 beats min−1) and CTmax (27.7 versus 25.9°C). Further, the Arrhenius breakpoint temperature and temperature at peak fH for free-swimming fish were considerably greater than for those tested in the respirometers and given a rapid screening protocol (18.4, 18.1 and 14.6°C; and 26.5, 23.2 and 20.2°C, respectively). Finally, the oxygen level at which bradycardia occurred was significantly higher in free-swimming salmon than in those in respirometers (∼62% versus 53% air saturation). These results: highlight the limitations of some lab-based methods of determining fH parameters and thermal tolerance in fishes; and suggest that scope for fH may be a more reliable and predictive measure of a fish's upper thermal tolerance than their peak fH.

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone) is a degradation product of 6PPD, an antioxidant widely used in rubber tires. 6PPD-quinone enters aquatic ecosystems through urban stormwater runoff and has been identified as the chemical behind the urban runoff mortality syndrome in coho salmon. However, the available data suggest that the acute effects of 6PPD-quinone are restricted to a few salmonid species and that the environmental levels of this chemical should be safe for most fish. In this study, larvae of a "tolerant" fish species, Danio rerio, were exposed to three environmental concentrations of 6PPD-quinone for only 24 h, and the effects on exploratory behavior, escape response, nonassociative learning (habituation), neurotransmitter profile, wake/sleep cycle, circadian rhythm, heart rate and oxygen consumption rate were analyzed. Exposure to the two lowest concentrations of 6PPD-quinone resulted in altered exploratory behavior and habituation, an effect consistent with some of the observed changes in the neurotransmitter profile, including increased levels of acetylcholine, norepinephrine, epinephrine and serotonin. Moreover, exposure to the highest concentration tested altered the wake/sleep cycle and the expression of per1a, per3 and cry3a, circadian clock genes involved in the negative feedback loop. Finally, a positive chronotropic effect of 6PPD-quinone was observed in the hearts of the exposed fish. The results of this study emphasize the need for further studies analyzing the effects of 6PPD-quinone in "tolerant" fish species.

In fishes, the impacts of environmental constraints undergone during development on the behavioural response of individuals are not well understood. Obtaining more information is important since the aquatic environment is widely exposed to pollution involving neurotoxic compounds likely to cause phenotypic changes that can affect animal fitness. We explored how early exposure to the pyrethroid insecticide permethrin (PM), a compound known for its neurotoxicity, influences the phenotypic traits in both larvae and adults of the self-fertilizing fish mangrove rivulus, Kryptolebias marmoratus. First, we investigated immediate effects of PM on larvae after one-week exposure (0–7 days post-hatching): larvae exposed to high concentration (200 µg.L-1) grew less, were less active, had negative thigmotaxis and were less likely to capture prey than control individuals and those exposed to low concentration (5 µg.L-1). No difference was found between treatments when considering oxygen consumption rate and cortisol levels. Persistent effects of early exposure to PM on adults (147–149 days post-hatching) showed that fish previously exposed to high concentration of PM overcompensated growth, leading them to finally be longer and heavier than fish from other treatments. Moreover, we evidenced that levels of cortisol interacted with early PM exposure to affect behaviours during dyadic contests. Fish were more likely to initiate fighting behaviours and were more likely to be aggressive when they have low pre-contest levels of cortisol, but these effects were less pronounced when individuals were exposed to PM. This study shows that PM can have both immediate and persistent effects on phenotypic traits in a self-fertilizing vertebrate and suggests that a pyrethroid can interact with hormones action to affect animal behaviour.

Understanding where and why organisms are experiencing thermal and hydric stress is critical for predicting species' responses to climate change. Biophysical models that explicitly link organismal functional traits like morphology, physiology, and behavior to environmental conditions can provide valuable insight into determinants of thermal and hydric stress. Here we use a combination of direct measurements, 3D modeling, and computational fluid dynamics to develop a detailed biophysical model of the sand fiddler crab, Leptuca pugilator. We compare the detailed model's performance to a model using a simpler ellipsoidal approximation of a crab. The detailed model predicted crab body temperatures within 1 °C of observed in both laboratory and field settings; the ellipsoidal approximation model predicted body temperatures within 2 °C of observed body temperatures. Model predictions are meaningfully improved through efforts to incorporate species-specific morphological properties rather than relying on simple geometric approximations. Experimental evaporative water loss (EWL) measurements indicate that L. pugilator can modify its permeability to EWL as a function of vapor density gradients, providing novel insight into physiological thermoregulation in the species. Body temperature and EWL predictions made over the course of a year at a single site demonstrate how such biophysical models can be used to explore mechanistic drivers and spatiotemporal patterns of thermal and hydric stress, providing insight into current and future distributions in the face of climate change.

Exposure of females to stressful conditions during pregnancy or oogenesis has a profound effect on the phenotype of their offspring. For example, offspring behavioural phenotype may show altered patterns in terms of the consistency of behavioural patterns and their average level of performance. Maternal stress can also affect the development of the stress axis in offspring leading to alterations in their physiological stress response. However, the majority of evidence comes from studies utilising acute stressors or exogenous glucocorticoids, and little is known about the effect of chronic maternal stress, particularly in the context of stress lasting throughout entire reproductive lifespan. To bridge this knowledge gap, we exposed female sticklebacks to stressful and unpredictable environmental conditions throughout the breeding season. We quantified the activity, sheltering and anxiety-like behaviour of offspring from three successive clutches of these females, and calculated Intra-class Correlation Coefficients for these behaviours in siblings and half-siblings. We also exposed offspring to an acute stressor and measured their peak cortisol levels. An unpredictable maternal environment had no modifying effect on inter-clutch acute stress responsivity, but resulted in diversification of offspring behaviour, indicated by an increased between-individual variability within families. This may represent a bet-hedging strategy, whereby females produce offspring differing in behavioural phenotype, to increase the chance that some of these offspring will be better at coping with the anticipated conditions.

Predicted climate change-induced increases in heat waves and hypoxic events will have profound effects on fishes, yet the capacity of parents to alter offspring phenotype via non-genetic inheritance and buffer against these combined stressors is not clear. This study tested how prolonged adult zebrafish exposure to combined diel cycles of thermal stress and hypoxia affect offspring early survival and development, parental investment of cortisol and heat shock proteins (HSPs), larval offspring stress responses, and both parental and offspring heat and hypoxia tolerance. Parental exposure to the combined stressor did not affect fecundity, but increased mortality, produced smaller embryos and delayed hatching. The combined treatment also reduced maternal deposition of cortisol and increased embryo hsf1, hsp70a, HSP70, hsp90aa and HSP90 levels. In larvae, basal cortisol levels did not differ between treatments, but acute exposure to combined heat stress and hypoxia increased cortisol levels in control larvae with no effect on larvae from exposed parents. In contrast, whereas larval basal hsf1, hsp70a and hsp90aa levels differed between parental treatments, the combined acute stressor elicited similar transcriptional responses across treatments. Moreover, the combined acute stressor only induced a marked increase in HSP47 levels in the larvae derived from exposed parents. Finally, combined hypoxia and elevated temperatures increased both thermal and hypoxia tolerance in adults and conferred an increase in offspring thermal but not hypoxia tolerance. These results demonstrate that intergenerational acclimation to combined thermal stress and hypoxia elicit complex carryover effects on stress responsiveness and offspring tolerance with potential consequences for resilience.

The oyster Crassostrea gigas is a major, global aquaculture species. As with any domestically-farmed species, the characterization of breeding lines that yield desired phenotypes is of immense value. An understanding of the fundamental biological bases of such phenotypes is needed to enhance aquaculture production. The aim of our study was to investigate the mechanisms of protein metabolic dynamics and energy allocation in oyster larvae. A series of controlled crosses yielded full-sibling larval families that allowed for measurements of integrative physiological processes during development. Experimentally, phenotypic contrasts between larval families were assayed by measuring: (1) growth and survival, (2) utilization of energy reserves of lipid and protein, (3) rates of protein synthesis and turnover, (4) respiration rates, and (5) transcriptome gene expression. Initially, newly-formed 2-day-old veliger larvae from four different families had similar sizes and physiologies, as measured by respiration, protein synthesis, turnover and content, the amount of energy allocated to protein synthesis, and gene expression pattern. Upon feeding, notable phenotypic contrasts became evident in different families. The larval family with faster growth had higher rates of protein synthesis and allocated a higher percentage of available energy to that single process. Based on family-specific differences, a series of samples was selected for developmental time-course analysis of changes in RNA pools. Principal component analyses of family-specific differential gene expression, combined with measured biochemical and physiological processes, led to the identification of two ribosomal gene biomarkers for protein synthesis. Such biomarkers could be potentially valuable tools for assessing complex traits that regulate physiological state, leading to optimization of breeding programs for oyster aquaculture.

Objective Altered temperature and dissolved oxygen (DO) regimes in the tailwaters below dams can cause stress to fish. Despite their widespread distribution in rivers across North America, Freshwater Drum Aplodinotus grunniens have received little attention relative to the effects of these potential stressors. Quantifying fish swimming performance and kinematics in simulated tailwater conditions can help to determine how riverine species are affected by dam water releases, with the ultimate goal of identifying improved management strategies for these systems. Methods We quantified Freshwater Drum swimming performance and kinematics by measuring critical swimming speed (in both relative [RUcrit; body lengths/s] and absolute [AUcrit; cm/s] units), tailbeat frequency, tailbeat amplitude, and Strouhal's number under all combinations of low-DO (4 mg/L), normoxic (9 mg/L), and high-DO (14 mg/L) conditions at low (10°C), intermediate (20°C), and warm (30°C) water temperatures using both 90- and 850-L swim flumes. Result Dissolved oxygen at these concentrations did not affect swimming performance. The effect of temperature on swimming performance depended on fish size; RUcrit, AUcrit, and tailbeat frequency decreased with fish length but increased with temperature. In contrast, tailbeat amplitude increased with fish length but did not differ across temperatures. Conclusion These results suggest that acute low- and high-DO exposure within the tested range may not affect swimming performance or kinematics. However, the influence of temperature on Freshwater Drum swimming performance suggests that the ability of fish to hold position in a tailrace or to successfully pass upstream of a dam may vary seasonally and may depend on the depth from which water is released from a reservoir, as release depth determines the water temperature.

Many salmonid species are particularly susceptible to chronic and acute temperature changes caused by global warming. We aimed to study the differences in metabolic and transcriptomic responses of a chronic heat stress on a control and selected (absence of early sexual maturation and growth) line of brook charr Salvelinus fontinalis (Mitchill, 1814). We exposed individuals to different temperatures for 35 days (15, 17, and 19 °C). High temperature reduced the growth rate (in length) and the Fulton condition factor. Both maximal metabolic rate and the aerobic scope were higher in fish reared at 17 °C, while they decreased in fish maintained at 19 °C. The relative gene expression of cytochrome c oxidase was lower at 19 °C than at 15 °C. The relative gene expressions of both liver and gill hsp90 was higher at the highest temperature. The standard metabolic rate, while not affected by temperature, was higher for the control line over the selected line. Only in the control line, the relative expression of catalase and of receptor of insulin-like growth factor-1 increased at 19 °C. Our results showed that the selected line was able to cope more effectively with the oxidative stress caused by the rise in temperature.

Species with a wide distribution can experience significant regional variation in environmental conditions, to which they can acclimatize or adapt. Consequently, the geographic origin of an organism can influence its responses to environmental changes, and therefore its sensitivity to combined global change drivers. This study aimed at determining the physiological responses of the northern shrimp, Pandalus borealis, at different levels of biological organization and from four different geographic origins, exposed to elevated temperature and low pH to define its sensitivity to future ocean warming and acidification. Shrimp sampled within the northwest Atlantic were exposed for 30 days to combinations of three temperature (2, 6 or 10°C) and two pH levels (7.75 or 7.40). Survival, metabolic rates, whole-organism aerobic performance and cellular energetic capacity were assessed at the end of the exposure. Our results show that shrimp survival was negatively affected by temperature above 6°C and low pH, regardless of their origin. Additionally, shrimp from different origins show overall similar whole-organism performances: aerobic scope increasing with increasing temperature and decreasing with decreasing pH. Finally, the stability of aerobic metabolism appears to be related to cellular adjustments specific to shrimp origin. Our results show that the level of intraspecific variation differs among levels of biological organization: different cellular capacities lead to similar individual performances. Thus, the sensitivity of the northern shrimp to ocean warming and acidification is overall comparable among origins. Nonetheless, shrimp vulnerability to predicted global change scenarios for 2100 could differ among origins owing to different regional environmental conditions.

There is increasing evidence that sunscreen, more specifically the organic ultra-violet filters (O-UVFs), are toxic for aquatic organisms. In the present study, we simulated an environmental sunscreen exposure on the teleost fish, Chelon auratus. The first objective was to assess their spatial avoidance of environmental concentrations of sunscreen products (i.e. a few µg.L-1 of O-UVFs). Our results showed that the fish did not avoid the contaminated area. Therefore, the second objective was to evaluate the toxicological impacts of such pollutants after 35 days exposure to concentrations of a few µg.L-1 of O-UVFs. At the individual level, O-UVFs increased the hepatosomatic index which could suggest pathological alterations of the liver or the initiation of the detoxification processes. At the cellular level, a significant increase of malondialdehyde was measured in the muscle of fish exposed to O-UVFs which suggests a failure of antioxidant defences and/or an excess of reactive oxygen species.

Physiological and behavioral traits of aquatic organisms are often highly dependent on environmental conditions, but genetic (family) effects often contribute to phenotypic variation. In this study, a series of physiological indices were used to assess the variability that exists among progeny of lake sturgeon ( Acipenser fulvescens Rafinesque, 1817) produced from eight different families. We designed a controlled experiment aimed to evaluate metabolic performance of age-0 lake sturgeon where growth, energy density, survival, metabolic rate, volitional swimming performance, and critical thermal maxima were quantified for fish reared under the same environmental conditions. We found a strong family effect for most metrics that were quantified and primarily influenced by the female. Furthermore, poor growth and survival within families were strongly correlated to low energy density levels and depressed routine metabolic rates at the yolk sac stage. Lastly, the quantification of energy density at the onset of exogenous feeding appeared to be an excellent predictor of future growth and survival. Our results suggest that the choice of female for production of progeny in conservation hatcheries will have significant impacts on the success of stock enhancement as a conservation strategy for lake sturgeon.

Titanium dioxide is a type of nanoparticle that is composed of one titanium atom and two oxygen atoms. One of its physicochemical activities is photolysis, which produces different reactive oxygen species (ROS). Atya lanipes shrimp affect detrital processing and illustrate the potential importance of diversity and nutrient availability to the rest of the food web. It is essential in removing sediments, which have an important role in preventing eutrophication. This study aimed to determine the toxic effect of changes in behavior and levels of oxidative stress due to exposure to titanium dioxide nanoparticles in Atya lanipes and to determine the effective concentration (EC50) for behavioral variables. The concentrations of TiO2 NPs tested were 0.0, 0.50, 1.0, 2.0, and 3.0 mg/L with the positive controls given 100 µg/L of titanium and 3.0 mg/L of TiO2 NPs ± 100 µg/L of titanium. After 24 h of exposure, significant hypoactivity was documented. The EC50 was determined to be a concentration of 0.14 mg/L. After the exposure to 10 mg/L of TiO2 NPs, oxidative stress in gastrointestinal and nervous tissues was documented. The toxic effects of this emerging aquatic pollutant in acute exposure conditions were characterized by sublethal effects such as behavior changes and oxidative stress.

Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. When fish experience periods of insufficient food intake, they undergo slower muscle growth or even muscle wasting, and those changes emerge in part from nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) affects Igf1 regulation of liver and skeletal muscle gene expression in gopher rockfish (Sebastes carnatus), a nearshore rockfish of importance for commercial and recreational fisheries in the northeastern Pacific Ocean, to understand how food limitation impacts Igf regulation of muscle growth pathways. Rockfish were either fed or fasted for 14 d, after which a subset of fish from each group was treated with recombinant Igf1 from sea bream (Sparus aurata). Fish that were fasted lost body mass and had lower body condition, reduced hepatosomatic index, and lower plasma Igf1 concentrations, as well as a decreased abundance of igf1 gene transcripts in the liver, increased hepatic mRNAs for Igf binding proteins igfbp1a, igfbp1b, and igfbp3a, and decreased mRNA abundances for igfbp2b and a putative Igf acid labile subunit (igfals) gene. In skeletal muscle, fasted fish showed a reduced abundance of intramuscular igf1 mRNAs but elevated gene transcripts encoding Igf1 receptors A (igf1ra) and B (igf1rb), which also showed downregulation by Igf1. Fasting increased skeletal muscle mRNAs for myogenin and myostatin1, as well as ubiquitin ligase F-box only protein 32 (fbxo32) and muscle RING-finger protein-1 (murf1) genes involved in muscle atrophy, while concurrently downregulating mRNAs for myoblast determination protein 2 (myod2), myostatin2, and myogenic factors 5 (myf5) and 6 (myf6 encoding Mrf4). Treatment with Igf1 downregulated muscle myostatin1 and fbxo32 under both feeding conditions, but showed feeding-dependent effects on murf1, myf5, and myf6/Mrf4 gene expression indicating that Igf1 effects on muscle growth and atrophy pathways is contingent on recent food consumption experience.

Fish adjust rates of somatic growth in the face of changing food consumption. As in other vertebrates, growth in fish is regulated by the growth hormone (Gh)/insulin-like growth factor-1 (Igf1) endocrine axis, and changes in food intake impact growth via alterations to Gh/Igf1 signaling. Understanding the time course by which the Gh/Igf1 axis responds to food consumption is crucial to predict how rapidly changes in food abundance might lead to altered growth dynamics. Here, we looked at the response times of plasma Igf1 and liver Igf1 signaling-associated gene expression to refeeding after food deprivation in juvenile gopher rockfish (Sebastes carnatus), one of several species of northern Pacific Ocean Sebastes rockfishes targeted by fisheries or utilized for aquaculture. Gopher rockfish were fasted for 30 d, after which a subset was fed to satiation for 2 h, while other rockfish continued to be fasted. Refed fish exhibited higher hepatosomatic index (HSI) values and increased Igf1 after food consumption. Gene transcripts for Gh receptor 1 (ghr1), but not ghr2, increased in the liver 2-4 d after eating. Transcripts encoding igf1also increased in the liver of refed fish by 4 d after feeding, only to return to levels similar as continually fasted rockfish by 9 d after feeding. Liver mRNA abundances for Igf binding protein (Igfbp) genes igfbp1a, igfbp1b, and igfbp3a declined within 2 d of feeding. These findings provide evidence that circulating Igf1 in rockfish reflects a fish's feeding experience within the previous few days, and suggest that feeding-induced increases in Igf1 are being mediated in part by altered liver sensitivity to Gh due to upregulated Gh receptor 1 expression.

Environmental hypoxia (low dissolved oxygen) is a significant threat facing fishes. As fishes require oxygen to efficiently produce ATP, hypoxia can significantly limit aerobic capacity. However, some fishes show respiratory flexibility that rescues aerobic performance, including plasticity in mitochondrial performance. This plasticity may result in increased mitochondrial efficiency (e.g., less proton leak), increased oxygen storage capacity (increased myoglobin), and oxidative capacity (e.g., higher citrate synthase activity) under hypoxia. We acclimated a hypoxia-tolerant fish, red drum (Sciaenops ocellatus), to 8-days of constant hypoxia to induce a hypoxic phenotype. Fish were terminally sampled for cardiac and red muscle tissue to quantify oxidative phosphorylation, proton leak, and maximum respiration in tissue from both hypoxia-acclimated and control fish. Tissue was also collected to assess the plasticity of citrate synthase enzyme activity and mRNA expression for select oxygen storage and antioxidant pathway transcripts. We found that mitochondrial respiration rates were not affected by hypoxia exposure in cardiac tissue, though citrate synthase activity and myoglobin expression were higher following hypoxia acclimation. Interestingly, measures of mitochondrial efficiency in red muscle significantly improved in hypoxia-acclimated individuals. Hypoxia-acclimated fish had significantly higher OXPHOS Control Efficiency, OXPHOS Capacity and Coupling Control Ratios (i.e., LEAK/OXPHOS). There was no significant change to citrate synthase activity or myoglobin expression in red muscle. Overall, these results suggest that red muscle mitochondria of hypoxia-acclimated fish more efficiently utilize oxygen, which may explain previous reports in red drum of improved aerobic swimming performance in the absence of improved maximum metabolic rate following hypoxia acclimation.

Unionid mussels are imperiled worldwide. Understanding the impacts of thermal and hypoxia stress on larval (glochidia) and adult physiology is critical for understanding the potential impacts of climate change. We tested whether brood viability (proportion of glochidia competent to attach to a host) was correlated with oxygen demand (MO 2 ), ability to regulate oxygen consumption (regulation index (RI)), and/or critical dissolved oxygen concentration (DO crit ). We then examined the effects of temperature on MO 2, RI, and DO crit. The results were coupled with a previous study to estimate the fraction of brooding female oxygen demand comprised of glochidial respiration. We found little evidence that respiratory patterns of glochidia changed with declining brood viability, but strong evidence for decreasing glochidial RI and increasing DO crit with increasing temperatures. Glochidial respiration temperature coefficient ( Q 10 ) values were approximately 2–3× those estimated for brooding females, indicating greater temperature sensitivity. The proportion of gravid female respiration comprised of glochidial respiration reached its maximum at temperatures (23–28 °C) coinciding with brood expulsion. These patterns suggest high temperatures may have deleterious effects on unionids by decreasing the hypoxia tolerance of glochidia, increasing the rate at which glochidia deplete energy reserves, and increasing the proportion of oxygen consumption by gravid females that is comprised of glochidial oxygen demand.

Unlike mammals, adult zebrafish undergo spontaneous recovery after major spinal cord injury. Whereas reactive gliosis presents a roadblock for mammalian spinal cord repair, glial cells in zebrafish elicit pro-regenerative bridging functions after injury. Here, we perform genetic lineage tracing, assessment of regulatory sequences and inducible cell ablation to define mechanisms that direct the molecular and cellular responses of glial cells after spinal cord injury in adult zebrafish. Using a newly generated CreERT2 transgenic line, we show that the cells directing expression of the bridging glial marker ctgfa give rise to regenerating glia after injury, with negligible contribution to either neuronal or oligodendrocyte lineages. A 1 kb sequence upstream of the ctgfa gene was sufficient to direct expression in early bridging glia after injury. Finally, ablation of ctgfa-expressing cells using a transgenic nitroreductase strategy impaired glial bridging and recovery of swim behavior after injury. This study identifies key regulatory features, cellular progeny, and requirements of glial cells during innate spinal cord regeneration.

Synopsis Shoaling behavior is known to increase survival rates during attacks from predators, minimize foraging time, favor mating, and potentially increase locomotor efficiency. The onset of shoaling typically occurs during the larval phase, but it is unclear how it may improve across ontogenetic stages in forage fishes. Warming is known to increase metabolic rates during locomotion in solitary fish, and shoaling species may adjust their collective behavior to offset the elevated costs of swimming at higher temperatures. In this study, we quantified the effects of warming on shoaling performance across the ontogeny of a small forage fish, zebrafish (Danio rerio) at different speeds. Shoals of larval, juvenile, and adult zebrafish were acclimated at two temperatures (28°C and 32°C), and metabolic rates were quantified prior to and following nonexhaustive exercise at high speed. Shoals of five individuals were filmed in a flow tank to analyze the kinematics of collective movement. We found that zebrafish improve shoaling swimming performance from larvae to juveniles to adults. In particular, shoals become more cohesive, and both tail beat frequency (TBF) and head-to-tail amplitude decrease with ontogeny. Early life stages have higher thermal sensitivity in metabolic rates and TBF especially at high speeds, when compared to adults. Our study shows that shoaling behavior and thermal sensitivity improve as zebrafish shift from larval to juvenile to adult stages.

Protective responses are pivotal in aiding organismal persistence in complex, multi-stressor environments. Multiple-stressor research has traditionally focused on the deleterious effects of exposure to concurrent stressors. However, encountering one stressor can sometimes confer heightened tolerance to a second stressor, a phenomenon termed ‘cross-protection’. Cross-protection has been documented in a wide diversity of taxa (spanning the bacteria, fungi, plant and animal kingdoms) and habitats (intertidal, freshwater, rainforests and polar zones) in response to many stressors (e.g. hypoxia, predation, desiccation, pathogens, crowding, salinity, food limitation). Remarkably, cross-protection benefits have also been shown among emerging, anthropogenic stressors, such as heatwaves and microplastics. In this Commentary, we discuss the mechanistic basis and adaptive significance of cross-protection, and put forth the idea that cross-protection will act as a ‘pre-adaptation’ to a changing world. We highlight the critical role that experimental biology has played in disentangling stressor interactions and provide advice for enhancing the ecological realism of laboratory studies. Moving forward, research will benefit from a greater focus on quantifying the longevity of cross-protection responses and the costs associated with this protective response. This approach will enable us to make robust predictions of species' responses to complex environments, without making the erroneous assumption that all stress is deleterious.

Near-future climate change projections predict an increase in sea surface temperature that is expected to have significant and rapid effects on marine ectotherms, potentially affecting a number of critical life processes. Also, some habitats undergo more thermal variability than others and the inhabitants thereof must be more tolerant to acute periods of extreme temperatures. Mitigation of these outcomes may occur through acclimation, plasticity, or adaptation, although the rate and extent of a species' ability to adjust to warmer temperatures is largely unknown, specifically as it pertains to effects on various performance metrics in fishes that inhabit multiple habitats throughout ontogenetic stages. Here, the thermal tolerance and aerobic performance of schoolmaster snapper (Lutjanus apodus Walbaum, 1792) collected from two different habitats were experimentally assessed under different warming scenarios (temperature treatments = 30, 33, 35, 36° C) to assess vulnerability to an imminently changing thermal habitat. Larger subadult and adult fish collected from a 12 m deep coral reef exhibited a lower critical thermal maximum (CTmax ) compared to smaller juvenile fish collected from a 1 m deep mangrove creek. However, CTmax of the creek-sampled fish was only 2° C above the maximum water temperature measured in the habitat from which they were collected, compared to a CTmax that was 8° C higher in the reef-sampled fish, resulting in a wider thermal safety margin at the reef site. A GLM showed a marginally significant effect of temperature treatment on resting metabolic rate (RMR) but there were no effects on any of the tested factors on maximum metabolic rate (MMR) or absolute aerobic scope (AAS). Post-hoc tests revealed that RMR was significantly higher for creek-collected fish at the 36° C treatment and significantly higher for reef-collected fish at 35° C. Swimming performance (measured by critical swimming speed [Ucrit ]) was significantly lower at the highest temperature treatment for creek-collected fish and trended down with each successive increase in temperature treatment for reef-collected fish. These results show that metabolic rate and swimming performance responses to thermal challenges are somewhat consistent across collection habitats, and this species may be susceptible to unique types of thermal risk depending on its habitat. We show the importance of intraspecific studies that couple habitat profiles and performance metrics to better understand possible outcomes under thermal stress. This article is protected by copyright. All rights reserved.

Mesophotic reefs have been proposed as climate change refugia but are not synonymous ecosystems with shallow reefs and remain exposed to anthropogenic impacts. Planulae from the reef-building coral Stylophora pistillata, Gulf of Aqaba, from 5- and 45-m depth were tested ex situ for capacity to settle, grow, and acclimate to reciprocal light conditions. Skeletons were scanned by phase contrast-enhanced micro-CT to study morphology. Deep planulae had reduced volume, smaller diameter on settlement, and greater algal symbiont density. Light conditions did not have significant impact on settlement or mortality rates. Photosynthetic acclimation of algal symbionts was evident within 21-35 days after settlement but growth rate and polyp development were slower for individuals translocated away from their parental origin compared to controls. Though our data reveal rapid symbiont acclimation, reduced growth rates and limited capacity for skeletal modification likely limit the potential for mesophotic larvae to settle on shallow reefs.

Food-deprivation state (fed, fasted, starved) affected rock crabs physiological and biochemical responses to hypoxia in Cancer irroratus. Fasted and starved crabs were better adapted to deal with hypoxia than fed animals; however, avoidance behavior is usually considered as the first defense to environmental stressors for decapod crustaceans. We examined the effects of food deprivation on the crab’s behavior to hypoxia using the Loligo® shuttle box system, an automated system with a pair of connected water chambers with regulated flow and oxygen level. Crabs (starved, fasted and fed) that were offered a choice of two different oxygen saturations did not appear to actively avoid the hypoxia regimes tested (50% and 20% oxygen saturation). We used novel algorithms to analyze the data and found that crabs altered rheotaxis (movement towards or away from a current of water) and corresponding moving speed as a function of oxygen saturation. The food-deprivation state did influence thigmotaxis (contact with walls/objects when exploring an open space): starved crabs became bolder and more likely to explore open areas of the apparatus. Technological advancements such as the fully automated shuttle box have improved our ability to collect and analyze behavioral data; however, our study also highlighted some of the potential problems of relying solely on such apparatus to study the behavior of benthic crustaceans.

Laboratory‐based studies examining fish physiological and behavioural responses to temperature can provide important insight into species‐specific habitat preferences and utilisation, and are especially useful in examining vulnerable life stages that are difficult to study in the wild. This study couples shuttle box behavioural experiments with respirometry trials to determine the temperature preferences and metabolic thermal sensitivity of juvenile California horn shark ( Heterodontus francisci ) and leopard shark ( Triakis semifasciata ). As juveniles, these two species often occupy similar estuarine habitats but display contrasting behaviours and activity levels – H. francisci are relatively sedentary, whereas T. semifasciata are more active and mobile. This study shows that juvenile H. francisci and T. semifasciata have comparable thermal preferences and occupy similar temperature ranges, but H. francisci metabolism is more sensitive to acute changes in temperature as expressed through a higher Q 10 ( H. francisci = 2.58; T. semifasciata = 1.97; temperature range: 12–24°C). Underlying chronic temperature acclimation to both warm (21°C) and cool (15°C) representative seasonal temperatures did not appear to significantly affect these parameters. These results are discussed in the context of field studies examining known distributions, habitat and movement patterns of H. francisci and T. semifasciata to better understand the role of temperature in species‐specific behaviour. Juvenile H. francisci likely target thermally stable environments, such as estuaries that are close to their preferred temperature, whereas juvenile T. semifasciata metabolism and behaviour appear less dependent on temperature.

Stress responses of fish to disruption of oxygen homeostasis include adjusted oxygen consumption rate (MO2) as well as the hyperventilation consisting of changes in breathing frequency (fv) and amplitude (fampl). However, studying the HVR in very small organisms such as zebrafish (Danio rerio) embryos and larvae is challenging, and breathing movements (i.e., fv) are usually manually counted, which is time- and human resource-intense, error-prone and does not provide information on the amplitude of breathing movements of the response, the breathing amplitude (fampl). Hence, in the present study, a new automated method was developed to simultaneously measure fv and fampl in small zebrafish embryos and larvae with the computer software DanioScope™. To compare HVR strategies at different life-stages of zebrafish and the physiologically linked MO2, hatched 4 d old embryos and early gill-breathing 12 d old larvae were treated with the HVR-inducing neurotoxic compound lindane (?-hexachlorocyclohexane; ?-HCH) as a model substance. Comparison of manually counted fv with fv data measured by DanioScope™ at both life-stages showed high to moderate agreement between the two methods with respect to fv in control fish and in fish treated with lower lindane concentrations (3 - 18% deviation at 25 µg/L ?-HCH). With increasing lindane concentrations (100 and 400 µg/L ?-HCH), however, manual counts showed an average underestimation of fv by up to 30%, mainly due to very fast, rapidly successive, and indistinct movements of the fish, which cannot be properly detected by manual counts. Automated measurement thus proved significantly more sensitive, although several pre- and post-processing steps are needed. The improved automated detection of fv and the first reliable estimation of fampl in small fish embryos and larvae, as well as the inclusion of MO2, may provide new insights into different respiratory strategies and may, thus, represent a tool to lower the detection limit for reactions of different life-stages of fish to environmental stressors. In the present study, this became evident, as early gill-breathing 12 d old zebrafish larvae showed symptoms of respiratory failure (i.e., increase in fv, fampl and MO2, followed by subsequent lethargy) after exposure to lindane, whereas skin-breathing in 4 d old embryos proved mainly insensitive to the paralytic effects of lindane.

Methamphetamine (METH) is a concerning drug of abuse that produces strong psychostimulant effects. The use of this substance, along with the insufficient removal in the sewage treatment plants, leads to its occurrence in the environment at low concentrations. In this study, brown trout (Salmo trutta fario) were exposed to 1 µg/L of METH as environmental relevant concentration for 28 days in order to elucidate the complex effects resulting from the drug, including behaviour, energetics, brain and gonad histology, brain metabolomics, and their relations. Trout exposed to METH displayed lowered activity as well as metabolic rate (MR), an altered morphology of brain and gonads as well as changes in brain metabolome when compared to controls. Increased activity and MR were correlated to an increased incidence of histopathology in gonads (females - vascular fluid and gonad staging; males - apoptotic spermatozoa and peritubular cells) in exposed trout compared to controls. Higher amounts of melatonin in brain were detected in exposed fish compared to controls. Tyrosine hydroxylase expression in locus coeruleus was related to the MR in exposed fish, but not in the control. Brain metabolomics indicated significant differences in 115 brain signals between control and METH exposed individuals, described by the coordinates within the principal component analyses (PCA) axes. These coordinates were subsequently used as indicators of a direct link between brain metabolomics, physiology, and behaviour - as activity and MR varied according to their values. Exposed fish showed an increased MR correlated with the metabolite position in PC1 axes, whereas the control had proportionately lower MR and PC1 coordinates. Our findings emphasize the possible complex disturbances in aquatic fauna on multiple interconnected levels (metabolism, physiology, behaviour) as a result of the presence of METH in aquatic environments. Thus, these outcomes can be useful in the development of AOP's (Adverse Outcome Pathways).

Background Fish have adapted to a diversity of environments but the neural mechanisms underlying natural aquatic behaviors are not well known. New method We have developed a small, customizable AC differential amplifier and surgical procedures for recording multi-unit extracellular signals in the CNS of marine and freshwater fishes. Results Our minimally invasive amplifier allowed fish to orient to flow and respond to hydrodynamic and visual stimuli. We recorded activity in the cerebellum and optic tectum during these behaviors. Comparison with existing methods Our system is very low-cost, hydrodynamically streamlined, and capable of high-gain in order to allow for recordings from freely behaving, fast fishes in complex fluid environments. Conclusions Our tethered approach allows access to record neural activity in a diversity of adult fishes in the lab, but can also be modified for data logging in the field.

The moon jellyfish Aurelia coerulea is the most common blooming scyphozoan jellyfish in global coastal waters. A. coerulea polyps can rapidly increase their population through asexual reproduction, which is influenced directly by the ambient seawater temperature. However, the physiological responses of A. coerulea polyps to future elevated seasonal seawater temperature scenarios are largely unknown. In this study, we performed an experiment to test the hypothesis that the elevated seasonal seawater temperatures (current seawater temperatures + 3°C) will increase the asexual reproduction, feeding, and respiration rates of A. coerulea polyps. After 42 days of exposure, the asexual reproduction and feeding rates of the A. coerulea polyps increased under the elevated seawater temperatures predicted for all seasons. The highest asexual reproduction rates occurred in predicted average summer seawater temperatures. The respiration rates of A. coerulea polyps were suppressed significantly under winter temperature conditions, suggesting that more available energy was allocated to asexual reproduction than to metabolism after warming. Overall, this study suggests that A. coerulea polyp populations will benefit from the predicted higher seawater temperatures in all four seasons, thereby further increasing the potential and scale of A. coerulea blooms.

Oceanic absorption of atmospheric CO2 results in alterations of carbonate chemistry, a process coined ocean acidification (OA). The economically and ecologically important eastern oyster (Crassostrea virginica) is vulnerable to these changes because low pH hampers CaCO3 precipitation needed for shell formation. Organisms have a range of physiological mechanisms to cope with altered carbonate chemistry; however, these processes can be energetically expensive and necessitate energy reallocation. Here, the hypothesis that resilience to low pH is related to energy resources was tested. In laboratory experiments, oysters were reared or maintained at ambient (400 ppm) and elevated (1300 ppm) pCO2 levels during larval and adult stages, respectively, before the effect of acidification on metabolism was evaluated. Results showed that oysters exposed to elevated pCO2 had significantly greater respiration. Subsequent experiments evaluated if food abundance influences oyster response to elevated pCO2. Under high food and elevated pCO2 conditions, oysters had less mortality and grew larger, suggesting that food can offset adverse impacts of elevated pCO2, while low food exacerbates the negative effects. Results also demonstrated that OA induced an increase in oyster ability to select their food particles, likely representing an adaptive strategy to enhance energy gains. While oysters appeared to have mechanisms conferring resilience to elevated pCO2, these came at the cost of depleting energy stores, which can limit the available energy for other physiological processes. Taken together, these results show that resilience to OA is at least partially dependent on energy availability, and oysters can enhance their tolerance to adverse conditions under optimal feeding regimes.

Providing optimal conditions for early-life gas bladder inflation of captive fish is one of the biggest challenges in fish culture. It also applies to laboratory fishes. Turquoise killifish (Nothobranchius furzeri Jubb, 1971) is a popular research model in biogerontology due to its short lifespan. Annual killifish in laboratory culture frequently suffer from an inability to inflate their gas bladder which may stem from suboptimal environmental conditions in captivity. Here, we investigate (1) the effect of dissolved oxygen (DO) saturation and (2) access to the water surface on gas bladder inflation and hatching success of turquoise killifish. We further histologically examine the gas bladder development from its primordial form to full inflation. In accordance with physoclistous nature of turquoise killifish, access to the water surface is not necessary for gas bladder inflation. We found that hatching success was highest in the treatment with constant or decreasing DO saturation. In contrast, the highest proportion of larvae with inflated gas bladders was found in the treatment with DO oversaturated water (130%) which was induced by the addition of an oxygen tablet. Larvae inflated their gas bladders within 2 to 48 h post-hatching. These findings represent a major step toward a solution to a persistent problem in laboratory culture of this increasingly important model organism.

In many fish species, ontogenetic dietary shifts cause changes in both quantitative and qualitative intake of energy, and these transitions can act as significant bottlenecks in survival within a given year class. In the present study, we estimated routine metabolic rate (RMR) and forced maximum metabolic rate (FMR) in age 0 lake sturgeon ( Acipenser fulvescens ) on a weekly basis from 6 to 76 days posthatch (dph) within the same cohort of fish. We were particularly interested in the period of dietary transition from yolk to exogenous feeding between 6 and 17 dph and as the fish transitioned from an artemia-based diet to a predominantly bloodworm diet between 49 and 67 dph. Measurement of growth rate and energy density throughout indicated that there was a brief period of growth arrest during the transition from artemia to bloodworm. The highest mass-specific RMR (mg O 2 kg -1 h -1 ) recorded throughout the first 76 d of development occurred during the yolk sac phase and during transition from artemia to bloodworm. Similarly, diet transition from artemia to bloodworm-when growth arrest was observed-increased scaled RMR (i.e., mg O 2 kg -0.89 h -1 ), and it did not significantly differ from scaled FMR. Log-log relationships between non-mass-specific RMR or FMR (i.e., mg O 2 h -1 ) and body mass significantly changed as the growing fish adapted to the nutritional differences of their primary diet. We demonstrate that dietary change during early ontogeny has consequences for growth that may reflect altered metabolic performance. Results have implications for understanding cohort and population dynamics during early life and effective management for conservation fish hatcheries.

Energetic cost of growth determines how much food-derived energy is needed to produce a given amount of new biomass and thereby influences energy transduction between trophic levels. Growth and development are regulated by hormones and are therefore sensitive to changes in temperature and environmental endocrine disruption. Here, we show that the endocrine disruptor bisphenol A (BPA) at an environmentally relevant concentration (10 µgl −1 ) decreased fish ( Danio rerio ) size at 30°C water temperature. Under the same conditions, it significantly increased metabolic rates and the energetic cost of growth across development. By contrast, BPA decreased the cost of growth at cooler temperatures (24°C). BPA-mediated changes in cost of growth were not associated with mitochondrial efficiency (P/O ratios (i.e. adenosine diphosphate (ADP) used/oxygen consumed) and respiratory control ratios) although BPA did increase mitochondrial proton leak. In females, BPA decreased age at maturity at 24°C but increased it at 30°C, and it decreased the gonadosomatic index suggesting reduced investment into reproduction. Our data reveal a potentially serious emerging problem: increasing water temperatures resulting from climate warming together with endocrine disruption from plastic pollution can impact animal growth efficiency, and hence the dynamics and resilience of animal populations and the services these provide.

Sickle cell disease (SCD) is an inherited blood disorder that affects millions of people worldwide, especially in low-resource regions of the world, where a rapid and affordable test to properly diagnose the disease would be highly valued. Magnetophoresis is a technique that could simultaneously analyze, quantify, and potentially separate the patient's sickle red blood cells (RBCs) from healthy RBCs, but the magnetic characteristics of sickle RBCs have yet to be reported. In this work, we present the single cell magnetic characterization of RBCs obtained from SCD patients. Sufficient single cells are analyzed from patient samples undergoing transfusion therapy and not yet having transfusion therapy (TP and NTP, respectively), such that means and distributions of these single RBC mobilities are created in the form of histograms which facilitated comparison to RBCs from healthy donors (HD). The magnetic characterization is obtained using a technique known as Cell Tracking Velocimetry (CTV) that quantitatively characterizes the RBC response to magnetic and gravitational fields. The magnetic properties of RBCs containing oxygenated, deoxygenated hemoglobin (Hb) and methemoglobin (oxyHb-RBCs, deoxyHb-RBCs, and metHb-RBCs) are further determined. The NTP samples reported the highest magnetic character, especially when compared to oxyHb-RBCs from HD, which implies impaired oxygen binding capabilities. Also, the oxygen-Hb equilibrium curves are obtained to estimate the magnetic character of the cells under intermediate oxygen levels. Our results confirm higher magnetic moment of SCD blood (NTP) under intermediate oxygen levels. These data demonstrate the potential feasibility of magnetophoresis to identify, quantify and separate sickle RBCs from healthy RBCs.

Macroinvertebrates that rely on a supply of planktonic larvae for recruitment play a significant role in maintaining productivity in mangrove ecosystems. Thus, identifying the spatial distribution and physiological limitations of invertebrate larval communities within mangroves is important for targeted conservation efforts to maintain population persistence amid the threat of climate change. Here, the role of spatial, lunar, and environmental factors in structuring invertebrate larval communities in Ting Kok, the second largest mangrove forest in Hong Kong, was examined. Results indicate that, spatially, invertebrate larval communities were influenced by environmental filtering, habitat type, and the lunar tidal cycle. This indicates the fundamental role of habitat heterogeneity and connectivity for the transport, distribution, and development of crustacean larvae. Larvae of key sesarmids exhibited metabolic depression at water temperatures forecasted to be regularly experienced by the year 2050, according to current climate projections. The impacts of climate change, coupled with habitat destruction and degradation of hydrological connectivity, make larval communities increasingly vulnerable to mass-mortality and displacement. This places ecosystem productivity and functionality at risk through cascading negative effects of recruitment limitation. Further focus on this subject will help disentangle the effects of process rates and scales of transport that underlie community assemblages in mangrove systems. Furthermore, identifying physiological bottlenecks of key taxa and habitat provisioning that enhance larval survival will be helpful to prioritize strategies for conservation management in dynamic intertidal settings.

Variations in dissolved oxygen levels are common in the Amazonian aquatic environments and the aquatic organisms that inhabit these environments developed a variety of adaptive responses to deal with such conditions. Some Amazonian fish species are tolerant to low oxygen levels and the cichlid Astronotus ocellatus is one of the most hypoxia-tolerant species. Herein, we aimed to unveil the biochemical and molecular responses that A. ocellatus presents when submitted to hypoxia. Hypoxia indicators were measured, such as plasma glucose, plasma lactate, hepatic glycogen and relative transcript levels of prolyl hydroxylase 2 (phd2) and hypoxia-inducible factor-1α (hif-1α) in juveniles of approximately 50 g exposed to 1, 3, and 5 hours of hypoxia (0.7 mg O2.L-1), followed by 3 hours of recovery in normoxia (6 mg O2.L-1). Fish exposed to hypoxia reduced liver glycogen levels within 3 hours of hypoxia, when comparing with 1 hour, and increased plasma glucose and lactate. Under the same condition, phd2 transcripts levels increased in gills, but decreased in liver. In contrast, hypoxia did not affect relative gene expression of hif-1α in both tissues. Based on the transcription pattern of phd2, these results showed that liver and gills of A. ocellatus have different molecular strategies to cope with environmental hypoxia.

Species are often exposed to novel thermal regimes as a result of anthropogenic activities. Understanding the extent to which populations are locally adapted to the thermal regime may allow us to better predict the response of organisms to novel thermal conditions. We collected virile crayfish, Faxonius virilis, from eight populations along a latitudinal gradient and measured their routine metabolic rates (RMR) and thermal tolerance. Countergradient variation suggests that organisms from northern latitudes may spend more energy foraging as an adaptation to the shorter growing season. Thus, we hypothesized that crayfish RMR would be positively related to latitude. We also expected high latitude populations to have a greater sensitivity to acute temperature change and a lower thermal tolerance. In support of our hypothesis, there was a significant positive relationship between latitude and crayfish RMR at night when crayfish are most active, and crayfish from high latitude populations were more thermally sensitive. Thus, changes in the thermal regime are likely to alter the activity level of this species, which could alter its ecological impacts. In addition, virile crayfish across the latitudinal gradient had a high thermal tolerance, which may contribute to the success of this species in novel environments.

The amphipod Gmelinoides fasciatus has invaded and established in numerous large lakes in Eurasia and, in the process, has displaced the native amphipod, Gammarus lacustris. The mechanism behind its invasion success is unclear and remains an important topic for invasion ecology. Three laboratory experiments were conducted to determine if superior predator avoidance and different types of bottom substrate could be important factors contributing to the invasion success of G. fasciatus. Our results indicate that, on gravel and sand substrates, G. fasciatus exhibited superior digging behaviour to avoid predation by fishes (perch and common roach), contrary to its native counterpart. In addition, G. fasciatus exhibited a more substantial reduction in activity than G. lacustris when in the presence of predatory fish kairomones. However, the presence of kairomones had little effect on digging behaviour. G. fasciatus consistently demonstrated superior predator avoidance abilities over G. lacustris, suggesting that this mechanism might play an important role in the invasion success of G. fasciatus.

Temperature is one of the most important factors governing the activity of ectothermic species, and it plays an important but less studied role in the manifestation of invasive species impacts. In this study, we investigated temperature-specific feeding and metabolic rates of invasive and native crayfish, and evaluated how temperature regulates their ecological impacts at present and in future according to different climatic scenarios by bioenergetics modelling. We conducted a series of maximum food consumption experiments and measured the metabolic rates of cold-adapted native noble crayfish (Astacus astacus) and invasive signal crayfish (Pacifastacus leniusculus) originally from a warmer environment over a temperature gradient resembling natural temperatures in Finland. The maximum feeding rates and routine metabolic rates (RMR) of native noble crayfish were significantly higher at low temperatures (< 10 °C than the rates of invasive signal crayfish. The RMRs of the species crossed at 18 °C, and the RMRs of signal crayfish were higher at temperatures above 18 °C. These findings indicate that the invader’s thermal niche has remained stable, and the potential impacts per capita are lower at suboptimal cold temperatures than for the native species. Our bioenergetics modelling showed that the direct annual predation impact of noble and signal crayfish seem similar, although the seasonal dynamics of the predation differs considerably between species. Our results highlight that the temperature-specific metabolic and feeding rates of species need to be taken into account in the impact assessment instead of simple generalisations of the direction or magnitude of impacts.

Lack of microplastics (MP) toxicity studies involving environmentally relevant concentrations and exposure times is concerning. Here we analyzed the potential adverse effects of low density polyethylene (LDPE) MP at environmentally relevant concentration in sub-chronic exposure to two amphipods Gmelinoides fasciatus and Gammarus lacustris, species that naturally compete with each other for their habitats. 14-day exposure to 2 µg/L (8 particles/L corresponding to low exposure) and 2 mg/L (~8400 particles/L, corresponding to high exposure) of 53–100 µm LDPE MP were used to assess ingestion and egestion of MP, evaluate its effects on amphipod mortality, swimming ability and oxidative stress level. Both amphipod species were effectively ingesting and egesting LDPE MP. On the average, 0.8 and 2.5 MP particles were identified in the intestines of each amphipod exposed to 2 µg/L and 2 mg/L LDPE MP, respectively. Therefore, intestinal MP after 14-day exposure did not fully reflect the differences in LDPE MP exposure concentrations. Increased mortality of both amphipods was observed at 2 mg/L LDPE MP and in case of G. lacustris also at 2 µg/L exposure. The effect of LDPE on swimming activity was observed only in case of G. fasciatus. Oxidative stress marker enzymes SOD, GPx and reduced glutathione GSH varied according to amphipod species and LDPE MP concentration. In general G. lacustris was more sensitive towards LDPE MP induced oxidative stress. Overall, the results suggested that in MP polluted environments, G. lacustris may lose its already naturally low competitiveness and become overcompeted by other more resistant species. The fact that in the sub-chronic foodborne exposure to environmentally relevant and higher LDPE MP concentrations all the observed toxicological endpoints were affected refers to the potential of MP to affect and disrupt aquatic communities in the longer perspective.

Hydropower development can significantly mitigate climate change and reduce carbon emissions, but it can also have substantial negative impacts on river environments and fish biodiversity. Fish passage facilities are built to ensure sustainable hydropower development and the biodiversity of fish populations. The locations of the entrances to these facilities play a key role in their efficiency. This study presents a reliable approach that combines the swimming ability of fish and a numerical flow field simulation to determine the optimal location for a fish passage facility entrance. In this study, we used the Gujun Reservoir upstream of the Yangtze River as a case study. A field experiment was conducted, and the swimming abilities of eight endemic fish species in the upstream region of the Yangtze River were measured. Among the tested species, the fastest induced swimming speed (0.14 m/s) was achieved by Glyptothorax sinense, while the slowest critical swimming speed (0.30 m/s) was observed for Paracobitis potanini. We propose that the velocity near the fish passage facility entrance should be higher than the maximum induced swimming speed and lower than the minimum critical swimming speed, making the suitable range between 0.14 and 0.30 m/s. On this basis, velocity fields 500 m downstream of the dam of the Gujun Reservoir under 4 operating conditions with discharge flows of 5.7 m3/s, 23.3 m3/s, 32.5 m3/s, and 41.1 m3/s were calculated. The results showed that the flow field variation downstream of the dam was between 0.1 and 0.9 m/s. After comparing the suitable areas for the target species, the left bank at location 2 was recommended as the optimal location for the fish passage facility entrance in the Gujun Reservoir.

Total dissolved gas (TDG) supersaturation from sources such as hydroelectric dams can cause harmful bubble growth in the tissues of aquatic animals, known as gas bubble trauma (GBT). Locomotion is known to exacerbate bubble growth in tissues during decompression under certain conditions (such as in diving animals), possibly because of increased bubble nucleation. As with decompression sickness, GBT is caused by the supersaturation of tissues with gas, and thus we hypothesize that locomotion promotes bubble nucleation in the tissues of fish exposed to TDG supersaturation. Many previous laboratory studies have tested the effects of TDG on fish exposed to low‐velocity, non‐directional flow, whereas fish in field conditions are exposed to higher‐velocity flows and are likely more active. Therefore, it is important to understand the effects of locomotion on GBT to apply laboratory results to active fish in field conditions. We exposed rainbow trout ( Oncorhynchus mykiss ) to either control (100% TDG) or TDG supersaturation (123% TDG) in either static or flowing water conditions (1.8 Bl/s) and recorded time to 50% loss of equilibrium (LOE). We observed no statistically significant difference in time to 50% LOE between flow conditions. Given the lack of statistically significant difference between static and flowing water, our findings indicate that results from GBT experiments on rainbow trout in non‐directional flow are applicable to more active individuals.

Taurine is a non-proteinogenic sulfonic acid found in high concentrations inside vertebrate cardiomyocytes and its movement across the sarcolemmal membrane is critical for cell volume regulation. Taurine deficiency is rare in mammals, where it impairs cardiac contractility and leads to congestive heart failure. In fish, cardiac taurine levels vary substantially between species and can decrease by up to 60% in response to environmental change but its contribution to cardiac function is understudied. We addressed this gap in knowledge by generating a taurine-deficient rainbow trout (Oncorhynchus mykiss) model using a feed enriched with 3% β-alanine to inhibit cellular taurine uptake. Cardiac taurine was reduced by 17% after 4 weeks with no effect on growth or condition factor. Taurine deficiency did not affect routine or maximum rates of O2 consumption, aerobic scope, or critical swimming speed in whole animals but cardiac contractility was significantly impaired. In isometrically contracting ventricular strip preparations, the force–frequency and extracellular Ca2+-sensitivity relationships were both shifted downward and maximum pacing frequency was significantly lower in β-alanine fed trout. Cardiac taurine deficiency reduces sarcoplasmic reticular Ca2+-ATPase activity in mammals and our results are consistent with such an effect in rainbow trout. Our data indicate that intracellular taurine contributes to the regulation of cardiac contractility in rainbow trout. Aerobic performance was unaffected in β-alanine-fed animals, but further study is needed to determine if more significant natural reductions in taurine may constrain performance under certain environmental conditions.

Swimming activity is essential for fishes to perform behaviors, such as feeding, migration or reproduction. Energetic costs related to swimming activity may be inferred by measuring aerobic and anaerobic metabolism, which is of interest for both conservation and aquaculture purpose. However, such measurements in free-swimming fish are not easily applicable in the field, therefore the use of remote sensors from telemetry field could offer promising tools to counter these limitations. In this work, we calibrated accelerometer sensors with the oxygen consumption rate (MO2) and the activity of white and red muscle during swimming in European sea bass (Dicentrarchus labrax), a key marine species of European aquaculture. We then provided insights of the fish physiological stress profile and growth rate following the implantation of such sensors. We finally showed some examples of how these sensors may be useful to monitor fish response to rearing conditions, including high stocking density and diet regimes. Altogether, this paper provides support to use the telemetry sensors as valuable tools for monitoring health and welfare of European sea bass in aquaculture conditions.

Given the threat of climate change to biodiversity, a growing number of studies are investigating the potential for organisms to adapt to rising temperatures. Earlier work has predicted that physiological adaptation to climate change will be accompanied by a shift in temperature preferences, but empirical evidence for this is lacking. Here, we test whether exposure to different thermal environments has led to changes in preferred temperatures in the wild. Our study takes advantage of a “natural experiment” in Iceland, where freshwater populations of threespine sticklebacks ( Gasterosteus aculeatus ) are found in waters warmed by geothermal activity year‐round (warm habitats), adjacent to populations in ambient‐temperature lakes (cold habitats). We used a shuttle‐box approach to measure temperature preferences of wild‐caught sticklebacks from three warm–cold population pairs. Our prediction was that fish from warm habitats would prefer higher water temperatures than those from cold habitats. We found no support for this, as fish from both warm and cold habitats had an average preferred temperature of 13°C. Thus, our results challenge the assumption that there will be a shift in ectotherm temperature preferences in response to climate change. In addition, since warm‐habitat fish can persist at relatively high temperatures despite a lower‐temperature preference, we suggest that preferred temperature alone may be a poor indicator of a population's adaptive potential to a novel thermal environment.

Aquatic ecosystems are globally significant sources of the greenhouse gas methane to the atmosphere. Until recently, methane production was thought to be a strictly anaerobic process confined primarily to anoxic sediments. However, supersaturation of methane in oxygenated waters has been consistently observed in lakes and the ocean (termed the ‘methane paradox’), indicating that methane can be produced under oxic conditions through unclear mechanisms. Here we show aerobic methane production from multiple sources in freshwater incubation experiments under different treatments and based on biogeochemical, metagenomic, and metatranscriptomic data. We find that aerobic methane production appears to be associated with (bacterio)chlorophyll metabolism and photosynthesis, as well as with Proteobacterial degradation of methylphosphonate. Genes encoding pathways for putative photosynthetic- and methylphosphonate-based methane production also co-occur in Proteobacterial metagenome-assembled genomes. Our findings provide insight into known mechanisms of aerobic methane production, and suggest a potential co-occurring mechanism associated with bacterial photosynthesis in aquatic ecosystems. The mechanisms underlying methane production in oxygenated waters of oceans and lakes are unclear. Here, Perez-Coronel and Beman show that aerobic methane production in freshwater incubation experiments is associated with (bacterio)chlorophyll metabolism and photosynthesis, and with Proteobacterial degradation of methylphosphonate.

For marine animals with biphasic life stages, different environmental conditions are experienced during ontogeny so that physiological constraints on early stages could explain adult distributions and life history traits. The invasive and cool-temperate adapted Mytilus galloprovincialis intertidal mussel approaches the eastern limit of its biogeographic distribution on the south coast of South Africa, where it shares a habitat with the warm-temperate adapted and indigenous Perna perna mussel. As adults, the two species exhibit different metabolic regulation capacities in response to temperature. We compared the acute metabolic response to temperature between species during the post-settlement recruit stage. Aerobic respiration rates of recently settled recruits were measured monthly for 5 months for temperatures 5 °C above or below the ambient field seawater temperature at the time of collection. Unlike adults, the capacity for aerobic metabolic regulation in response to temperature differed little between species under the conditions tested, indicating a similar degree of phenotypic or developmental plasticity in response to the thermal environment. In addition, monthly variations in metabolic patterns indicate unexpectedly high plasticity in response to recent seasonal thermal history for both species.

Pseudunio auricularius (Spengler, 1793) is one of the most threatened unionid species worldwide. Translocation is considered one of the ultimate actions that can save this species from extinction in the Iberian Peninsula. Since 2013, massive mortalities have been recorded in the Canal Imperial de Aragón (CIA), an anthropogenic habitat where the highest density of P. auricularius had been recorded in Spain. An adequacy habitat index was calculated assigning scores to different environmental variables to select the most suitable river stretches receiving the translocated specimens. A total of 638 specimens have been translocated: 291 in 2017, 291 in 2018, and 56 in 2019. The first-year survival in the group of individuals translocated in 2017 was 41.6%. The next year, 95% of these specimens were found alive, suggesting a successful initial establishment. Specimens translocated in 2018 and 2019 showed a survival of c. 69% and 49%, respectively. In contrast, the control group left in CIA in 2017 showed a much lower survival rate of 19.7% after one year, which remained equally low during the next two years. Currently, the conditions in the Ebro River seem to allow a higher survival rate for P. auricularius than those in the CIA; nevertheless, future monitoring should confirm their long-term success.

Significance Plastic individuals can buffer environmental changes, maintaining a stable performance across gradients. Plasticity is therefore thought to be particularly beneficial for the survival of wild populations that experience large environmental fluctuations, such as diel and seasonal temperature changes. Maintaining plasticity is widely assumed to be costly; however, empirical evidence demonstrating this cost is scarce. Here, we predict that if plasticity is costly, it would be readily lost in a stable environment, such as a laboratory. To test this, we measured a diverse range of phenotypic traits, spanning gene expression, physiology, and behavior, in wild and laboratory zebrafish acclimated to 15 temperatures. We show that laboratory fish have lost plasticity in many traits, demonstrating that maintaining plasticity carries a cost. Plasticity can allow organisms to maintain consistent performance across a wide range of environmental conditions. However, it remains largely unknown how costly plasticity is and whether a trade-off exists between plasticity and performance under optimal conditions. Biological rates generally increase with temperature, and to counter that effect, fish use physiological plasticity to adjust their biochemical and physiological functions. Zebrafish in the wild encounter large daily and seasonal temperature fluctuations, suggesting they should display high physiological plasticity. Conversely, laboratory zebrafish have been at optimal temperatures with low thermal fluctuations for over 150 generations. We treated this domestication as an evolution experiment and asked whether this has reduced the physiological plasticity of laboratory fish compared to their wild counterparts. We measured a diverse range of phenotypic traits, from gene expression through physiology to behavior, in wild and laboratory zebrafish acclimated to 15 temperatures from 10 °C to 38 °C. We show that adaptation to the laboratory environment has had major effects on all levels of biology. Laboratory fish show reduced plasticity and are thus less able to counter the direct effects of temperature on key traits like metabolic rates and thermal tolerance, and this difference is detectable down to gene expression level. Rapid selection for faster growth in stable laboratory environments appears to have carried with it a trade-off against physiological plasticity in captive zebrafish compared with their wild counterparts.

Collecting animals from the field and bringing them into the laboratory elicits acute and chronic stress responses that may affect the interpretation of experimental outcomes. The effects of prolonged laboratory holding (three months) on labile traits (metabolic rate and spontaneous activity) were quantified for the Atlantic rock crab Cancer irroratusSay, 1817. The effects of diet (heterogenous versus homogenous) on crab condition (hemolymph protein density, crab mass, and chelal compression strength) were also assessed. When offered a heterogeneous diet C. irroratus displayed a clear preference for mussels and an aversion to herring and algae. The amount crabs ate in the laboratory was negatively correlated to the density of hemolymph protein at the time of collection, which affirms the strong link between nutritional status and hemolymph protein in crustaceans. It also suggests that crabs in good nutritional condition may forgo eating even a high-quality meal if they are stressed. Overall, providing a heterogenous diet did not significantly improve survival rates or affect labile-trait responses in crabs. In contrast, prolonged holding in the laboratory had considerable effects on labile traits: resting metabolic rate (RMR) was highest after one week, but declined over the holding period. There was also a reduction in variation of locomotor activity for approximately 4 weeks. Acute stress responses (increased RMR and activity) also occurred after transfer from holding tanks to experimental chambers, likely due to animal handling. Given the increasing attention paid to animal sentience and welfare, especially for decapod crustaceans, the amount of time that wild crustaceans are held in the laboratory should be considered carefully.

Carryover effects of environmental stressors occur when experiences of the environment in earlier life stages or seasons influence the performance of individuals later in life. These can be especially critical for species that have diverse developmental transition periods in their life cycle, such as salmonid fish. Sublethal changes in metabolism, size, or growth experienced in early life stages may have a long‐lasting effect on the subsequent life performance of these species, but very few studies have formally tested these changes in relation to environmental stressors. Here, we investigated whether different types of fine sediment result in carryover effects that change the life performance of migratory brown trout. First, we manipulated the early habitat conditions of brown trout through the life stages from egg to fry by incubating them in varying substrate treatments (i.e., gravel without added sediment, gravel with added fine sand, and gravel with added organic matter). Exposure to fine sediment during early development had serious effects on the metabolism, size, escape responses, timing of emergence, and potential survival of early life stages. These carryover effects were persistent and remained present over the critical life shift from relying on parentally provided resources as immobile eggs to independent exogenous feeding as parr. Second, fish were relocated as parr to either their original or different treatment environments and their metabolism, size, and growth were reanalyzed. The effects of environmental stress were observed later in their life cycle when fry from the gravel treatment were relocated to sand or organic‐rich treatments. These were found to be significantly smaller in size and had a higher metabolic rate than fry maintained in their original treatment environment. Together, our study experimentally demonstrated that the carryover effects of environmental stressors experienced in early stages may influence the fitness outcomes of migratory fish later in life. We suggest that sublethal environmental stressors should be better considered in restoration schemes and management strategies to reverse the current trend of declining salmonid populations.

Barnacles are sessile suspension feeders whose feeding efficiency and behavior is largely determined by the movement of water through their environment. Barnacles expend energy to feed actively in environments with low flow velocity, whereas they may feed passively at higher flow velocities, which is more efficient than active feeding. Many intertidal barnacles have been shown to switch between active and passive feeding modes as water velocities change, but little is known about the behavior of epibiotic species attached to mobile hosts, which are exposed to more consistent feeding currents. To assess the response of epibiotic barnacles to flow, laboratory-reared sea-turtle barnacles, Chelonibia testudinaria (Linnaeus, 1758), were subjected to a wide range of water velocities in both the presence and absence of food particles. Their behaviors were video-recorded and categorized using an automated behavior recognition algorithm compiled in R. Individuals of C. testudinaria only displayed passive feeding behavior, but did not feed at lowest test velocities. This species fed most at flow velocities between 25 cm s–1 and 40 cm s–1 (linear mixed effects model, F = 19.30, P < 0.001), a range that correlates well with the average swimming speed of two common host species, the loggerhead and green sea turtles, on which C. testudinaria resides. Chelonibia testudinaria displayed longer average feeding durations when food particles were absent than when food was abundant (linear mixed effects model, F = 11.76, P = 0.001), a result that is in line with the expectations of optimal foraging theory for suspension-feeding invertebrates. Lack of active feeding in this species may have evolved following the establishment of its epibiotic nature and may make this obligate epibiotic species entirely reliant on its hosts’ movements to provide a feeding current. This is the only barnacle species known to not facultatively switch between active and passive feeding modes.

Within Salmonidae, spawning and rearing in brackish water is rare; however, brackish-water resident lake trout (Salvelinus namaycush) have recently been documented in the Arctic. Additionally, early rearing in brackish-water environments increased the fish’s ability to ionoregulate in elevated salinities. Here, we examined the impact of a freshwater (FWR, 0 ppt) or brackish-water (BWR, 5 ppt) rearing environment on salinity preference in lake trout using a dynamic choice experiment. We observed significant differences in salinity preference between our treatments suggesting the importance of early environment in shaping salinity preference. Contrary to our predictions, FWR lake trout selected higher salinity (17.3 ppt) compared to BWR fish (4.8 ppt). Four of the seven FWR fish had preferred salinities near 30 ppt, which is considered physiologically challenging and potentially lethal for lake trout based on direct transfer experiments. Thus, heightened FWR salinity preference might not be a true preference but rather due to a reduced ability to sense differences in salinity, and a result of chance as mean preferred salinity was near half that of the upper and lower thresholds, and variance was larger. Selection of lower salinity by BWR fish suggests that the ability to sense and select different salinities is present in lake trout as a species and appears to be linked to difference in early rearing at elevated salinities.

Under the background of climate change, increasing attention has focused on the effects of ocean deoxygenation on marine organisms. However, few studies address the effects of different food deprivation states on hypoxia tolerance. We therefore investigated the metabolic responses of the Atlantic rock crab, Cancer irroratus (starved 28–35 days, fasted 3–5 days and recently fed). Starved-crab exhibited the lowest critical oxygen saturation (Scrit), while fed-crab had the highest Scrit. The fed-crab maintained an elevated postprandial oxygen consumption (MO2) even below the Scrit of fasted-crab indicating reserved aerobic scopes for critical activities in severe hypoxia. Following feeding, hypoxia (50% and 20% oxygen saturation, SO2) retarded the specific dynamic action resulting in lower peak MO2 and longer duration. The starved-crab exhibited a lower peak MO2, prolonged duration and higher energy expenditure than fasted-crab after feeding. The decline in arterial PO2 was most pronounced below the Scrit for both fasted- and starved-crab. The higher hemocyanin concentration ([Hc]) of fasted-crab (than starved-crab) suggested they had improved oxygen transport capacity, but hypoxia did not increase [Hc] during the 72-h experiment. Following feeding, the fasted-crab significantly increased l-lactate concentration ([l-lactate]) in 20% SO2, which was not observed in starved-crab. These results suggest starvation may trigger a cross-tolerance to hypoxia. Because crabs can undergo long periods of food deprivation in their natural environment, future studies should consider how this may affect their ability to deal with environmental perturbations.

Offshore migration of Pacific salmon Oncorhynchus spp. is partly triggered by increasing body size and high motility in the early stages of life. The survival of juvenile salmon may depend on their growth rate during the first few months in the sea, and this factor partly regulates the dynamics of adult populations. Here, we assessed the effects of water temperature and food availability on the growth of juvenile chum salmon O. keta. In addition, by combining the measurements of metabolic performance for growth and activity (Absolute Aerobic Scope: AAS) with a bioenergetics model, we estimated the energy allocation for different activities in the juveniles. Under high temperatures (14 °C), juveniles reared at low food levels (1% body weight) allocated less than half their energy for growth than those reared at high food levels (4% body weight). These findings suggest that high temperature and low food level constrain the growth of juveniles, providing an insight into the effect of the recent increase in warm and low-nutrient water masses on survival of juveniles and catches of adult chum salmon on the Pacific side of Honshu Island, Japan.

Temperature and salinity often define the distributions of aquatic organisms. This is at least partially true for Delta Smelt, an imperiled species endemic to the upper San Francisco Estuary. While much is known about the tolerances and distribution of Delta Smelt in relation to these parameters, little is known regarding the temperature and salinity preferences of the species. Therefore, the temperature and salinity preferences of sub-adult Delta Smelt were investigated across a wide range of thermal (8–28 °C) and salinity (0–23 ppt) conditions. Replicates of ten fish were allowed to swim between two circular chambers with different temperature or salinity, and the distribution of fish between the chambers was recorded. We found that Delta Smelt showed no temperature preference below 15 °C, a modest aversion to the warmer tank from 15 to 28 °C, and a strong aversion to the warmer tank with elevated mortality at temperatures above 28 °C. Delta Smelt also preferred lower salinities, and this preference became more pronounced as salinity increased toward 23 ppt. These results indicate that Delta Smelt can tolerate high temperatures and salinities for a short time, and that their preferences for lower temperature and salinity strengthens as these variables increase.

The effect of salinity on oxygen consumption rate and hemolymph osmolarity of the palaemonid prawn Macrobrachium tenellum (Smith, 1871) maintained at 0, 5, 10, 15, 20 and 25 psu was analyzed. Oxygen consumption rate was measured in respiratory chambers and osmolality from samples of hemolymph. Oxygen consumption rose significantly beyond 15 psu, with individuals showing hyper regulatory behavior from 0 to 10 psu, being able to maintain its internal solutes concentration (426–504 mmol kg–1) higher than that of the water (153–348 mmol kg–1). They acted as hypo-regulators from 15 to 25 psu as their internal solute concentration (454–562 mmol kg–1) was lower than that of the water (459–744 mmol kg–1). The isosmotic point was 505 mmol kg–1 at 16 psu, and survival was high in all salinities. The osmotic behavior of M. tenellum allows it to successfully invade fresh water by keeping constant the ionic and osmotic concentrations of both extra- and intra-cellular solute concentrations, always above fresh water, but varying its O2 consumption as salinity changes. The implications of such adaptations for the dispersal of the species into freshwater habitats is discussed.

Sportfishing and hatchery practices routinely subject fish to acute temperature changes through placement of fish in live wells and normal handling and transportation procedures. Acute temperature changes alter metabolic rate in ectotherms; however, the rapidity of the response to reach a new homeostatic state is not well known. Therefore, the response duration in metabolic rate after acute temperature change was measured in two centrarchid species, the Largemouth Bass Micropterus salmoides and Redear Sunfish Lepomis microlophus, which are representative of two different body shapes and are both commonly pursued in recreational fishing and reared in hatcheries. Largemouth Bass were acclimated to either 20°C or 30°C, and Redear Sunfish were acclimated to 24°C. Aerobic metabolic rate was measured immediately after acute temperature change (−4, +0, or +4°C) and was measured repeatedly in cycles of 5.5 or 10.0 min, respectively, until the metabolic rate stabilized. In Largemouth Bass, the metabolic rate stabilized similarly or more slowly following a moderate high-temperature shock (+4°C; 44 min) compared to transfer to conditions with no temperature change (+0°C) or a moderate low-temperature shock (−4°C; 16–48 min). In contrast, the metabolic rate in Redear Sunfish stabilized faster after transfer to +4°C (15 min) than after transfer to −4°C or +0°C (both 31 min), possibly because the elevated metabolic rate after transfer was sustained. Notably, for both species, metabolic rates stabilized at a generally lower level after transfer to −4°C than after transfer to +0°C or +4°C. Therefore, the duration until stabilization of metabolic rate after acute temperature change may depend upon species and acclimation temperature, although for both species examined, the energy savings in reduced metabolic rates after moderate cold shock may be beneficial for recovery from sportfishing or hatchery practices.

Metabolic rate has long been used in animal adaptation and performance studies, and individual oxygen consumption is used as proxy of metabolic rate. Stygofauna are organisms adapted to groundwater with presumably lower metabolic rates than their surface relatives. How stygofauna will cope with global temperature increase remains unpredictable. We studied the thermal acclimation and metabolic scaling with body mass of a stygobitic crustacean, Proasellus lusitanicus, in the climate change scenario. We measured oxygen consumption rates in a thermal ramp-up experiment over four assay temperatures and tested two hypotheses: (i) P. lusitanicus exhibits narrow thermal plasticity, inadequate for coping with a fast-increasing thermal regime; and (ii) oxygen consumption rates scale with the body mass by a factor close to 0.75, as commonly observed in other animals. Our results show that P. lusitanicus has low thermal plasticity in a fast-increasing thermal regime. Our data also suggest that oxygen consumption rates of this species do not follow mass-dependent scaling, potentially representing a new trait of metabolic optimization in groundwater habitats, which are often limited in food and oxygen. Species with limited dispersal capacities and rigid metabolic guilds face extinction risk due to climate change and omitting groundwater ecosystems from climate change agendas emphasizes the unprotected status of stygofauna.

Sexual signals produced by males play a central role in sexual selection, but the relationship between these traits and the quality of the bearer are often ambiguous. Secondary sexual traits may represent genetic quality of the bearer, resulting in positive relationships with physiological state, or may be costly to produce, showing trade-off with physiological state. A number of studies have explored the relationships between secondary sexual traits and other functional traits, but few have studied their fitness consequences. We studied the link between diverse physiological traits and both morphological and behavioural sexual traits and examined how their interplay influences offspring viability in the three-spined stickleback. Male sticklebacks showing nest building and courtship behaviour were smaller than those not investing in reproductive activities. There was no evidence that the expression of red nuptial colouration and the quality of courtship behaviour of males are positively related to their metabolic rates, swim ability, oxidative damage and mtDNA copy number. However, individuals showing larger red nuptial colour areas had higher levels of oxidative DNA damage in their sperm. Male courtship behaviour and aggressiveness, but not red colour area, were good predictors of offspring hatching and survival. Our results suggest that, in our study population at the southern edge of the species’ distribution, sexual colouration of male sticklebacks was not a good indicator of their body state, but both courtship quality and aggressiveness during the courtship are reliable cues of their gamete quality, influencing the viability of their offspring. Thus, females that choose mates based on their courtship behaviour will have high fitness. In the study population, which represents a fast pace-of-life with high reproductive rate and short lifespan, sexual ornaments of males may not honestly signal their physiological and physical state because they invest at maximum in a single reproductive season despite high costs.

Herein, we aimed to establish an aerobic exercise-induced physiological myocardial hypertrophy zebrafish (Danio rerio) model and to explore the underlying molecular mechanism. After 4 weeks of aerobic exercise, the AMR and Ucrit of the zebrafish increased and the hearts were enlarged, with thickened myocardium, an increased number of myofilament attachment points in the Z-line, and increased compaction of mitochondrial cristae. We also found that the mTOR signaling pathway, angiogenesis, mitochondrial fusion, and fission event, and mitochondrial autophagy were associated with the adaptive changes in the heart during training. In addition, the increased mRNA expression of genes related to fatty acid oxidation and antioxidation suggested that the switch of energy metabolism and the maintenance of mitochondrial homeostasis induced cardiac physiological changes. Therefore, the zebrafish heart physiological hypertrophy model constructed in this study can be helpful in investigating the cardioprotective mechanisms in response to aerobic exercise.

Fish that strike angling lures often have a set of characteristics that predispose them to capture. Vulnerable fish may then be removed from a population, either through harvest or incidental mortality, and in turn leave individuals in a population that are less vulnerable to angling. Over time, the removal of vulnerable individuals can erode capture rates, possibly resulting in evolutionary changes if traits that result in capture correlate with characteristics such as fecundity or growth. We sought to define the mechanisms driving individual angling vulnerability in Muskellunge Esox masquinongy, with the intent of informing management activities to conserve populations. The behavior of individually identified Muskellunge (n = 68; mean TL = 310.2 mm; range = 229–350 mm) was assessed using standard open-field tests; the fish were then stocked into earthen-bottom ponds to assess angling vulnerability. After angling, all captured fish and a subset of uncaptured fish were assessed for metabolic parameters. Results indicated that larger Muskellunge displaying low levels of exploration and aggression were preferentially captured. Behaviors such as boldness and activity did not influence capture, and metabolic parameters did not differ between captured and uncaptured fish.

Oceanic oxygen minimum zones (OMZs) are globally significant sites of biogeochemical cycling where microorganisms deplete dissolved oxygen (DO) to concentrations <20 µM. Amid intense competition for DO in these metabolically challenging environments, aerobic nitrite oxidation may consume significant amounts of DO and help maintain low DO concentrations, but this remains unquantified. Using parallel measurements of oxygen consumption rates and 15N-nitrite oxidation rates applied to both water column profiles and oxygen manipulation experiments, we show that the contribution of nitrite oxidation to overall DO consumption systematically increases as DO declines below 2 µM. Nitrite oxidation can account for all DO consumption only under DO concentrations <393 nM found in and below the secondary chlorophyll maximum. These patterns are consistent across sampling stations and experiments, reflecting coupling between nitrate reduction and nitrite-oxidizing Nitrospina with high oxygen affinity (based on isotopic and omic data). Collectively our results demonstrate that nitrite oxidation plays a pivotal role in the maintenance and biogeochemical dynamics of OMZs. Oxygen is fundamental for marine life, yet it is absent from large areas of the ocean. Here the authors demonstrate that microbial nitrite oxidation effectively consumes oxygen where oxygen concentrations are low, playing a pivotal role in these regions.

The role of the blood–brain barrier ATP-binding cassette protein transporter P-glycoprotein (P-gp) in protecting zebrafish (Danio rerio) from the central nervous system neurotoxicant ivermectin (IVM, 22,23-dihydroavermectin B1a + 22,23-dihydroavermectin B1b) was examined in the absence and presence of the competitive inhibitor cyclosporin A (CsA). Zebrafish injected intraperitoneally with 1, 2, 5, or 10 µmol/kg IVM exhibited mortality 30 min following administration at the highest dose. At sublethal doses > 1 µmol/kg, IVM altered the swimming performance, exploratory behaviour, motor coordination, escape response and olfactory response in exposed fish. When fish were exposed to IVM in the presence of CsA, alterations in swimming and behaviours increased significantly and at the highest IVM/CsA ratio resulted in a complete lack of exploratory and olfactory behaviours. In separate experiments, fish were either fed or fasted, and the effects of IVM and CsA administration were examined. The effects of IVM administration and the exacerbated effects seen with CsA co-administration were not affected by fasting. This study provides evidence that P-gp provides a protective role in the BBB of fish against environmental neurotoxicants. The results also show that P-gp activity is maintained even under conditions of food deprivation, suggesting that this chemical defence system is prioritized over other energy expenditures during diet limitation.

Understanding the mechanisms of biological responses to environmental change is a central theme in comparative and evolutionary physiology. Here, we analyzed variation in physiological responses to temperature, using 21 full-sibling larval families of the Pacific oyster, Crassostrea gigas. Pedigrees were confirmed with genetic markers for adult broodstock obtained from our breeding program. From these 21 larval families, 41 determinations of thermal sensitivity (Q10 values) were assayed for larvae of different sizes. For respiration, thermal sensitivity was consistent within a larval family during growth, but showed significant differences among families. Different Q10 values were evident among 21 larval families, with family accounting for 87% of variation. Specifically, four larval families maintained an increased thermal sensitivity for respiration (Q10 of 3). This physiology would confer resilience to rising temperature by matching the increased energy demand of protein synthesis (Q10 of 3 previously reported). For protein synthesis, differences in Q10 values were also observed. Notably, a family was identified that had a decreased thermal sensitivity for protein synthesis (Q10 of 1.7 cf. Q10 of 3 for other families), conferring an optimal energy allocation with rising temperature. Different thermal sensitivities across families for respiration (energy supply) and protein synthesis (energy demand) were integrated into models of energy allocation at the whole-organism level. The outcome of these analyses provides insights into the physiological bases of optimal energy allocation with rising temperature. These transgenerational (egg-to-egg) experiments highlight approaches to dissect components of phenotypic variance to address long-standing questions of genetic adaptation and physiological resilience to environmental change.

The metabolic rate (ṀO2) of eurythermal fishes changes in response to temperature, yet it is unclear how changes in mitochondrial function contribute to changes in ṀO2. We hypothesized that ṀO2 would increase with acclimation temperature in the threespine stickleback (Gasterosteus aculeatus) in parallel with metabolic remodeling at the cellular level but that changes in metabolism in some tissues, such as liver, would contribute more to changes in ṀO2 than others. Threespine stickleback were acclimated to 5, 12 and 20°C for 7 to 21 weeks. At each temperature, standard and maximum metabolic rate (SMR and MMR, respectively), and absolute aerobic scope (AAS) were quantified, along with mitochondrial respiration rates in liver, oxidative skeletal and cardiac muscles, and the maximal activity of citrate synthase (CS) and lactate dehydrogenase (LDH) in liver, and oxidative and glycolytic skeletal muscles. SMR, MMR and AAS increased with acclimation temperature, along with rates of mitochondrial phosphorylating respiration in all tissues. Low SMR and MMR at 5°C were associated with low or undetectable rates of mitochondrial complex II activity and a greater reliance on complex I activity in liver, oxidative skeletal muscle and heart. SMR was positively correlated with cytochrome c oxidase (CCO) activity in liver and oxidative muscle, but not mitochondrial proton leak, whereas MMR was positively correlated with CCO activity in liver. Overall, the results suggest that changes in ṀO2 in response to temperature are driven by changes in some aspects of mitochondrial function in some, but not all, tissues of threespine stickleback.

Excessive alcohol consumption can cause alcoholic myopathy, but the molecular mechanism is still unclear. In this study, zebrafish were exposed to 0.5% alcohol for eight weeks to investigate the effect of alcohol on skeletal muscle and its molecular mechanism. The results showed that the body length, body weight, cross-sectional area of the skeletal muscle fibers, Ucrit, and MO2max of the zebrafish were significantly decreased after alcohol exposure. The expression of markers of skeletal muscle atrophy and autophagy was increased, and the expression of P62 was significantly reduced. The content of ROS, the mRNA expression of sod1 and sod2, and the protein expression of Nox2 were significantly increased. In addition, we found that the inflammatory factors Il1β and Tnfα were significantly enriched in skeletal muscle, and the expression of the HMGB1/TLR4/NF-κB signaling axis was also significantly increased. In summary, in this study, we established a zebrafish model of alcohol-induced skeletal muscle atrophy and further elucidated its pathogenesis.

Many fishes use their tail as the main thrust producer during swimming. This fin's diversity in shape and size influences its physical interactions with water as well as its ecological functions. Two distinct tail morphologies are common in bony fishes: flat, truncate tails which are best suited for fast accelerations via drag forces, and forked tails that promote economical, fast cruising by generating lift-based thrust. This assumption is based primarily on studies of the lunate caudal fin of Scombrids (i.e. tuna, mackerel), which is comparatively stiff and exhibits an airfoil-type cross-section. However, this is not representative of the more commonly observed and taxonomically widespread flexible forked tail, yet similar assumptions about economical cruising are widely accepted. Here, we present the first comparative experimental study of forked versus truncate tail shape and compare the fluid mechanical properties and energetics of two common nearshore fish species. We examined the hypothesis that forked tails provide a hydrodynamic advantage over truncate tails at typical cruising speeds. Using experimentally derived pressure fields, we show that the forked tail produces thrust via acceleration reaction forces like the truncate tail during cruising but at increased energetic costs. This reduced efficiency corresponds to differences in the performance of the two tail geometries and body kinematics to maintain similar overall thrust outputs. Our results offer insights into the benefits and tradeoffs of two common fish tail morphologies and shed light on the functional morphology of fish swimming to guide the development of bio-inspired underwater technologies.

Fisheries biologists have been hesitant to use passive integrated transponder (PIT) tags in small‐bodied fishes (40–200 mm TL) such as darters (Percidae: Etheostomatinae) because of the fishes' size and potential effect on swimming performance. The authors used constant acceleration trials to evaluate the swimming performance of Arkansas darters Etheostoma cragini in control (no incision or tag), sham (incision and suture) or PIT tagged (surgically implanted 8 × 1.4 mm intra‐peritoneal PIT tag) treatments. Tag retention and fish survival were monitored for up to 199 days post‐tagging. Maximum swimming velocity did not differ between control, sham and PIT tag treatments, nor was maximum swimming velocity affected by the tagging procedure. Tag retention was 100%, and the overall survival of tagged fish was 88% in the swimming study, and 100% in the long‐term study, suggesting that small PIT tags are suitable for use in darters. The authors include a brief meta‐analysis on the results reported by 20 studies that PIT tagged small‐bodied fishes, representing 38 species and nine families of freshwater fish.

European sea bass is a species of great commercial value for fisheries and aquaculture. Rising temperatures may jeopardize the performance and survival of the species across its distribution and farming range, making the investigation of its thermal responses highly relevant. In this article, the metabolic scope, performance, and tolerance of juvenile E. sea bass reared under three high water temperatures (24, 28, 33°C), for a period of three months was evaluated via analysis of selected growth performance and physiological indicators. Effects on molecular, hormonal, and biochemical variables were analyzed along with effects of acclimation temperature on the metabolic rate and Critical Thermal maximum (CTmax). Despite signs of thermal stress at 28°C indicated by high plasma cortisol and lactate levels as well as the upregulation of genes coding for Heat Shock Proteins (HSP), E. sea bass can maintain high performance at that temperature which is encouraging for the species culture in the context of a warming ocean. Critical survivability thresholds appear sharply close to 33°C, where the aerobic capacity declines and the overall performance diminishes. European sea bass demonstrates appreciable capacity to cope with acute thermal stress exhibiting CTmax as high as 40°C for fish acclimated at high temperatures, which may indicate resilience to future heatwaves events.

Predictions of individual responses to climate change are often based on the assumption that temperature affects the metabolism of individuals independently of their body mass. However, empirical evidence indicates that interactive effects exist. Here, we investigated the response of individual standard metabolic rate (SMR) to annual temperature range and forecasted temperature rises of 0.6–1.2°C above the current maxima, under the conservative climate change scenario IPCC RCP2.6. As a model organism, we used the amphipod Gammarus insensibilis, collected across latitudes along the western coast of the Adriatic Sea down to the southernmost limit of the species' distributional range, with individuals varying in body mass (0.4–13.57 mg). Overall, we found that the effect of temperature on SMR is mass dependent. Within the annual temperature range, the mass-specific SMR of small/young individuals increased with temperature at a greater rate (activation energy: E=0.48 eV) than large/old individuals (E=0.29 eV), with a higher metabolic level for high-latitude than low-latitude populations. However, under the forecasted climate conditions, the mass-specific SMR of large individuals responded differently across latitudes. Unlike the higher-latitude population, whose mass-specific SMR increased in response to the forecasted climate change across all size classes, in the lower-latitude populations, this increase was not seen in large individuals. The larger/older conspecifics at lower latitudes could therefore be the first to experience the negative impacts of warming on metabolism-related processes. Although the ecological collapse of such a basic trophic level (aquatic amphipods) owing to climate change would have profound consequences for population ecology, the risk is significantly mitigated by phenotypic and genotypic adaptation.

The shared-pathway hypothesis offers a cellular explanation for the connection between ketocarotenoid pigmentation and individual quality. Under this hypothesis, ketocarotenoid metabolism shares cellular pathways with mitochondrial oxidative phosphorylation such that red carotenoid-based coloration is inextricably linked mitochondrial function. To test this hypothesis, we exposed Tigriopus californicus copepods to a mitochondrially targeted protonophore, 2,4-dinitrophenol (DNP), to induce proton leak in the inner mitochondrial membranes. We then measured whole-animal metabolic rate and ketocarotenoid accumulation. As observed in prior studies of vertebrates, we observed that DNP treatment of copepods significantly increased respiration and that DNP-treated copepods accumulated more ketocarotenoid than control animals. Moreover, we observed a relationship between ketocarotenoid concentration and metabolic rate, and this association was strongest in DNP-treated copepods. These data support the hypothesis that ketocarotenoid and mitochondrial metabolism are biochemically intertwined. Moreover, these results corroborate observations in vertebrates, perhaps suggesting a fundamental connection between ketocarotenoid pigmentation and mitochondrial function that should be explored further.

This study assessed the energy budget for juvenile Atlantic Sea Scallop, Placopecten magellanicus, during a natural drop in temperature (15.6°C to 5.8°C) over an 8-week time period during the fall at three different enrichment levels of carbon dioxide (CO2). Every 2 weeks, individuals were sampled for ecophysiological measurements of feeding activity, respiration rate (RR) and excretion rate (ER) to enable the calculation of scope for growth (SFG) and atomic oxygen:nitrogen ratios (O:N). In addition, 36 individuals per treatment were removed for shell height, dry tissue weight (DTW) and dry shell weight (DSW). We found a significant decrease in feeding rates as CO2 increased. Those rates also were significantly affected by temperature, with highest feeding at 9.4°C. No significant CO2 effect was observed for catabolic energy processes (RR and ER); however, these rates did increase significantly with temperature. The O:N ratio was not significantly affected by CO2, but was significantly affected by temperature. There was a significant interaction between CO2 and temperature for ER and the O:N ratio, with low CO2 levels resulting in a U-shaped response that was not sustained as CO2 levels increased. This suggests that the independent effects of CO2 and temperature observed at low levels are different once a CO2 threshold is reached. Additionally, there were significant differences in growth estimators (shell height and DSW), with the best growth occurring at the lowest CO2 level. In contrast to temperature variations that induced a trade-off response in energy acquisition and expenditure, results from this research support the hypothesis that sea scallops have a limited ability to alter physiological processes to compensate for increasing CO2.

The hypoxic ventilatory response (HVR) in fish is an important reflex that aids O2 uptake when low environmental O2 levels constrain diffusion. In developing zebrafish (Danio rerio), the acute HVR is multiphasic, consisting of a rapid increase in ventilation frequency (fV) during hypoxia onset, followed by a decline to a stable plateau phase above fV under normoxic conditions. In this study, we examined the potential role of catecholamines in contributing to each of these phases of the dynamic HVR in zebrafish larvae. We showed that adrenaline elicits a dose-dependent β-adrenoreceptor (AR)-mediated increase in fV that does not require expression of β1-ARs, as the hyperventilatory response to β-AR stimulation was unaltered in adrb1−/− mutants, generated by CRISPR/Cas9 knockout. In response to hypoxia and propranolol co-treatment, the magnitude of the rapidly occurring peak increase in fV during hypoxia onset was attenuated (112±14 breaths min−1 without propranolol to 68±17 breaths min−1 with propranolol), whereas the increased fV during the stable phase of the HVR was prevented in both wild type and adrb1−/− mutants. Thus, β1-AR is not required for the HVR and other β-ARs, although not required for initiation of the HVR, are involved in setting the maximal increase in fV and in maintaining hyperventilation during continued hypoxia. This adrenergic modulation of the HVR may arise from centrally released catecholamines because adrenaline exposure failed to activate (based on intracellular Ca2+ levels) cranial nerves IX and X, which transmit O2 signals from the pharyngeal arch to the central nervous system.

Juvenile fall-run Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento–San Joaquin River Basin experience temporally and spatially heterogenous temperature regimes, between cool upper tributaries and the warm channelized Delta, during freshwater rearing and outmigration. Limited water resources necessitate human management of dam releases, allowing temperature modifications. The objective of this study was to examine the effect of temperature on specific dynamic action (SDA), or the metabolic cost associated with feeding and digestion, which is thought to represent a substantial portion of fish energy budgets. Measuring SDA with respect to absolute aerobic scope (AAS), estimated by the difference between maximum metabolic rate (MMR) and standard metabolic rate (SMR), provides a snapshot of its respective energy allocation. Fish were acclimated to 16°C, raised or lowered to each acute temperature (13°C, 16°C, 19°C, 22°C or 24°C), then fed a meal of commercial pellets weighing 2% of their wet mass. We detected a significant positive effect of temperature on SMR and MMR, but not on AAS. As expected, there was no significant effect of temperature on the total O2 cost of digestion, but unlike other studies, we did not see a significant difference in duration, peak metabolic rate standardized to SMR, time to peak, percent of meal energy utilized, nor the ratio of peak O2 consumption to SMR. Peak O2 consumption represented 10.4–14.5% of AAS leaving a large amount of aerobic capacity available for other activities, and meal energy utilized for digestion ranged from 5.7% to 7.2%, leaving substantial remaining energy to potentially assimilate for growth. Our juvenile fall-run Chinook salmon exhibited thermal stability in their SDA response, which may play a role in maintaining homeostasis of digestive capability in a highly heterogeneous thermal environment where rapid growth is important for successful competition with conspecifics and for avoiding predation.

The impacts of warming temperatures associated with climate change on performance are poorly understood in most mammals. Thermal performance curves are a valuable means of examining the effects of temperature on performance traits, but they have rarely been used in endotherms. Here, we examined the thermal performance curve of endurance running capacity at high temperatures in the deer mouse (Peromyscus maniculatus). Endurance capacity was measured using an incremental speed test on a treadmill, and subcutaneous temperature in the abdominal region was measured as a proxy for body temperature (Tb). Endurance time at 20°C was repeatable but varied appreciably across individuals, and was unaffected by sex or body mass. Endurance capacity was maintained across a broad range of ambient temperatures (Ta) but was reduced above 35°C. Tb during running varied with Ta, and reductions in endurance were associated with Tb greater than 40°C when Ta was above 35°C. At the high Ta that limited endurance running capacity (but not at lower Ta), Tb tended to rise throughout running trials with increases in running speed. Metabolic and thermoregulatory measurements at rest showed that Tb, evaporative water loss and breathing frequency increased at Ta of 36°C and above. Therefore, the upper threshold temperatures at which endurance capacity is impaired are similar to those inducing heat responses at rest in this species. These findings help discern the mechanisms by which deer mice are impacted by warming temperatures, and provide a general approach for examining thermal breadth of performance in small mammals.

Swimming performance is a well‐established key physiological parameter of fish that is highly linked to their fitness in the wild. In the context of fish restocking purposes, it therefore appears crucial to study this specific behaviour. Here, the authors investigated intra and interspecies differences in the swimming performance of hatchery‐reared post‐larvae and juveniles belonging to two Mediterranean candidate threatened species, the common dentex, Dentex dentex (Sparidae), and the brown meagre, Sciaena umbra (Sciaenidae), with body sizes ranging from 8 to 37 mm total length (TL, from 24 to 58 days post‐hatch). The swimming abilities were estimated through the calculation of their critical swimming speed ( U crit ), their relative U crit and their Reynolds number ( R e ). Two different patterns were observed between D. dentex and S. umbra, showing a different effect of ontogeny on the performance of both species. The relative U crit of S. umbra decreased linearly through ontogeny, whereas the relative U crit and U crit of D. dentex increased linearly through the range of sizes tested. The ontogenetic change in U crit of S. umbra occurred in two stages: a first stage of sharp improvement and a second stage of a slow decrease in performance. Both stages were separated by a breakpoint that coincided with the appearance of a refusal to swim behaviour that occurred shortly after the end of metamorphosis and can potentially be associated with the establishment of this species sedentary behaviour. The swimming performance of both species showed ontogenetic differences. Sciaena umbra had the highest relative performance when its body sizes were the smallest, whereas D. dentex showed the highest relative performance when its body sizes were the largest. These results will be linked to future research on both of these species concerning their escape, exploratory and predatory behaviours, and for restocking purposes to draw a more realistic overview of hatchery‐reared juvenile performance. Knowledge of both species’ behavioural and swimming performance through ontogeny is important to consider when using hatchery‐reared fish juveniles for restocking, as size‐at‐release can have a large impact on fish survival and thus on restocking success.

Physiological and environmental stressors can cause osmotic stress in fish hearts, leading to a reduction in intracellular taurine concentration. Taurine is a β-amino acid known to regulate cardiac function in other animal models but its role in fish has not been well characterized. We generated a model of cardiac taurine deficiency (TD) by feeding brook char (Salvelinus fontinalis) a diet enriched in β-alanine, which inhibits cardiomyocyte taurine uptake. Cardiac taurine levels were reduced by 21% and stress-induced changes in normal taurine handling were observed in TD brook char. Responses to exhaustive exercise and acute thermal and hypoxia tolerance were then assessed using a combination of in vivo, in vitro and biochemical approaches. Critical thermal maximum was higher in TD brook char despite significant reductions in maximum heart rate. In vivo, TD brook char exhibited a lower resting heart rate, blunted hypoxic bradycardia and a severe reduction in time to loss of equilibrium under hypoxia. In vitro function was similar between control and TD hearts under oxygenated conditions, but stroke volume and cardiac output were severely compromised in TD hearts under severe hypoxia. Aspects of mitochondrial structure and function were also impacted in TD permeabilized cardiomyocytes, but overall effects were modest. High levels of intracellular taurine are required to achieve maximum cardiac function in brook char and cardiac taurine efflux may be necessary to support heart function under stress. Taurine appears to play a vital, previously unrecognized role in supporting cardiovascular function and stress tolerance in fish.

With the growing prevalence of hypoxia (O2 levels ≤2 mg l−1) in aquatic and marine ecosystems, there is increasing interest in the adaptive mechanisms fish may employ to better their performance in stressful environments. Here, we investigated the contribution of a proposed strategy for enhancing tissue O2 extraction – plasma-accessible carbonic anhydrase (CA-IV) – under hypoxia in a species of estuarine fish (red drum, Sciaenops ocellatus) that thrives in fluctuating habitats. We predicted that hypoxia-acclimated fish would increase the prevalence of CA-IV in aerobically demanding tissues to confer more efficient tissue O2 extraction. Furthermore, we predicted the phenotypic changes to tissue O2 extraction that occur with hypoxia acclimation may improve respiratory and swim performance under 100% O2 conditions (i.e. normoxia) when compared with performance in fish that have not been acclimated to hypoxia. Interestingly, there were no significant differences in relative CA-IV mRNA expression, protein abundance or enzyme activity between the two treatments, suggesting CA-IV function is maintained under hypoxia. Likewise, respiratory performance of hypoxia-acclimated fish was similar to that of control fish when tested in normoxia. Critical swim speed (Ucrit) was significantly higher in hypoxia-acclimated fish but translated to marginal ecological benefits with an increase of ∼0.3 body lengths per second. Instead, hypoxia-acclimated fish may have relied more heavily on anaerobic metabolism during their swim trials, utilizing burst swimming 1.5 times longer than control fish. While the maintenance of CA-IV may still be an important contributor for hypoxia tolerance, our evidence suggests hypoxia-acclimated red drum are using other mechanisms to cope in an O2-depleted environment.

Nile tilapia (Oreochromis niloticus) is one of the most important food fishes in global aquaculture. The optimal rearing temperature for Nile tilapia is 27–30 °C; however, in some Asian breeding areas, such as south China, water temperatures in summer frequently exceed 35 °C for several days. Potential effects of long-term exposure to high temperatures on the survival and metabolism of tilapia are unclear. In this study, genetically improved farmed tilapia, age six weeks, were exposed to water temperatures of 28, 32, and 36 °C for 15 weeks. Mean survival rates and tolerance to hypoxia were significantly reduced, and respiratory rates were increased in fish reared at 36 °C, compared to the 28 and 32 °C treatments (p

Plasma serotonin (5-hydroxytryptamine, 5-HT) homeostasis is maintained through the combined processes of uptake (via the 5-HT transporter SERT, and others), degradation (via monoamine oxidase, MAO) and excretion. Previous studies have shown that inhibiting SERT, which would inhibit 5-HT uptake and degradation, attenuates parts of the cardiovascular hypoxia reflex in gulf toadfish (Opsanus beta), suggesting that these 5-HT clearance processes may be important during hypoxia exposure. Therefore, the goal of this experiment was to determine the effects of mild hypoxia on 5-HT uptake and degradation in the peripheral tissues of toadfish. We hypothesized that 5-HT uptake and degradation would be upregulated during hypoxia, resulting in lower plasma 5-HT, with uptake occurring in the gill, heart, liver and kidney. Fish were exposed to normoxia (97.6% O2 saturation, 155.6 Torr) or 2 min, 40 min or 24 h mild hypoxia (50% O2 saturation, ∼80 Torr), then injected with radiolabeled [3H]5-HT before blood, urine, bile and tissues were sampled. Plasma 5-HT levels were reduced by 40% after 40 min of hypoxia exposure and persisted through 24 h. 5-HT uptake by the gill was upregulated following 2 min of hypoxia exposure, and degradation in the gill was upregulated at 40 min and 24 h. Interestingly, there was no change in 5-HT uptake by the heart and degradation in the heart decreased by 58% within 2 min of hypoxia exposure and by 85% at 24 h. These results suggest that 5-HT clearance is upregulated during hypoxia and is likely driven, in part, by mechanisms within the gill and not the heart.

High recreational catch rates of istiophorid billfishes in the eastern tropical Pacific (ETP) have led to substantial eco-tourism derived economic benefits for the countries in the region, prompting many countries to mandate catch-and-release practices for recreational anglers. Previous estimates of billfish post-release behaviours and recovery periods after these physiologically stressful capture events, however, vary widely depending on the type of tag used. Using high-resolution, multi-sensor biologging tags, we provide a fine-scale, detailed view of the behaviour and recovery periods of blue marlin (Makaira nigricans; n = 9) and sailfish (Istiophorus platypterus, Istiophoridae; n = 9) caught in a typical recreational fishery in the ETP. Angling times ranged from 4 to 90 min, and fish were monitored for periods of 6–70 h after release. Blue marlin showed a characteristic long, deep dive immediately after release, with significantly greater duration associated with longer fight times, a behaviour not typical for sailfish. Diving depths were, however, much shallower than those previously reported for both species due to the shallow thermocline and oxycline present in the ETP. Data from 40 derived metrics from acceleration (i.e. tailbeat period, amplitude, pitch, etc.) and physical parameters (i.e. depth, speed, temperature, oxygen saturation, etc.) used to quantify a recovery period suggest blue marlin and sailfish recover 9.0 ± 3.2 and 4.9 ± 2.8 h after release, respectively. Our high-resolution assessment of post-release behaviour suggests that these billfish are capable of rapid physiological recovery after capture in recreational fisheries, and that catch-and-release practices like those used here can be an effective approach to conserve and sustain billfish populations in the ETP. Predicted climate change caused shallowing of the oxygen minimum zone, however, would increase the vertical habitat compression present in this region, potentially prolonging or inhibiting recovery.

The cavin proteins are essential for caveola biogenesis and function. Here, we identify a role for the muscle-specific component, Cavin4, in skeletal muscle T-tubule development by analyzing two vertebrate systems, mouse and zebrafish. In both models, Cavin4 localized to T-tubules, and loss of Cavin4 resulted in aberrant T-tubule maturation. In zebrafish, which possess duplicated cavin4 paralogs, Cavin4b was shown to directly interact with the T-tubule–associated BAR domain protein Bin1. Loss of both Cavin4a and Cavin4b caused aberrant accumulation of interconnected caveolae within the T-tubules, a fragmented T-tubule network enriched in Caveolin-3, and an impaired Ca2+ response upon mechanical stimulation. We propose a role for Cavin4 in remodeling the T-tubule membrane early in development by recycling caveolar components from the T-tubule to the sarcolemma. This generates a stable T-tubule domain lacking caveolae that is essential for T-tubule function.

An understanding of the risks associated with diluted bitumen (dilbit) transport through Pacific salmon habitat necessitates the identification and quantification of hazards posed to early life stages. Sockeye from the embryo to juvenile stage (8 months old) were exposed to four concentrations of the water-soluble fraction of Cold Lake dilbit (summer blend; concentrations of 0, 13.7, 34.7, and 124.5 μg/L total polycyclic aromatic compounds). Significant mortality (up to 18% over controls) only occurred in the embryo to swim-up fry stage. Impaired growth was seen in the alevin, swim-up, and juvenile stages (maximum reduction 15% in mass but not fork length). Reductions in both critical (maximum 24% reductions) and burst (maximum 47% reductions) swimming speed in swim-up fry and juveniles were seen. Alterations in energy substrate reserves (reductions in soluble protein and glycogen content, elevations in whole-body lipid and triglyceride levels) at all stages may underlie the effects seen in swimming and growth. Dilbit exposure induced a preexercise physiological stress response that affected the recovery of postexercise biochemistry (cortisol, glycogen, lactate, triglyceride concentrations). The transcript abundance of the cytochrome P450 1A gene (cyp1a) was quantified in alevin head regions (containing the heart) and in the hearts of swim-up fry and juveniles and showed a concentration-dependent increase in the expression of cyp1a at all life stages. Environ Toxicol Chem 2022;41:1937–1949. © 2022 SETAC

The excessive worldwide production of plastic materials results in omnipresent microplastic pollution. Scientific studies dealing with the impacts of microplastics on aquatic ecosystems focus mainly on the marine environment, documenting the effect on the functional traits of various organisms. Polystyrene, one of the most commonly used plastics, has become a widely used model in this respect. In our study, freshwater shrimps (Neocardina heteropoda) were exposed to virgin polystyrene particles (size 0.5 mm; nominal concentration 8 mgL−1), and their behavioral and physiological responses were compared to control shrimp. The exposed shrimps exhibited modified activity patterns (greater speeds, accelerations and distances moved), accompanied by a lowered standard metabolic rate (SMR). The observed effects differed in their progression from the 7th to 14th day of exposure, from undetectable changes (distance, SMR) to significant differences (speed, acceleration). Significant differences were also detected in the behavioral syndromes expressed by the exposed and controlled shrimps, indicating that the microplastics influence not only the particular traits, but also their functional relationships. As such, our study contributes to the integration of behavioral ecotoxicology in risk assessment, documenting the adverse performance of freshwater invertebrates exposed to microplastics with the potential to transpose the problem to higher levels of the food web.

Thermal tolerance is crucial to understanding the biology of fishes and their responses to changes in temperatures, such as that produced by climate change. Shortnose sturgeon (Acipenser brevirostrum) is an endangered species (USA) and a species of special concern (Canada) that live on the eastern coast of North America. Although previous studies have focused on the acute critical thermal maximum (CTmax) of shortnose sturgeon, nothing is known with respect to their acute critical thermal minimum (CTmin) and the overall thermal tolerance of this species. This study examined the upper (CTmax) and lower (CTmin) thermal tolerance of shortnose sturgeon acclimated to 12 and 18°C. CTmax increased with increasing acclimation temperature; however, there was no significant relationship between acclimation temperature and CTmin. Taken together, the results of the present study show that shortnose sturgeon are well adapted to tolerate acute exposures to both cold and warm water environments.

In rainbow trout, dietary carbohydrates are poorly metabolized compared with other macronutrients. One prevalent hypothesis suggests that high dietary amino acid levels could contribute to the poor utilization of carbohydrates in trout. In mammals, alanine is considered an important gluconeogenic precursor, but has recently been found to stimulate AMP-activated protein kinase (AMPK) to reduce glucose levels. In trout, the effect of alanine on glucose flux is unknown. The goal of this study was to determine the effects of 4 h exogenous alanine infusion on glucose metabolism in rainbow trout. Glucose flux, and the rate of glucose appearance (Ra) and disposal (Rd) were measured in vivo. Key glycolytic and gluconeogenic enzyme expression and activity, and cell signaling molecules relevant to glucose metabolism were assessed in the liver and muscle. The results show that alanine inhibits glucose Ra (from 13.2±2.5 to 7.3±1.6 μmol kg−1 min−1) and Rd (from 13.2±2.5 to 7.4±1.5 μmol kg−1 min−1) and the slight mismatch between Ra and Rd caused a reduction in glycemia, similar to the effects of insulin in trout. The reduction in glucose Rd can be partially explained by a reduction in glut4b expression in red muscle. In contrast to mammals, trout alanine-dependent glucose-lowering effects did not involve hepatic AMPK activation, suggesting a different mechanistic basis. Interestingly, protein kinase B (AKT) activation increased only in muscle, similar to effects observed in insulin-infused trout. We speculate that alanine-dependent effects were probably mediated through stimulation of insulin secretion, which could indirectly promote alanine oxidation to provide the needed energy.

Climate change and anthropological activities have led to an expansion of hypoxia into the natural habitat of Cancer irroratus. In this study, we examined the effects of hypoxia and food deprivation state on food intake and subsequent gastric processing. Three different techniques were used to measure food intake. The gravimetric analysis of dry food pellets was the most accurate method. In severe hypoxia (20% oxygen), rock crabs reduced food intake, and more crabs refused to eat. Compared with fasted crabs, more starved crabs tended to eat in severe hypoxia. Subsequently, prolonged gastric emptying times paralleled the previously measured postprandial oxygen consumption in hypoxia. Starved crabs also exhibited slightly longer transit times for digesta compared with fasted crabs. These results suggest that although a trade-off may occur in starved rock crabs between the need to procure nutrients and deal with hypoxic stress, impaired digestive processing may still deleteriously affect these animals.

European sea bass (Dicentrarchus labrax) is a large, economically important fish species with a long generation time whose long-term resilience to ocean acidification (OA) and warming (OW) is not clear. We incubated sea bass from Brittany (France) for two generations (>5 years in total) under ambient and predicted OA conditions (PCO2: 650 and 1700 µatm) crossed with ambient and predicted OW conditions in F1 (temperature: 15–18°C and 20–23°C) to investigate the effects of climate change on larval and juvenile growth and metabolic rate. We found that in F1, OA as a single stressor at ambient temperature did not affect larval or juvenile growth and OW increased developmental time and growth rate, but OAW decreased larval size at metamorphosis. Larval routine and juvenile standard metabolic rate were significantly lower in cold compared with warm conditioned fish and also lower in F0 compared with F1 fish. We did not find any effect of OA as a single stressor on metabolic rate. Juvenile PO2,crit was not affected by OA or OAW in both generations. We discuss the potential underlying mechanisms resulting in the resilience of F0 and F1 larvae and juveniles to OA and in the beneficial effects of OW on F1 larval growth and metabolic rate, but contrastingly in the vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

Deoxygenation and warming affect adult fish physiology in all aquatic ecosystems, but how these stressors impact the energetics of sensitive developing stages is largely unknown. Addressing this knowledge gap, we investigated chronic and acute effects of two stressors (high-temperature and hypoxia) in yolk-sac larval (48-168 hpf) zebrafish (Danio rerio) energy budgets measuring, oxygen consumption rate (ṀO2), growth rate (absolute (AGR) & specific (SGR)), % net conversion efficiency (KN), net cost of growth (Cr) and scaling relationships. Embryos and larvae were raised under four chronic treatments, 1) control (28°C & pO2 21kPa, T28O21), 2) high-temperature (31°C & pO2 21kPa, T31O21), 3) hypoxia (28°C & pO2 11kPa, T28TO11), and 4) high-temperature and hypoxia (31°C & pO2 11kPa, T31O11). From each chronic treatment, larvae were acutely exposed to the same combinations of stressors for 1h in a respirometer. At hatching, larvae from chronic high-temperature (T31O21 & T31O11) treatments were larger, (higher dry mass (MD) & standard length (Ls)) than controls (T28O21 & T28O11), but by the end of the yolk-sac stage, increased metabolic demands diverted energy away from growth increasing Cr and lowering % KN. Control metabolic scaling relationships were significant (metabolic exponent b, log-log slope; 0.83±0.68±95% CI, combined b of 1.19±0.25) and differed from 0.75, but metabolic levels (La) were lower (2.11±0.90) in acute hypoxia (3.35±1.52) and high-temperature/hypoxia (2.61±1.55). Thus, high-temperature dominated larval energetics acting synergistically with hypoxia increasing cumulative energetic costs and making allostasis difficult compared to older stages.

Rapid turning and swimming contribute to ecologically important behaviors in fishes such as predator avoidance, prey capture, mating and the navigation of complex environments. For riverine species, such as knifefishes, turning behaviors may also be important for navigating locomotive perturbations caused by turbulent flows. Most research on fish maneuvering focuses on fish with traditional fin and body morphologies, which primarily use body bending and the pectoral fins during turning. However, it is uncertain how fishes with uncommon morphologies are able to achieve sudden and controllable turns. Here, we studied the turning performance and the turning hydrodynamics of the black ghost knifefish (Apteronotus albifrons, N=6) which has an atypical elongated ribbon fin. Fish were filmed while swimming forward at ∼2 body lengths s−1 and feeding from a fixed feeder (control) and an oscillating feeder (75 Hz) at two different amplitudes. 3D kinematic analysis of the body revealed the highest pitch angles and lowest body bending coefficients during steady swimming. Low pitch angle, high maximum yaw angles and large body bending coefficients were characteristic of small and large turns. Asynchrony in pectoral fin use was low during turning; however, ribbon fin wavelength, frequency and wave speed were greatest during large turns. Digital particle image velocimetry (DPIV) showed larger counter-rotating vortex pairs produced during turning by the ribbon fin in comparison to vortices rotating in the same direction during steady swimming. Our results highlight the ribbon fin's role in controlled rapid turning through modulation of wavelength, frequency and wave speed.

Wild animals have parasites that can compromise their physiological and/or behavioural performance. Yet, the extent to which parasite load is related to intraspecific variation in performance traits within wild populations remains relatively unexplored. We used pumpkinseed sunfish (Lepomis gibbosus) and their endoparasites as a model system to explore the effects of infection load on host aerobic metabolism and escape performance. Metabolic traits (standard and maximum metabolic rates, aerobic scope) and fast-start escape responses following a simulated aerial attack by a predator (responsiveness, response latency and escape distance) were measured in fish from across a gradient of visible (i.e. trematodes causing black spot disease counted on fish surfaces) and non-visible (i.e. cestodes in fish abdominal cavity counted post-mortem) endoparasite infection. We found that a higher infection load of non-visible endoparasites was related to lower standard and maximum metabolic rates, but not aerobic scope in fish. Non-visible endoparasite infection load was also related to decreased responsiveness of the host to a simulated aerial attack. Visible endoparasites were not related to changes in metabolic traits or fast-start escape responses. Our results suggest that infection with parasites that are inconspicuous to researchers can result in intraspecific variation in physiological and behavioural performance in wild populations, highlighting the need to more explicitly acknowledge and account for the role played by natural infections in studies of wild animal performance.

Ocean acidification (OA) resulting from anthropogenic CO2 emissions is impairing the reproduction of marine organisms. While parental exposure to OA can protect offspring via carryover effects, this phenomenon is poorly understood in many marine invertebrate taxa. Here, we examined how parental exposure to acidified (pH 7.40) versus ambient (pH 7.72) seawater influenced reproduction and offspring performance across six gametogenic cycles (13 weeks) in the estuarine sea anemone Nematostella vectensis. Females exhibited reproductive plasticity under acidic conditions, releasing significantly fewer but larger eggs compared to ambient females after 4 weeks of exposure, and larger eggs in two of the four following spawning cycles despite recovering fecundity, indicating long-term acclimatization and greater investment in eggs. Males showed no changes in fecundity under acidic conditions but produced a greater percentage of sperm with high mitochondrial membrane potential (MMP; a proxy for elevated motility), which corresponded with higher fertilization rates relative to ambient males. Finally, parental exposure to acidic conditions did not significantly influence offspring development rates, respiration rates, or heat tolerance. Overall, this study demonstrates that parental exposure to acidic conditions impacts gamete production and physiology but not offspring performance in N. vectensis, suggesting that increased investment in individual gametes may promote fitness.

Heatwaves are increasing in frequency and intensity under climate change. Freshwater ecosystems are among the most thermally impacted systems, within which agricultural streams are experiencing the most extreme heatwaves and deserve prioritised focus. Heatwaves are approaching the upper thermal limits of many fishes but have received little attention to date. To study whether and how fish tolerate heatwaves from a physiological perspective, we simulated single, multiple, and extended heatwaves at 32 and 34°C in the laboratory, based on high‐resolution summer temperatures recorded in agricultural versus forested streams in Illinois, U.S.A. By investigating the effects of heatwaves on 25°C acclimated fathead minnow Pimephales promelas, an important prey species across North America, we witnessed its high thermal resilience, including a rapid return to metabolic homeostasis after single and multiple heatwaves, measured by oxygen consumption rate. During an extended heatwave, fathead minnow were still able to partially lower oxygen consumption rate after the initial exposure. We also found transient increases in their critical thermal maximum, especially after higher intensity and frequency of heatwaves. However, the thermal resilience of fathead minnow did come with costs, including reduced anaerobic capacity indicated by decreased lactate dehydrogenase activity and impaired antioxidant defence indicated by reduced superoxide dismutase in white muscle. By monitoring metabolic costs and physiological adjustments of fish during and after heatwaves, we showed that fathead minnow were resilient to simulated current and near‐future heatwaves, which may allow them to cope with thermal extremes expected in agricultural streams. Overall, the real‐time monitoring of fish responses to heatwaves incorporates natural dynamics of thermal patterns. It facilitates mechanistic understandings of how fish react to thermal challenges in the real world and offers opportunities to incorporate high‐resolution metabolic costs into future bioenergetic modelling.

In the present study, oxygen consumption of two sturgeon species, beluga (Huso huso), sterlet (Acipenser ruthenus), and their hybrid reared in a recirculating aquaculture system were compared over body intervals from 54–107 g to determine the interspecific variation of metabolic rate. Metabolic rates were measured using the intermittent-flow respirometry technique. Standard oxygen consumption rates (SMR, mg O2 h−1) of sterlet were 30% higher compared with beluga and 22% higher compared with bester hybrid. The routine metabolic rate (RMR, mg O2 h−1) averaged 1.58 ± 0.13 times the SMR for A. ruthenus, 1.59 ± 0.3 for H. huso, and 1.42 ± 0.15 for the hybrid bester. However, the study revealed no significant differences (p > 0.05) between mean values of SMR and RMR for beluga and bester hybrid. The scaling coefficient reflected a closed isometry for the hybrid (b = 0.97), while for the purebred species the coefficient of 0.8 suggests a reduction in oxygen consumption with increasing body mass. These findings may contribute to understanding the differences in growth performances and oxygen requirements of the studied species reared in intensive aquaculture system.

Phenotypic adjustments to environmental variation are particularly relevant to cope with putative environmental mismatches often imposed by natal dispersal. We used an intergenerational cross‐transplant field‐based experiment to evaluate the morphological and physiological effects of parental and postsettlement water flow environments on the orange‐fin anemonefish Amphiprion chrysopterus through ontogeny (at pre‐ and postsettlement stages). Offspring born from parents under high water flow had an 18% higher caudal fin aspect ratio (a compound measure of shape) at the presettlement stage, 10% slower growth after settlement, and 55% lower survival after settlement compared to offspring from low water flow parents. At the presettlement stage, caudal fin length was determined by parental caudal fin length. At the postsettlement stage, fish survived equally well with similar phenotypes in both high and low developmental flow environments. However, results suggest potential developmental phenotypic plasticity in caudal fin length, which increases more under low water flow during development. After settlement, growth was the only morphological or physiological trait that was associated with parental water flow, which was lower from parents under high flow, as was survival. These results give important insights into the parental contribution, both genetic and nongenetic, in determining early offspring phenotype and subsequent growth and survival. Our results also suggest that offspring may possess flexibility to cope with a wide range of local environments including those different from their parents. Overall, the findings of this study show the fitness consequences of living in different environments and the likely trade‐offs between parental and offspring fitness in a wild population.

Many insect species harbour heritable bacterial endosymbionts. Some facultative endosymbionts provide benefits to their hosts under certain environmental conditions. Facultative endosymbionts are expected to impose additional energetic expenditures to their host, reducing host fitness. While there is accumulating evidence in plant sucking insects that facultative endosymbionts reduce the fitness of their host under permissive conditions, no direct energy costs associated with facultative endosymbionts have been identified. Using the standard metabolic rate (SMR) as a measure of the energy cost of self-maintenance, we investigated whether two common facultative endosymbionts Hamiltonella defensa or Regiella insecticola increase the maintenance cost of the pea aphid Acyrthosiphon pisum which could translate into host fitness reduction ('compensation hypothesis'). In addition, we tested if there was a link between SMR and the aphid fitness and whether it depended on endosymbiont density and aphid energetic reserves. Finally, we measured SMR at different temperatures to assess the impact of suboptimal thermal conditions on physiological cost of endosymbionts. In the presence of facultative endosymbionts, aphids expressed generally a lower fitness and a higher SMR compared to uninfected ones, in accordance with the 'compensation hypothesis'. However, the SMR difference between infected and uninfected aphids tended to decrease with increasing temperature. Complex host genotype-by-symbiont genotype-by-temperature interactions on SMR were also revealed. Energetic budget of adult aphids appeared weakly influenced by the aphid genotype and endosymbiont species, suggesting that facultative endosymbionts primarily impact the consumption of energy resources rather than their acquisition. Density of facultative endosymbionts varied largely among aphid lines but was not associated with the fitness nor metabolic rate of aphids. This work supports the energy basis of facultative endosymbiont associated fitness costs and raises new questions about the effect of facultative endosymbionts on the energy metabolism of their host.

p-Toluene sulfonamide (p-TSA), a small molecular drug with antineoplastic activity is widely gaining interest from researchers because of its pharmacological activities. In this study, we explored the potential cardio and neural toxicity of p-TSA in sublethal concentrations by using zebrafish as an in vivo animal model. Based on the acute toxicity assay, the 96hr LC50 was estimated as 204.3 ppm, suggesting the overall toxicity of p-TSA is relatively low in zebrafish larvae. For the cardiotoxicity test, we found that p-TSA caused only a minor alteration in treated larvae after no overall significant alterations were observed in cardiac rhythm and cardiac physiology parameters, as supported by the results from expression level measurements of several cardiac development marker genes. On the other hand, we found that acute p-TSA exposure significantly increased the larval locomotion activity during the photomotor test while prolonged exposure (4 days) reduced the locomotor startle reflex activities in zebrafish. In addition, a higher respiratory rate and blood flow velocity was also observed in the acutely treated fish groups compared to the untreated group. Finally, by molecular docking, we found that p-TSA has a moderate binding affinity to skeletal muscle myosin II subfragment 1 (S1), ATPase activity, actin- and Ca2+-stimulated myosin S1 ATPase, and v-type proton ATPase. These binding interactions between p-TSA and proteins offer insights into the potential molecular mechanism of action of p-TSA on observed altered responses toward photo and vibration stimuli and minor altered vascular performance in the zebrafish larvae.

There is a scientific debate whether oxygen concentration may be a factor driving the pattern of size decrease at higher temperature. Central to this debate is the fact that oxygen availability relative to demand for living organisms decreases with increasing temperature. We examined whether rotifers Lecane inermis exposed to hypoxic conditions would evolve smaller sizes than rotifers exposed to normoxic conditions, using experimental evolution with the same fluctuating temperature but differentiated by three regimes of oxygen availability: normoxia, hypoxia throughout the whole thermal range, and hypoxia only at the highest temperature. Immediately after the six-month experiment (more than 90 generations), we tested the plasticity of size responses to temperature in three post-evolution groups, and we related these responses to fitness. The results show that normoxic rotifers had evolved significantly larger sizes than two hypoxic rotifer groups, which were similar in size. All three groups displayed similar plastic body size reductions in response to warming over the range of temperatures they were exposed to during the period of experimental evolution, but they showed different and complex responses at two temperatures below this range. Any type of plastic response to different temperatures resulted in a similar fitness pattern across post-evolution groups. We conclude that (i) these rotifers showed a genetic basis for the pattern of size decrease following evolution under both temperature-dependent and temperature-independent hypoxia; and (ii) plastic body size responds consistently to temperatures that are within the thermal range that the rotifers experienced during their evolutionary history, but responses become more noisy at novel temperatures, suggesting the importance of evolutionary responses to reliable environmental cues.

After being exposed to environmental stimuli during early developmental stages, some organisms may gain or weaken physiological regulating abilities, which would have long-lasting effects on their performance. Environmental hypoxia events can have significant effects on marine organisms, but for breeding programs and other practical applications, it is important to further explore the long-term physiological effects of early hypoxia exposure in economically significant species. In this study, the Pacific abalone Haliotis discus hannai was exposed to moderate hypoxia (∼4 mg/L) from zygote to trochophora, and the assessments of hypoxia tolerance were conducted on the grow-out stage. The results revealed that juvenile abalones exposed to hypoxia at the early development stages were more hypoxia-tolerant but with slower weight growth, a phenomenon called the trade-off between growth and survival. These phenotypic effects driven by the hypoxia exposure were explained by strong selection of genes involved in signal transduction, autophagy, apoptosis, and hormone regulation. Moreover, long non-coding RNA regulation plays an important role modulating carry-over effects by controlling DNA replication and repair, signal transduction, myocardial activity, and hormone regulation. This study revealed that the ability to create favorable phenotypic differentiation through genetic selection and/or epigenetic regulation is important for the survival and development of aquatic animals in the face of rapidly changing environmental conditions.

Competition and metabolism should be linked. Intraspecific variation in metabolic rates and, hence, resource demands covary with competitive ability. The effects of metabolism on conspecific interactions, however, have mostly been studied under laboratory conditions. We used a trait‐specific response‐surface design to test for the effects of metabolism on pairwise interactions of the marine colonial invertebrate, Bugula neritina in the field. Specifically, we compared the performance (survival, growth, and reproduction) of focal individuals, both in the presence and absence of a neighbor colony, both of which had their metabolic phenotype characterized. Survival of focal colonies depended on the metabolic phenotype of the neighboring individual, and on the combination of both the focal and neighbor colony metabolic phenotypes that were present. Surprisingly, we found pervasive effects of neighbor metabolic phenotypes on focal colony growth and reproduction, although the sign and strength of these effects showed strong microenvironmental variability. Overall, we find that the metabolic phenotype changes the strength of competitive interactions, but these effects are highly contingent on local conditions. We suggest future studies explore how variation in metabolic rate affects organisms beyond the focal organism alone, particularly under field conditions.

Exaggerated secondary sexual characteristics are apparently costly and seem to defy natural selection. This conundrum promoted the theory of sexual selection. Accordingly, exaggerated secondary sexual characteristics might be ornaments on which female choice is based and/or armaments used during male–male competition. Males of many cichlid fish species, including the adaptive radiation of Nicaraguan Midas cichlids, develop a highly exaggerated nuchal hump, which is thought to be a sexually selected trait. To test this hypothesis, we conducted a series of behavioral assays in F2 hybrids obtained from crossing a species with a relatively small hump and one with an exaggerated hump. Mate‐choice experiments showed a clear female preference for males with large humps. In an open‐choice experiment with limited territories, couples including large humped males were more successful in acquiring these territories. Therefore, nuchal humps appear to serve dual functions as an ornament for attracting mates and as an armament for direct contest with rivals. Although being beneficial in terms of sexual selection, this trait also imposes fitness costs on males possessing disproportionally large nuchal humps since they exhibit decreased endurance and increased energetic costs when swimming. We conclude that these costs illustrate trade‐offs associated with large hump size between sexual and natural selection, which causes the latter to limit further exaggeration of this spectacular male trait.

As coral reefs face warming oceans and increased coral bleaching, a whitening of the coral due to loss of microalgal endosymbionts, the possibility of evolutionary rescue offers some hope for reef persistence. In tightly linked mutualisms, evolutionary rescue may occur through evolution of one or both partners. Many obligate mutualisms are composed of relatively small, fast-growing symbionts with greater potential to evolve on ecologically relevant time scales than their relatively large, slower growing hosts. We examined the potential for adaptation of the upside-down sea jelly Cassiopea xamachana to increased temperature via evolution of its microalgal endosymbiont, Symbiodinium microadriaticum. We quantified trait variation among five algal genotypes in response to three temperatures and fitness of hosts infected with each genotype. All genotypes had positive growth rates at each temperature, but rates of respiration and photosynthesis decreased with increasing temperature. Responses varied among genotypes but were unrelated to genetic similarity. The effect of temperature on asexual reproduction and the timing of development in the host also depended on the genotype of the symbiont. Natural selection could favor different algal genotypes at different temperatures, affecting host fitness. This eco-evolutionary interaction may be a critical component of understanding species resilience in increasingly stressful environments.

The peroxisome proliferator-activated receptor γ coactivator 1 α (PGC-1α) is central to the regulation of cellular and mitochondrial energy homeostasis in mammals, but its role in other vertebrates remains unclear. Indeed, previous work suggests extensive structural and functional divergence of PGC-1α in teleosts but this remains to be directly tested. Here, we describe the initial characterization of heterozygous PGC-1α mutant zebrafish lines created by CRISPR-Cas9 disruptions of an evolutionarily conserved regulatory region of the PGC-1α proximal promoter. Using qPCR, we confirmed the disruption of PGC-1α gene expression in striated muscle, leading to a simultaneous fourfold increase in mixed skeletal muscle PGC-1α mRNA levels and an opposite fourfold downregulation in cardiac muscle. In mixed skeletal muscle, most downstream effector genes were largely unaffected yet two mitochondrial lipid transporters, carnitine palmitoyltransferase-1 and -2, were strongly induced. Conversely, PGC-1α depression in cardiac muscle reduced the expression of several transcriptional regulators (estrogen-related receptor α, nuclear respiratory factor 1, and PGC-1β) without altering metabolic gene expression. Using high-resolution respirometry, we determined that white muscle exhibited increased lipid oxidative capacity with little difference in markers of mitochondrial abundance. Finally, using whole animal intermittent respirometry, we show that mutant fish exhibit a twofold higher basal metabolism than their wild-type counterparts. Altogether, this new model confirms a central but complex role for PGC-1α in mediating energy utilization in zebrafish, and we propose its use as a valuable tool to explore the intricate regulatory pathways of energy homeostasis in a popular biomedical model.

Obesity is a worldwide public health problem with increasing prevalence and affects 80% of diabetes mellitus type 2 cases. Zebrafish (Danio rerio) is an established model organism for studying obesity and diabetes including diabetic microvascular complications. We aimed to determine whether physical activity is an appropriate tool to examine training effects in zebrafish and to analyse metabolic and transcriptional processes in trained zebrafish. A 2- and 8-week experimental training phase protocol with adult zebrafish in a swim tunnel system was established. We examined zebrafish basic characteristics before and after training such as body weight, body length and maximum speed and considered overfeeding as an additional parameter in the 8-weeks training protocol. Ultimately, the effects of training and overfeeding on blood glucose, muscle core metabolism and liver gene expression using RNA-Seq were investigated. Zebrafish maximum speed was correlated with body length and was significantly increased after 2 weeks of training. Maximum swim speed further increased after 8 weeks of training in both the normal-fed and the overfed groups, but training was found not to be sufficient in preventing weight gain in overfed fish. Metabolome and transcriptome profiling in trained fish exhibited increased blood glucose levels in the short-term and upregulated energy supply pathways as well as response to oxidative stress in the long-term. In conclusion, swim training is a valuable tool to study the effects of physical activity in zebrafish, which is accompanied by metabolic and transcriptional adaptations.

SURF1 deficiency (OMIM # 220110) causes Leigh syndrome (LS, OMIM # 256000), a mitochondrial disorder typified by stress-induced metabolic strokes, neurodevelopmental regression and progressive multisystem dysfunction. Here, we describe two novel surf1−/− zebrafish knockout models generated by CRISPR/Cas9 technology. While gross larval morphology, fertility, and survival into adulthood appeared unaffected, surf1−/− mutants manifested adult-onset ocular anomalies and decreased swimming activity, as well as classical biochemical hallmarks of human SURF1 disease, including reduced complex IV expression and enzymatic activity and increased tissue lactate. surf1−/− larvae also demonstrated oxidative stress and stressor hypersensitivity to the complex IV inhibitor, azide, which exacerbated their complex IV deficiency, reduced supercomplex formation, and induced acute neurodegeneration typical of LS including brain death, impaired neuromuscular responses, reduced swimming activity, and absent heartrate. Remarkably, prophylactic treatment of surf1−/− larvae with either cysteamine bitartrate or N-acetylcysteine, but not other antioxidants, significantly improved animal resiliency to stressor-induced brain death, swimming and neuromuscular dysfunction, and loss of heartbeat. Mechanistic analyses demonstrated cysteamine bitartrate pretreatment did not improve complex IV deficiency, ATP deficiency, or increased tissue lactate but did reduce oxidative stress and restore glutathione balance in surf1−/− animals. Overall, two novel surf1−/− zebrafish models recapitulate the gross neurodegenerative and biochemical hallmarks of LS, including azide stressor hypersensitivity that was associated with glutathione deficiency and ameliorated by cysteamine bitartrate or N-acetylcysteine therapy.

Nanoparticles are man-made materials defined as materials smaller than 100 nm in at least one dimension. Titanium oxide nanoparticles are of great interest because of their extensive use in self-care products. There is a lack of nanotoxicological studies of TiO2 NPs in benthic organisms to have evidence about the effects of these pollutants in freshwater ecosystems. Atya lanipes is a scraper/filter that can provide a good nanotoxicological model. This study aims to determine how the TiO2 NPs can develop a toxic effect in the larvae of the Atya lanipes shrimp and to document lethal and sublethal effects after acute exposures to TiO2 NP suspensions of: 0.0, 1.0, 10.0, 50.0, 100.0, and 150.0 mg/L. The results show that early exposure to TiO2 NPs in Atya lanipes creates an increase in mortality at 48 and 72 h exposures, hypoactivity in movements, and morphological changes, such as less pigmentation and the presence of edema in exposed larvae. In conclusion, TiO2 NPs are toxic contaminants in the larval stage of the Atya lanipes. It is necessary to regulate these nanoparticles for purposes of the conservation of aquatic biodiversity, especially for freshwater shrimp larvae and likely many other larvae of filter-feeding species.

The speckled peacock bass Cichla temensis is a popular sport and food fish that generates substantial angling tourism and utilitarian harvest within its range. Its popularity and value make this species important for management and a potential aquaculture candidate for both fisheries enhancement and food fish production. However, little is known of optimal physiochemical conditions in natural habitats, which also are important for the development of hatchery protocols for handling, spawning and grow‐out. Speckled peacock bass have been documented to have high sensitivity to extreme temperatures, but the metabolic underpinnings have not been evaluated. In this study, the effects of temperature (25, 30 and 35°C) on the standard metabolic rate (SMR) and lower dissolved oxygen tolerance (LDOT) of juvenile speckled peacock bass (mean ± standard error total length 153 ± 2 mm and wet weight 39.09 ± 1.37 g) were evaluated using intermittent respirometers after an acclimation period of 2 weeks. Speckled peacock bass had the highest SMR at 35°C (345.56 ± 19.89 mgO 2 kg −1 h −1 ), followed by 30°C (208.16 ± 12.45 mgO 2 kg −1 h −1 ) and 25°C (144.09 ± 10.43 mgO 2 kg −1 h −1 ). Correspondingly, the Q 10, or rate of increase in aerobic metabolic rate (MO 2 ) relative to 10°C, for 30–35°C was also greater (2.76) than from 25 to 30°C (2.08). Similarly, speckled peacock bass were the most sensitive to hypoxia at the warmest temperature, with an LDOT at p O 2 of 90 mmHg (4.13 mg l −1 ) at 35°C compared to p O 2 values of 45 mmHg (2.22 mg l −1 ) and 30 mmHg (1.61 mg l −1 ) at 30 and 25°C, respectively. These results indicate that speckled peacock bass are sensitive to temperatures near 35°C, therefore we recommend managing and rearing this species at 25–30°C.

Total dissolved gas (TDG) supersaturation caused by flood discharge water is becoming a serious environmental problem that threatens the survival of fish. The swimming ability of fish may be influenced by TDG supersaturation. To investigate the effects of continuous exposure to TDG supersaturation on fish swimming ability, we measured the critical swimming speed ( U crit ) and burst swimming speed ( U burst ) of grass carp continuously exposed to TDG supersaturation. The U crit values of grass carp were 6.34–3.68 body length per second (BL/s) at 100%, 105%, 110%, 115%, 120%, 125%, 130% and 135% TDG, while the U burst values were 10.2–8.96 BL/s at these TDG levels. The swimming ability ( U crit and U burst ) of grass carp decreased with increasing TDG levels and was significantly decreased at higher TDG levels (>120%). A swimming ability recovery test was used to investigate the effects of recovery on the swimming ability of grass carp continuously exposed to TDG supersaturation. When grass carp experienced exposures of 115%, 120%, 125%, 130% and 135% TDG, the recovery ratios of U crit were 76%–82% and 77%–86% after recovering for 1 and 2 h, respectively, in freshwater (100% TDG). The recovery ratios of U burst of grass carp were 84%–98% and 95%–97% under the same recovery conditions and TDG levels. The results showed that the recovery ratios of both U crit and U burst increased with the extension of the recovery time. The swimming ability of grass carp provided with a 2‐h recovery time recovered almost completely.

Hermit crabs (Paguroidea; Latreille 1802) offer great opportunities to study animal behaviour and physiology. However, the animals’ size and sex cannot be determined when they are inside their shell; information crucial to many experimental designs. Here, we tested the effects of the two most common procedures used to make crabs leave their shells: heating the shell apex and cracking the shell with a bench press. We compared the effects of each of the two procedures on the metabolic rate, hiding time, and duration of the recovery time relative to unmanipulated hermit crabs. The hermit crabs forced to abandon their shell through heating increased their respiratory rate shortly after the manipulation (1 h) and recovered their metabolic rate in less than 24 h, as occurs in individuals suddenly exposed to high temperatures in the upper-intertidal zone. Hermit crabs removed from their shells via cracking spent more time hiding in their new shells; this effect was evident immediately after the manipulation and lasted more than 24 h, similar to responses exhibited after a life-threatening predator attack. Both methods are expected to be stressful, harmful, or fear-inducing; however, the temperature required to force the crabs to abandon the shell is below the critical thermal maxima of most inhabitants of tropical tide pools. The wide thermal windows of intertidal crustaceans and the shorter duration of consequences of shell heating compared to cracking suggest heating to be a less harmful procedure for removing tropical hermit crabs from their shells.

Despite the importance of Atlantic salmon in marine aquaculture production systems, remarkably little is known about the effects of hydrogen sulfide (H2S) on the physiology of the species. In recent years, mass mortalities of Atlantic salmon have been reported in recirculating aquaculture systems (RAS) due to acute H2S exposure. This highlights the importance of obtaining a better understanding of tolerance thresholds and metabolic responses to this toxic gas. The toxicity of H2S is exerted at the level of the mitochondria, where impairment of the enzyme cytochrome c oxidase inhibits cellular respiration. Because H2S depresses oxygen uptake (MO2), intermittent flow-through respirometry, a common method for assessing the metabolic response to various stressors in fishes, is a suitable method to determine concentration thresholds for when H2S affects the metabolism of Atlantic salmon. During exposure trials, 3 size groups (range ?100-500 g) of fish were acclimated to control conditions to obtain baseline measurements, whereafter they were exposed to progressively increasing H2S concentrations (0.53 ± 0.14 µM h-1) until MO2 decreased below the standard metabolic rate or loss of equilibrium occurred, which we considered to be the critical H2S concentration (H2Scrit). Fish were then allowed to recover in H2S free water to determine the excess oxygen consumption (EOC) following H2S exposure. The results show that Atlantic salmon have a lower tolerance to H2S than previously estimated, with a mean H2Scrit of 1.78 ± 0.39 µM H2S, which was independent of size. During recovery, the estimated EOC greatly exceeded the accumulated oxygen deficit (DO2) in all groups, and the small salmon had a significantly larger EOC. While the magnitude of the EOC was greater for small salmon, it did not differ in duration (recovery time) among the different sizes of fish. The larger EOC showed that H2S exposure had a greater effect on the recovery phase of the small salmon, and exposure to H2S may leave the fish more vulnerable to other stressors post-exposure. This study provides specific values that underline the sensitivity of Atlantic salmon to acute H2S exposure and emphasizes the importance of the aquaculture industry to implement mitigating strategies for the occurrence of H2S at production facilities.

In the developing embryos of egg-laying vertebrates, O 2 flux takes place across a fixed surface area of the eggshell and the chorioallantoic membrane. In the case of crocodilians, the developing embryo may experience a decrease in O 2 flux when the nest becomes hypoxic, which may cause compensatory adjustments in blood O 2 transport. However, whether the switch from embryonic to adult hemoglobin isoforms (isoHbs) plays some role in these adjustments is unknown. Here, we provide a detailed characterization of the developmental switch of isoHb synthesis in the American alligator, Alligator mississippiensis. We examined the in vitro functional properties and subunit composition of purified alligator isoHbs expressed during embryonic developmental stages in normoxia and hypoxia (10% O 2 ). We found distinct patterns of isoHb expression in alligator embryos at different stages of development, but these patterns were not affected by hypoxia. Specifically, alligator embryos expressed two main isoHbs: HbI, prevalent at early developmental stages, with a high O 2 affinity and high ATP sensitivity, and HbII, prevalent at later stages and identical to the adult protein, with a low O 2 affinity and high CO 2 sensitivity. These results indicate that whole blood O 2 affinity is mainly regulated by ATP in the early embryo and by CO 2 and bicarbonate from the late embryo until adult life, but the developmental regulation of isoHb expression is not affected by hypoxia exposure.

Conservation of species facing environmental change requires an understanding of interpopulation physiological variation. However, physiological data are often scarce and therefore pooled across populations and species, erasing potentially important variability between populations. Interpopulation variation in thermal physiology has been observed within the Salmonidae family, although it has not been associated with seasonally distinct migratory phenotypes (i.e., seasonal runs). To resolve whether thermal physiology is associated with life-history strategy, we acclimated four Sacramento River juvenile Chinook salmon (Oncorhynchus tshawytscha) populations (Coleman fall-run, Feather River fall-run, Feather River spring-run, and Sacramento River winter-run) exhibiting different seasonal migratory phenotypes (fall-, spring-, and winter-run), at 11, 16, and 20 °C and assessed variation in growth rate, critical thermal maxima, and temperature-dependent metabolic traits. We identified population differences in the physiological parameters measured and found compelling evidence that the critically endangered and endemic Sacramento River winter-run Chinook population exhibits thermal physiology associated with its early-migration life-history strategy. Acclimation to warm temperatures limited the growth and metabolic capacity of winter-run Chinook salmon, highlighting the risk of future environmental warming to this endemic population.

Morphological effects of crude oil exposure on early development in fishes have been well documented, but crude oil's metabolic effects and when in early development these effects might be most prominent remains unclear. We hypothesized that zebrafish (Danio rerio) exposed to crude oil as a high energy water accommodated fraction (HEWAF) would show increased routine oxygen consumption (?O2) and critical oxygen tension (PCrit) and this effect would be dependent upon day of HEWAF exposure, revealing critical windows of development for exposure effects. Zebrafish were exposed to 0%, 10%, 25%, 50% or 100% HEWAF for 24 h during one of the first six days post-fertilization (dpf). Survival rate, body mass, routine ?O2, and PCrit were then measured at 7 dpf. Survival rate and especially body mass were both decreased based on both exposure concentration and day of crude oil exposure, with the largest decrease when HEWAF exposure occurred at 3 dpf. HEWAF effects on routine ?O2 also differed depending upon exposure day. The largest effect occurred at 3 dpf, when ?O2 increased significantly by ~60% from 10.1 ± 0.8 µmol O2/g/h compared to control group value of 6.3 ± 0.4 µmol O2/g/h. No significant effects of HEWAF exposure on any day were evident for PCrit (85 ± 4 mmHg in the control population). Overall, the main effects on body mass and ?O2 measured at 7 dpf occurred when HEWAF exposures occurred at ~3 dpf. This critical window for metabolism in zebrafish larvae coincides with time of hatching, which may represent an especially vulnerable period in development.

Chronic elevation of circulating cortisol is known to have deleterious effects on fish, but information about the consequences of prolonged cortisol elevation on the metabolism of fish is scarce. To test the effects of chronic cortisol elevation on the aerobic performance of rainbow trout, we examined how two severities of chronically elevated plasma cortisol levels affected the oxygen uptake during rest and after exhaustive exercise using a high (HC) and a medium cortisol (MC) treatment. High cortisol doses significantly affected standard (SMR) and maximum metabolic rates (MMR) compared to control fish. In comparison, the medium cortisol treatment elevated maximum metabolic rates (MMR) but did not significantly influence SMR compared to a sham group (S) and control group (C). The medium cortisol treatment resulted in a significantly increased metabolic scope due to an elevation of MMR, an effect that was abolished in the HC group due to co-occuring elevations in SMR. The elevated SMR of the HC-treated fish could be explained by increased in vitro oxygen uptake rates (MO 2 ) of specific tissues, indicating that the raised basal metabolism was caused, in part, by an increase in oxygen demand of specific tissues. Haematological results indicated an increased reliance on anaerobic metabolic pathways in cortisol-treated fish under resting conditions.

Increasing ocean temperatures have been demonstrated to have a range of negative impacts on coral reef fishes. However, despite a wealth of studies of juvenile/adult reef fish, studies of how early developmental stages respond to ocean warming are limited. As overall population persistence is influenced by the development of early life stages, detailed studies of larval responses to ocean warming are essential. Here, in an aquaria-based study we investigate how temperatures associated with future warming and present-day marine heatwaves (+3 °C) impact the growth, metabolic rate, and transcriptome of 6 discrete developmental stages of clownfish larvae (Amphiprion ocellaris). A total of 6 clutches of larvae were assessed, with 897 larvae imaged, 262 larvae undergoing metabolic testing and 108 larvae subject to transcriptome sequencing. Our results show that larvae reared at +3 °C grow and develop significantly faster and exhibit higher metabolic rates than those in control conditions. Finally, we highlight the molecular mechanisms underpinning the response of larvae from different developmental stages to higher temperatures, with genes associated with metabolism, neurotransmission, heat stress and epigenetic reprogramming differentially expressed at +3 °C. Overall, these results indicate that clownfish development could be altered under future warming, with developmental rate, metabolic rate, and gene expression all affected. Such changes may lead to altered larval dispersal, changes in settlement time and increased energetic costs.

Dissolved oxygen (DO) saturation in the water is a crucial factor in fish performance and welfare. Exposure to low DO can affect a wide variety of functions such as metabolic rate and physiological adaptations including hematological, hormonal, biochemical and osmoregulatory alterations in blood and plasma. In the present study European sea bass, Dicentrarchus labrax and gilthead seabream, Sparus aurata were reared for approximately 3 months at different levels of DO saturation, namely 40–60%, 60–80% and 80–100% at a temperature of 26.5 °C. Both species showed reduced performance at the lowest DO regime compared to the highest, as well as a reduced aerobic capacity as indicated by the aerobic scope and the post-stress lactate concentrations. Blood samples were collected before and after exposure to an acute chasing and confinement stress. Hematocrit, hemoglobin and mean corpuscular hemoglobin concentration were affected by DO saturation in Dicentrarchus. labrax but not in parus aurata. Cortisol levels in fish plasma and scales were similar between different DO regimes in both species, while in plasma it was increased after exposure to acute stress. Moreover, in both species post-stress levels of osmolality and lactate were higher at the lowest DO examined, indicative of osmoregulatory imbalance. Based on multivariate analysis glucose and lactate were highly affected by acute stress in low oxygen saturation in D. labrax, while osmolality was mostly affected in S. aurata. Overall, this study provided a detailed insight in the effects of DO in the physiology of D. labrax and S. aurata.

The interactive effects of ocean acidification (OA) and copper (Cu) ions on the mussel Mytilus galloprovincialis are not well understood. The underlying mechanisms also remain obscure. In this study, individuals of M. galloprovincialis were exposed for 28 days to 25 µg/L and 50 µg/L Cu ions at two pH levels (ambient level - pH 8.1; acidified level - pH 7.6). The mussels were then monitored for 56 days to determine their recovery ability. Physiological parameters (clearance rate and respiration rate), oxidative stress and neurotoxicity biomarkers (activities of superoxide dismutase, lipid peroxidation, catalase, and acetylcholinesterase), as well as the recovery ability of these parameters, were investigated in two typical tissues (i.e., gills and digestive glands). Results showed that (1) OA affected the bioconcentration of Cu in the gills and digestive glands of the mussels; (2) both OA and Cu can lead to physiological disturbance, oxidative stress, cellular damage, energy metabolism disturbance, and neurotoxicity on M. galloprovincialis; (3) gill is more sensitive to OA and Cu than digestive gland; (4) Most of the biochemical and physiological alternations caused by Cu and OA exposures in M. galloprovincialis can be repaired by the recovery experiments; (5) integrated biomarker response (IBR) analysis demonstrated that both OA and Cu ions exposure caused survival stresses to the mussels, with the highest effect shown in the co-exposure treatment. This study highlights the necessity to include OA along with pollutants in future studies to better elucidate the risks of ecological perturbations. The work also sheds light on the recovery of marine animals after short-term environmental stresses when the natural environment has recovered.

Intrinsic and extrinsic inhibition of neuronal regeneration obstruct spinal cord (SC) repair in mammals. In contrast, adult zebrafish achieve functional recovery after complete SC transection. While studies of innate SC regeneration have focused on axon regrowth as a primary repair mechanism, how local adult neurogenesis affects functional recovery is unknown. Here, we uncover dynamic expression of zebrafish myostatin b (mstnb) in a niche of dorsal SC progenitors after injury. mstnb mutants show impaired functional recovery, normal glial and axonal bridging across the lesion, and an increase in the profiles of newborn neurons. Molecularly, neuron differentiation genes are upregulated, while the neural stem cell maintenance gene fgf1b is downregulated in mstnb mutants. Finally, we show that human fibroblast growth factor 1 (FGF1) treatment rescues the molecular and cellular phenotypes of mstnb mutants. These studies uncover unanticipated neurogenic functions for mstnb and establish the importance of local adult neurogenesis for innate SC repair.

Na+,K+-ATPase (NKA) a-subunit 1a (a1a) and 1b (a1b) gene expressions in the gills are changeable in response to ambient salinity in a few salmonids. In this study, the expressions were compared among ambient salinities and used to infer sea entry migration of chum salmon Oncorhynchus keta fry. The expression of a1a decreased from the 2 days after seawater (SW) transfer from freshwater (FW) and was significantly lower in SW-acclimated fry than that in FW-fry. On the other hand, the expression of a1b peaked on the first to second day after SW transfer and then settled to a level 2-fold higher than in FW-fry. In fry caught in the waterfronts of the beaches, the expression levels were quite similar to those on the first and second days after SW transfer, whereas, in fry caught off beach, the expressions were identical to those of SW-acclimated fry. These suggest that fry adapt to SW with moving along the shoal in the bay, and move to off beach after completing SW adaptation. One of the physiological significances in a usage of waterfront may be to transform the gills to SW type. Only fry on the 2 days after SW transfer failed to exhibit condition factor-dependency of burst swimming, probably due to physiological perturbation, which may be related to poor predation avoidance. The physiological approach used in this study inferred sea entry migration of fry; furthermore, it shows the possible significance of adaptation to SW in the shoal is to reduce predation risk.

Climate warming is a threat of imminent concern that may exacerbate the impact of nitrate pollution on fish fitness. These stressors can individually affect the aerobic capacity and stress tolerance of fish. In combination, they may interact in unexpected ways where exposure to one stressor may heighten or reduce the resilience to another stressor and their interactive effects may not be uniform across species. Here, we examined how nitrate pollution under a warming scenario affects the aerobic scope (AS), and the hypoxia and heat stress susceptibility of a generally tolerant fish species, common carp Cyprinus carpio. We used a 3 × 2 factorial design, where fish were exposed to one of three ecologically relevant levels of nitrate (0, 50, or 200 mg NO 3 - L -1 ) and one of two temperatures (18 °C or 26 °C) for 5 weeks. Warm acclimation increased the AS by 11% due to the maintained standard metabolic rate and increased maximum metabolic rate at higher temperature, and the AS improvement seemed greater at higher nitrate concentration. Warm-acclimated fish exposed to 200 mg NO 3 - L -1 were less susceptible to acute hypoxia, and fish acclimated at higher temperature exhibited improved heat tolerance (critical thermal maxima, CTMax) by 5 °C. This cross-tolerance can be attributed to the hematological results including maintained haemoglobin and increased haematocrit levels that may have compensated for the initial surge in methaemoglobin at higher nitrate exposure.

The cardiovascular performance of salmonids in aquaculture can be impaired by acute climate warming, posing risks for fish survival. Exercise training and functional feeds have been shown to be cardioprotective in mammals but their action on the fish heart and its upper thermal performance has not been studied. To investigate this, rainbow trout were trained at a moderate water velocity of 1 body length per second (bl s -1 ) for 6 h per day, either alone or in combination with one of two functional feed-supplements, allicin and fucoidan. After 6 weeks of exercise training and feeding, maximum heart rate and the temperature coefficient of heart rate were significantly higher in the trained fish as compared to untrained ones. There was a slight increase in hematocrit in trained control fish reared on a normal diet (TC group) compared to untrained fish fed with the same diet (CC). This implies that exercise training enhanced oxygen delivery to trout tissues via an increase of cardiac blood flow in warm water. However, cardiac thermal tolerance was not affected by exercise training or feeding, except from the temperature of peak heart rate which was higher in the trained group fed with fucoidan supplement (TF) as compared to the untrained group fed with same diet (CF). Allicin supplement caused a significant reduction in the maximum heart rate and the temperature coefficient of heart rate, especially in trained fish, while fucoidan supplement did not cause any effect on heart rate. No differences were observed in growth performance among groups. However, fish fed with fucoidan-supplemented diet had a slight reduction in feed conversion efficiency. We suggest further investigations to understand the antagonistic effect of allicin supplemental feeding and exercise training on cardiovascular performance. More studies are also required to investigate if other exercise training intensities could increase cardiac thermal tolerance.

The use of insect meal in aquafeed formulations has recently gained attention. Detailed knowledge about the inclusion levels for pikeperch ( Sander lucioperca ), a promising candidate for intensive aquaculture in Europe remains, however, fragmented. In the present study, 4 isoproteic (45% dry matter) and isoenergetic (21 MJ/kg) diets were formulated, including a control diet (H0) containing 30% fishmeal (FM) on an as-fed basis and the other 3 diets in which FM protein was replaced by defatted black soldier fly ( Hemetia illucens ) meal (HIM) at 25%, 50%, and 100% (diet abbreviation H9, H18 and H36, corresponding to an inclusion level of 9%, 18% and 36%, respectively). The feeding trial was performed in triplicate groups of 50 juvenile pikeperch (mean weight, 68.7 g) fed with experimental diets for 84 d during which the growth performance, nutrient digestibility, fillet quality and economic and environmental sustainability of rearing pikeperch were evaluated. Our findings indicated that pikeperch in H0, H9, and H18 groups displayed better results regarding growth performance indices, except for survival rate where no significant difference among groups was recorded ( P = 0.642). A significantly lower organ-somatic index, including hepatosomatic, viscerosomatic and perivisceral fat index, was found in fish in H18 groups than other groups ( P < 0.05). Inclusion of HIM affected the digestibility of the nutrients and resulted in an almost linear reduction in the apparent digestibility coefficient of dry matter and protein. Concerning the fillet quality, dietary HIM negatively affected the protein and ash contents of the fish fillets, while the crude fat remained unchanged. Dietary HIM did not significantly modify total saturated, monounsaturated and polyunsaturated fatty acids in the fillets of fed pikeperch ( P > 0.05) but did reduce total n-3 fatty acids ( P = 0.001) and increased total n-6 ( P < 0.001). Increasing inclusion levels of HIM reduced the environmental impacts associated with fish in-to-fish out ratio but entailed heavy burdens on energy use and eutrophication. Low and moderate inclusion levels of HIM did not negatively affect land use and water use compared to an HIM-free diet ( P > 0.05). The addition of HIM at a level as low as 9% elicited a similar carbon footprint to that of the control diet. The economic conversion ratio and economic profit index were negatively affected at increased insect meal inclusion levels. This study has shown that the incorporation of HIM in feed formulations for pikeperch is feasible at inclusion levels of 18% without adverse effects on growth performance parameters. The feasibility also highlighted the environmental benefits associated with land use and marine resources required to produce farmed fish.

Oculocutaneous albinism is the result of a combination of homozygous recessive mutations that block the synthesis of the tyrosine and melatonin hormones. This disability is associated with physiological limitations, e.g., visual impairment expressed by lower visual acuity and movement perception, and eventually leads to acrophobia and/or photophobia, suggesting a potentially higher stress level associated with the behavioral responses of individuals with albinism to external stimuli compared to their pigmented conspecifics. However, in fish, differences in behavioral and/or physiological responses and stress levels between these phenotypes have been poorly documented. While acoustic perception of albino individuals is well known, the use of olfactory sensors for social communication, e.g., for the preference for familiar conspecifics, remains poorly understood. We performed two laboratory experiments with albino and pigmented European catfish Silurus glanis to observe: i) their behavioral and physiological responses to short-term stress induced by a combination of air exposure and novel environmental stressors and ii) their ability to use odor keys to recognize of familiar conspecifics and the influence of lateralization on this preference. In response to stress stimuli, albino fish showed higher movement activities and ventilatory frequencies and more often changed their swimming directions compared to their pigmented conspecifics. Blood plasma analysis showed significantly higher values of stress-, deprivation-, and emotional arousal-associated substances, e.g., glucose and lactate, as well as of substances released during intensive muscle activity of hyperventilation and tissue hypoxia, e.g., hemoglobin, mean corpuscular hemoglobin, erythrocytes, and neutrophil granulocytes. A preference test between environments with and without scented water showed the preference by both albino and pigmented catfish for environments with scent of familiar conspecifics, and both groups of fish displayed left-side lateralization associated with the observation of conspecifics and group coordination. The results tended to show higher physiological and behavioral responses of albinos to stress stimuli compared to the responses of their pigmented conspecifics, but the uses of olfactory sensors and lateralization were not differentiated between the two groups.

The Alaska blackfish ( Dallia pectoralis ) is a facultative air-breather endemic to northern latitudes where it remains active in winter under ice cover in cold hypoxic waters. To understand the changes in cellular Ca 2+ cycling that allow the heart to function in cold hypoxic water, we acclimated Alaska blackfish to cold (5 °C) normoxia or cold hypoxia (2.1-4.2 kPa; no air access) for 5-8 weeks. We then assessed the impact of the acclimation conditions on intracellular Ca 2+ transients (Δ[Ca 2+ ] i ) of isolated ventricular myocytes and contractile performance of isometrically-contracting ventricular strips. Measurements were obtained at various contractile frequencies (0.2-0.6 Hz) in normoxia, during acute exposure to hypoxia, and reoxygenation at 5 °C. The results show that hypoxia-acclimated Alaska blackfish compensate against the depressive effects of hypoxia on excitation-contraction coupling by remodelling cellular Δ[Ca 2+ ] i to maintain ventricular contractility. When measured at 0.2 Hz in normoxia, hypoxia-acclimated ventricular myocytes had a 3.8-fold larger Δ[Ca 2+ ] i peak amplitude with a 4.1-fold faster rate of rise, compared to normoxia-acclimated ventricular myocytes. At the tissue level, maximal developed force was 2.1-fold greater in preparations from hypoxia-acclimated animals. However, maximal attainable contraction frequencies in hypoxia were lower in hypoxia-acclimated myocytes and strips than preparations from normoxic animals. Moreover, the inability of hypoxia-acclimated ventricular myocytes and strips to contract at high frequency persisted upon reoxygenation. Overall, the findings indicate that hypoxia alters aspects of Alaska blackfish cardiac myocyte Ca 2+ cycling, and that there may be consequences for heart rate elevation during hypoxia, which may impact cardiac output in vivo.

Ocean deoxygenation is a pressing concern in the face of climate change. In response to prolonged hypoxia, fishes have demonstrated the ability to dynamically regulate hemoglobin (Hb) expression to enhance oxygen (O2) uptake. Here, we examined hypoxia-inducible Hb expression in red drum (Sciaenops ocellatus) and the subsequent implications on Hb-O2 binding affinity and aerobic scope. Fish were acclimated to 30 % air saturation for 1 d, 4 d, 8 d, 2 w, or 6 w, and red blood cells were collected for gene expression and biochemical profiling. Hypoxia acclimation induced significant up-regulation of one Hb subunit isoform (hba 2) relative to control by 4 d with consistent upregulation thereafter. Hematocrit increased in hypoxia, with no changes in the allosteric modulator [NTP] at any time point. Changes in Hb expression co-occurred with a reduced Root effect (~26 % in normoxia, ~14 % in hypoxia) at a physiologically relevant pH while increasing O2 binding affinity (i.e., lower P50). These changes correlated with increased maximum metabolic rate and aerobic scope relative to controls when fish were tested in hypoxia. These results demonstrate an important role for Hb multiplicity in improving O2 affinity and maximizing respiratory performance in hypoxia.

Intertidal animals experience cycles of tidal emersion from water and are vulnerable to copper (Cu) exposure due to anthropogenic toxicant input into marine waters. Both emersion and Cu toxicity can cause damage to physiological processes like aerobic metabolism, ammonia excretion, and osmoregulation, but the interactions of the combination of these two stressors on marine invertebrates are understudied. Mixed effects of 96 h of low and high Cu exposure (20 and 200 µg/L) followed by 6 h of tidal emersion were evaluated on the intertidal sea cucumber Cucumaria miniata. The respiratory tree accumulated the highest concentrations of Cu, followed by the introvert retractor muscle, body wall, and coelomic fluid. Emersion affected accumulation of Cu, perhaps by inhibiting excretion. 200 µg/L of Cu increased lactate production in the respiratory tree, indicative of damaged aerobic metabolism. Cu diminished ammonia excretion, but emersion increased oxygen uptake and ammonia excretion upon re-immersion. The combination of the two stressors did not have any interactive effects on metabolism or ammonia excretion. Neither Cu exposure nor emersion altered ion (sodium, potassium, calcium, magnesium) content of the coelomic fluid. Overall, results of this study suggest that Cu exposure does not alter C. miniata's high tolerance to emersion, and some potential strategies that this species uses to overcome environmental stress are illuminated.

Standard metabolic rate (SMR) and maximum metabolic rate (MMR) were determined for Nile tilapia acclimated to six different experimental temperatures from 18 °C to 38 °C. SMR increased exponentially with temperature, from 79.8 mg O 2 kg -1 h -1 at 18 °C, to 255.1 mg O 2 kg -1 h -1 at 38 °C (Q 10 = 1.79). The main increase in Q 10 occurred within the highest temperature range, whereas in the lower temperature from 18 °C to 22 °C, temperature did not significantly affect SMR. MMR showed a hyperbolic correlation with increasing temperature, rising from 240.5 mg O 2 kg -1 h -1 at 18 °C to a peak of 373.8 mg O 2 kg -1 h -1 at 30 °C, before decreasing again at higher temperatures. Absolute aerobic scope (AAS) peaked at 26.0 °C, which we conclude to be the optimal temperature for Nile tilapia. The optimal temperature range, defined as the thermal range where 80% or more of the metabolic scope (MS) can be maintained, occurred between 19.5 and 32.1 °C. The lower (TC MIN ) and upper (TC MAX ) critical temperatures occurred at 13.1 °C and 38.8 °C. Nile tilapia showed a 4-fold scope for increasing ventilation frequency from 24 opercular beats min -1 (OB min -1 ) during SMR at 18 °C, to a maximum of 100 OB min -1 which occurred during MMR at 34 °C. f V during MMR increased with temperature, but above 30 °C became uncoupled with MO 2, as fish were unable to sustain their rates of oxygen consumption despite a high f V. There was a strong correlation between f V and SMR (r 2 = 0.83) across all temperatures indicating that f V is a good predictor of SMR. However, the correlation between MMR and f V was weak (r 2 = 0.06), due to a strong interacting effect of temperature. When selecting data from the thermal optimum range, a good correlation between f V and MO 2 was obtained (r 2 = 0.74).

Swimming performance is extremely important to critical activities of fishes, such as foraging, anti-predator, and migration. As one of primary stock enhancement fish species in China, it is imperative to study on swimming performance of the large yellow croaker (Larimichthys crocea). In the present study, the swimming performance of juvenile large yellow croaker was investigated, including the behavior, muscle morphology, stress physiology, and genetic mechanisms underlying the individual difference. Juveniles of the croaker were individually subjected to the critical swimming speed (Ucrit) test, and thereby divided into fast (36.47 cm/s) and slow (18.65 cm/s) groups. The juveniles in the fast group had significantly higher tail beat frequency, smaller muscle fiber diameter and more muscle fiber number, as well as lower plasma cortisol and corticotropin releasing hormone (CRH) levels than those in the slow group. Meanwhile, expression levels of hsp70 and pcna in the brain were significantly higher in the fast group than in the slow group, however no significant difference was observed in syt1a expression. Furthermore, the key genes and pathways involved in the swimming performance were assessed by mapping the white skeletal muscle transcriptome. We found that a total of 157 transcripts was differentially expressed between the fast and slow groups, enriched in oxidative phosphorylation, glycosaminoglycan biosynthesis, nicotinate and nicotinamide metabolism, cellular senescence, and cardiac muscle contraction pathways. A multitude of mitochondrial NADH dehydrogenase subunits and solute carrier family genes were especially related. In conclusion, we for the first time found that fish swimming performance directly links to muscle fiber plasticity, stress physiology, and molecular base divergence in the large yellow croaker. The present results lay a foundation for ethological-character-based selective breeding for the large yellow croaker in the regards of swimming performance.

Spontaneous triploidization has been widely documented in cultured populations of many sturgeon species and the evidence of its occurrence in the wild has also been provided. We compared the critical swimming speed (Ucrit) of nine-month-old normoploid and triploidized individuals (obtained from normal fertilization or from normal fertilization followed by induction of the second polar body retention, respectively) of sterlet (Acipenser ruthenus), Siberian sturgeon (Acipenser baerii), and their reciprocal hybrids. Moreover, we assessed the primary haematological indices (blood haemoglobin concentration, Hb; haematocrit, PCV; erythrocyte count, RBC count), secondary haematological indices (mean erythrocyte volume, MEV; mean erythrocyte haemoglobin, MEH; mean erythrocytic haemoglobin concentration, MEHC) and plasma/serum chemistry (cortisol, osmolality and glucose) of both non-exercised and exercised sturgeons to investigate the ploidy-related differences. We found that in both purebreds and hybrids, triploidized sturgeons exhibited the same absolute and corrected Ucrit as normoploids. Triploidized sturgeons had lower RBC counts and larger erythrocytes with more haemoglobin than normoploids, but the increase in ploidy did not affect Hb, PCV, MEHC, plasma cortisol, plasma osmolality or serum glucose, except for the greater PCV in triploidized sterlet × Siberian sturgeon and higher levels of serum glucose in triploidized Siberian sturgeon × sterlet than in normoploids of the same hybrids. The magnitudes of exercise-induced changes in the inspected parameters were consistent between normoploid and triploidized populations. We conclude that juvenile triploidized sterlet, Siberian sturgeon, sterlet × Siberian sturgeon and Siberian sturgeon × sterlet were able to fully compensate for having fewer erythrocytes in their Hb and PCV and had the same oxygen carrying capacity as normoploids. Moreover, the magnitude of haematological and blood chemistry responses to exhaustive exercise did not differ between normoploid and triploidized sturgeons, and triploidization did not result in altered swimming performance.

Breeding programs for barramundi (Lates calcarifer) are impeded by the lack of control over the sexual development of broodstock. As a protandrous hermaphrodite, barramundi initially sexually mature as male at 2–3 years (2–4 kg body weight; BW), before changing sex to female at 4–6 years (>6–8 kg BW). Recently, precocious female barramundi have been generated using a single intramuscular estrogen implant, providing the potential to speed up the sex change process and implement same-age mating of male and female broodfish. However, the functional maturation of hormonally-induced precocious females and their ability to spawn and produce viable progeny remains untested. Male barramundi (~2.2 kg BW, 57.8 cm total length; TL) were hormonally induced to sex change using an estrogen implant. The precocious female barramundi were cannulated at 6 (T1), 8 (T2), 10 (T3), 11.5 (T4) and 13 (T5) months after sex change, with oocytes measured and staged to determine reproductive condition. At T3, four females (~4.2 kg BW, 67.8 cm TL) with oocytes >350 µm in size were transferred to a spawning tank along with four males to assess their spawning performances. Mass spawning events were induced at T3, T4 and T5, and eggs released on the first and second spawning nights were collected to determine rates of fertilization, hatching and larval survival at 24 and 48 h post-hatch. At each cannulation event (T1 - T5), several precocious females were confirmed to have mature oocytes and were considered ready for induced spawning. Conversely, in some individuals, only immature oocytes were during each cannulation event. The four precocious females induced to spawn generated large numbers of eggs, with 7.7 million (T3), 10.9 million (T4) and 9.1 million (T5) eggs obtained across the two nights of each mass spawning event. Fertilization of oocytes was not observed at T3 and was likely due to male inactivity. Spawning performance improved considerably for T4 and T5 spawns, with the highest fertilization rate (64%) and hatching rate (72%) observed during T5 - Night 1. Furthermore, larval survival at 24 and 48 h after hatching was 99% and 94%, respectively. Total larval production across both nights of the T5 spawn exceeded 3 million individuals. Spawning performances of precocious females were comparable to routine commercial stocks of large females (8–15 kg), and confirmed that precociously induced female barramundi can produce the quantity of seedstock required in existing selective breeding programs. Further research examining the factors involved in promoting oocyte growth and maturation is needed to enhance the rate at which mature precocious females are available for spawning.

Polycyclic aromatic hydrocarbons (PAH) are products of incomplete combustion which are ubiquitous pollutants and constituents of harmful mixtures such as tobacco smoke, petroleum and creosote. Animal studies have shown that these compounds exert developmental toxicity in multiple organ systems, including the nervous system. The relative persistence of or recovery from these effects across the lifespan remain poorly characterized. These studies tested for persistence of neurobehavioral effects in AB* zebrafish exposed 5–120 hours post-fertilization to a typical PAH, benzo[a]pyrene (BAP). Study 1 evaluated the neurobehavioral effects of a wide concentration range of BAP (0.02–10 μM) exposures from 5–120 hpf during larval (6 days) and adult (6 months) stages of development, while study 2 evaluated neurobehavioral effects of BAP (0.3–3 μM) from 5–120 hpf across four stages of development: larval (6 days), adolescence (2.5 months), adulthood (8 months) and late adulthood (14 months). Embryonic BAP exposure caused minimal effects on larval motility, but did cause neurobehavioral changes at later points in life. Embryonic BAP exposure led to nonmonotonic effects on adolescent activity (0.3μM hyperactive, Study 2), which attenuated with age, as well as startle responses (0.2 μM enhanced, Study 1) at 6 months of age. Similar startle changes were also detected in Study 2 (1.0μM), though it was observed that the phenotype shifted from reduced pretap activity to enhanced posttap activity from 8–14 months of age. Changes in the avoidance (0.02–10 μM, Study 1) and approach (reduced, 0.3μM, Study 2) of aversive/social cues were also detected, with the latter attenuating from 8–14 months of age. Fish from study 2 were maintained into aging (18 months) and evaluated for overall and tissue-specific oxygen consumption to determine whether metabolic processes in the brain and other target organs show altered function in late life based on embryonic PAH toxicity. BAP reduced whole animal oxygen consumption, and overall reductions in total basal, mitochondrial basal, and mitochondrial maximum respiration in target organs, including the brain, liver and heart. The present data show that embryonic BAP exposure can lead to neurobehavioral impairment across the life-span, but that these long-term risks differentially emerge or attenuate as development progresses. Keywords: zebrafish, polycyclic hydrocarbon, benzo-a-pyrene, aging, neurobehavioral toxicology

Ocean acidification is predicted to have a wide range of impacts on fish, but there has been little focus on broad-ranging pelagic fish species. Early life stages of fish are thought to be particularly susceptible to CO2 exposure, since acid-base regulatory faculties may not be fully developed. We obtained yellowfin tuna (Thunnus albacares) from a captive spawning broodstock population and exposed them to control or 1900 µatm CO2 through the first three days of development as embryos transitioned into yolk sac larvae. Metabolic rate, yolk sac depletion, and oil globule depletion were measured to assess overall energy usage. To determine if CO2 altered protein catabolism, tissue nitrogen content and nitrogenous waste excretion were quantified. CO2 exposure did not significantly impact embryonic metabolic rate, yolk sac depletion, or oil globule depletion, however, there was a significant decrease in metabolic rate at the latest measured yolk sac larval stage (36 h post fertilization). CO2-exposure led to a significant increase in nitrogenous waste excretion in larvae, but there were no differences in nitrogen tissue accumulation. Nitrogenous waste accumulated in embryos as they developed but decreased after hatch, coinciding with a large increase in nitrogenous waste excretion and increased metabolic rate in newly hatched larvae. Our results provide insight into how yellowfin tuna are impacted by increases in CO2 in early development, but more research with higher levels of replication is needed to better understand long-term impacts and acid-base regulatory mechanisms in this important pelagic fish.

Ocean acidification may increase the risk of disease outbreaks that would challenge the future persistence of marine organisms if their immune system and capacity to produce vital structures for survival (e.g., byssus threads produced by bivalves) are compromised by acidified seawater. These potential adverse effects may be exacerbated by microplastic pollution, which is forecast to co-occur with ocean acidification in the future. Thus, we evaluated the impact of ocean acidification and microplastics on the health of a mussel species (Mytilus coruscus) by assessing its physiological performance, immunity and byssus properties. We found that ocean acidification and microplastics not only reduced hemocyte concentration and viability due to elevated oxidative stress, but also undermined phagocytic activity of hemocytes due to lowered energy budget of mussels, which was in turn caused by the reduced feeding performance and energy assimilation. Byssus quality (strength and extensibility) and production were also reduced by ocean acidification and microplastics. To increase the chance of survival with these stressors, the mussels prioritized the synthesis of some byssus proteins (Mfp-4 and Mfp-5) to help maintain adhesion to substrata. Nevertheless, our findings suggest that co-occurrence of ocean acidification and microplastic pollution would increase the susceptibility of bivalves to infectious diseases and dislodgement risk, thereby threatening their survival and undermining their ecological contributions to the community.

Fish from commercially farmed stocks are often released into the natural environment to supplement wild populations. This practice is often applied to salmonid fish as they are an essential fishery resource and also used for recreational angling. However, farmed fish tend to show lower survival rates after release than wild fish. For this reason, the release of semi-wild fish is increasingly used in Japan; these fish are generated using female fish from domesticated stocks and male fish of wild origin. The survival rate of released semi-wild fish is higher than that of farmed fish, but the reason for this is unknown. This study compared the metabolism and swimming performance of semi-wild and farmed masu salmon (Oncorynchus masou). The analyses showed that resting metabolic rate (RMR), maximum metabolic rate (MMR) and swimming speeds that minimize energy costs of travel (optimal swimming speed) were higher in semi-wild fish than in farmed fish. Critical swimming speed did not differ significantly between the two groups of fish. Semi-wild fish with high RMR may have a social status advantage over farmed fish because a previous study reported that SMR, which is the value closest to basal metabolism significantly affects feeding motivation. This means that individuals with higher social status may be more motivated to feed. As RMR is proportional to food requirements, then release programs should be planned taking food resources at the release site into consideration.

The Alaska blackfish (Dallia pectoralis) is the only air-breathing fish in the Arctic. In the summer, a modified esophagus allows the fish to extract oxygen from the air, but this behavior is not possible in the winter because of ice and snow cover. The lack of oxygen (hypoxia) and near freezing temperatures in winter is expected to severely compromise metabolism, and yet remarkably, overwintering Alaska blackfish remain active. To maintain energy balance in the brain and limit the accumulation of reactive oxygen species (ROS), we hypothesized that cold hypoxic conditions would trigger brain mitochondrial remodeling in the Alaska blackfish. To address this hypothesis, fish were acclimated to warm (15 °C) normoxia, cold (5 °C) normoxia or cold hypoxia (5 °C, 2.1–4.2 kPa; no air access) for 5–8 weeks. Mitochondrial respiration, ADP affinity and H 2 0 2 production were measured at 10 °C in isolated brain homogenates with an Oroboros respirometer. Cold acclimation and chronic hypoxia had no effects on mitochondrial aerobic capacity or ADP affinity. However, cold acclimation in normoxia led to a suppression of brain mitochondrial H 2 0 2 production, which persisted and became more pronounced in the cold hypoxic fish. Overall, our study suggests cold acclimation supresses ROS production in Alaska blackfish, which may protect the fish from oxidative stress when oxygen becomes limited during winter.

Aquatic organisms are exposed to complex mixtures of pesticides in the environment, but traditional risk assessment approaches typically only consider individual compounds. In conjunction with exposure to pesticide mixtures, global climate change is anticipated to alter thermal regimes of waterways, leading to potential co-exposure of biota to elevated temperatures and contaminants. Furthermore, most studies utilize aqueous exposures, whereas the dietary route of exposure may be more important for fish owing to the hydrophobicity of many pesticides. Consequently, the current study aimed to determine the effects of elevated temperatures and dietary pesticide mixtures on swimming performance and lipid metabolism of juvenile Chinook salmon, Oncorhynchus tshawytscha. Fish were fed pesticide-dosed pellets at three concentrations and three temperatures (11, 14 and 17 °C) for 14 days and swimming performance (Umax) and expression of genes involved in lipid metabolism and energetics were assessed (ATP citrate lyase, fatty acid synthase, farnesoid x receptor and liver x receptor). The low-pesticide pellet treatment contained five pesticides, p,p’-DDE, bifenthrin, esfenvalerate, chlorpyrifos and fipronil at concentrations based on prey items collected from the Sacramento River (CA, USA) watershed, with the high-pesticide pellet treatment containing a six times higher dose. Temperature exacerbated effects of pesticide exposure on swimming performance, with significant reductions in Umax of 31 and 23% in the low and high-pesticide pellet groups relative to controls at 17 °C, but no significant differences in Umax among pesticide concentrations at 11 or 14 °C. At 14 °C there was a significant positive relationship between juvenile Chinook salmon pesticide body residues and expression of ATP citrate lyase and fatty acid synthase, but an inverse relationship and significant downregulation at 17 °C. These findings suggest that temperature may modulate effects of environmentally relevant pesticide exposure on salmon, and that pesticide-induced impairment of swimming performance may be exacerbated under future climate scenarios.

In this study we investigated potential impacts of Cu exposure at low, environmentally relevant, concentrations on early live stages of Atlantic cod ( Gadus morhua ). Cod embryos and larvae were exposed to 0.5 μg/L (low), 2 μg/L (medium), and 6 μg/L (high) Cu from 4 to 17 days post fertilisation (dpf). Hatching success, mortality, oxygen consumption, biometric traits, and malformations were determined. A dynamic energy budget (DEB) model was applied to identify potential impacts on bioenergetics. A positive correlation was found between Cu exposure concentrations and Cu body burden in eggs, but not in larvae. The tested concentrations did not increase mortality in neither embryos nor larvae, or larvae deformations. Further, the DEB model did not indicate effects of the tested Cu concentrations.

The photophobia of Conopomorpha sinensis was explored using eight kinds of LED lights, including those with single wavelengths as follows: 400, 460, 520, 600, 660 and 740 nm, and mixed wavelengths: MixW and MixY. The results showed that 460 nm (blue light), 520 nm (green light) and MixW (white light) were the most effective wavelengths for controlling C. sinensis, effectively reducing pest activity by 98.2%, 99.2% and 99.3%, respectively. Egg production decreased by 99.3%, 93.0% and 98.6% under these treatments with a light intensity of 0.5 μmol m−2 s−1, respectively. The C. sinensis damage rate was 72% in the dark control group and 10%, 6%, and 16% under continuous light at night with 460, 520 nm and MixW light, respectively. To further investigate the effect of different wavelengths of light applied to the whole plant at night on Yu-Her-Pao litchi fruit quality, the fruits under 460, 520 nm and MixW light at night were 23.4, 29.8 and 26.6 g in weight and 17.5, 19.3 and 17.8°Brix in total soluble solids, respectively. There was no significant difference in fruit weight or total soluble solids under 520 nm or bagging with no light at night. Thus, 520 nm green light at night had the least effect on fruit quality. HPLC results showed that the sucrose, glucose, fructose, citric acid, L-malic acid, and shikimic acid contents in fruits under 520 nm green light illumination at night were significantly higher than those under other light treatments. Only the fumaric acid content was significantly less than that under the other light treatments. There is no known previous research on the effects of continuous application of light to whole fruit trees and different light wavelengths on fruit quality. The results of this study showed that 520 nm green light at night could prevent and control C. sinensis and maintain fruit quality. These experimental results represent important progress in reducing the use of pesticides in the litchi industry.

Measures of fitness are valuable tools to predict species' responses to environmental changes, like increased water temperature. Aerobic scope (AS) is a measure of an individual's capacity for aerobic processes, and frequently used as a proxy for fitness. However, AS is complicated by individual variation found not only within a species, but within similar body sizes as well. Maximum metabolic rate (MMR), one of the factors determining AS, is constrained by an individual's ability to deliver and extract oxygen (O2) at the tissues. Recently, data has shown that red blood cell carbonic anhydrase (RBC CA) is rate-limiting for O2 delivery in red drum (Sciaenops ocellatus). We hypothesized increased temperature impacts MMR and RBC CA activity in a similar manner, and that an individual's RBC CA activity drives individual variation in AS. Red drum were acutely exposed to increased temperature (+6 °C; 22 °C to 28 °C) for 24 h prior to exhaustive exercise and intermittent-flow respirometry at 28 °C. RBC CA activity was measured before temperature exposure and after aerobic performance. Due to enzymatic thermal sensitivity, acute warming increased individual RBC CA activity by 36%, while there was no significant change in the control (22 °C) treatment. Interestingly, average MMR of the acute warming treatment was 36% greater than that of control drum. However, we found no relationships between individual RBC CA activity and their respective MMR and AS at either temperature. While warming similarly affects RBC CA activity and MMR, RBC CA activity is not a predictor of individual MMR.

As the prevalence of obesity has steadily increased on a global scale, research has shifted to explore potential contributors to this pandemic beyond overeating and lack of exercise. Environmental chemical contaminants, known as obesogens, alter metabolic processes and exacerbate the obese phenotype. Diethylhexyl phthalate (DEHP) is a common chemical plasticizer found in medical supplies, food packaging, and polyvinyl materials, and has been identified as a probable obesogen. This study investigated the hypothesis that co-exposure to DEHP and overfeeding would result in decreased lipid mobilization and physical fitness in Danio rerio (zebrafish). Four treatment groups were randomly assigned: Regular Fed (control, 10 mg/fish/day with 0 mg/kg DEHP), Overfed (20 mg/fish/day with 0 mg/kg DEHP), Regular Fed + DEHP (10 mg/fish/day with 3 mg/kg DEHP), Overfed + DEHP (20 mg/fish/day with 3 mg/kg DEHP). After 24 weeks, swim tunnel assays were conducted on half of the zebrafish from each treatment to measure critical swimming speeds (Ucrit); the other fish were euthanized without swimming. Body mass index (BMI) was measured, and tissues were collected for blood lipid characterization and gene expression analyses. Co-exposure to DEHP and overfeeding decreased swim performance as measured by Ucrit. While no differences in blood lipids were observed with DEHP exposure, differential expression of genes related to lipid metabolism and utilization in the gastrointestinal and liver tissue suggests alterations in metabolism and lipid packaging, which may impact utilization and ability to mobilize lipid reserves during physical activity following chronic exposures.

Organic ultraviolet filters (UVFs) are contaminants of concern, ubiquitously found in many aquatic environments due to their use in personal care products to protect against ultraviolet radiation. Research regarding the toxicity of UVFs such as avobenzone, octocrylene and oxybenzone indicate that these chemicals may pose a threat to invertebrate species; however, minimal long-term studies have been conducted to determine how these UVFs may affect continuously exposed populations. The present study modeled the effects of a 5-generation exposure of Daphnia magna to these UVFs at environmental concentrations. Avobenzone and octocrylene resulted in minor, transient decreases in reproduction and wet mass. Oxybenzone exposure resulted in > 40% mortality, 46% decreased reproduction, and 4-fold greater reproductive failure over the F0 and F1 generations; however, normal function was largely regained by the F2 generation. These results indicate that Daphnia are able to acclimate over long-term exposures to concentrations of 6.59 µg/L avobenzone, ~0.6 µg/L octocrylene or 16.5 µg/L oxybenzone. This suggests that short-term studies indicating high toxicity may not accurately represent long-term outcomes in wild populations, adding additional complexity to risk assessment practices at a time when many regions are considering or implementing UVF bans in order to protect these most sensitive invertebrate species.

Current approaches in chemical hazard assessment face significant challenges because they rely on live animal testing, which is time-consuming, expensive, and ethically questionable. These concerns serve as an impetus to develop new approach methodologies (NAMs) that do not rely on live animal tests. This study explored a molecular benchmark dose (BMD) approach using a 7-day embryo-larval fathead minnow (FHM) assay to derive transcriptomic points-of-departure (tPODs) to predict apical BMDs of fluoxetine (FLX), a highly prescribed and potent selective serotonin reuptake inhibitor frequently detected in surface waters. Fertilized FHM embryos were exposed to graded concentrations of FLX (confirmed at < LOD, 0.19, 0.74, 3.38, 10.2, 47.5 µg/L) for 32 days. Subsets of fish were subjected to omics and locomotor analyses at 7 days post-fertilization (dpf) and to histological and biometric measurements at 32 dpf. Enrichment analyses of transcriptomics and proteomics data revealed significant perturbations in gene sets associated with serotonergic and axonal functions. BMD analysis resulted in tPOD values of 0.56 µg/L (median of the 20 most sensitive gene-level BMDs), 5.0 µg/L (tenth percentile of all gene-level BMDs), 7.51 µg/L (mode of the first peak of all gene-level BMDs), and 5.66 µg/L (pathway-level BMD). These tPODs were protective of locomotor and reduced body weight effects (LOEC of 10.2 µg/L) observed in this study and were reflective of chronic apical BMDs of FLX reported in the literature. Furthermore, the distribution of gene-level BMDs followed a bimodal pattern, revealing disruption of sensitive neurotoxic pathways at low concentrations and metabolic pathway perturbations at higher concentrations. This is one of the first studies to derive protective tPODs for FLX using a short-term embryo assay at a life stage not considered to be a live animal under current legislations.

In recent years, Arctic char populations in Iceland have declined and the objective of this experiment was to throw further light on these changes by examining the effect of temperature (5, 9, 13, 17, and 21 °C) on the survival, growth rate, metabolism, and physiological indices of juvenile Arctic charr (initial mean body mass 4.02 ± 0.8 g). Mortality was 60% at 21 °C while at lower temperatures it was below 5%. However, Arctic charr populations in Iceland are declining in locations where the ambient temperature is lower, suggesting that other factors may be more important in determining the abundance of the species. The optimum temperature for growth was near 14 °C. The growth rate was progressively reduced at supra-optimum temperatures with almost no growth at 21 °C. Indicators of energy reserves: condition factor, relative intestinal mass, and hepatosomatic index are all consistent with reduced feed intake at supra-optimum temperatures. The standard and maximum metabolic rate (SMR; MMR), as well as the aerobic scope for activity (AS), were maximum at 13 °C. The routine metabolic rate (RMR) increased exponentially with temperature and, at T21, it was equal to the MMR suggesting, that the RMR was limited by the MMR. Moreover, increased heart- and gill mass at 21 °C are consistent with increased stress on the cardiovascular system. These findings are in keeping with the OCLTT hypothesis that the thermal tolerance of fish is limited by the capacity of the cardiovascular system to deliver oxygen and support metabolism. Taken together, the results of this experiment suggest, that growth rate is reduced at supra-optimum temperatures because of reduced energy intake, increased metabolic demand, and limitations in the capacity of the cardiovascular system to support metabolic rate at high temperatures. At lower temperatures, growth does not appear to be limited by the AS.

Ocean acidification (OA) and microplastics (MPs) contamination are two results of human excises. In regions like estuarine areas, OA and MPs exposure are happening at the same time. The current research investigated the synthesized effects of OA and MPs exposure for a medium-term duration on the physiology and energy budget of the thick shell mussel Mytilus coruscus. Mussels were treated by six combinations of three MPs levels (0, 10 and 1000 items L-1) × two pH levels (7.3, 8.1) for 21 d. As a result, under pH 7.3, clearance rate (CR), food absorption efficiency (AE), respiration rate (RR), and scope for growth (SFG) significantly decreased, while the fecal organic dry weight ratio (E) significantly increased. 1000 items L-1 MPs led to decrease of CR, E, SFG and increase of AE under pH 8.1. Interactive effects from combination of pH and MPs were found in terms of CR, AE, E and RR, but not for SFG of M. coruscus.

The Acartia tonsa, a calanoid copepod species, has high survival and thermal acclimation capacity in aquatic environments characterized by temperature variations. Dynamic and static thermal polygon areas of this species are 495 °C2 and 267 °C2 for nauplii stage, while adult stage has 747 °C2 and 411 °C2 dynamic and static thermal polygon area, respectively. In addition, Acartia tonsa is a copepod species which is more resistant to both high and low lethal temperatures, with its resistance zone of 105 °C2 and 131 °C2 for nauplii and adults, respectively. Acartia tonsa nauplii acclimated to 18 °C, 23 °C and 28 °C have lover and upper thermal limit (CTMin-CTMax) of 6.82–26.15 °C, 8.65–29.49 °C, and 11.70–34.10 °C, respectively. This species in the adult stage has a CTMin-CTMax of 4.47–30.30 °C, 6.35–33.94 °C, and 9.92–35.90 °C at acclimation temperatures mentioned above. Its broad dynamic and static thermal tolerance polygon areas and, accordingly, its significant thermal limits allow Acartia tonsa to survive at warm or cold extremes in their natural environment.

Establishing a suitable location for a fish collection system is crucial for luring and collecting fish and requires the swimming characteristics of fish to be considered. This study aimed to identify a suitable location to lure fish to the fish collecting system (or barge) on the Hong River. For this purpose, a 3D computational fluid dynamics model for the downstream of dam was verified using Acoustic Doppler current Profiler (ADCP) velocity data to simulate the flow field of river channel considering of seven typical operation scenarios. The swimming performance of five endemic fish (Bagarius rutilus, Cyprinus carpio rubrofuscus, Semilabeo obscures, Channa argus, and Opsariichthys bidens) were evaluated using three indexes, i.e., induced flow velocity, critical swimming speed, burst swimming speed, to determine their migration behavior zones by analyzing different flow velocities. By adapting the simulated flow fields in each operation scenario, potential fish migration aggregation zones were analyzed. The results suggested that the most optimal position for placing the FCP was in the left bank of river channel at X = 400–500 m in typical operation scenarios. This study provides a reference for designing FCP for fish pass facilities that combine fish swimming behavior and hydraulic variables of the river channel.

Nanoplastics are being detected with increasing frequency in aquatic environments. Although evidence suggests that nanoplastics can cause overt toxicity to biota across different trophic levels, but there is little understanding of how materials such as differently charged polystyrene nanoplastics (PS-NP) impact fish development and behavior. Following exposure to amino-modified (positive charge) PS-NP, fluorescence accumulation was observed in the zebrafish brain and gastrointestinal tract. Positively charged PS-NP induced stronger developmental toxicity (decreased spontaneous movement, heartbeat, hatching rate, and length) and cell apoptosis in the brain and induced greater neurobehavioral impairment as compared to carboxyl-modified (negative charge) PS-NP. These findings correlated well with fluorescence differences indicating PS-NP presence. Targeted neuro-metabolite analysis by UHPLC-MS/MS reveals that positively charged PS-NP decreased levels of glycine, cysteine, glutathione, and glutamic acid, while the increased levels of spermine, spermidine, and tyramine were induced by negatively charged PS-NP. Positively charged PS-NP interacted with the neurotransmitter receptor N-methyl-D-aspartate receptor 2B (NMDA2B), whereas negatively charged PS-NP impacted the G-protein-coupled receptor 1 (GPR1), each with different binding energies that led to behavioral differences. These findings reveal the charge-specific toxicity of nanoplastics to fish and provide new perspective for understanding PS-NP neurotoxicity that is needed to accurately assess potential environmental and health risks of these emerging contaminants.

Anthropogenic releases of plastics, persistent organic pollutants (POPs), and heavy metals can impact the environment, including aquatic ecosystems. Nanoplastics (NPs) have recently emerged as pervasive environmental pollutants that have the ability to adsorb POPs and can cause stress in organisms. Among POPs, DDT and its metabolites are ubiquitous environmental pollutants due to their long persistence. Despite the discontinued use of DDT in Europe, DDT and its metabolites (primarily p,p'-DDE) are still found at detectable levels in fish feed used in salmon aquaculture. Our study aimed to look at the individual and combined toxicity of NPs (50 mg/L polystyrene) and DDE (100 μg/L) using zebrafish larvae as a model. We found no significant morphological, cardiac, respiratory, or behavioural changes in zebrafish larvae exposed to NPs alone. Conversely, morphological, cardiac and respiratory alterations were observed in zebrafish larvae exposed to DDE and NPs + DDE. Interestingly, behavioural changes were only observed in zebrafish larvae exposed to NPs + DDE. These findings were supported by RNA-seq results, which showed that some cardiac, vascular, and immunogenic pathways were downregulated only in zebrafish larvae exposed to NPs + DDE. In summary, we found an enhanced toxicological impact of DDE when combined with NPs.

The invasive mussel Mytilus galloprovincialis is a heat-tolerant species relative to its competative congener M. trossulus, that dominates warm seawater environments but it is unknown how multiple stressors (MS) may affect its physiology. Our study determined the effects of MS on the metabolic rate (MR), superoxide dismutase (SOD) antioxidant enzyme activity, and clearance rate (CR) of M. galloprovincialis. Mussels were exposed for 7 d to hyposalinity (20, 28, 34 ppt) then to heat shock (17, 20, 25 °C) after which MR and SOD activity were determined. CR was quantified following a 30 min MS exposure. We found a significant influence of MS on MR, SOD, and CR. We identified synergistic effects on MR under the most extreme treatment. SOD activity was the greatest under 20 °C exposure while CR declined under heat shock. Thus, our study suggests that mussels experiencing MS may become energy limited as MR increases and feeding rates decrease.

Relatively warm environments caused by global warming enhance the productivity of aquaculture activities in tropical/subtropical regions; however, the intermittent cold stress (ICS) caused by negative Arctic Oscillation can still result in major economic losses. In contrast to endotherms, ectothermic fishes experience ambient temperature as an abiotic factor that is central to performance and survival. Therefore, the occurrence of extreme temperatures caused by climate change has ignited a surge of scientific interest from ecologists, economists and physiologists. In this study, we test the transgenerational effects of rearing cold-experienced (CE) and cold-naïve (CN) strains of tropical tilapia. Our results show that compared to CN tilapia, the CE strain preferentially converts carbohydrates into lipids in liver at a regular temperature of 27 °C. Besides, at a low temperature of 22 °C, the CE strain exhibits a broader aerobic scope than CN fish, and their metabolite profile suggests a metabolic shift towards the utilization of glutamate derivatives. Therefore, in response to thermal perturbations, this transgenerational metabolic adjustment provides evidence into the adaptive trade-off mechanisms in tropical fish. Nevertheless, global warming may result in less thermal variation each year, and the stabilized ambient temperature may cause tropical tilapia to gradually exhibit lower energy deposits in liver. In addition to those habitants in cold and temperate regions, a lack of cold exposure to multiple generations of fish may decrease the native cold-tolerance traits of subtropical/tropical organisms; this notion has not been previously explored in terms of the biological effects under anthropogenic climate change.

As alternatives to perfluorooctane sulfonate (PFOS), 6:2 Cl-PFESA (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) are frequently detected in aquatic environments, but little is known about their neurotoxicity, especially in terms of circadian rhythms. In this study, adult zebrafish were chronically exposed to 1 µM PFOS, F-53B and OBS for 21 days taking circadian rhythm-dopamine (DA) regulatory network as an entry point to comparatively investigate their neurotoxicity and underlying mechanisms. The results showed that PFOS may affect the response to heat rather than circadian rhythms by reducing DA secretion due to disruption of calcium signaling pathway transduction caused by midbrain swelling. In contrast, F-53B and OBS altered the circadian rhythms of adult zebrafish, but their mechanisms of action were different. Specifically, F-53B might alter circadian rhythms by interfering with amino acid neurotransmitter metabolism and disrupting blood-brain barrier (BBB) formation, whereas OBS mainly inhibited canonical Wnt signaling transduction by reducing cilia formation in ependymal cells and induced midbrain ventriculomegaly, finally triggering imbalance in DA secretion and circadian rhythm changes. Our study highlights the need to focus on the environmental exposure risks of PFOS alternatives and the sequential and interactive mechanisms of their multiple toxicities.

Intertidal and estuarine bivalves are adapted to fluctuating environmental conditions but the cellular adaptive mechanisms under combined stress scenarios are not well understood. The Hong Kong oysters Crassostrea hongkongensis experience periodic hypoxia/reoxygenation and salinity fluctuations during tidal cycles and extreme weather, which can negatively affect the respiratory organs (gills) involved in oxygen uptake and transport. We determined the effects of periodic hypoxia under different salinities on the oxidative stress response in Hong Kong oysters. Oxidative stress parameters (activities of superoxide dismutase (SOD), and catalase (CAT), tissue levels of malondialdehyde (MDA) and protein carbonyl content (PCC)) were determined in the gills of oysters exposed to diel-cycling hypoxia (hypoxia at night: 12h at 2 mg/L, reoxygenation: 12h at 6 mg/L) and normal dissolved oxygen (DO) (6 mg/L) under three salinities (10, 25, and 35‰) for 28 days. Oxygen regime in combination with salinity changes had significant interactive effects on all studied parameters except SOD. Salinity, DO and their interactions increased PCC after 14 and 28 days of exposure, and the combination of hypoxia/reoxygenation and decreased salinity showed the most severe effect. MDA content of the gills increased only after the long-term (28 days) exposure in decreased or increased salinity under normal DO treatments, showing PCC was more sensitive than MDA as biomarker of oxidative stress. Low salinity suppressed SOD activity regardless of the DO, whereas hypoxia induced SOD responses. CAT activities decreased significantly under high salinity with hypoxia/reoxygenation conditions. Our findings highlighted that periodic hypoxia/reoxygenation with salinity change induced antioxidant responses, which can impact the health of Hong Kong oyster C. hongkongensis and prolonged salinity stress may be one reason for the mortality during its aquaculture process.

Hydrogen peroxide (H2O2) is applied in various environments. It could be present at concentrations ranging from nanomolar to micromolar in a water system. It is produced through pollutants and natural activities. Since few studies have been conducted about the impact of naturally produced H2O2 on aquatic organisms, the objective of the present study was to monitor changes in responses of aquatic model organisms such as zebrafish and antibiotic-resistant bacteria to different exogenous H2O2 exposure. Increases in exposure concentration and time induced decreases in the perception of zebrafish larvae (up to 69%) and movement of adult zebrafish (average speed, average acceleration, movement distance, and activity time) compared to the control (non-exposed group). In addition, as a function of H2O2 exposure concentration (0–100,000 nM) and time, up to 20-fold increase (p = 5.00*10-6) of lipid peroxidation compared to control was observed. For microorganisms, biofilm, an indirect indicator of resistance to external stressors, was increased up to 68% and gene transfer was increased (p = 2.00*10-6) by more than 30% after H2O2 exposure. These results imply that naturally generated H2O2 could adversely affect aquatic environment organisms and public health. Thus, more careful attention is needed for H2O2 production in an aquatic system.

Environmental temperature during early life may have prolonged effects on growth and fatty acid metabolism, which could strongly influence overwintering survival in the first year of life for temperate-zone fish. In the present study, we examined how temperature during early life history might influence growth performance and fatty acid metabolism in age-0 Lake Sturgeon (Acipenser fulvescens) when exposed to cold temperatures at later stages. Fish were initially at 16 °C and subsequently held at 16 °C or 20 °C for 60 days beginning at 34 days post fertilization (dpf). Then, all fish were subsequently raised at the same temperature of 16 °C until the onset of cold conditioning at 158 dpf where temperature was gradually decreased to 3.5 °C and remained there for two weeks. Samples were collected before (151 dpf) and after cold conditioning (199 dpf) to measure total length, body mass, whole body metabolic rate, fatty acid profile in phospholipids and triglycerides and mRNA expression of genes associated with fatty acid desaturation, elongation and ß-oxidation. Results revealed that before cold conditioning, total length and body mass did not differ between temperature groups, but fish raised at 20 °C showed a lower condition factor. During the cold conditioning, only fish raised at 16 °C grew significantly longer and heavier. There was no difference in metabolic rates between treatments. Significant increases in total monounsaturated fatty acids with decreases in total saturated fatty acids were identified in phospholipids and triglycerides in both temperature groups after the cold conditioning; however, the 20 °C group did not significantly increase levels of gene expression associated with fatty acid desaturation (SCD and FADS1) whereas the 16 °C group did. Our results suggest that thermal experience during early life may influence overwintering survival of age-0 Lake Sturgeon.

Some species of fish can be induced to swim under optimal conditions aiming to improve their growth performance and welfare. This study was undertaken to investigate the effects of induced sustained swimming on the growth performance, metabolic parameters [standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute aerobic scope (AAS), and excess post-exercise oxygen consumption (EPOC)], external morphology, skeletal muscle fiber characteristics and distribution of juvenile gilthead seabream (Sparus aurata), as well as immune and metabolic markers. Fish with a body mass of 26.89 ± 0.26 g and a total length of 12.27 ± 0.04 cm were induced to swim continuously at 1.1 body lengths s-1 (S group) or maintained under minimal water flow with fish displaying spontaneous swimming activity (C group) for 13 weeks. The water current in the S group was maintained at a similar level and by the end of the trial; the swimming speed was 0.8 body lengths s-1. Long-term induced swimming activity had no significant effect on the growth rate, feed efficiency, or red and white muscle cross-sectional area, fiber diameter, and density. However, swimming significantly changed the body shape of gilthead seabream, with the S group having shallower bodies, more pronounced nuchal humps, flatter abdomens, and larger caudal fins compared with the C group. SMR, MMR, AAS, and EPOC were similar in both experimental groups. Hematocrit and plasma lactate levels were significantly higher in the S group, whereas plasma glucose, protease, and anti-protease activities were not different between both groups. Despite the lack of changes in growth performance, feed efficiency, skeletal muscle morphological traits, and metabolic rates, induced swimming changed the body shape of seabream, and increased the oxygen-carrying capacity and plasma lactate levels.

Ocean acidification and microplastics pollution are two consequences of anthropogenic activities. In regions such as estuarine areas, ocean acidification (OA) and microplastics (MPs) pollution are occurring simultaneously. The present study tested the combined effects of OA and MPs on the embryonic development and physiological response of the larval oyster Crassostrea rivularis in a short exposure duration. The fertilization process was exposed to six combinations of three MPs levels (0, 10 and 1000 items L-1) × two pH levels (7.3, 8.1) for 9 d after hatching. As a result, the hatching rate was not affected by either pH reduction or MPs exposure, while the deformation rate increased under low pH, MPs exposure and their combination. Larval shell length was reduced under low pH, MPs exposure and the combined exposure of the two factors. Furthermore, swimming speed decreased under low pH throughout the experiment but the MPs' effect was limited. Predictably, MPs in the body increased with the increase of MPs concentration. Compared to low pH, the oyster ingested more MPs under normal pH. But combined OA and MPs didn't affect the MPs intake. Moreover, no significant effects of OA and MPs on total antioxidant capacity and malondialdehyde were observed. However, alkaline phosphatase was significantly affected by low pH and MPs exposure independently. PCA showed that development of C. rivularis larvae changed over time and MPs concentration increase augmented intake of MPs by oysters. Consequently, we speculate that OA and MPs exposure may harm oyster C. rivularis embryonic and larval development, but not induce their antioxidant response in a short duration. Long term study about combined effects of OA and MPs on C. rivularis development is needed in the future.

In farmed animals, individuality have demonstrated links to performance traits, health and disease susceptibility, and animal welfare. This research aims at exploring whether there are differences in the secretion of hormones in the caudal neurosecretory system of different individuailty, and investigating whether it is related to physiological behaviors. In the experiment we selected through multiple behavioral tests two types of olive flounders, bold individuals (BI) and shy individuals (SI), and found that they differed in behavior and physiology. The standard metabolic rate, maximum metabolic rate, and absolute aerobic scope of BI were markedly higher than those of SI. Additionally, the swimming speed of BI was also higher than that of SI in the natural photoperiod. BI and SI showed distinct coping styles to deal with acute stress. Overall, the number of Dahlgren cells secreting UI, the relative UI and CRH mRNA expression in the caudal neurosecretory system (CNSS) of SI was relatively higher than that in BI. By contrast, the number of Dahlgren cells secreting UII and the mRNA expression of UII was lower than that of BI. Through the correlation analysis, it was found that there were some differences in hormone secretion among different individuality groups, which indicated individuality affected hormone production and the number of secretion cells and existed correlation with respiratory metabolism, spontaneous behavior, appetite. It means differences in the regulation mechanism of the flounders in BI and SI.

Understanding environmental constraints and associated physiological adaptations of culture organisms is key for the implementation of off-shore grow-out facilities. In the southeast Pacific Ocean along the coasts of Chile and Peru, seasonal upwelling events lead to hypoxic conditions, which are projected to increase in both frequency and intensity with climate change. Aquaculture operations must take into account the physiological adaptability of a species for environmental conditions. For Cojinoba (Seriolella violacea), a native target species for aquaculture diversification in northern Chile, little is known in regard to physiological capacity for hypoxia. Therefore, hypoxia tolerance studies were conducted followed by measurement of resting and active metabolism and associated energy facilitation in response to hypoxia in juvenile Cojinoba. Hypoxia tolerance studies found they were resilient to dissolved oxygen levels of 1.0 mg O2 L¯1 for 8 h. Swimming metabolism studies exposed Cojinoba to normoxia (7.5 mg O2 L¯1) or hypoxia (1.0 mg O2 L¯1), and quantified minimum metabolic rate (MO2 min), active metabolic rate (MO2 max), critical swimming speed (Ucrit) and associated energetic metabolites and hematological variables. In hypoxia, there was a decrease in MO2 max (34%) leading to a large (82%) decrease in aerobic metabolic scope. MO2 min decreased as well by 12%, with lactate increasing presumably to temporarily maintain basic metabolic function. In addition, Ucrit decreased by 53% in hypoxia, although tail beat frequency was similar in normoxia and hypoxia up to a velocity of 40 cm s-1. Moreover, although erythrocyte concentration increased in hypoxia, hemolysis was observed in exercised fish in this condition. There was a notable increase (5-fold compared to normoxia) in lactate levels of exercised fish in the hypoxia group, which suggests a quick conversion to anaerobic metabolic pathways to maintain energy balance when swimming in hypoxic environments. Therefore, Cojinoba have adaptive responses that may facilitate survival during severe hypoxic events although overall physiological performance is diminished.

Fish are known to show high intraspecific phenotypic variation during early life history. Specifically environmental temperature during early life can result in developmental plasticity, which will influence developmental trajectory and ultimately individual fitness. In the present study, we examined long-term effects of early rearing temperature on growth, energy density, body composition (i.e., whole body glucose, triglyceride and protein concentration) and aerobic scope of age-0 Lake Sturgeon (A. fulvescens) to determine if temperature manipulation after yolk absorption would have a long-term impact on these traits. At 58 days post hatch, fish were subjected to one of three temperature manipulations (16 °C; control, 18 °C and ambient river temperature in a range of 14.0–19.4 °C; Ambient) for 35 days after which all fish were raised in Ambient conditions until 360 days post hatch, including 4 months of natural winter temperatures. We hypothesized that temperature conditions experienced before the first winter of life would result in short-term effects of improved growth and energy reserves. Our results showed that temperature manipulation may result in a short-term, reversible effect of improved growth prior to overwintering without a longer-term effect on growth. Enhanced somatic growth of total length and body mass prior to winter did not translate into improved energy reserves, and observed differences in growth rate between treatments did not correlate with aerobic scope. Our data demonstrate that a subtle change in temperature during early life history in Lake Sturgeon may result in short term positive effects on growth rate. These data may enhance current conservation aquaculture operations to promote winter survival in fall released fingerlings without long-term implications on growth phenotypes.

Many aquatic insects are exposed to the dual stressors of heavy metal pollution and rising water temperatures from global warming. These stresses may interact and have stronger impacts on aquatic organisms if heavy metals interfere with the ability of these organisms to handle high temperatures. Here we focus on the effect of copper on upper thermal limits of giant salmonfly nymphs (Order: Plecoptera, Pteronarcys californica), a stonefly species which is common in parts of western North America. Experimental exposure to copper reduced upper thermal limits by ∼ 10 °C in some cases and depressed the hypoxia tolerance (P crit ) of nymphs by ∼ 0.5 mg L -1 DO. These results suggest that copper inhibits the delivery of oxygen, which may explain, in part, the strong reductions in CT MAX that we report. Fluorescence microscopy of Cu-exposed individuals indicated high levels of copper in chloride cells but no clear evidence of damage to or high levels of copper on the gills themselves. Our study indicates that populations of aquatic insects from copper-polluted environments may be further at risk to future warming than those from uncontaminated environments.

Upside-down jellyfish (Cassiopea spp.) are predominantly tropical, but there have been recent reports of medusae in temperate environments. In 2017 they were recorded in temperate Lake Macquarie, Australia, where they have a tendency to disappear from this area through late winter (Austral, August). This raises questions about the role of temperature as a controlling factor of their abundance, and future density increases with warming oceans as a result of climate change. Here we test the degree to which temperature may drive winter die-offs of the medusa stage in temperate environments, and how this may change with altered thermal regimes. We assessed the physiological response of Cassiopea (via measurement of bell pulsation rate, bell diameter, and routine metabolic rate) under a regime mirroring Lake Macquarie's seasonal temperature drop (autumn into winter) compared to three other temperature profiles: 1) seasonal profile with predicted climate change (+ 2 °C), 2) stable temperatures equivalent to the end of autumn (20 °C) and, 3) a profile that mimicked the increasing temperatures from winter into summer (20 °C increasing to 24 °C). Overall, the results indicate that, compared to the ambient state, elevated temperatures can have positive effects on performance of Cassiopea medusae as evidenced by greater bell pulsation rate and bell diameter. The rate of bell diameter decline was lower in all elevated temperature treatments relative to the ambient profile. This highlights the capacity for elevated temperatures in the future to slow the rate of bell degradation, contributing to an increased probability of overwinter survival, thus increasing the size and duration of Cassiopea blooms in temperate waterways such as Lake Macquarie.

Aquaculture of the Pacific white shrimp Litopenaeus vannamei in low-salinity water is a viable industry and production strategy in the southeastern United States. A major challenge facing this industry is a phenomenon called late-term mortality which is thought to be driven by thermal stress at the end of the growing season when water temperatures can reach or exceed 36 °C in shrimp production ponds. To investigate the physiological mechanisms behind upper lethal limits in shrimp, we evaluated linkages between empirically measured thermal limits and absolute aerobic scope (AAS), or ability to provide energy above that needed for basic maintenance. In this study, we tested whether thermal tolerance decreases with increasing shrimp age/size and whether AAS is a useful concept for understanding the physiological basis of thermal tolerance in shrimp. We exposed two size classes (small: 2.07 ± 0.86 and large: 24.64 ± 2.55 g) of shrimp to increasing temperature at a rate of 1 °C/h from 28 to 42 °C. At each temperature, we used intermittent respirometry to estimate resting metabolic rate and we directly measured lethal thermal tolerance by evaluating critical thermal maximum (CTmax). Additionally, we used the electron transport system assay to estimate maximum metabolic rate (RMR) at temperatures from 9 to 45 °C. Small shrimp had a higher CTmax than large shrimp, with upper lethal limits of 40.6 and 39.0 °C, respectively. For both size-classes, AAS reached its minimum (AASmin) at temperatures near the peak RMR (RMRpeak) and within 2 °C of CTmax. Large shrimp exhibited a lower temperature at AASmin than that of the smaller shrimp. Reductions in AAS appear to be one of the underlying physiological drivers of thermal tolerance in L. vannamei and an indicator of increasing thermal stress. Changes in the temperature at which AAS reaches its minimum may be a useful predictor of shifts in thermal tolerance among shrimp size-classes.

A series of acute stressors can force the animal into a pathological condition and disease susceptibility in different individuals. Taurine has an important effect on relieving and reducing the animal anxiety. In order to know whether taurine has anti-stress effect on olive flounder (Paralichthys olivaceus) with bold and shy coping style, we demonstrate that, repeated acute stress suppress energy expenditure and manifest high behavioral plasticity. Interestingly, treatment with taurine attenuated stress in the divergent behavioral types: 1. Taurine reduced the stress response of flounders in terms of respiratory metabolism and spontaneous activity; 2. Taurine deactivated both of shy individuals “freeze-hide” and bold individuals “fight-flight” response during a threat encounter; 3. Treatment with taurine also significantly reduced the plasma epinephrine (EPI), norepinephrine (NE), adreno-cortico-tropic-hormone (ACTH) and cortisol, and the expression of corticotropin-releasing hormone (CRH), urotensin I (UI) and urotensin II (UII) in hypothalamus and caudal neurosecretory system (CNSS) during stress. Overall, our study demonstrates that taurine can effectively promote anti-stress ability and passivate stress response in flounder by modulating stress axis.

Technologies associated with hydraulic fracturing continue to be prevalent in many regions worldwide. As a result, the production of flowback and produced water (FPW) – a wastewater generated once pressure is released from subterranean wellbores – continues to rise in regions experiencing fracturing activities, while waste management strategies attempt to mitigate compounding burdens of increased FPW production. The heightened production of FPW increases the potential for release to the environment. However, relatively few studies have directly investigated how ecosystems and organisms may be latently affected long after exposures occur. The current study examines rainbow trout exposed in ovo at select critical cardiac developmental time points to differing dilutions and lengths of time (acute versus chronic) to determine how FPW-mediated exposure in ovo may alter later cardiac function and development. After exposure, we allowed fish to grow for ~ 8 months post-fertilization and measured fish swimming performance, aerobic scope, and cardiac structure of juvenile trout. Acute 48 h embryonic 5% FPW exposure at either 3 days post-fertilization (dpf) or 10 dpf significantly reduced later swimming performance and aerobic scope in juvenile trout. In ovo exposure to 2.5% FPW at 3 dpf yielded significant decreases in these metrics as well, while exposing trout to 2.5% FPW at 10 dpf did not induce as significant effects. Morphometric analyses of heart muscle tissue in all treatments decreased compact myocardium thickness. Chronic 1% FPW in ovo exposure for 28 days induced similar reductions in swimming performance, aerobic scope, and decreased compact myocardium thickness as acute exposures. Overall, our results demonstrate that FPW exposure during egg development ultimately results in persistently impaired heart morphology and resulting physiological (swimming) performance.

Due to increasing anthropogenic impacts, heatwaves and prolonged exposure to elevated concentrations of ammonia (HEA) may occur in aquatic environments as a single stressor or a combination thereof, potentially impacting the physiology of exposed animals. In the current study, common water fleas Daphnia magna were exposed for one week to either a 5°C increase in temperature, an increase of 300 µmol l-1 total environmental ammonia, or to both of these stressors simultaneously. Exposure to elevated temperature caused a decrease in MO2, ammonia excretion rates, a downregulation of mRNA coding for key Krebs cycle enzymes and the energy consuming Na+/K+-ATPase and V-type H+-ATPase, as well as the energy distributing crustacean hyperglycemic hormone Rh-protein. High environmental ammonia inflicted a lesser inhibitory effect on the energy metabolism of Daphnia, but initiated ammonia detoxification processes via urea synthesis evident by elevated urea excretion rates and a mRNA upregulation of arginase. Effects observed under the combined stressors resembled largely the effects seen after acclimation to elevated temperature alone, potentially due to the animals’ capability to efficiently detoxify critical ammonia loads. The observed physiological effects and potential threats of the environmental stressor are discussed in detail.

The current study involved exposing adult F0 Gulf killifish (Fundulus grandis) to Macondo-252 oil for 36 to 44 days and assessing the effects of this oiling on the swimming performance and morphology in two generations of progeny reared in clean water. Following exposure to oil, the F0 fish were used as broodstock to generate four lineages of F1 fish using a full-matrix mating design derived from the gametes of clean and oil-exposed parents. Later, the four lineages of F1 fish were used as broodstock to create an F2 generation of the same four lineages. We found few differences in embryonic outcome (% dead,% hatched, and% unhatched) in any of the four lineages of F1 and F2 fish. However, as adults, F1 and F2 fish derived from oil-exposed males from the F0 generation had significantly lower critical swimming speeds (U) than both the control and maternally oil-exposed lineages. Additionally, progeny of oil-exposed fish had altered body shape based on the statistical analysis of two-dimensional landmark-based geometric morphometrics. Fish from oil-exposed lineages showed increased body depth, altered spinal curvature, and changes in the upward angle of projection of the head. Both generations had a significant main effect of maternal and paternal oil exposure on shape; however, F0 paternal oil exposure explained more of the variance in shape across both generations relative to F0 maternal exposure. Our findings demonstrate that parental exposure to oil can impact the shape and aerobic swimming capacity of offspring for at least two generations after the original paternal oiling.

The transportation of heavy crudes such as diluted bitumen (dilbit) sourced from Canadian oil sands through freshwater habitat requires the generation of information that will contribute to risk assessments, spill modelling, management, and remediation for the protection of aquatic organisms. Juvenile sockeye salmon (Oncorhynchus nerka) were exposed acutely (96 h) or subchronically (28 d) to the water-soluble fraction (WSFd) of Cold Lake Blend dilbit at initial total polycyclic aromatic compound (TPAC) concentrations of 0, 13.7, 34.7, and 124.5 µg/L. A significant induction (>3-fold) of hepatic liver ethoxyresorufin-O-deethylase (EROD) activity was induced by 96 h in fish exposed to [TPAC] = 34.7 µg/L and at =13.7 µg/L for a 28 d exposure. Exposure resulted in a typical physiological stress response and disturbance of ion homeostasis; this included elevations in plasma [cortisol], [lactate], [Na+], and [Cl-], and significant reductions in muscle [glycogen]. Critical swimming speed (Ucrit) was significantly reduced (28.4%) in the acute exposure at [TPAC] 124.5 µg/L; reductions of 14.2% and 35.4% were seen in fish subchronically exposed at the two highest concentrations. Reductions in Ucrit were related to significant reductions in aerobic scope (24.3-46.6%) at [TPAC]s of 34.7 and 124.5 µg/L, respectively. Exposure did not impair the ability to mount a secondary stress response following burst exercise, however, the time required for biochemical parameters to return to baseline values was prolonged. Alterations in critical systems supporting swimming, exercise recovery and the physiological stress response could result in decreased salmonid fitness and contribute to population declines if a dilbit spill occurs.

Ectotherms can respond to climate change via evolutionary adaptation, usually resulting in an increase of their upper thermal tolerance. But whether such adaptation influences the phenotypic plasticity of thermal tolerance when encountering further environmental stressors is not clear yet. This is crucial to understand because organisms experience multiple stressors, besides warming climate, in their natural environment and pollution is one of those. Here, we studied the phenotypic plasticity of thermal tolerance in three-spined stickleback populations inhabiting spatially replicated thermally polluted and pristine areas before and after exposing them to a sublethal concentration of copper for one week. We found that the upper thermal tolerance and its phenotypic plasticity after copper exposure did not depend on the thermal history of fish, suggesting that five decades of thermal pollution did not result in evolutionary adaptation to thermal tolerance. The upper thermal tolerance of fish was, on the other hand, increased by ∼ 1.5 °C after 1-week copper exposure in a sex-specific manner, with males having higher plasticity. To our knowledge this is the first study that shows an improvement of the upper thermal tolerance as a result of metal exposure. The results suggest that three-spined sticklebacks are having high plasticity and they are capable of surviving in a multiple-stressor scenario in the wild and that male sticklebacks seem more resilient to fluctuating environmental conditions than female.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is the most widely used antioxidant in automobile tyres and many rubber products. We investigated the impact of 6PPD and 6PPD quinone on acute toxicity, morphology, swimming behaviour, heart rate, and oxygen consumption in zebrafish larvae. Zebrafish embryos were exposed to 6PPD and 6PPD quinone at concentrations of 1, 10, and 25 µg/L during the development period of 1-96 hpf. In the present study, 6PPD quinone was found to be toxic to zebrafish larvae with a 24 h LC 50 of 308.67 µg/L. No significant mortality was observed at any of the tested concentrations. A dose-dependent reduction in swimming performance was observed in the exposed larvae at 116 hpf for both toxicants. Overall, our study shows that exposure of zebrafish embryos to 6PPD and 6PPD quinone at environmentally relevant concentrations (1 µg/L) does not affect its behaviour. However, exposure to higher but still sublethal concentrations of 6PPD and 6PPD quinone (10 and 25 µg/L) can affect behavioural endpoints. These findings reveal the toxicity of 6PPD and 6PPD quinone to early life stages of fish.

The Antarctic ecosystem is progressively exposed to anthropogenic contaminants, such as polycyclic aromatic hydrocarbons (PAHs). So far, it is largely unknown if PAHs leave a mark in the physiology of high-Antarctic fish. We approached this issue via two avenues: first, we examined the functional response of the aryl hydrocarbon receptor (Ahr), which is a molecular initiating event of many toxic effects of PAHs in biota. Chionodraco hamatus and Trematomus loennbergii served as representatives for high-Antarctic Notothenioids, and Atlantic cod, Gadus morhua as non-polar reference species. We sequenced and cloned the Ahr ligand binding domain (LBD) of the Notothenioids and deployed a GAL4-based luciferase reporter gene assay expressing the Ahr LBD. Benzo[a]pyrene (BaP), beta-naphthoflavone and chrysene were used as ligands for the reporter gene assay. Second, we investigated the energetic costs of Ahr activation in isolated liver cells of the Notothenioids during acute, non-cytotoxic BaP exposure. In the reporter assay, the Ahr LBD of Atlantic cod and the Antarctic Notothenioids were activated by the ligands tested herein. In the in vitro assays with isolated liver cells of high-Antarctic Notothenioids, BaP exposure had no effect on overall respiration, but caused shifts in the respiration dedicated to protein synthesis. Thus, our study demonstrated that high-Antarctic fish possess a functional Ahr that can be ligand-activated in a concentration-dependent manner by environmental contaminants. This is associated with altered cost for cellular protein synthesis. Future studies have to show if the toxicant-induced activation of the Ahr pathway may lead to altered organism performance of Antarctic fish.

Like all taxa, populations of aquatic insects may respond to climate change by evolving new physiologies or behaviors, shifting their range, exhibiting physiological and behavioral plasticity, or going extinct. We evaluated the importance of plasticity by measuring changes in growth, survival and respiratory phenotypes of salmonfly nymphs (the stonefly Pteronarcys californica) in response to experimental combinations of dissolved oxygen and temperature. Overall, smaller individuals grew more rapidly during the 6-week experimental period, and oxygen and temperature interacted to affect growth in complex ways. Survival was lower for the warm treatment, although only four mortalities occurred (91.6% versus 100%). Nymphs acclimated to warmer temperatures did not have higher critical thermal maxima (CTmax), but those acclimated to hypoxia had CTmax values (in normoxia) that were higher by approximately 1°C. These results suggest possible adaptive plasticity of systems for taking up or delivering oxygen. We examined these possibilities by measuring the oxygen sensitivity of metabolic rates and the morphologies of tracheal gill tufts located ventrally on thoracic segments. Mass-specific metabolic rates of individuals acclimated to warmer temperatures were higher in acute hypoxia but lower in normoxia, regardless of their recent history of oxygen exposure during acclimation. The morphology of gill filaments, however, changed in ways that appeared to depress rates of oxygen delivery in functional hypoxia. Our combined results from multiple performance metrics indicate that rising temperatures and hypoxia may interact to magnify the risks to aquatic insects, but that physiological plasticity in respiratory phenotypes may offset some of these risks.

Many marine animals perform fascinating survival hydrodynamics and perceive their surroundings through optimally evolved sensory systems. For instance, phocid seal whiskers have undulations that allow them to resist noisy self‐induced vortex‐induced vibrations (VIV) while locking their vibration frequencies to wakes generated by swimming fishes. In this study, fully 3D‐printed microelectromechanical systems (MEMS) sensors with high gauge factor graphene nanoplatelets piezoresistors are developed to explain the exquisite sensitivity of whisker‐inspired structures to upstream wakes. The sensors are also used to measure natural frequencies of excised harbor ( Phoca vitulina ) and grey ( Halichoerus grypus ) seal whiskers and determine the effect of whisker orientation on the VIV, which can explain the possible natural orientation of whiskers during active hunting. Experimental investigations conducted in a recirculating water flume show that whisker‐inspired sensors successfully sense an upstream wake located up to 10× the whisker diameter by locking to the frequency of the wake generator, thus mimicking the sensing mechanism of the seal whisker. The combination of VIV reduction and frequency‐locking with the upstream wake generator demonstrates the whisker‐inspired sensor's high signal‐to‐noise ratio, indicating its efficiency in long‐distance wake sensing as well as its potential as an alternative to visual and acoustic sensors in underwater robots.

In this study, ballan wrasse Labrus bergylta were subjected to either a conventional 1-day or an extended 5-day respirometry protocol. Additionally, in the 5-day protocol the fish were subjected to a 12-hour light-dark cycle to assess effects of photoperiods on metabolic rates (ṀO2 ). Diurnal patterns in routine and resting ṀO2 were not observed, suggesting that circadian rhythms in metabolism largely are driven by activity patterns rather than being of endogenous origin. Moreover, lack of a detectable circadian ṀO2 may be an adaptation to lower costs of living in ballan wrasse. Protocol length influenced standard metabolic rates (SMR) where estimates decreased by 13% and 17% when using 48 hours and 5 days, respectively, compared to 24 hours. The maximum metabolic rate (MMR) and the derived absolute aerobic scope (MMR- SMR) were unaffected by protocol length. However, factorial scopes (MMR / SMR) were reduced from 8.5 to 6.4 in the 5-day protocol, showing that factorial scopes are more sensitive to how SMR are obtained. The critical oxygen tension (Pcrit ) was reduced from 15% PO2 in the 1-day group to 11% PO2 in the 5-day group. However, ṀO2 in response to decreasing PO2 was similar, which together with a similar oxygen extraction coefficient, α (ṀO2 /PO2 ), suggested that the higher Pcrit in the 1-day group was an artefact of overestimating SMR. Finally, α was 12% lower at MMR compared to at Pcrit, which either means that MMR was underestimated in proportion to this difference or that α is not constant in the entire PO2 range. In summary, this study found that a conventional 1-day respirometry protocol may overestimate SMR and thereby alter the derived Pcrit and aerobic scope, while α is unaffected by protocol length. Moreover, alternating light conditions in the absence of other stressors did not influence ṀO2 in ballan wrasse. This article is protected by copyright. All rights reserved.

Parasites are widespread in nature, where they affect the energy budget of hosts, and depending on the imposed pathogenic severity, this may reduce host fitness. However, the energetic costs of parasite infections are rarely quantified. In this study, we measured metabolic rates in recently seawater adapted Atlantic salmon (Salmo salar) infected with the ectoparasitic copepod Lepeophtheirus salmonis and used an aerobic scope framework to assess the potential ecological impact of this parasite–host interaction. The early chalimus stages of L. salmonis did not affect either standard or maximum metabolic rates. However, the later mobile pre-adult stages caused an increase in both standard and maximum metabolic rate yielding a preserved aerobic scope. Notably, standard metabolic rates were elevated by 26%, presumably caused by increased osmoregulatory burdens and costs of mobilizing immune responses. The positive impact on maximum metabolic rates was unexpected and suggests that fish are able to transiently overcompensate energy production to endure the burden of parasites and thus allow for continuation of normal activities. However, infected fish are known to suffer reduced growth, and this suggests that a trade-off exists in acquisition and assimilation of resources despite an uncompromised aerobic scope. As such, when assessing impacts of environmental or biotic factors, we suggest that elevated routine costs may be a stronger predictor of reduced fitness than the available aerobic scope. Furthermore, studying the effects on parasitized fish in an ecophysiological context deserves more attention, especially considering interacting effects of other stressors in the Anthropocene.

Aerobic metabolism generates 15–20 times more energy (ATP) than anaerobic metabolism, which is crucial in maintaining energy budgets in animals, fueling metabolism, activity, growth and reproduction. For ectothermic water‐breathers such as fishes, low dissolved oxygen may limit oxygen uptake and hence aerobic metabolism. Here, we assess, within a phylogenetic context, how abiotic and biotic drivers explain the variation in hypoxia tolerance observed in fishes. To do so, we assembled a database of hypoxia tolerance, measured as critical oxygen tensions ( P crit ) for 195 fish species. Overall, we found that hypoxia tolerance has a clear phylogenetic signal and is further modulated by temperature, body mass, cell size, salinity and metabolic rate. Marine fishes were more susceptible to hypoxia than freshwater fishes. This pattern is consistent with greater fluctuations in oxygen and temperature in freshwater habitats. Fishes with higher oxygen requirements (e.g. a high metabolic rate relative to body mass) also were more susceptible to hypoxia. We also found evidence that hypoxia and warming can act synergistically, as hypoxia tolerance was generally lower in warmer waters. However, we found significant interactions between temperature and the body and cell size of a fish. Constraints in oxygen uptake related to cellular surface area to volume ratios and effects of viscosity on the thickness of the boundary layers enveloping the gills could explain these thermal dependencies. The lower hypoxia tolerance in warmer waters was particularly pronounced for fishes with larger bodies and larger cell sizes. Previous studies have found a wide diversity in the direction and strength of relationships between P crit and body mass. By including interactions with temperature, our study may help resolve these divergent findings, explaining the size dependency of hypoxia tolerance in fish.

This study asked whether interindividual variation in maximum and standard aerobic metabolic rates of the Gulf killifish, Fundulus grandis, correlate with gill morphology and cardiac mitochondrial bioenergetics, traits reflecting critical steps in the O2 transport cascade from the environment to the tissues. Maximum metabolic rate (MMR) was positively related to body mass, total gill filament length, and myocardial oxygen consumption during maximum oxidative phosphorylation (multiple R2=0.836). Standard metabolic rate (SMR) was positively related to body mass, total gill filament length, and myocardial oxygen consumption during maximum electron transport system activity (multiple R2=0.717). After controlling for body mass, individuals with longer gill filaments, summed over all gill arches, or greater cardiac respiratory capacity had higher whole-animal metabolic rates. The overall model fit and the explanatory power of individual predictor variables were better for MMR than for SMR, suggesting that gill morphology and myocardial bioenergetics are more important in determining active rather than resting metabolism. After accounting for body mass, heart ventricle mass was not related to variation in MMR or SMR, indicating that the quality of the heart (i.e., the capacity for mitochondrial metabolism) was more influential than heart size. Finally, the myocardial oxygen consumption required to offset the dissipation of the transmembrane proton gradient in the absence of ATP synthesis was not correlated with either MMR or SMR. The results support the idea that interindividual variation in aerobic metabolism, particularly maximum metabolic rate, is associated with variation in specific steps in the O2 transport cascade.

The critical oxygen tension (Pcrit) for fishes is the oxygen level below which oxygen consumption (MO2) becomes dependent upon ambient oxygen partial pressure (PO2). We compare multiple curve-fitting approaches to estimate Pcrit of the Gulf killifish, Fundulus grandis Baird Girard, 1853, during closed and intermittent-flow respirometry. Fitting two line segments of MO2 versus PO2 produced high and variable estimates of Pcrit, as did nonlinear regression using a hyperbolic (Michaelis-Menton) function. Using nonlinear regression fit to an exponential (modified Weibull) function, or linear regression of MO2 versus PO2 at low PO2, and determining Pcrit as the PO2 when MO2 equals standard metabolic rate (SMR) yielded values that were consistent across fish and among experimental trials. The magnitude of the difference in Pcrit determined by alternative calculation methods exceeded the differences determined in closed and intermittent-flow respirometry, highlighting the need to standardize analytical as well as experimental approaches in determining Pcrit.

Copepods dominate zooplankton biomass of the upper ocean, especially in the highly seasonal northern boreal and Polar Regions, for which specific life-cycle traits such as the accumulation of lipid reserves, migration into deep water, and diapause, are key adaptations. Understanding such traits is central to determining the energetic consequences of high latitude range shifts related to climate change and ultimately, biogeochemical models of carbon flow. Using the calanoid copepod Calanus finmarchicus, we explore a new indicator of diapause, swimming activity, and assess its relationship with respiration. Stage CV copepods were sampled in late summer from shallow (epipelagic) and deep (mesopelagic) water at both on-shelf and off-shelf locations within the Fram Strait at a time when the animals had entered diapause. Using high-throughput quantitative behaviour screening on ex situ swimming activity, we found that irrespective of sampling station copepods from the mesopelagic show highly reduced activity (88.5 ± 3.4 % reduction) when compared to those from the epipelagic. This was supported by morphometric analyses which found that copepods from the mesopelagic were generally larger (12.4 ± 8.8 % increase) and had more lipid reserves (19.3 ± 2.2 % increase) than epipelagic individuals. On average, copepods from the off-shelf station exhibited respiration rates similar to overwintering rates observed elsewhere (1.23 ± 0.76 µg C d-1), while respiration rates of copepods from the shelf station were more consistent with active metabolism (2.46 ± 1.02 µg C d-1). Nevertheless, active and diapausing rates were observed in individuals from both stations at both epi- and mesopelagic depths. We suggest that rapid screening of activity may provide an early indicator of diapause before it becomes fully apparent and consistent in other physiological indicators. Ultimately, swimming activity may provide a useful tool to assess the putative endogenous and exogenous factors involved in diapause onset, provide a handle on the energetics of diapause, and input to biogeochemical carbon models on C. finmarchicus.

Multiple lines of evidence suggest that an inability of the ventricle to contract in coordination with the pacemaker during anoxia exposure may suppress cardiac pumping rate in anoxia-tolerant turtles. To determine under what extracellular conditions the ventricle could be the weak link that limits cardiac pumping, we compared, under various extracellular conditions, the intrinsic contractile properties of isometrically-contracting ventricular and atrial strips obtained from 21 °C- to 5 °C- acclimated turtles ( Trachemys scripta ) that had been exposed to either normoxia or anoxia (16 h at 21 °C; 12 days at 5 °C). We found that combined extracellular anoxia, acidosis, and hyperkalemia (AAK), severely disrupted ventricular, but not right or left atrial, excitability and contractibility of 5 °C anoxic turtles. However, combined hypercalcemia and heightened adrenergic stimulation counteracted the negative effects of AAK. We also report that the turtle heart is resilient to prolonged diastolic intervals, which would ensure that contractile force is maintained if arrhythmia were to occur during anoxia exposure. Finally, our findings reinforce that prior temperature and anoxia experiences are central to the intrinsic contractile response of the turtle myocardium to altered extracellular conditions. At 21 °C, prior anoxia exposure preconditioned the ventricle for anoxic and acidosis exposure. At 5 °C, prior anoxia exposure evoked heightened sensitivity of the ventricle to hyperkalemia, as well as all chambers to combined hypercalcemia and increased adrenergic stimulation. Overall, our findings show that the ventricle could limit cardiac pumping rate during prolonged anoxic submergence in cold-acclimated turtles if hypercalcemia and heightened adrenergic stimulation are insufficient to counteract the negative effects of combined extracellular anoxia, acidosis, and hyperkalemia.

Despite well-known systemic immune reactions in peripheral trauma, little is known about their roles in posttraumatic neurological disorders, such as anxiety, sickness, and cognitive impairment. Leukocyte invasion of the brain, a common denominator of systemic inflammation, is involved in neurological disorders that occur in peripheral inflammatory diseases, whereas the influences of peripheral leukocytes on the brain after peripheral trauma remain largely unclear. In this study, we found that leukocytes, largely macrophages, transiently invaded the brain of zebrafish larvae after peripheral trauma through vasculature-independent migration, which was a part of the systemic inflammation and was mediated by interleukin-1b (il1b). Notably, myeloid cells in the brain that consist of microglia and invading macrophages were implicated in posttraumatic anxiety-like behaviors, such as hyperactivity (restlessness) and thigmotaxis (avoidance), while a reduction in systemic inflammation or myeloid cells can rescue these behaviors. In addition, invading leukocytes together with microglia were found to be responsible for the clearance of apoptotic cells in the brain; however, they also removed the nonapoptotic cells, which suggested that phagocytes have dual roles in the brain after peripheral trauma. More importantly, a category of conserved proteins between zebrafish and humans or rodents that has been featured in systemic inflammation and neurological disorders was determined in the zebrafish brain after peripheral trauma, which supported that zebrafish is a translational model of posttraumatic neurological disorders. These findings depicted leukocyte invasion of the brain during systemic inflammation after peripheral trauma and its influences on the brain through il1b-dependent mechanisms. Invasion of the brain by white blood cells followed tail amputation in zebrafish, the resulting systemic inflammation producing anxiety-like behaviors. Scientists have long recognised an association between systemic inflammation following peripheral traumatic injury such as limb loss and post-traumatic neurological disorders such as anxiety and depression. Raymond Chuen-Chung Chang at the University of Hong Kong, Alvin Chun-Hang Ma at Hong Kong Polytechnic University, China, and co-workers found that following trauma, white cells, mainly macrophages, flowed from neighboring tissues into the hindbrain, before spreading throughout the brain. This influx of white cells, mediated by the small signaling protein interleukin-1b, triggered anxiety-like behaviors such as hyperactivity and avoidance in the zebrafish. The researchers emphasize that the links between systemic inflammation following peripheral trauma and neurological responses require extensive further research.

At early life stages invasive fishes may have no innate or learned behavioral responses to native predators. However, social cues expressed by shoal mates is one strategy species use to assess risk. By shoaling and using social cues, fishes may identify and mimic others with anti-predator behaviors to increase their own survival. Ability of non-native fishes, such as bighead carp (Hypophthalmichthys nobilis), to mimic native species that have experienced predatory threats is not known. In this experimental study, we varied the number of experienced individuals and the species composition to contrast the responses of naïve juvenile bighead carp exposed to predatory kairomones when grouped with differing numbers of either experienced conspecific or experienced heterospecific (golden shiner, Notemigonus crysoleucas) shoal mates. We found fully naïve groups of bighead carp did not respond to largemouth bass kairomones, but that naïve individuals could mimic anti-predatory behaviors of experienced individuals, even when those experienced individuals were heterospecifics. Diverse alarm responses of bighead carp to composition and experience suggest that responses of this species are plastic. Through changing responses based on shoal experience level and composition, plastic social learning highlights how naïve individuals may adapt to novel predator threats, which could inform predictions of non-native persistence in novel waterways.

Approximately 36,000 units of red blood cells (RBCs) are used every day in the U.S. and there is a great challenge for hospitals to maintain a reliable supply, given the 42-day expiration period from the blood donation date. For many years, research has been conducted to develop ex vivo storage solutions that limit RBC lysis and maintain a high survival rate of the transfused cells. However, little attention is directed towards potential fractionation methods to remove unwanted cell debris or aged blood cells from stored RBC units prior to transfusion, which could not only expand the ex vivo shelf life of RBC units but also avoid adverse events in transfused patients. Such fractionation methods could also limit the number of transfusions required for treating certain pathologies, such as sickle cell disease (SCD). In this work, magnetic fractionation is studied as a potential technology to fractionate functional and healthy RBCs from aged or sickle cells. It has been reported that during ex vivo RBC storage, RBCs lose hemoglobin (Hb) and lipid content via formation of Hb-containing exosomes. Given the magnetic character of deoxygenated- or met-Hb, in this work, we propose the use of a quadrupole magnetic sorter (QMS) to fractionate RBCs based on their Hb content from both healthy stored blood and SCD blood. In our QMS, a cylindrical microchannel placed inside the center of the quadrupolar magnets is subjected to high magnetic fields and constant field gradients (286 T/m), which causes the deflection of the paramagnetic, Hb-enriched, and functional RBCs from their original path and their collection into a different outlet. Our results demonstrated that although we could obtain a significant difference in the magnetic mobility of the sorted fractions (corresponding to a difference in more than 1 pg of Hb per cell), there exists a tradeoff between throughput and purity. Therefore, this technology when optimized could be used to expand the ex vivo shelf life of RBC units and avoid adverse events in transfused individuals or SCD patients requiring blood exchange therapy.

Interference competition over food and territory can shape population structure and habitat use within and between species. The introduction of invasive species often leads to novel competitive interactions over shared resources and invaders can eventually exclude the native species from preferred habitats. Invasive brook trout ( Salvelinus fontinalis ) introduced to northern Europe have excluded native brown trout ( Salmo trutta ) from numerous headwater streams. The fact that invasive brook trout can displace the more aggressive brown trout is puzzling. However, the earlier spawning and hatching of brook trout, compared to brown trout, may lead to unequal competition due to size advantage and prior resident status of brook trout at the fry stage. In this study, we examine the effect of competition between brown trout and brook trout using the natural size distribution of the two species. In two consecutive experiments, we first measured space use and feeding of a fry (age 0+) in the presence of a juvenile (age 1+). In experiment 2, we assessed territorial interactions between the species at the fry stage (age 0+) and if smaller brown trout could compensate the disadvantage by manipulating residence duration. Fry of brook trout feed sooner and spend more time close to the larger individual than brown trout fry. We also found that brook trout fry won most territorial contests against brown trout, and that increased residence duration led to longer and more aggressive interactions. The results suggest that smaller brown trout are displaced to suboptimal habitats in the presence of a larger brook trout. Therefore, the later emergence from gravel beds resulting in the naturally occurring size disadvantage of brown trout at the fry stage may lead to unequal territorial interactions that could explain why brown trout are displaced from preferred habitats in sympatry with brook trout.

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is a widely prescribed antidepressant that is detected in municipal wastewater effluents at µg/L concentrations. It has been shown to impact the early life stages of fish, including neurodevelopment and behaviour in larvae, but whether such early exposures have longer-term consequences are far from clear. Here, we sought to determine whether zygotic deposition of venlafaxine, mimicking a maternal transfer scenario, disturbs the metabolic rate and behavioural performance using zebrafish (Danio rerio). This was tested using freshly fertilized embryos (1–4 cell stage) microinjected with either 0, 1 or 10 ng of venlafaxine and raised to either juvenile (60 days post-fertilization) or adult (10–12 months post-fertilization). Zygotic venlafaxine exposure led to a reduction in the active metabolic rate and aerobic scope, but this was only observed in female fish. On the other hand, the total distance travelled in an open field assessment was greater at the highest concentration of venlafaxine only in the adult males. At the juvenile stage, behavioural assessments demonstrated that venlafaxine exposure may increase boldness—including hyperactivity, lower thigmotaxis, and a reduction in the distance to a novel object. Taken together, these results demonstrate that zygotic venlafaxine exposure may impact developmental programming in a sex-specific manner in fish.

Commercial fishery harvest can influence the evolution of wild fish populations. Our knowledge of selection on morphology is however limited, with most previous studies focusing on body size, age, and maturation. Within species, variation in morphology can influence locomotor ability, possibly making some individuals more vulnerable to capture by fishing gears. Additionally, selection on morphology has the potential to influence other foraging, behavioral, and life‐history related traits. Here we carried out simulated fishing using two types of gears: a trawl (an active gear) and a trap (a passive gear), to assess morphological trait‐based selection in relation to capture vulnerability. Using geometric morphometrics, we assessed differences in shape between high and low vulnerability fish, showing that high vulnerability individuals display shallower body shapes regardless of gear type. For trawling, low vulnerability fish displayed morphological characteristics that may be associated with higher burst‐swimming, including a larger caudal region and narrower head, similar to evolutionary responses seen in fish populations responding to natural predation. Taken together, these results suggest that divergent selection can lead to phenotypic differences in harvested fish populations.

In many cases, understanding species’ responses to climate change requires understanding variation among individuals in response to such change. For species with strong symbiotic relationships, such as many coral reef species, genetic variation in symbiont responses to temperature may affect the response to increased ocean temperatures. To assess variation among symbiont genotypes, we examined the population dynamics and physiological responses of genotypes of Breviolum antillogorgium in response to increased temperature. We found broad temperature tolerance across genotypes, with all genotypes showing positive growth at 26, 30, and 32°C. Genotypes differed in the magnitude of the response of growth rate and carrying capacity to increasing temperature, suggesting that natural selection could favor different genotypes at different temperatures. However, the historical temperature at which genotypes were reared (26 or 30°C) was not a good predictor of contemporary temperature response. We found increased photosynthetic rates and decreased respiration rates with increasing contemporary temperature, and differences in physiology among genotypes, but found no significant differences in the response of these traits to temperature among genotypes. In species with such broad thermal tolerance, selection experiments on symbionts outside of the host may not yield results sufficient for evolutionary rescue from climate change.

The cardiac developmental network has been associated with myocardial regenerative potential. However, the embryonic signals triggered following injury have yet to be fully elucidated. Nkx2.5 is a key causative transcription factor associated with human congenital heart disease and one of the earliest markers of cardiac progenitors, thus it serves as a promising candidate. Here, we show that cardiac-specific RNA-sequencing studies reveal a disrupted embryonic transcriptional profile in the adult Nkx2.5 loss-of-function myocardium. nkx2.5−/− fish exhibit an impaired ability to recover following ventricular apex amputation with diminished dedifferentiation and proliferation. Complex network analyses illuminate that Nkx2.5 is required to provoke proteolytic pathways necessary for sarcomere disassembly and to mount a proliferative response for cardiomyocyte renewal. Moreover, Nkx2.5 targets embedded in these distinct gene regulatory modules coordinate appropriate, multi-faceted injury responses. Altogether, our findings support a previously unrecognized, Nkx2.5-dependent regenerative circuit that invokes myocardial cell cycle re-entry, proteolysis, and mitochondrial metabolism to ensure effective regeneration in the teleost heart. Cardiac developmental genes have been associated with regenerative potential. Here the authors identify a Nkx2.5-dependent gene regulatory network operating through ect2, psmb3, and psmd7 to orchestrate cell cycle re-entry, proteolysis, and mitochondrial metabolism during myocardial repair.

The red swamp crayfish (Procambarus clarkii) is the most widely spread freshwater crayfish worldwide. Competing physiological traits can influence invasion success in any given environment by limiting the available scope for aerobically demanding activities. While high flows have been associated with reduced crayfish movement upstream, the effects of flow alteration on their metabolic demands have been largely overlooked. In this study, we estimated routine metabolic rate (RMR) at rest and oxygen consumption rates of crayfish under different current velocities in a flume respirometer, while maximum metabolic rate (MMR) was determined using the exhaustive chase protocol. We also measured some morphometric variables in males and females of crayfish. Oxygen uptake substantially increased with crayfish size and current velocity due to increased energy expenditure to overcome drag and hold a stationary position. Sexual dimorphism in morphological traits did not lead to sexual differences in oxygen uptake. Moreover, we found that individuals operated close to their maximum aerobic capacity at elevated current velocities (≥ 25 cm s−1). This suggested that the high flow-driven energetic demand may compromise the energy available for reproduction, growth and dispersal, thereby affecting overall fitness. These metabolic constraints could partly explain the failed invasions of invasive crayfish in fast-flowing waters.

Cold water pollution (CWP) is caused by releases of unseasonably cold water from large, thermally stratified dams. Rapid and prolonged decreases in water temperature can have depressive effects on the metabolism, growth and swimming performance of fish. However, it is unknown if reducing the rate of temperature decrease could mitigate these negative effects by allowing thermal acclimation/acclimatization to occur. This study investigated the rate of temperature decrease as a potential CWP mitigation strategy in juvenile Murray cod Maccullochella peelii. M. peelii were exposed to a gradual, intermediate or rapid temperature decrease from 24 to 14°C. Energetic costs, locomotor performance, growth and survival were measured to determine if the initial thermal regime affected the thermal acclimation capacity of M. peelii. Cold exposure had significant acute and lasting depressive effects regardless of the rate of temperature decrease, although M. peelii showed varying degrees of thermal compensation in swimming performance and metabolism after 8 weeks of exposure to low temperatures. The short‐term effects of CWP‐like reductions in temperature are significant, but over time M. peelii can offset some of the depressive effects of CWP through thermal plasticity. This study highlights the importance of understanding physiological responses of fish to inform management and conservation. We conclude that rate of water temperature decline cannot be used to mitigate the sublethal effects of CWP on juvenile M. peelii but may still be useful for managing the negative effects in other native Australian fish species.

Burst swimming velocity (Uburst) was compared between wild and hatchery-reared chum salmon fry. In the hatchery-reared fry, Uburst was significantly correlated with the condition factor, but not with the body mass and fork length. In the wild-reared fry, on the other hand, Uburst ranged widely and did not correlate with condition factor. These suggest that well-balanced growth under satisfactory nutrient condition at the early developmental stage improves Uburst, and in the wild-reared fry, their cautiousness and various experiences may override the condition factor dependency of Uburst.

Heat waves constitute a challenge for aquatic ectotherms. However, the thermal tolerance of animals and their individual phenotypic plasticity to respond to heat waves may be influenced by thermal history. We tested these hypotheses by comparing the upper thermal tolerance and the individual capacities of three‐spined sticklebacks from populations with different thermal histories to respond to heat waves. Two populations originated from thermally polluted nuclear power plant (NPP) habitats, while four locations represented geographically adjacent control areas. To disentangle the genetic adaptation from the phenotypic plastic response, we measured the individual upper thermal tolerance and the responses at molecular level in common‐garden conditions before and after a laboratory‐mimicked heat wave. We found that the sticklebacks exhibit considerable phenotypic plasticity in thermal tolerance since the heat wave increased fish upper thermal tolerance significantly. The individual plasticity to respond to the heat wave was also negatively correlated with initial thermal tolerance. On the other hand, neither the thermal tolerance nor the plastic responses differed between NPP and control sites despite detection of significant but low genome‐wide divergence in 10 out of 15 pairwise comparisons. Our results suggest that five decades of NPP activity with warmer water have not resulted in a detectable evolutionary change in either the upper thermal tolerance or its plasticity in three‐spined sticklebacks potentially rendering them sensitive to frequent heat waves.

Chemical UV filters are increasingly used in cosmetics to protect skin from UV radiation. As a consequence, they are released into the aquatic environment via recreational activities and wastewaters. In aquatic ecosystems, fish eggs in contact with sediment can be affected by organic and lipophilic pollutants such as UV filters. The present study aims to evaluate the toxicity of six individual UV filters, diethylhexyl butamido triazone (DBT), diethylamino hydroxybenzoyl hexyl benzoate (DHHB), ethylhexyl triazone (ET), 2-ethylhexyl salicylate (ES), homosalate (HS), and octocrylene (OC), in the embryo-larval stages of zebrafish Danio rerio. Contamination of fish eggs and larvae with UV filters occurred through contact with spiked sediment for 96 h at a concentration of 10 μg g−1. Among the six UV filters tested, OC delayed hatching success, whereas ES significantly increased the heartbeat rate of embryo–larvae after sediment exposure, probably as a stress response.

Obesity and metabolic syndrome are of increasing global concern. In order to understand the basic biology and etiology of obesity, research has turned to animals across the vertebrate spectrum including zebrafish. Here, we carefully characterize zebrafish in a long-term obesogenic environment as well as zebrafish that went through early lifetime caloric restriction. We found that long-term obesity in zebrafish leads to metabolic endpoints comparable to mammals including increased adiposity, weight, hepatic steatosis and hepatic lesions but not signs of glucose dysregulation or differences in metabolic rate or mitochondrial function. Malnutrition in early life has been linked to an increased likelihood to develop and an exacerbation of metabolic syndrome, however fish that were calorically restricted from five days after fertilization until three to nine months of age did not show signs of an exacerbated phenotype. In contrast, the groups that were shifted later in life from caloric restriction to the obesogenic environment did not completely catch up to the long-term obesity group by the end of our experiment. This dataset provides insight into a slowly exacerbating time-course of obesity phenotypes.

In animals living in groups, the social environment is fundamental to shaping the behaviors and life histories of an individual. A mismatch between individual and group behavior patterns may have disadvantages if the individual is incapable of flexibly changing its state in response to the social environment that influences its energy gain and expenditure. We used different social groups of juvenile three‐spined sticklebacks ( Gasterosteus aculeatus ) with experimentally manipulated compositions of individual sociability to study the feedback between individual and group behaviors and to test how the social environment shapes behavior, metabolic rate, and growth. Experimentally created unsociable groups, containing a high proportion of less sociable fish, showed bolder collective behaviors during feeding than did corresponding sociable groups. Fish within groups where the majority of members had a level of sociability similar to their own gained more mass than did those within mismatched groups. Less sociable individuals within sociable groups tended to have a relatively low mass but a high standard metabolic rate. A mismatch between the sociability of an individual and that of the majority of the group in which it is living confers a growth disadvantage probably due to the expression of nonadaptive behaviors that increase energetic costs.

The physiological response of two species of mussels ( Mytilus edulis and M. galloprovincialis ) and two species of oysters ( Crassostrea gigas and Ostrea edulis ) to temperature, oxygen levels and food concentration, factors likely to vary as a result of climate change, was determined experimentally. Bivalves of similar size from different origins were exposed to six temperatures (3, 8, 15, 20, 25 and 30 °C) at two food regimes (2 and 10 μg Chl a L −1 ) for 6 weeks. In a parallel running experiment M. edulis from the same batches were exposed to three different temperatures (15, 20 and 25 °C) and three different oxygen levels (30, 50 and 100%) at two food regimes (2 and >8 μg Chl a L −1 ) for 3–4 weeks. Survival during the experiment ranged from 93% to 100% except for the mussels exposed to 30 °C which showed 100% mortality after three to 32 days. Higher food conditions showed higher optimal temperatures for growth of mussels and oysters. In addition, at the high food treatment, reduced O 2 saturation resulted in lower growth of mussels. At the low food treatment there were no differences in growth among the different O 2 levels at the same temperature. At high food concentration treatment, M. edulis growth was higher with low temperature and high oxygen level. Condition index was higher at higher food concentrations and decreased with increasing temperature. In addition, condition was lower at low oxygen saturation. Lower clearance rates were observed at high food concentrations. At 100% saturation of oxygen, mussel clearance rate increased with temperature at High food regime, but not at Low food regime. Mussel clearance rates were significantly reduced with low oxygen concentrations together with high temperature. Oxygen consumption significantly increased with temperature. Oxygen saturation was the main factor affecting mussel clearance rate. High temperature and low oxygen concentration combined significantly reduced clearance rate and increased oxygen consumption. These response curves can be used to improve parameterisation of individual shellfish growth models taking into consideration factors in the context of climate change: temperature, food concentration, oxygen concentration and their interactions. The observation that abiotic factors interact in affecting mussels and oysters is an important result to take into account.

Aim Although zebrafish are gaining popularity as biomedical models of cardiovascular disease, our understanding of their cardiac control mechanisms is fragmentary. Our goal was to clarify the controversial role of the ß1‐adrenergic receptor (AR) in the regulation of heart rate in zebrafish. Methods CRISPR‐Cas9 was used to delete the adrb1 gene in zebrafish allowing us to generate a stable adrb1 −/− line. Larval heart rates were measured during pharmacological protocols and with exposure to hypercapnia. Expression of the five zebrafish adrb genes were measured in larval zebrafish hearts using qPCR. Results Compared with genetically matched wild‐types ( adrb1 +/+ ), adrb1 −/− larvae exhibited ~20 beats min −1 lower heart rate, measured from 2 to 21 days post‐fertilization (dpf). Nevertheless, adrb1 −/− larvae exhibited preserved positive chronotropic responses to pharmacological treatment with AR agonists (adrenaline, noradrenaline, isoproterenol), which were blocked by propranolol (general ß‐AR antagonist). Regardless of genotype, larvae exhibited similar increases in heart rate in response to hypercapnia (1% CO 2 ) at 5 dpf, but tachycardia was blunted in adrb1 −/− larvae at 6 dpf. adrb1 gene expression was abolished in the hearts of adrb1 −/− larvae, confirming successful knockout. While gene expression of adrb2a and adrb3a was unchanged, adrb2b and adrb3b mRNA levels increased in adrb1 −/− larval hearts. Conclusion Despite adrb1 contributing to the setting of resting heart rate in larvae, it is not strictly essential for zebrafish, as we generated a viable and breeding adrb1 −/− line. The chronotropic effects of adrenergic stimulation persist in adrb1 −/− zebrafish, likely due to the upregulation of other ß‐AR subtypes.

Goldfish enter a hypometabolic state to survive chronic hypoxia. We recently described tissue-specific contributions of membrane lipid composition remodeling and mitochondrial function to metabolic suppression across different goldfish tissues. However, the molecular and especially epigenetic foundations of hypoxia tolerance in goldfish under metabolic suppression are not well understood. Here we show that components of the molecular oxygen-sensing machinery are robustly activated across tissues irrespective of hypoxia duration. Induction of gene expression of enzymes involved in DNA methylation turnover and microRNA biogenesis suggest a role for epigenetic transcriptional and post-transcriptional suppression of gene expression in the hypoxia-acclimated brain. Conversely, mechanistic target of rapamycin-dependent translational machinery activity is not reduced in liver and white muscle, suggesting this pathway does not contribute to lowering cellular energy expenditure. Finally, molecular evidence supports previously reported chronic hypoxia-dependent changes in membrane cholesterol, lipid metabolism and mitochondrial function via changes in transcripts involved in cholesterol biosynthesis, β-oxidation, and mitochondrial fusion in multiple tissues. Overall, this study shows that chronic hypoxia robustly induces expression of oxygen-sensing machinery across tissues, induces repressive transcriptional and post-transcriptional epigenetic marks especially in the chronic hypoxia-acclimated brain and supports a role for membrane remodeling and mitochondrial function and dynamics in promoting metabolic suppression.

The amazon fishes’ responses to hypoxia seem to be related to the Amazon basin diversity of aquatic environments, which present drastic daily and seasonal variations in the dissolved oxygen concentration. Among these fishes’ adaptation to hypoxia, behavioral, metabolic, physiological, and biochemical responses are well known for some species. In this work, we aimed to identify how two different aquatic environments, normoxic forest streams and hypoxic lakes, dictate the responses to hypoxia for two cichlid species, Mesonauta festivus and Aequidens pallidus. In our results, we found that A. pallidus is less tolerant to hypoxia, which seems to be related to this animal’s natural normoxic environment. Even though this species modulated the mitochondrial respiration in order to improve the oxygen use, it also showed a lower decrease in metabolic rate when exposed to hypoxia and no activation of the anaerobic metabolism. Instead, M. festivus showed a higher decrease in metabolic rate and an activation of the anaerobic metabolism. Our data reveal that the natural dissolved oxygen influences the hypoxia tolerance and the species’ tolerance is related to its ability to perform metabolic depression. The interest results are the absence of mitochondrial respiration influences in these processes. The results observed with A. pallidus bring to light also the importance of preserving the forests, in which streams hold very specialized species acclimated to normoxia and lower temperature. The importance of hypoxia tolerance is, thus, important to keep fish assemblage and is thought to be a strong driver of fish biodiversity.

Stock enhancement based on hatchery-reared fish has become one of the most common forms of management practices in marine fisheries resource restoration. However, unnatural rearing environments may cause hatchery-reared fish to diverge phenotypically from wild conspecifics, with negative consequences for post-release performance in the natural environments. To better evaluate the suitability of releasing hatchery-reared fish, it is necessary to understand the phenotypic effects of captive rearing, through comparisons with wild conspecifics. In this study, we compared body morphology, swimming performance, and biochemical body composition between hatchery-reared and wild marbled rockfish (Sebastiscus marmoratus) from the same general gene pool. The results show that the overall body profile differed significantly between the groups, with hatchery-reared individuals having a deeper body (in particular in the head and trunk regions), narrower caudal peduncles, and higher condition factor, as compared to wild conspecifics. Hatchery-reared rockfish also had relatively shorter fins, for a given size. In terms of swimming performance, the hatchery-reared rockfish performed worse than the wild, with slower burst swimming speeds and poorer endurance. Wild rockfish had higher body protein content but lower lipid levels compared to the hatchery-reared individuals. These results suggest that hatchery rearing conditions have a great impact on the phenotypic development, with possibly high effects on their post-release performance of the hatchery-reared marbled rockfish. Modifications for the hatchery environment and operation should be investigated with an aim to minimize the divergence in phenotypic development for production of more wild-like fish for stocking.

Cultured fish can be induced to swim, although the suitability and benefits remain to be tested. Sustained swimming exercise (SSE) training and detraining (DET) were applied in juvenile gilthead sea bream (Sparus aurata) and the metabolic rates were investigated. Fish with a total body mass of 80.5 ± 1.5 g and total length 17.2 ± 0.1 cm were maintained untrained (spontaneously swimming activity, UNT), swim-trained (induced sustained swimming activity, SSE) at 1 BL s-1 for 28 days, or detrained (28 days of swimming followed by 10 days of untraining, DET). Standard metabolic rate (SMR), maximum metabolic rate (MMR), and excess post-exercise oxygen consumption (EPOC) were assessed (n = 10). In addition, the effects of SSE training (51 days) on blood and plasma parameters were investigated before and immediately after applying a high-intensity swimming (HIS) protocol. SMR, MMR, and EPOC values were not different between SSE, UNT, or DET fish (143.2, 465.5 mg O2 kg-1 h-1, and 459.1 mg O2 kg-1, respectively). Spite the lack of differences between treatments, the dispersion in the residuals for SMR, MMR, and absolute aerobic scope (AAS) values followed the order UNT > DET > SSE, indicating that swim training decreases the individual variation of these metabolic parameters. Haematological parameters, plasma glucose, lactate, and cortisol levels were similar between SSE and UNT groups before HIS. Plasma glucose and lactate levels increased in both groups after HIS, being higher in the SSE group. Plasma cortisol levels were similar between both groups after HIS. Results suggest that SSE training improves energy use and reduces individual variation in SMR and MMR, an effect that declines with detraining.

Flows in river habitats are characterized by unsteady turbulence due to the existence of woody debris, boulders, and vegetation. As a representative aquatic species, fish is important for the riverine ecosystems with its complex behavioral responses to turbulent flows. Previous studies investigated the fish-vortices interaction with vortex streets by placing objects with simplified geometries centred at the flow. However, complex river morphology in natural rivers reuslts in much more spatially heterogeneous flows due to randomly distributed obstructions. Thus, a semi-circular cylinder patch located on one side of flume is used to mimic a vegetation patch at the riverbank. The patch varies in diameter (D0 = 16, 20, 24 cm) and density (φ = 0.04, 0.1), while the flow velocity is fixed at 25 cm/s. Fish are observed to swim in three typical patterns, which are "swim around (Pattern 1)", "spill (Pattern 2)", and "swim through (Pattern 3)". For flow with a dense patch, all three patterns are recorded, but only patterns 1 and 2 are seen in sparse patches. We notice that in patterns 1 and 2, fish prefer to hold place in zones of low velocity and low turbulence. Moreover, variations in patch diameter have little influence on pattern selection. Results showed that tail beat amplitude (TBA*) in each zone displayed more variations compared with tail beat frequency (TBF). In addition, spearman rank tests revealed that TBA* is affected by none of the four hydrodynamic variables ( U, u std, τ xy, Ω z ) whereas flow velocity imposes the most influence on TBF. Both diameter and density of the patch displayed no significant influence on TBA* and TBF. This article is protected by copyright. All rights reserved.

Predator-prey interactions exert significant influence over the survival of juvenile fish cohorts. Therefore, susceptibility of a habitat to invasion is influenced by the capacity of native predators to regulate invasive species through consumption. Closely related predators often share similar characteristics (e.g., odors or body morphometry), and prey species capable of expressing generalized behavioral responses to predators with similar characteristics may increase their chances for survival. Here, we examined how naïve juvenile silver carp (Hypophthalmichthys molitrix), an invasive Asian carp, respond to three predator odors from predators commonly found in Midwestern lakes and rivers of the USA. We tested two congeneric species of bass (largemouth Micropterus salmoides and smallmouth M. dolomieu bass) and one outgroup, longnose gar (Lepisosteus osseus). Additionally, we tested how silver carp conditioned to recognize the odor of one group, largemouth bass, responded to the predator odors of the congeneric species and the outgroup. We found that juvenile silver carp showed no innate response to any of the three predator odors. Additionally, although they could be conditioned to recognize predator odors from largemouth bass, they were unable to generalize predator odors to smallmouth bass or longnose gar odor. These results suggest that invasive species could be less likely to persist in environments with diverse predator communities than environments of equal densities with uniform predator communities and that future studies should continue to explore this area as well as focus on understanding dynamics in predator-prey interactions of invasive species.

Significance In diving birds like penguins, physiologic considerations suggest that increased hemoglobin (Hb)-O 2 affinity may improve pulmonary O 2 extraction and enhance dive capacity. We integrated experimental tests on whole-blood and native Hbs of penguins with protein engineering experiments on reconstructed ancestral Hbs. The experiments involving ancestral protein resurrection enabled us to test for evolved changes in Hb function in the stem lineage of penguins after divergence from their closest nondiving relatives. We demonstrate that penguins evolved an increased Hb-O 2 affinity in conjunction with a greatly augmented Bohr effect (i.e., reduction in Hb-O 2 affinity at low pH) that should maximize pulmonary O 2 extraction without compromising O 2 delivery at systemic capillaries. Dive capacities of air-breathing vertebrates are dictated by onboard O 2 stores, suggesting that physiologic specialization of diving birds such as penguins may have involved adaptive changes in convective O 2 transport. It has been hypothesized that increased hemoglobin (Hb)-O 2 affinity improves pulmonary O 2 extraction and enhances the capacity for breath-hold diving. To investigate evolved changes in Hb function associated with the aquatic specialization of penguins, we integrated comparative measurements of whole-blood and purified native Hb with protein engineering experiments based on site-directed mutagenesis. We reconstructed and resurrected ancestral Hb representing the common ancestor of penguins and the more ancient ancestor shared by penguins and their closest nondiving relatives (order Procellariiformes, which includes albatrosses, shearwaters, petrels, and storm petrels). These two ancestors bracket the phylogenetic interval in which penguin-specific changes in Hb function would have evolved. The experiments revealed that penguins evolved a derived increase in Hb-O 2 affinity and a greatly augmented Bohr effect (i.e., reduced Hb-O 2 affinity at low pH). Although an increased Hb-O 2 affinity reduces the gradient for O 2 diffusion from systemic capillaries to metabolizing cells, this can be compensated by a concomitant enhancement of the Bohr effect, thereby promoting O 2 unloading in acidified tissues. We suggest that the evolved increase in Hb-O 2 affinity in combination with the augmented Bohr effect maximizes both O 2 extraction from the lungs and O 2 unloading from the blood, allowing penguins to fully utilize their onboard O 2 stores and maximize underwater foraging time.

Physical exercise stimulates adult neurogenesis, yet the underlying mechanisms remain poorly understood. A fundamental component of the innate neuroregenerative capacity of zebrafish is the proliferative and neurogenic ability of the neural stem/progenitor cells. Here, we show that in the intact spinal cord, this plasticity response can be activated by physical exercise by demonstrating that the cholinergic neurotransmission from spinal locomotor neurons activates spinal neural stem/progenitor cells, leading to neurogenesis in the adult zebrafish. We also show that GABA acts in a non-synaptic fashion to maintain neural stem/progenitor cell quiescence in the spinal cord and that training-induced activation of neurogenesis requires a reduction of GABAA receptors. Furthermore, both pharmacological stimulation of cholinergic receptors, as well as interference with GABAergic signaling, promote functional recovery after spinal cord injury. Our findings provide a model for locomotor networks’ activity-dependent neurogenesis during homeostasis and regeneration in the adult zebrafish spinal cord. The mechanisms stimulating adult neurogenesis are unclear. Here, the authors show the contribution of cholinergic and GABAergic signalling within the locomotor network to spinal cord neurogenesis during homeostasis and regeneration, showing neurogenesis depends on circuit activity in the adult zebrafish.

Significance Biology has long-standing rules about how metabolism and demography should covary. These rules connect physiology to ecology but remarkably, these rules have only ever been tested indirectly. Using a model marine invertebrate, we created experimental field populations that varied in metabolic rate but not body size. We show that metabolism qualitatively affects population growth and carrying capacity in ways predicted by theory but that scaling relationships for these parameters, as well as estimates of energy use at carrying capacity, depart from classic predictions. That metabolism affects demography in ways that depart from canonical theory has important implications for predicting how populations may respond to global change and size-selective harvesting. Metabolism should drive demography by determining the rates of both biological work and resource demand. Long-standing “rules” for how metabolism should covary with demography permeate biology, from predicting the impacts of climate change to managing fisheries. Evidence for these rules is almost exclusively indirect and in the form of among-species comparisons, while direct evidence is exceptionally rare. In a manipulative field experiment on a sessile marine invertebrate, we created experimental populations that varied in population size (density) and metabolic rate, but not body size. We then tested key theoretical predictions regarding relationships between metabolism and demography by parameterizing population models with lifetime performance data from our field experiment. We found that populations with higher metabolisms had greater intrinsic rates of increase and lower carrying capacities, in qualitative accordance with classic theory. We also found important departures from theory—in particular, carrying capacity declined less steeply than predicted, such that energy use at equilibrium increased with metabolic rate, violating the long-standing axiom of energy equivalence. Theory holds that energy equivalence emerges because resource supply is assumed to be independent of metabolic rate. We find this assumption to be violated under real-world conditions, with potentially far-reaching consequences for the management of biological systems.

Fish in coastal ecosystems can be exposed to acute variations in CO2 of between 0.2 and 1 kPa CO2 (2000–10,000 µatm). Coping with this environmental challenge will depend on the ability to rapidly compensate for the internal acid–base disturbance caused by sudden exposure to high environmental CO2 (blood and tissue acidosis); however, studies about the speed of acid–base regulatory responses in marine fish are scarce. We observed that upon sudden exposure to ∼1 kPa CO2, European sea bass (Dicentrarchus labrax) completely regulate erythrocyte intracellular pH within ∼40 min, thus restoring haemoglobin–O2 affinity to pre-exposure levels. Moreover, blood pH returned to normal levels within ∼2 h, which is one of the fastest acid–base recoveries documented in any fish. This was achieved via a large upregulation of net acid excretion and accumulation of HCO3− in blood, which increased from ∼4 to ∼22 mmol l−1. While the abundance and intracellular localisation of gill Na+/K+-ATPase (NKA) and Na+/H+ exchanger 3 (NHE3) remained unchanged, the apical surface area of acid-excreting gill ionocytes doubled. This constitutes a novel mechanism for rapidly increasing acid excretion during sudden blood acidosis. Rapid acid–base regulation was completely prevented when the same high CO2 exposure occurred in seawater with experimentally reduced HCO3− and pH, probably because reduced environmental pH inhibited gill H+ excretion via NHE3. The rapid and robust acid–base regulatory responses identified will enable European sea bass to maintain physiological performance during large and sudden CO2 fluctuations that naturally occur in coastal environments.

Animals inhabiting the intertidal zone are exposed to abrupt changes in environmental conditions associated with the rise and fall of the tide. For convenience, the majority of laboratory studies on intertidal organisms have acclimated individuals to permanently submerged conditions in seawater tanks. In this study, green shore crabs, Carcinus maenas, were acclimated to either a simulated tidal regime of continuous emersion–immersion (‘tidal’) or to permanently submerged conditions (‘non-tidal’) to assess their physiological responses to subsequent emersion. Tidal crabs exhibited an endogenous rhythm of oxygen consumption during continuous submersion with lower oxygen consumption during periods of anticipated emersion, which was not detected in non-tidal crabs. During emersion, tidal crabs were able to buffer apparent changes in acid–base balance and exhibited no change in venous pH, whereas non-tidal crabs developed an acidosis associated with a rise in lactate levels. These results indicate that tidal crabs were better able to sustain aerobic metabolism and had lower metabolic costs during emersion than non-tidal crabs. It is likely that the elevated levels of haemocyanin exhibited by tidal crabs allowed them to maintain oxygen transport and buffer pH changes during emersion. This suggests that acclimation of C. maenas to submerged conditions results in a loss of important physiological mechanisms that enable it to tolerate emersion. The results of this study show that caution must be taken when acclimating intertidal organisms to submerged conditions in the laboratory, as it may abolish important physiological responses and adaptations that are critical to their performance when exposed to air.

Fishing‐associated selection is one of the most important human‐induced evolutionary pressures for natural populations. However, it is unclear whether fishing leads to heritable phenotypic changes in the targeted populations, as the heritability and genetic correlations of traits potentially under selection have received little attention. In addition, phenotypic changes could arise from fishing‐associated environmental effects, such as reductions in population density. Using fish reared at baseline and reduced group density and repeatedly harvested by simulated trawling, we show that trawling can induce direct selection on fish social behaviour. As sociability has significant heritability and is also genetically correlated with activity and exploration, trawling has the potential to induce both direct selection and indirect selection on a variety of fish behaviours, potentially leading to evolution over time. However, while trawling selection was consistent between density conditions, the heritability and genetic correlations of behaviours changed according to the population density. Fishing‐associated environmental effects can thus modify the evolutionary potential of fish behaviour, revealing the need to use a more integrative approach to address the evolutionary consequences of fishing.

Food availability and temperature influence energetics of animals and can alter behavioral responses such as foraging and spontaneous activity. Food availability, however, is not necessarily a good indicator of energy (ATP) available for cellular processes. The efficiency of energy transduction from food‐derived substrate to ATP in mitochondria can change with environmental context. Our aim was to determine whether the interaction between food availability and temperature affects mitochondrial efficiency and behavior in zebrafish ( Danio rerio ). We conducted a fully factorial experiment to test the effects of feeding frequency, acclimation temperature (three weeks to 18 or 28°C), and acute test temperature (18 and 28°C) on whole‐animal oxygen consumption, mitochondrial bioenergetics and efficiency (ADP consumed per oxygen atom; P:O ratio), and behavior (boldness and exploration). We show that infrequently fed (once per day on four days per week) zebrafish have greater mitochondrial efficiency than frequently fed (three times per day on five days per week) animals, particularly when warm‐acclimated. The interaction between temperature and feeding frequency influenced exploration of a novel environment, but not boldness. Both resting rate of producing ATP and scope for increasing it were positively correlated with time spent exploring and distance moved in standardized trials. In contrast, behavior was not associated with whole‐animal aerobic (oxygen consumption) scope, but exploration was positively correlated with resting oxygen consumption rates. We highlight the importance of variation in both metabolic (oxygen consumption) rate and efficiency of producing ATP in determining animal performance and behavior. Oxygen consumption represents energy use, and P:O ratio is a variable that determines how much of that energy is allocated to ATP production. Our results emphasize the need to integrate whole‐animal responses with subcellular traits to evaluate the impact of environmental conditions on behavior and movement.

Exercise capacity, measured by treadmill in humans and other mammals, is an important diagnostic and prognostic index for patients with cardiomyopathy and heart failure. The adult zebrafish is increasingly used as a vertebrate model to study human cardiomyopathy due to its conserved cardiovascular physiology, convenience for genetic manipulation, and amenability to high-throughput genetic and compound screening. Owing to the small size of its body and heart, new phenotyping assays are needed to unveil phenotypic traits of cardiomyopathy in adult zebrafish. Here, we describe a swimming-based functional assay that measures exercise capacity in an adult zebrafish doxorubicin-induced cardiomyopathy model. This protocol can be applied to any adult zebrafish model of acquired or inherited cardiomyopathy and potentially to other cardiovascular diseases. Graphic abstract: Clinical relevance of the swimming-based phenotyping assay in adult zebrafish cardiomyopathy models.

Long-term imbalance between fatigue and recovery may eventually lead to muscle weakness or even atrophy. We previously reported that excessive exercise induces pathological cardiac hypertrophy. However, the effect of excessive exercise on the skeletal muscles remains unclear. In the present study, we successfully established an excessive-exercise-induced skeletal muscle atrophy zebrafish model, with decreased muscle fiber size, critical swimming speed, and maximal oxygen consumption. High-throughput RNA-seq analysis identified differentially expressed genes in the model system compared with control zebrafish. Gene ontology and KEGG enrichment analysis revealed that the upregulated genes were enriched in autophagy, homeostasis, circadian rhythm, response to oxidative stress, apoptosis, the p53 signaling pathway, and the FoxO signaling pathway. Protein–protein interaction network analysis identified several hub genes, including keap1b, per3, ulk1b, socs2, esrp1, bcl2l1, hsp70, igf2r, mdm2, rab18a, col1a1a, fn1a, ppih, tpx2, uba5, nhlrc2, mcm4, tac1, b3gat3, and ddost, that correlate with the pathogenesis of skeletal muscle atrophy induced by excessive exercise. The underlying regulatory pathways and muscle-pressure-response-related genes identified in the present study will provide valuable insights for prescribing safe and accurate exercise programs for athletes and the supervision and clinical treatment of muscle atrophy induced by excessive exercise.

The UAB Nathan Shock Center focuses on comparative energetics and aging. Energetics, as defined for this purpose, encompasses the causes, mechanisms, and consequences of the acquisition, storage, and use of metabolizable energy. Comparative energetics is the study of metabolic processes at multiple scales and across multiple species as it relates to health and aging. The link between energetics and aging is increasingly understood in terms of dysregulated mitochondrial function, altered metabolic signaling, and aberrant nutrient responsiveness with increasing age. The center offers world-class expertise in comprehensive, integrated energetic assessment and analysis from the level of the organelle to the organism and across species from the size of worms to rats as well as state-of-the-art data analytics. The range of services offered by our three research cores, (1) The Organismal Energetics Core, (2) Mitometabolism Core, and (3) Data Analytics Core, is described herein.

The present study was designed to assess the performance of the freshwater prawn Macrobrachium tenellum in optimal and sub-optimal dissolved oxygen conditions, considering increasing environmental pressures. Thermal tolerance and thermal metabolic scope (TMS) with related integrated biomarker response (IBR) were measured in prawns exposed to normoxia (80% air saturation), mild (40% air saturation) and severe hypoxia (25% air saturation) at three exposure time points (10, 20 and 30 days). Effects of hypoxia on thermal tolerance were not detectable over time; they were perhaps masked by hyperventilation, or by an increase or diversion of haemolymph processes. After 30 days, TMS was 11% higher in mild hypoxia compared with normoxia, while it was 64% lower in severe hypoxia, indicating the loss of aerobic metabolism capacity during the latter. Mild-hypoxia prawns maintained a high IBR over time, supported by antioxidant enzyme activities (mainly superoxide dismutase), which helped avoid the serious oxidative damage (proteins and lipids) seen in severe hypoxia animals, as well as lower acetylcholinesterase activity that indicated failure of communication between the nervous and locomotor systems. Our results documented a high tolerance by M. tenellum to mild-hypoxia events, which should be further tested under seasonal and extreme habitat/tank temperatures.

The purpose of this study was to investigate if the cardiovascular system is important for ammonia excretion in the early life stages of zebrafish. Morpholino knockdowns of cardiac troponin T (TNNT2) or vascular endothelial growth factor A (VEGFA) provided morphants with nonfunctional circulation. At the embryonic stage [30–36 h postfertilization (hpf)], ammonia excretion was not constrained by a lack of cardiovascular function. At 2 days postfertilization (dpf) and 4 dpf, morpholino knockdowns of TNNT2 or VEGFA significantly reduced ammonia excretion in all morphants. Expression of rhag, rhbg, and rhcgb showed no significant changes but the mRNA levels of the urea transporter ( ut) were upregulated in the 4 dpf morphants. Taken together, rhag, rhbg, rhcgb, and ut gene expression and an unchanged tissue ammonia concentration but an increased tissue urea concentration, suggest that impaired ammonia excretion led to increased urea synthesis. However, in larvae anesthetized with tricaine or clove oil, ammonia excretion was not reduced in the 4 dpf morphants compared with controls. Furthermore, oxygen consumption was reduced in morphants regardless of anesthesia. These results suggest that cardiovascular function is not directly involved in ammonia excretion, but rather reduced activity and external convection may explain reduced ammonia excretion and compensatory urea accumulation in morphants with reduced cardiovascular function.

Doxorubicin is a cornerstone chemotherapeutic drug widely used to treat various cancers; its dose‐dependent cardiomyopathy, however, is one of the leading causes of treatment‐associated mortality in cancer survivors. Patients’ threshold doses leading to doxorubicin‐induced cardiomyopathy (DIC) and heart failure are highly variable, mostly due to genetic variations in individuals’ genomes. However, genetic susceptibility to DIC remains largely unidentified. Here, we combined a genetic approach in the zebrafish ( Danio rerio ) animal model with a genome‐wide association study (GWAS) in humans to identify genetic susceptibility to DIC and heart failure. We firstly reported the cardiac and skeletal muscle‐specific expression and sarcomeric localization of the microtubule‐associated protein 7 domain‐containing protein 1b (Map7d1b) in zebrafish, followed by expression validation in mice. We then revealed that disruption of the map7d1b gene function exaggerated DIC effects in adult zebrafish. Mechanistically, the exacerbated DIC are likely conveyed by impaired autophagic degradation and elevated protein aggregation. Lastly, we identified 2 MAP7D1 gene variants associated with cardiac functional decline and heart failure in cancer patients who received doxorubicin therapy. Together, this study identifies MAP7D1 as a clinically relevant susceptibility gene to DIC and heart failure, providing useful information to stratify cancer patients with a high risk of incurring severe cardiomyopathy and heart failure after receiving chemotherapy.

We indirectly assessed if altered transarcolemmal Ca 2+ flux accompanies the decreased cardiac activity displayed by Trachemys scripta with anoxia exposure and cold acclimation. Turtles were first acclimated to 21°C or 5°C and held under normoxic (21N; 5N) or anoxic conditions (21A; 5A). We then compared the response of intrinsic heart rate ( f H ) and maximal developed force of spontaneously contracting right atria ( F max,RA ), and maximal developed force of isometrically-contracting ventricular strips ( F max,V ), to Ni 2+ (0.1 – 10 mM), which respectively blocks T-type Ca 2+ channels, L-type Ca 2+ channels and the Na + -Ca 2+ -exchanger at the low, intermediate and high concentrations employed. Dose-response curves were established in simulated in vivo normoxic (Sim Norm) or simulated in vivo anoxic extracellular conditions (21A and 5A preparations). Ni 2+ decreased intrinsic f H, F max,RA and F max,V of 21N tissues in a concentration-dependent manner, but the responses were blunted in 21A tissues in Sim Norm. Similarly, dose-response curves for F max,RA and F max,V of 5N tissues were right-shifted, whereas anoxia exposure at 5°C did not further alter the responses. The influence of Sim Anx was acclimation temperature-, cardiac chamber- and contractile parameter-dependent. Combined, the findings suggest that: (1) reduced transarcolemmal Ca 2+ flux in the cardiac pacemaker is a potential mechanism underlying the slowed intrinsic f H of anoxic turtles at 21°C, but not 5°C, (2) a downregulation of transarcolemmal Ca 2+ flux may aid cardiac anoxia survival at 21°C and prime the turtle myocardium for winter anoxia and (3) confirm that altered extracellular conditions with anoxia exposure can modify turtle cardiac transarcolemmal Ca 2+ flux. Keywords: anoxia, temperature, cardiac pacemaker, cardiac regulation, ion channels, myocardial contractile properties, red-eared slider

Tralopyril (TP), an antifouling biocide, is widely used to prevent heavy biofouling, and can have potential risks to aquatic organisms. In this study, the effect of TP on locomotor activity and related mechanisms were evaluated in zebrafish (Danio rerio) larvae. TP significantly reduced locomotor activity after 168 -h exposure. Adverse modifications in tail muscle tissue, the nervous system, and energy metabolism were also observed in larvae. TP caused thinning of the muscle bundle in the tail of larvae. In conjunction with the metabolomics results, changes in dopamine (DA) and acetylcholine (ACh), acetylcholinesterase (AChE) activity, and the expression of genes involved in neurodevelopment, indicate that TP may disrupt the nervous system in zebrafish larvae. The change in metabolites (e.g., glucose 6-phosphate, cis-Aconitic acid, acetoacetyl-CoA, coenzyme-A and 3-Oxohexanoyl-CoA) involved in carbohydrate and lipid metabolism indicates that TP may disrupt energy metabolism. TP exposure may inhibit the locomotor activity of zebrafish larvae by impairing tail muscle tissue, the nervous system, and energy metabolism.

This article reports on the thermal tolerance, metabolic capacity and performance of juvenile meagre (Argyrosomus regius) reared under three high water temperatures (24, 29 and 34 °C) for three months. The analysis includes the thermal effects on the growth performance, metabolism and physiology of meagre, including a range of molecular, haematological, metabolic, enzymatic and hormonal indicators, as well as the effects on the proximate composition and ingestion speed. Meagre performs best between 24 and 29 °C while the temperature of 34 °C is very close to the upper end of its temperature tolerance range. At 34 °C meagre exhibits a poor growth performance and physiological status, increased blood clotting, high mortality rates and a diminished capacity for aerobic metabolism, as indicated by its low aerobic scope (129 mg kg-1 h-1). Meagre may tolerate short exposures to high temperatures after sufficient acclimation (Critical thermal maximum of 37.5 °C after acclimation to 29 °C) but its overall performance declines under prolonged exposure, suggesting that this emerging aquaculture species may be vulnerable to global warming. Our work corroborates previous findings on the thermal preferences of the species, identifies critical biological thresholds, and provides insights into the effects of prolonged exposure to high temperature regimes.

Central retinal artery occlusion (CRAO) is an obstruction of the retinal artery carrying oxygen to the cells in the inner retinal layers. This lack of oxygen may result in irreversible loss of sight if not treated within 24−36 h. We propose a dextran-based oxygen nanobubble (DONB) platform for intravitreal delivery of oxygen to rescue the inner retina from such ischemic damage. The size distribution of DONBs was 119.6 ± 44.9 nm and the zeta (ζ)-potential was −35.54 ± 10.54 mV. The DONBs were found to be stable in amber vials at 5 ± 3 °C for over 4 months and the formulation was not cytotoxic. The therapeutic efficacy of DONBs was first evaluated in retinal precursor cell lines which showed excellent recovery and then in a hypoxia/reperfusion rat eye model. Oxygen distribution measurements and histology indicated excellent recovery of the ganglion and inner retinal cell layers. Electroretinography exhibited normal retinal function. Our unique approach suggests a promising pathway to treat CRAO, a blinding condition for which no effective treatment exists.

It is now recognized that parental diets could highly affect offspring metabolism and growth. Studies in fish are, however, lacking. In particular, the effect of a parental diet high in carbohydrate (HC) and low in protein (LP) on progeny has never been examined in higher trophic level teleost fish. Thus, two-year old male and female rainbow trout (Oncorhynchus mykiss) were fed either a control diet (0% carbohydrate and 63.89% protein) or a diet containing 35% carbohydrate and 42.96% protein (HC/LP) for a complete reproductive cycle for females and over a 5-month period for males. Cross-fertilizations were then carried out. To evaluate the effect of the parental diet on their offspring, different phenotypic and metabolic traits were recorded for offspring before their first feeding and again three weeks later. When considering the paternal and maternal HC/LP nutrition independently, fry phenotypes and transcriptomes were only slightly affected. The combination of the maternal and paternal HC/LP diets altered the energy metabolism and mitochondrial dynamics of their progeny, demonstrating the existence of a synergistic effect. The global DNA methylation of whole fry was also highly affected by the HC/LP parental diet, indicating that it could be one of the fundamental mechanisms responsible for the effects of nutritional programming.

Recent and potential expansions in the transportation of diluted bitumen (dilbit) through marine terminals in coastal regions of British Columbia require the examination of potential risks to estuarine species such as Pacific salmon. The estuarine habitat of out-migrated pink salmon (Oncorhynchus gorbuscha) exhibits dynamic temperature and salinity regimes, possibly modifying dilbit exposure, bioavailability and/or its effects. To examine dilbit toxicity and its modification by environmental stressors, juvenile pinks were subchronically exposed for 3 months to the water-accommodated fraction (WAF) of Cold Lake Blend dilbit (winter) in seawater at three salinities (7, 14, and 28‰ [temperature 12.5 °C]) and three temperatures (8.5, 12.5, and 16.5 °C [salinity of 28‰]). Temperature and salinity alone did not affect any measured endpoints in control fish. Dilbit exposure induced higher mortality at high (16.5 °C) and low temperatures (8.5 °C) as well as at higher salinity (28‰) in fish exposed to the highest dilution of WAF [total polycyclic aromatic compounds (TPAC) = 128.9 µg/L]. A concentration-dependent reduction of growth was evident in fish exposed to the medium (TPAC = 97.3 µg/L) and high dilution of WAF at higher temperatures (12.5 and 16.5 °C) and high salinity (28‰). At 28‰, swimming performance (Uburst) was decreased in fish exposed to the highest concentration of dilbit at all 3 temperatures. Gill Na+-K+-ATPase activity, white muscle lactate, glycogen, and triglyceride concentrations were altered by dilbit exposure and modified by temperature and salinity. In addition, gene expression associated with phase I biotransformation, energy metabolism, mitochondrial activity, and inflammation showed significant upregulation with exposure and temperature stress. Dilbit exposure at PAC concentrations in the ppb range, affected pink salmon at the molecular, biochemical, and whole organism level; effects that were exacerbated by environmental temperature and salinity.

Due to anthropogenic activities that have increased global climate change and nutrient discharges, severe hypoxic events have frequently occurred in coastal waters in recent years. Relying on coastal waters, the aquaculture area has suffered ecological and economic losses caused by hypoxia, especially in summer. In this study, to investigate the stress resistance of the Pacific abalone Haliotis discus hannai (DD) and the hybrid H. discus hannai ? × H. fulgens ? (DF), a combination of physiological, biochemical, and metabolomic methods were used to compare the metabolic responses of these two abalones to acute hypoxia (~0.5 mg O2/L, 12 h) and reoxygenation (~6.6 mg O2/L, 10–20 h). Hemolymph characteristics and aerobic/anaerobic respiratory capacity changed significantly under hypoxia or reoxygenation conditions, and they were regulated in different trends in two abalones. The contents of hepatopancreas glycogen in two abalones reached the trough after 10 h recovery, implying that short-term hypoxia leads to a long-lasting (several hours) imprint on the energy storage of abalone. In response to dissolved oxygen fluctuation, metabolic profiles of two abalones changed in distinct ways both in the hypoxia group or the reoxygenation group. The conversion of carbohydrate metabolism and amino acid metabolism indicated that hypoxia prompts abalone to change the way of energy metabolism, which may also reflect the difference in the energy utilization of DD and DF abalones. In addition, 3 metabolites (L-glutamate, 2-hydroxy-butanoic acid, and 2-methyl-3-hydroxybutyric acid) as potential biomarkers for hypoxia and reoxygenation response in abalone were determined by operating characteristic analysis (ROC). Overall, this study provides information towards understanding the damage caused by frequent hypoxic events and implies the metabolic shifts that occur under hypoxia and reoxygenation conditions in DD and DF abalones.

Domestication and selective breeding can mitigate current bottlenecks in European perch aquaculture. Monitoring the condition and stress tolerance of European perch stocks from different recirculating aquaculture systems is of general interest to set the baseline values of promising candidates for further breeding processes. We recorded morphometric, behavioural (critical swimming speed, activity, aggressiveness, propensity to approach a novel object), and physiological parameters (plasma cortisol, glucose, ion concentrations, enzyme activity levels) after stress induction across four European perch stocks obtained from different aquaculture facilities in France (I and II), Denmark, and Hungary. The European perch stock from Denmark revealed the population with the most pronounced activity pattern. This was reflected by the highest relative swimming speed and a high percentage of bold-exploratory behaviour, which coincides with increased aggressive interactions within this stock. Additionally, we detected a higher tolerance to adverse environmental challenges in the perch stock from Denmark compared with the stocks from France and Hungary. The observed characteristics suggest that the stock from Denmark has a higher potential in the future framework of selective-breeding assessment. Further in-depth research is required to elucidate which traits and genetic as well as epigenetic components accelerate the domestication processes of European perch aquaculture and promote selective breeding processes.

This study examined the effects of elevated temperature and dietary Thermal Care, Bio-Mos and GroBiotic A on production performance and blood chemistry parameters in rainbow trout (Oncorhynchus mykiss). Rainbow trout under supraoptimal thermal conditions (18 °C) exhibited increased growth and feed intake but no change in feed efficiency for 6 weeks. This suggests that rearing fish at 18 °C may enhance production performance during the early stages of the grow-out process. By 12 weeks, fish at 18 °C showed increased feed intake, decreased feed efficiency, but no change in growth. Additionally, fish at 18 °C had lower protein content, protein retention efficiency, and energy retention efficiency. Elevated temperature did not change relative maximum swimming speed but did increase hematological parameters, thereby increasing the fish's oxygen supply capacity. There was preliminary evidence that Thermal Care improved rainbow trout growth under optimal thermal conditions (15 °C). However, fish fed Thermal Care at 18 °C exhibited increased feed intake but one of the lowest final fish weights leading to the lowest feed efficiency. Additionally, Grobiotic A impacted acid-base balance through changes in blood pH, TCO2, and HCO3- although the relevance of these interactions remains to be determined. By the end of the experiment, there were no noticeable benefits of including Thermal Care or Bio-Mos or GroBiotic A on production performance at either culture temperature.

Some hypoxia-tolerant species, such as goldfish, experience intermittent and severe hypoxia in their natural habitat, causing them to develop multiple physiological adaptations. However, in fish, the metabolic impact of regular hypoxic exposure on swimming performance in normoxia is less well understood. Therefore, we experimentally tested whether chronic exposure to constant (30 days at 10% air saturation) or intermittent hypoxia (3 h in normoxia and 21 h in hypoxia, 5 days a week) would result in similar metabolic and swimming performance benefits after reoxygenation. Moreover, half of the normoxic and intermittent hypoxic fish were put on a 20-day normoxic training regime. After these treatments, metabolic rate (standard and maximum metabolic rates: SMR and MMR) and swimming performance [critical swimming speed (Ucrit) and cost of transport (COT)] were assessed. In addition, enzyme activities [citrate synthase (CS), cytochrome c oxidase (COX) and lactate dehydrogenase (LDH)] and mitochondrial respiration were examined in red muscle fibres. We found that acclimation to constant hypoxia resulted in (1) metabolic suppression (−45% SMR and −27% MMR), (2) increased anaerobic capacity (+117% LDH), (3) improved swimming performance (+80% Ucrit, −71% COT) and (4) no changes at the mitochondrial level. Conversely, the enhancement of swimming performance was reduced following acclimation to intermittent hypoxia (+45% Ucrit, −41% COT), with a 55% decrease in aerobic scope, despite a significant increase in oxidative metabolism (+201% COX, +49% CS). This study demonstrates that constant hypoxia leads to the greatest benefit in swimming performance and that mitochondrial metabolic adjustments only provide minor help in coping with hypoxia.

Hypoxia is a growing concern in aquatic ecosystems. Historically, scientists have used the P crit (the dissolved oxygen level below which an animal can no longer oxyregulate) to infer hypoxia tolerance across species. Here, we tested the hypothesis that the P crit is positively correlated with temperature in the mayfly, Neocloeon triangulifer. Cross-temperature comparisons showed a modest ( r = 0.47), but significant ( p < 0.0001) association between temperature and P crit despite relatively large interindividual variability (Coefficient of Variance (CV) = 39.9% at 18 °C). We used the expression of hypoxia-responsive genes EGL-9 (an oxygen sensing gene and modulator of HIF-1a activity) and LDH (a hypoxia indicator) to test whether oxygen partial pressure near the P crit stimulates expression of hypoxia-responsive genes. Neither gene was upregulated at oxygen levels above the estimated P crit, however, at or below the P crit estimates, expression of both genes was stimulated (~20- and ~3-fold change for EGL-9 and LDH, respectively). Finally, we evaluated the influence of hypoxic exposure time and pretreatment conditions on the mRNA expression levels of hypoxia-responsive genes. When larvae were exposed to a gradual reduction of DO, hypoxic gene expression was more robust than during instantaneous exposure to hypoxia. Our data provide modest support for traditional interpretation of the P crit as a physiologically meaningful shift from aerobic to anaerobic metabolism in N. triangulifer. However, we also discuss limitations of the P crit as a proxy measure of hypoxia tolerance at the species level. Keywords: Hypoxia, Pcrit, Gene expression, Temperature, Mayfly

Significance Swimming ability has contributed to the evolutionary success of fishes, and its mechanics have been studied extensively. Most fishes swim primarily through undulation of their body and caudal fin (BCF) and have been historically divided into four major kinematic modes based on their morphology. Here, we compare kinematics of BCF locomotion in 44 species. Contrary to expectations and despite considerable morphological diversity, fishes share major kinematic features during steady swimming and are placed on a continuum rather than in discrete categories. This suggests a unifying BCF mechanism to generate efficient aquatic propulsion. Our work reevaluates a well-established hypothesis in biomechanics, highlighting the importance of avoiding a priori partitioning of fishes into modes, to further our understanding of aquatic locomotion. Fishes exhibit an astounding diversity of locomotor behaviors from classic swimming with their body and fins to jumping, flying, walking, and burrowing. Fishes that use their body and caudal fin (BCF) during undulatory swimming have been traditionally divided into modes based on the length of the propulsive body wave and the ratio of head:tail oscillation amplitude: anguilliform, subcarangiform, carangiform, and thunniform. This classification was first proposed based on key morphological traits, such as body stiffness and elongation, to group fishes based on their expected swimming mechanics. Here, we present a comparative study of 44 diverse species quantifying the kinematics and morphology of BCF-swimming fishes. Our results reveal that most species we studied share similar oscillation amplitude during steady locomotion that can be modeled using a second-degree order polynomial. The length of the propulsive body wave was shorter for species classified as anguilliform and longer for those classified as thunniform, although substantial variability existed both within and among species. Moreover, there was no decrease in head:tail amplitude from the anguilliform to thunniform mode of locomotion as we expected from the traditional classification. While the expected swimming modes correlated with morphological traits, they did not accurately represent the kinematics of BCF locomotion. These results indicate that even fish species differing as substantially in morphology as tuna and eel exhibit statistically similar two-dimensional midline kinematics and point toward unifying locomotor hydrodynamic mechanisms that can serve as the basis for understanding aquatic locomotion and controlling biomimetic aquatic robots.