A recent study published in Journal of Comparative Physiology B investigated how diet-induced changes in taurine availability influence cardiac function and the response to hypoxia in brook char (Salvelinus fontinalis). The work addresses an important but comparatively understudied aspect of fish physiology: how nutrition can influence cardiovascular function and an animal's ability to cope with environmental stress.

Hypoxia represents a threat to many fish species, requiring compensatory cardiovascular responses to maintain oxygen uptake, delivery and aerobic function. At the same time, climate change and other anthropogenic pressures are altering aquatic food webs and the nutritional landscape available to fish. Understanding how diet interacts with environmental stress may therefore be important for predicting the resilience of fish under changing conditions.

The researchers studied brook char fed either a control diet or a diet enriched with β-alanine. β-alanine competes with taurine for transport into cells, and the enriched diet produced a 29% reduction in cardiac taurine concentration under normoxic conditions. The researchers then investigated how these fish responded to declining oxygen using a combination of respirometry, cardiovascular measurements, electrocardiography and biochemical analyses.

Central to the measurement of whole-animal metabolic responses was an intermittent-flow respirometry system. Following a minimum of 16 hours of overnight recovery, oxygen consumption was continuously measured before hypoxia was induced by allowing the fish to progressively deplete the oxygen within the system. Oxygen consumption was automatically calculated with AutoResp™ from the decline in dissolved oxygen during each measurement period.

This approach allowed the researchers to follow how oxygen consumption changed as water oxygen levels declined. Hypoxia and diet both influenced oxygen consumption, with taurine-deficient fish showing significantly lower oxygen consumption at an oxygen partial pressure of 12.5 kPa. Gill ventilation increased during hypoxia in both groups, although the increase was only statistically significant in control fish.

The authors also directly measured heart rate, stroke volume and cardiac output during hypoxia and reoxygenation. Taurine-deficient fish had lower resting heart rates and exhibited a smaller relative bradycardia during hypoxia, while stroke volume increased in both diet groups at low oxygen. Cardiac output therefore remained relatively stable throughout the hypoxia exposure.

The results did not fully support the researchers' original hypothesis that impaired taurine transport would restrict the increase in stroke volume during hypoxia. Instead, lactate remained low, suggesting the hypoxic exposure had not produced sufficient anaerobic end-product accumulation for disrupted cardiac volume regulation to become a major constraint. Nevertheless, diet-induced taurine deficiency altered resting cardiac function and reduced the magnitude of the overall cardiorespiratory response to hypoxia.

The study highlights an important connection between nutrition, cardiovascular function and environmental stress tolerance. As aquatic food webs change, shifts in dietary composition may influence how effectively fish respond to challenges such as hypoxia or high temperatures. Combining whole-animal respirometry with direct cardiovascular and biochemical measurements provides a powerful approach for disentangling these interactions.

The paper, “Diet affects the cardiorespiratory response to hypoxia and autonomic control of the heart in brook char (Salvelinus fontinalis),” was published in Journal of Comparative Physiology B and can be found online at https://doi.org/10.1007/s00360-026-01673-0

Do you want to learn more about the respirometry tools used in this paper?

• Resting respirometry systems
• AutoResp™ respirometry software