Environmental influences on fish cardiovascular function and control

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Fish have a truly global distribution and live in waters where temperatures range from -1.8 to 42oC, that can contain little to no oxygen (i.e., are hypoxic), and may vary dramatically in salt content (e.g., estuaries). Further, human activities (including accelerated climate change) are placing added pressures on these fish, and in some areas this has lead to the displacement or extinction of species. Physiological adjustments that promote an increase in oxygen delivery to the tissues (e.g. more blood pumped by the heart, an increase in blood haemoglobin levels, adjustments in ventilation, the redistribution of blood flow) are critical if fish are to survive short- and long-term variations in these environmental variables. Indeed, it has been suggested that limitations in cardiac function as temperatures increase are a primary determinant of a fish's thermal tolerance. The proposed research will provide important insights into: 1) what factors (mechanisms) limit heart function in fishes at high temperatures; 2) interactions between the fish's immune system, stress physiology and cardiovascular function; 3) why heart function is compromised following acclimation to prolonged hypoxia; and 4) how much blood flows to the ovaries (eggs), whether it can be controlled, and how it is impacted by changes in temperature, water oxygen levels and salinity. The latter studies are important because the maintenance of oxygen and nutrient delivery to the eggs under varied environmental conditions is likely vital to ensuring that a large number of viable offspring are produced, and thus, the health of fish populations.