Advancing Our Understanding of How Cardiovascular Control, Function and Plasticity Influence Fish Performance and Ecophysiology

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The cardiorespiratory system (gills, heart, blood, blood vessels) is critical to the survival of fish as it ensures adequate oxygen and nutrient delivery to the tissues. In addition, it is important that these nutrients and oxygen are used efficiently by mitochondria (the 'powerhouses' of cells) so that enough energy is produced to meet the fish's demands (even under stressful conditions). My research program examines how metabolic rate, heart function, blood vessel physiology, mitochondrial function and stress physiology differ between fish species/populations, and how this allows them to survive under challenging conditions; including climate change. While we have made tremendous progress in understanding fish cardiorespiratory function and its relationship to performance / survival over the past decade, this research has left many important questions unanswered. My trainees (6 graduate and 5 undergraduate students, and 1 post-doc) and I will address a number of these in this grant. Three fundamental questions in fish cardiovascular physiology are: 1) what factors determine between individual, and between species, differences in maximum heart rate and function?; 2) what limits heart function at high temperatures?; and 3) what mechanisms constrain the capacity of fishes to increase stroke volume (how much blood is pumped per heart beat) as temperatures change. We will address all of these questions. Recent studies in my lab have also shown that fish exposed to low oxygen levels (hypoxia) are unable to increase their heart rate when exposed to high temperatures, and that this makes them susceptible to heat waves. Thus, we will perform several experiments to examine the physiological and control mechanisms leading to this limitation. Further, we will investigate whether the capacity of the fish to extract oxygen from their blood, and mitochondrial function, are key determinants of how tolerant they are of severe hypoxic (low oxygen) conditions and high temperatures, respectively. Finally, we will conduct a number of studies on very small coronary vessels (i.e., microvessels, the ones that are most important in controlling blood flow to tissues), and similar vessels in the gonads (ovaries and testes) of fish. The former studies are a continuation of previous work, and are critical to perform as coronary blood flow is key to cardiac performance under stressful conditions. The studies on gonad vessels will be performed because blood flow to these organs is important for egg and sperm development / quality (i.e., producing the next generation), respectively, and data on coronary vessels may not reflect how temperature or various hormones affect vessel dilation/constriction, and thus blood flow, in other tissues. Collectively, this research will greatly enhance our knowledge of how the fish cardiorespiratory system responds to both acute and chronic stressors, and will have important implications for fish management and conservation.