Physiological and behavioural effects of digestion in aquatic vertebrates

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The gastrointestinal tract is an essential, multifunctional organ at the front line of nutrient and energy acquisition. These functions can ultimately produce a variety of downstream consequences affecting multiple physiological systems. As a result, most physiological studies focus on unfed animals. This removes any complicating effects digestion may have on the phenomena being studied. However feeding and digestion are essential for life and a consummate view of physiology must include physiology during digestion. It is upon this that my program is based - to gain a fundamental understanding of the effects of digestion on the physiology, and by extension behaviour, of aquatic animals. The influence of digestion on the overall salt and water balance of fish forms the basis of my previous work which I intend to continue exploring, asking questions like how does the physiology of fish adjust to maintain homeostasis during digestion, and what influence does the surrounding environment have? Specifically, I will investigate the role of salt and water transport mechanisms in maintaining balance during digestion, revealing the mechanism responsible for correcting salt and water imbalances. I will also investigate the role of hormonal regulation of these transport mechanisms to uncover how these transporters are regulated across the entire animal. Physiology itself is not the only factor to consider when examining animals during digestion - their behaviour is affected as well and an intimate link exists between behaviour and physiology, each influencing the other. Using information that I have previously discovered I will continue this research asking questions like how does the behaviour of fishes change while digesting a meal and what is the physiology driving these changes? Specifically, I will look at the salinity preference of fish along with any anticipatory changes in salt and water transport prior to feeding. These will reveal how physiology shapes the behaviour of animals during digestion. All together these themes begin to form the ultimate goal of my research program - a fundamental understanding of the effects of digestion on physiology and behaviour and determining how these effects have evolved in response to a varying environment. A majority of research focusing on fish physiology is conducted on fasting fish to remove the consequences of digestion on physiology. In this light, my work will provide a more complete picture of how fish survive and transform the field of fish physiology. By understanding the role of digestion in shaping and controlling the physiology of the whole organism, predictions can be made regarding the effects of stressors, both natural and man-made in nature, on fish species. These predictions can be used to preserve our essential aquatic resources by forming policy with a more complete understanding of how fish survive and adapt. Overall, life is a complex interaction of a multitude of physiological functions at all levels of integration, meshing together perfectly to sustain an animal in its environment. The complex interactions of digestion with other physiological systems is an important facet of this and what is at stake is the future of aquatic resources. By understanding more clearly how organisms balance and maintain homeostasis, especially during digestion which has gone overlooked, we can more clearly understand what fish require to survive and how they adapt to change.