Physiology of digestion in aquatic animals

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A primary function of the gastrointestinal tract (GIT) is the provisioning of energy and nutrient building blocks for growth and homeostasis. However, the GIT is also used for physiology underlying salinity adaptations in fishes such as ion regulation and nitrogen balance. These various roles require integration between separate organs including the GIT, gill, and kidney, and ultimately produce downstream consequences for these systems during digestion. Thus, the physiology of fishes is primarily studied through the lens of unfed animals, to remove the complicating impacts of digestion. However, to obtain a more realistic understanding of fish physiology, one that includes the critical act of digestion, we must study its impacts on physiology. Thus, the long-term objective of my research program is to gain a holistic understanding of the impact of digestion on fish physiology using comparative and integrative approaches. My short terms goals are to: 1)mechanistically characterize fish physiology during digestion using two fish species, one an herbivorous fish and one an omnivorous fish, and integrative approaches from gene expression to whole animal physiology. I will examine coordinated animal-wide alterations to physiology during digestion that reflect dietary composition. 2)determine how the environment affects digestive physiology, specifically exploring the impact of salinity. I will study the impact of increased salinity on physiology during digestion, reflecting the demands of specific habitats. Comparing and contrasting herbivores and omnivores will reveal how diet composition will impact these changes. 3)explore the functional impact of removal and alteration of bacteria and archaea on the physiology of fish during digestion. I will determine how microorganisms provide diet and environmentally dependent functionality to the GIT of fish. By comparing herbivores against omnivores in this proposal, we can better understand how physiological responses to the digestion of a meal are dependent on diet and provide contrast for existing paradigms that are primarily based on unfed carnivorous fish. Furthermore, by integrating across biological levels, we expose multiple levels of responses and reveal the complex and influential impacts of digestion across physiological systems. While the focus of my program is on the digestive tract, ultimately we will consider the consequences of GIT function for the physiology of the whole organism, its performance, and its role in the ecosystem in response to environmental change. The impact of my work is in contributions made to fish physiology knowledge, revising our understanding by adding digestion and diet to existing paradigms. This work is applicable across biological fields from evolution to conservation and can be used to establish policies and aide in aquaculture. The projects associated with my program will provide excellent training for undergraduate and graduate students.