Transport and Metabolism in Fish

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This application opens new frontiers in a long term research program aimed at understanding the mechanisms involved in the transport and metabolism of nutrients, wastes, ions, acid-base equivalents, and respiratory gases in fish, and how these processes are modified by environmental conditions and phylogeny. Mechanisms are analyzed at molecular, cellular, organ system, whole animal, and behavioral levels simultaneously. A comparative approach is used with respect to organisms (trout, killifish, oscars, sharks, lungfish, hagfish) and stressors (NH3, O2, CO2, salinity, exercise, feeding). The four main areas are: (i) the physiology of ammonia and urea metabolism; (ii) the previously overlooked role of the skin in ionoregulation, acid-base regulation, N-waste excretion and feeding; (iii) the key contributions of passive transport processes (i.e. permeability regulation) in ionoregulation and osmoregulation; and (iv) aspects of euryhalinity which have previously received little attention. Particular projects focus on the control of gene expression of ammonia-transporting Rh proteins, the functions of ammonia as a respiratory gas, its interaction with O2 and CO2, and the role of the intestine in N-metabolism in trout and sharks. The partitioning of exchange processes between skin and gills in trout, and the importance of transport through the skin in two ancient fish of key phylogenetic importance, the Agnathan hagfish and the Dipnoan lungfish, will be examined, together with the molecular and cellular mechanisms involved. The contributions of transcellular versus paracellular permeability regulation to the osmo-respiratory compromise at the gills and to water absorption at the gut will be evaluated in trout and killifish, together with a critical assessment of the relationship between paracellular permeability and transepithelial resistance. The contributions of electro-physiological events, volume regulation, and behavior to euryhalinity will be examined in these same species. Overall, this program will train 3 PDFs, 5 Ph.D.'s, 3 M.Sc.'s, and 15 undergraduates in innovative areas of integrative physiology. It will also underpin a parallel applied program in aquatic toxicology, aquaculture, and environmental management.