Transport and Metabolism in Fish

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In a country with the longest coastline in the world, with 1/7 of the world's freshwater, & an economy where fish and fisheries contribute over $17B annually (sportfishing ~ $10B, commercial fishing ~ $6B, aquaculture ~ $1B), the importance of understanding the basic physiology of fish & protecting the health of natural waters cannot be overstated. The present application opens new frontiers in a long term research program aimed at understanding the mechanisms involved in the transport & metabolism of nutrients, wastes, ions, acid-base equivalents, & respiratory gases in fish, & how these processes are modified by environmental conditions & phylogeny. This basic research program underpins a parallel applied program in aquatic toxicology, aquaculture, & environmental management. Mechanisms are analyzed at molecular, cellular, organ system, whole animal, & behavioral levels simultaneously. A comparative approach is used with respect to species (trout, killifish, sharks, hagfish, zebrafish etc.) & stressors (ammonia, O2, CO2, salinity, exercise, feeding). The four main areas are: (i) the physiology of ammonia & urea metabolism; (ii) the “osmorespiratory compromise” which is the functional tradeoff between ion/water vs O2 exchange at the gills; (iii) the physiology of feeding; (iv) the importance of dissolved organic matter (DOM, an abundant, ubiquitous but poorly understood component of all natural waters) in regulating gill physiology. Particular projects focus on the functions of NH3 as a respiratory gas in the regulation of breathing, its interactions with O2 & CO2, the control of gene expression of ammonia-transporting Rh proteins in the gills & kidney, & their roles in the homeostatic regulation of ions, acid-base status, & N-wastes. The mechanisms of N-scavenging are examined in N-limited sharks. The different types of osmorespiratory compromise, the contributions of transcellular vs paracellular pathways, & their cellular/molecular bases are investigated in relation to salinity, habitat, & behaviour of different species. Multiple aspects of feeding physiology are explored, including the importance of acid-base signals, the upregulation of transport pathways associated with food ingestion, & the metabolism of the gut itself. The O2 costs of feeding & their interactions with hypoxia & exercise performance are quantified. Through collaboration with a chemist, the relationships between the physical chemistry of different types of DOM molecules & their supportive actions on gill ionoregulatory function are examined. Particular emphasis is placed on the role(s) of metal-binding moieties in DOM molecules, on structural changes in gills associated with DOM exposures, & on the adaptation of fish to native DOMs. Overall, this program will train 3 postdoctoral fellows, 5 PhDs, & 15 undergrads in innovative aspects of integrative fish physiology.