The present study investigated the effects of stress and exercise on seawater (SW) adaptation and cortisol dynamics in juvenile steelhead (Oncorhynchus mykiss). To examine the effects of stress, fish acclimated to freshwater (FW) were subjected for 3 hours to confinement stress in FW, and subsequently SW (25 ppt) was introduced to all tanks. Fish were sampled immediately after the stress treatment, and 1, 7, and 14 days after introduction of SW. Electrolytes, cortisol, glucose and lactate followed the typical pattern that we expected after stress treatment in FW. Fish regained osmotic balance within 24 hours. Glucose concentrations were increasing throughout the experiment and lactate levels stayed elevated during the time spent in SW. IGF-1 did not show an immediate response to stress but after transfer to SW we detected significantly higher concentrations for control fish at days 1 and 14. The differences in IGF-1 levels between stressed and control fish are not reflected in SW adaptability but positive correlations between IGF-1 and electrolyte levels in control fish may indicate its role for osmoregulation. Confinement stress did not impair feed intake subsequently in SW, but our results suggest that feed intake was suppressed by the change of the media from FW to SW. The second study investigated the effects of exercise treatment in FW on SW adaptation and cortisol dynamics in juvenile steelhead. Plasma cortisol and in vitro cortisol secretion by interrenal cells after a 24 hr SW challenge test were neither affected by moderate exercise nor by water temperature (13��C, 21��C), however, plasma osmolality was lower in exercised fish compared to unexercised fish. Half-life (T[subscript 1/2]) of ��H-cortisol was shorter in fish exposed to exercise whereas metabolic clearance rate (MCR) did not respond to exercise treatment. Uptake and retention of corticosteroids in liver and gall bladder were enhanced in exercised fish, and retention of corticosteroids in muscle tissue was longer in unexercised fish. Our findings suggest that exercise likely decreases stress levels in fish and improves the adaptation to seawater (SW) in juvenile steelhead. / Graduation date: 2004

Gene expression profiles of tissues and cell-lines can be powerful tools for documenting the genetic response to a particular treatment, such as stressors. However, there is a paucity of information on the genetic stress response in the brain. Therefore, we attempted to profile gene expression in the brain of juvenile steelhead trout (Oncorhynchus mykiss) in response to stressors commonly encountered in aquaculture settings and similar to those encountered in hydropower dam mitigation efforts. We subjected fish to a combined out-of-water and low-water stressor totaling three hours. Plasma stress response factors indicate that fish were undergoing a physiological stress response after 3 hours of continuous stressor. We utilized suppression subtractive hybridization to identify cDNA fragments up- or down-regulated in the brain upon completion of the stressor. Forward and reverse subtractions, and sub-cloning of the purified PCR products yielded 59 clones all of which were sequenced. Sequenced cDNA fragments were subjected to BLASTn and BLASTx searches over the course of one year. Fragments fell into the following functional categories: those associated with ATP generation, signal transduction, ion transport, translational machinery, DNA packaging and mobilization, cell structure, and cDNA fragments with cryptic function. Of the 59, 12 were selected for further analysis, and 5 were confirmed to be differentially expressed by northern hybridization. The differentially expressed genes included cytochrome b, NADH dehydrogenase subunit 2, ATPsynthase subunit 6, a cDNA fragment with unknown function, and neuron specific gene 1. Our results present a first attempt to profile gene expression in the brain of fish and demonstrate the power of molecular tools at capturing large amounts of biological information without having to target any one particular gene. A gene expression profile of the brain consequent to stress provides a catalog of responses at a given time point. This catalog can then be used to isolate full-length cDNAs, localize mRNAs in the brain or other tissue, as probes to determine expression patterns and time courses of gene expression in other tissues, and for the quantification of cDNA molecules with real time PCR. / Graduation date: 2003