Graduation date: 1994

The environment under which fish are maintained as broodstock before reproduction is often stressful; however, the impact of stress on broodstock and gamete quality is not well known. We investigated the effects of stress over the final stages (i.e. the 3 months preceding ovulation) of sexual maturation of female rainbow trout, Oncorhynchus mykiss, on their reproductive performance and physiology and that of their progeny. Stress was administered over the period of early vitellogenesis (one and a half months), late vitellogenesis-final maturation (one and a half months), or during both periods (three months). Each stress treatment and control was triplicated with eight females in each replicate (n=24 fish per treatment). The eggs and progeny of each female were kept separate and observations made for four months after transfer to rearing tanks. Cortisol levels were measured in plasma, ovarian fluid and eggs by radioimmunoassay. Fish that experienced stress during final maturation and those that were under stress during the whole experiment spawned on average two weeks earlier than the control group. In contrast, fish stressed during the period of early vitellogenesis spawned at the same time as the controls. Absolute fecundity and fertilization were not significantly affected in any treatment group; however, significant differences were found in relative fecundity. Stress applied early in vitellogenesis resulted in smaller eggs and swim-up fry; but, these differences were not found in juveniles 8 weeks after hatching. Furthermore, we found no differences in survival of the progeny or resistance to the fish pathogen Vibrio anguillarum. Circulating levels of cortisol were high at ovulation in all groups, but significantly less cortisol was observed in the ovarian fluid and eggs. Sex hormone concentrations were high in plasma; however, they were several orders of magnitude lower in the ovarian fluid. These differences were not as extreme as those observed for cortisol. Lower levels of cortisol and sex steroids in ovarian fluid and eggs compared to that which is available from plasma suggests that there is a mechanism by which the female protects the eggs from potentially deleterious effects of prolonged exposure to elevated concentrations of steroids. / Graduation date: 1996

Graduation date: 1993

This thesis tests the hypothesis that innate immunity may be enhanced immediately following a stressful event. The experiments characterize the acute effects of the fight or flight response on some immunological and endocrine parameters in rainbow trout (Oncorhynchus mykiss). Plasma cortisol and catecholamines were elevated within seconds of the initiation of an acute handling stressor consisting of 30 seconds in the air and five, 10 or 20 minutes in a shallow bucket of water. Plasma lysozyme activity increased after stress, however, the increases were not statistically significant unless variation was reduced by serial bleeding of the same individual trout before and after stress. A more "resting" fish was achieved by use of the anesthetic 2-phenoxy-ethanol which was surreptitiously introduced into the tanks before the initial bleed. Individual fish were then revived in freshwater and stressed as before. Enhancement of lysozyme activity was evident although levels of plasma stress hormones in fish that were anesthetized, revived and stressed were less than when fish were similarly stressed without anesthetic. Levels of cortisol and catecholamines increased within seconds of capture and aerial exposure, returned to near pre-stress levels after the fish had been placed in a shallow bucket of water for 30 seconds, then increased again. Evaluation of the influence of acute stress on survival following challenge with the pathogen Vibrio anguillarum yielded equivocal data. Results presented here suggest that enhancement of innate defenses as part of the fight or flight response merits further evaluation. / Graduation date: 1997