| Résumé | As in other vertebrates, fish react to stressful events by eliciting responses at the neuroendocrine, metabolic and cellular levels. Despite the large number of studies that have characterized the stress response in fish, we still have a poor understanding of the functional significance of these changes with respect to fish health, reproduction and growth. This is because, most of the research to date has focused on the response to acute stress and little is known about how fish cope with long-term stress. Thus, we are using both integrated and comparative approaches to investigate the effects of long-term stress in fish. Atlantic salmon (Salmo salar) and haddock (Melanogrammus aeglefinus) were stressed by daily handling (30 seconds out of water) for a period of 4 weeks, and biochemical and molecular techniques were used to study the endocrine (free and total cortisol), metabolic (glucose), and cellular (heat shock proteins) responses to this stressor. Effects on growth were also examined. We found distinct differences between these species in their response to long-term stress (Fig. 1). In haddock, plasma cortisol (free and total) was significantly elevated over the first two weeks when compared to controls, before declining to basal levels by week 3, but plasma glucose levels were unchanged throughout the stress period. In contrast, Atlantic salmon plasma cortisol (free and total) levels remained low throughout the stress period, and plasma glucose levels increased during the first week before returning to resting levels (second week). Long-term stress also had a significant suppressive effect on growth in haddock, but not in Atlantic salmon. Further, neither of these species showed evidence of an increased hsp70 response after exposure to the imposed long-term stress. These results will be discussed with respects to which of the measured parameters are sensitive indicators of stress in fish. |
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