Stress and food deprivation: linking physiological state to migration success in a teleost fish
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abstract
Food deprivation (FD) is a naturally occurring stressor that is thought to influence the ultimate life-history strategy of individuals. Little is known about how FD interacts with other stressors to influence migration success. European populations of brown trout (Salmo trutta) exhibit partial migration, whereby a portion of the population smoltifies and migrates to the ocean, and the rest remain in their natal stream. This distinct, natural dichotomy of life-history strategies provides an excellent opportunity to explore the roles of energetic state (as affected by FD) and activation of the glucocorticoid stress response in determining life-history strategy and survival of a migratory species. Using an experimental approach, the relative influences of short-term FD and experimental cortisol elevation (i.e., intra-coelomic injection of cortisol suspended in cocoa butter) on migratory status, survival, and growth of juvenile brown trout relative to a control were evaluated. Fewer fish migrated in both the FD and cortisol treatments; however, migration of cortisol and control treatments occurred at the same time while the FD treatment was delayed for approximately one week. A significantly greater proportion of trout in the FD treatment remained in their natal stream, but unlike the cortisol treatment, there were no long-term negative effects of FD on growth, relative to the control. Overall survival rates were comparable between the FD and control treatments, but significantly lower for the cortisol treatment. Food availability and individual energetic state appear to dictate the future life-history strategy (migrate or remain resident) of juvenile salmonids while experimental elevation of the stress hormone cortisol caused impaired growth and reduced survival of both resident and migratory individuals.
