Stress coping in rainbow trout, behavioral correlates and neuroendocrine mechanisms

In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability, and high responding (HR) and low responding (LR) lines of rainbow trout have been generated by individual selection for consistently high or low post-stress cortisol values. In addition to post-stress plasma cortisol concentrations these rainbow trout strains differ in several other traits. For instance, sympathetic reactivity shows an opposite pattern as compared to plasma cortisol, LR trout responding to acute stress with larger increase in plasma catecholamine levels than HR trout. Moreover, this differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. The LR strain tends to show proactive behaviors such as enhanced aggression, social dominance, and rapid resumption of feed intake after stress whereas the HR strain display more of a reactive behavioral profile. Furthermore, differences gene expression profiles and brain monoamine neurochemistry have also been reported in these lines. Studies on the HR and LR trout lines may provide a physiological and genetic basis for new marker-assisted selection strategies in the finfish aquaculture industry, as well as increased knowledge of the function and evolution of central neuroendocrine signaling systems.