�VERLI, �; POTTINGER, TG; WINBERG, S; University of Oslo, Oslo, Norway; National Environmental Research Council, Windermere, UK; Uppsala University, Uppsala, Sweden: Behavioral and Neuroendocrine Correlates of Artificial Selection for Stress Responsiveness in Rainbow Trout

In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability. Consequently, 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. Using 2nd and 3rd generation fish, we tested the hypothesis that differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. LR fish showed a tendency to become socially dominant, a rapid recovery of food intake after transfer to a novel environment, and a reduced locomotor response in a territorial intrusion test. Furthermore, a concomitant increase in brain stem and optic tectum concentrations of the monoamine neurotransmitters serotonin (5-Hydroxytryptamine, 5-HT, dopamine (DA), and norepinephrine (NE) and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress in HR, but not LR trout. A divergent pattern was seen in the hypothalamus, where LR fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). Thus, selection for a single trait, cortisol responsiveness, in rainbow trout is associated with concurrent changes in both behavior and central signaling systems. We suggest the hypothesis that HR and LR trout lines represent selection for a suite of traits, which together constitute the genetic basis of individually specific physiological/behavioral stress coping styles.