Behavioral indicators of stress-coping style in rainbow trout: Do males and females react differently to novelty?

It is becoming increasingly clear that individual differences in the behavioral response to stressful situations are associated with distinct physiological profiles, and stress coping characteristics are of fundamental importance to fitness and life history. Teleost fishes display considerable variation in reproductive strategy, but sex differences in stress-coping style have not been described previously in fish. Prior to sexual maturation, the glucocorticoid response to stress is not affected by sex in salmonid fish. Nevertheless, behavior in novel and stressful situations differed between immature male and female rainbow trout (Oncorhynchus mykiss). When tested 1 week following transport to a new rearing facility, females resumed feeding after transfer to social isolation quicker than males. The locomotor response to acute confinement stress also varied between sexes, with females settling down and ceasing to move in a panic-like manner quicker than males. There was a strong correlation between behavior in the two test situations: individuals that readily resumed feeding behavior in a new environment also moved less in the acute stress test. Thus, the time to resume feeding after a stressful experience is a precise indicator of stress-coping style in salmonid fish, which is likely to reflect the dynamics of neuroendocrine stress responses. Furthermore, these observations could reflect a sex difference in the response to novel and stressful situations, which occur even in the absence of differences in glucocorticoid responsiveness.