Determining stress-responsiveness in family groups of Atlantic salmon (Salmo salar) using non-invasive measures

In this study, we examined variation in stress-responsiveness between 10 full sibling families of Atlantic salmon from a commercial breeding programme. Behavioural observations (locomotor activity during acute confinement and feeding response after placement in a novel environment) and cortisol release into the water were used as non-invasive markers of stress-responsiveness. Locomotor activity during acute stress was highly correlated with cortisol release rate, while feeding response did not correlate with either of the other two markers. Locomotor activity and cortisol release rate differed significantly between families, whereas feeding response did not. These results provide further support for hypothalamus-pituitary-interrenal responsiveness being a heritable (genetic) trait. Furthermore, results from an infectious pancreas necrosis virus (IPNV) challenge (carried out within the breeding programme from which our experimental fish originated) indicated a positive correlation between stress-responsiveness and mortality at the family level. In summary, the behavioural measure of locomotor activity during acute confinement provides a simple alternative measure of stress-responsiveness to physiological measures of cortisol, and families characterised by high stress-responsiveness showed increased susceptibility to IPNV.