SELECTION FOR HIGH AND LOW CORTISOL STRESS RESPONSE IN ATLANTIC SALMON (SALMO-SALAR) AND RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The results of blood cortisol assays of hatchery-reared families of Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) have led to the suggestion that there is a genetic basis for the response to stress. A selection programme that started in 1982 was aimed at establishing high and low cortisol response lines of the two species. The object is to reveal possible genetic linkages between stress response parameters and immune parameters in order to obtain an indirect measure for disease resistance. Analyses of blood sampled after exposing the F1 generation to a standardized stressor showed that the Atlantic salmon stress response, in terms of plasma cortisol and glucose levels, was significantly different between the two lines. In rainbow trout, the differences between lines were less pronounced, but significant sire effects were revealed within and between the two lines, supporting the evidence of a genetic component to the stress response. The levels of lysozyme, a non-specific immune measure, were higher in the high cortisol stress response lines that in the low cortisol lines. In Atlantic salmon, mortality during the course of the study was significantly higher in the line selected for high cortisol stress response.