GENETIC COMPONENTS OF POSTSTRESS CORTISOL AND LYSOZYME ACTIVITY IN ATLANTIC SALMON - CORRELATIONS TO DISEASE RESISTANCE

Cortisol, lysozyme and serum haemolytic activities were measured in 80 full-sib families of Atlantic salmon following standardized confineme nt stress. Heritability estimates of lysozyme activity were of medium magnitude (0.19 +/- 0.11), whereas heritability estimates of cortisol and serum haemolytic activity were low and not significantly different from zero. The genetic correlation between the cortisol stress respon se and lysozyme activity was negative, but with a large error (r = - 0 .58 +/- 0.59). Siblings of the experimental fish had previously been c hallenged by three bacterial pathogens, Aeromonas salmonicida (causing furunculosis), Renibacterium salmoninarum (causing bacterial kidney d isease, BKD) and Vibrio salmonicida (causing cold-water vibriosis). Co rtisol levels in stressed fish were not genetically correlated to surv ival against any of the three diseases, while evidence was found for a negative genetic correlation between lysozyme activity in stressed fi sh and survival after challenge with furunculosis and BKD. It is sugge sted that increased lysozyme activity following stress is not a reflec tion of a superior immune mobilization of the fish, but an indication of how easily the fish become stressed. The reported heritability esti mates give evidence that post-stress lysozyme activity has a better pr ospect in terms of selecting for enhanced stress tolerance, and thus d isease resistance, than has the cortisol stress response.