Genetic components of post-stress cortisol and lysozyme activity in Atlantic salmon; correlations to disease resistance

Abstract

Cortisol, lysozyme and serum haemolytic activities were measured in 80 full-sib families of Atlantic salmon following standardized confinement 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 response and lysozyme activity was negative, but with a large error (r= - 0·58±0±59). Siblings of the experimental fish had previously been challenged by three bacterial pathogens, Aeromonas salmonicida (causing furunculosis), Renibacterium salmoninarum (causing bacterial kidney disease, BKD) and Vibrio salmonicida (causing cold-water vibriosis). Cortisol levels in stressed fish were not genetically correlated to survival against any of the three diseases, while evidence was found for a negative genetic correlation between lysozyme activity in stressed fish and survival after challenge with furunculosis and BKD. It is suggested that increased lysozyme activity following stress is not a reflection of a superior immune mobilization of the fish, but an indication of how easily the fish become stressed. The reported heritabitity estimates give evidence that poststress lysozyme activity has a better prospect in terms of selecting for enhanced stress tolerance, and thus disease resistance, than has the cortisol stress response.