Disease resistance in Atlantic salmon (Salmo salar) selected for high or low responses to stress

Abstract Two lines of Atlantic salmon, which had been selected for either high or low stress response following measurements of blood cortisol levels after a standardized stress, were challenged by three bacterial pathogens. The pathogenic agents were Aeromonas salmonicida , which causes furunculosis, Vibrio salmonicida , which causes cold-water vibriosis, and Renibacterium salmoninarum , which causes bacterial kidney disease (BKD). Following challenge with furunculosis bacteria, the mortality rates during the experiments, and the cumulative mortality at the end of the experiments, were significantly higher in the high than in the low stress response line of fish. In the course of the study it appeared that the fish challenged with cold-water vibriosis and BKD had also been previously infected with furunculosis bacteria. Following challenge with cold-water vibriosis, the high-stress line displayed a poorer performance than the low-stress line in this situation of double infection whereas there were no significant differences between the two lines following BKD challenge. The immunity of the parental generation of the challenged fish was assessed by measurements of serum haemolytic activity. The results indicated a significantly lowered immunity in fish of the high-stress response line.