Genetic variation in the humoral immune response against Vibrio salmonicida and in antibody titre against Vibrio anguillarum and total IgM in Atlantic salmon (Salmo salar).

Total IgM level and antibody titre to Vibrio anguillarum O-antigen after bath-vaccination, and specific antibody response to V. salmonicida O-antigen at three different samplings were analysed in family material of Atlantic salmon (Salmo salar), consisting of 791 fish belonging to 34 maternal full-sib groups within 12 paternal half-sib groups. The fish were immunized twice, and blood samples collected three times. After the third blood sampling, the fish were challenged with V. anguillarum. Medium to low genetic variation was recorded in total IgM and in the antibody titres against V. anguillarum O-antigen and V. salmonicida O-antigen, with heritability estimates of 0.12, 0.18 and from 0.03 to 0.12, respectively. Moderate to high genetic and phenotypic correlations were found between the V. salmonicida O-antigen titres at different samplings. Genetic and phenotypic correlations between the initial titres were moderate to low. The effect of different immune traits, including Aeromonas salmonicida A-layer titres (previously described), on the ability to survive the challenge was examined. The likelihood of surviving the challenge was affected positively by the A. salmonicida A-layer titre at the second sampling, and almost significantly affected by the initial V. anguillarum O-antigen titre. Production traits, such as mean slaughter weight and mean proportion of survivors in a corresponding full-sib material, were obtained in the sea-rearing period. No significant full-sib correlation between immune parameters and production traits was detected.