GENETIC-VARIATION IN THE HUMORAL IMMUNE-RESPONSE AGAINST VIBRIO-SALMONICIDA AND IN ANTIBODY TITER AGAINST VIBRIO-ANGUILLARUM AND TOTAL IGM IN ATLANTIC SALMON (SALMO-SALAR)

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