Genetic variation in antibody response to diphtheria toxoid in Atlantic salmon and rainbow trout

Antibody response to diphtheria toxoid in rainbow trout (202 fish belonging to 28 full-sib pairs within 14 half-sib groups) and Atlantic salmon (791 fish belonging to 34 full-sib pairs within 12 half-sib groups) was determined by analyzing blood samples taken on three different occasions. The fish were immunized twice with the antigen during the experiment. Antibody levels were measured by an enzyme-linked immunoadsorbent assay (ELISA). A method of estimating titers from three serum dilutions was worked out to avoid end-point titration of the large number of samples. The rainbow trout responded well to immunization, and genetic variation in antibody titers was observed both before and after the first immunization (h2 = 0.2). The Atlantic salmon had high initial titers to diphtheria toxoid and the response to immunization was weak. This suggests an impact of natural or cross-reacting antibodies. The heritabilities for antibody levels were lower in this species (0.12 and less). There were high genetic and phenotypic correlations between the antibody measurements at the three samplings. Antibody response to diphtheria toxoid correlated negatively with survival after challenge with V. anguillarum. No correlation was observed between antibody level and production traits (mean slaughter weight and survival rate) for full-sib groups reared at different sea locations.