GENETIC-VARIATION IN ANTIBODY-RESPONSE TO DIPHTHERIA TOXOID IN ATLANTIC SALMON AND RAINBOW-TROUT

Antibody response to diphtheria toroid in rainbow trout (202 fish belo nging to 28 full-sib pairs within 14 half-sib groups) and Atlantic sal mon (791 fish belonging to 34 full-sib pairs within 12 half-sib groups ) was determined by analyzing blood samples taken on three different o ccasions. The fish were immunized twice with the antigen during the ex periment. Antibody levels were measured by an enzyme-linked immunoadso rbent assay (ELISA). A method of estimating titers from three serum di lutions was worked out to avoid end-point titration of the large numbe r of samples. The rainbow trout responded well to immunization, and ge netic variation in antibody titers was observed both before and after the first immunization (h(2)=0.2). The Atlantic salmon had high initia l titers to diphtheria toroid and the response to immunization was wea k. This suggests an impact of natural or cross-reacting antibodies. Th e 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 t o diphtheria toroid correlated negatively with survival after challeng e with V. anguillarum. No correlation was observed between antibody le vel and production traits (mean slaughter weight and survival rate) fo r full-sib groups reared at different sea locations.