GENETIC-VARIATION IN IMMUNE PARAMETERS AND ASSOCIATIONS TO SURVIVAL IN ATLANTIC SALMON

Lysozyme activity, haemolytic activity, total level of IgM, and levels of antibodies against A-layer from Aeromonas salmonicida and O-antige n from Vibrio salmonicida, respectively, were determined in 77 full-si b groups of Atlantic salmon in order to evaluate their possible use as immune parameters for indirect selection to improve disease resistanc e. Fish from parallel full-sib groups had previously been challenged w ith Aeromonas salmonicida (causing furunculosis), Renibacterium salmon inarum (causing bacterial kidney disease, BKD) and Vibrio salmonicida (causing cold-water vibriosis). Heritabilities were estimated for each of the immune parameters and correlations between the least square me ans of the full-sib groups for the different immune parameters and sur vival rates in the parallel full-sib groups were determined. A signifi cant genetic variation in lysozyme activity was found, as well as an a pparent genetic association between low lysozyme activity and high sur vival rates. Low heritabilities and low univariate correlations with s urvival in the full-sib groups were estimated for all of the other imm une parameters. An analysis of the multivariate associations between t he full-sib mean values of the complete set of immune parameters, and survival rates in the parallel full-sib groups in each of the challeng e tests, revealed that, at low levels of lysozyme activity and with lo w antibody titres against V. salmonicida O-antigen, increased IgM leve ls seemed to increase survival from furunculosis.