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-antigen from Vibrio salmonicida , respectively, were determined in 77 full-sib groups of Atlantic salmon in order to evaluate their possible use as immune parameters for indirect selection to improve disease resistance. Fish from parallel full-sib groups had previously been challenged with Aeromonas salmonicida (causing furunculosis), Renibacterium salmoninarum (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 means of the full-sib groups for the different immune parameters and survival rates in the parallel full-sib groups were determined. A significant genetic variation in lysozyme activity was found, as well as an apparent genetic association between low lysozyme activity and high survival rates. Low heritabilities and low univariate correlations with survival in the full-sib groups were estimated for all of the other immune parameters. An analysis of the multivariate associations between the full-sib mean values of the complete set of immune parameters, and survival rates in the parallel full-sib groups in each of the challenge tests, revealed that, at low levels of lysozyme activity and with low antibody titres against V. salmonicida O-antigen, increased IgM levels seemed to increase survival from furunculosis.