Difference in skin immune responses to infection with salmon louse (Lepeophtheirus salmonis) in Atlantic salmon (Salmo salar L.) of families selected for resistance and susceptibility.

Atlantic salmon is susceptible to the salmon louse (Lepeophtheirus salmonis) and the variation in susceptibility within the species can be exploited in selective breeding programs for louse resistant fish. In this study, lice counts were completed on 3000 siblings from 150 families of Atlantic salmon identified as high resistant (HR) and low resistant (LR) families in two independent challenge trials. Skin samples behind the dorsal fin (nearby lice attachment) were collected from ten extreme families (HR or LR) and analyzed by qPCR for the expression of 32 selected genes, including a number of genes involved in T helper cell (Th) mediated immune responses, which have been previously implied to play important roles during salmon louse infections.