Genetic variation in susceptibility of Atlantic salmon to the sea louse Caligus elongatus Nordmann, 1832

Differences in susceptibility of distinct full-sibling families of Atlantic salmon, Salmo salar, to infection with the sea louse Caligus elongatus were investigated. Infection intensity with mobile stages of sea lice was monitored on 419 individual salmon from 73 full-sibling families held in a single sea pen and exposed to similar numbers of infectious larvae originating from nearby fish. The average intensity of infection calculated from the family groups ranged from 5 to 25, with 70 families having an average intensity of 10 or more preadult or adult sea lice. The overall average intensity was 15.30 and the prevalence was 100%. The calculated genetic heritability (h(2)) was 0.22, which indicates that this variability in susceptibility to infection may be heritable. This level of heritability also suggests that selection for improved resistance to sea lice is feasible.