Genetic variation in resistance of Atlantic salmon (Salmo salar) to the salmon louse Lepeophtheirus salmonis

The heritabilities for the number of lice recorded on naïve fish were in general higher than when recorded on re-infected fish. The genetic correlations between these two lice counts were positive (0.26-0.35) but not significantly different from zero. The heritability for the number of lice recorded during a controlled challenge test was 0.26 ± 0.07. The genetic correlation between the numbers of lice recorded in the challenge test and during a natural infection was very high (rg = 0.88). It is concluded that the potential for improving resistance to sea lice in Atlantic salmon by selective breeding is good. As natural infection is highly variable in time and magnitude, it is recommended that challenge tests should be used in selective breeding to increase the resistance of salmon to L. salmonis.