Genetic (co)variation of vaccine injuries and innate resistance to furunculosis (Aeromonas salmonicida) and infectious salmon anaemia (ISA) in Atlantic salmon (Salmo salar)

Side effects from vaccination, seen as adhesion and discoloration (melanin) of the visceral and parietal peritoneum, were subjectively scored at harvest on pedigreed individuals of two year-classes of Atlantic salmon; i.e., on 1664 offspring of 60 sires and 120 dams (year-class 1995) and 1282 offspring of 32 sires and 62 dams (year-class 1997). The 1995 year-class individuals were from a single farmed strain and were reared in a net-cage at one farm only, while the 1997 year-class individuals represented four farmed strains and two wild river strains and were reared in a net-cage at each of two different farms. At harvest, the males had significantly higher adhesion and melanin score than the females, and the farmed strains equal or lower adhesion and melanin score than the wild strains. The estimated heritability across the two year-classes was 0.19 ± 0.03 for adhesion score (0.22 ± 0.04 on the liability scale) and 0.18 ± 0.03 for melanin score (0.31 ± 0.06 on the liability scale) and the genetic correlation between the traits 0.71 ± 0.08. The genetic correlation between body weight (heritability 0.27 ± 0.04) and adhesion or melanin score was − 0.45 ± 0.10 and − 0.27 ± 0.11, thus reflecting an association between reduced body weight and increased vaccine lesions. Most likely these correlations were partly caused by negative non-genetic effects of vaccine lesions on growth rate, rather than by a true genetic correlation which cannot be obtained from the present data. Two additional samples of non-vaccinated full- and half-sib pre-smolt offspring of the same sires and dams were challenged either by using cohabitants infected with Aeromonas salmonicida or by intraperitoneal injection with infectious salmon anaemia (ISAV). Heritability estimates of survival in the challenge tests were 0.31 ± 0.03 (0.47 ± 0.05 on the liability scale) for furunculosis and 0.26 ± 0.03 (0.40 ± 0.04 on the liability scale) for ISAV. The genetic correlation of adhesion or melanin score with survival during the challenge tests was all low and not significantly different from zero, thus revealing no genetic association between vaccine lesions and resistance to furunculosis and ISA. Therefore vaccine lesions are most likely caused by other components of the immune systems than those responsible for the observed genetic variation in the innate resistance to furunculosis and ISA.