Genetic correlations between growth rate and resistance to vibriosis and viral nervous necrosis in Atlantic cod (Gadus morhua L.)

The aims of this study were to estimate genetic (co)variance components of Atlantic cod for body weight at 2.5 years of age (BW) and resistance to vibriosis (a bacterial disease) and viral nervous necrosis (VNN). The traits were recorded on seven discrete year-classes: five year-classes for vibriosis (11,936 individuals), two year-classes for VNN (6185 individuals) and five year-classes for BW (22,703 individuals), with each trait recorded on separate sub-samples of the full-sib families. Three genetic groups were defined in the dataset: coastal cod south (CCS), coastal cod north (CCN) and north-east Arctic cod (NEAC). Significant differences between the groups were found only for VNN resistance, with expected survival rates of (approx.) 52% vs. 13% in CCS and NEAC, respectively. Furthermore, significant favorable heterosis was estimated for BW (+ 147 g) and vibriosis resistance (~ 22% relative increase in survival). All three traits had significant heritability estimates, with a moderate heritability for vibriosis resistance (0.16 ± 0.04), exceptionally high heritability for VNN resistance (0.68 ± 0.14) and a moderate to high heritability for BW (0.28 ± 0.05). All estimated genetic correlations between the traits were weak and not significantly different from zero. Common environmental family effects explained 5.6% and 6.6% of the liability variance for vibriosis and VNN, and 8.6% of the phenotypic variance for BW. The significant heritabilities and low genetic correlations indicate that joint genetic improvement of vibriosis resistance, VNN resistance and growth rate would be feasible.