Heritability of resistance to viral nervous necrosis in Atlantic cod (Gadus morhua L.)

Nodavirus are the causative agents of viral nervous necrosis (VNN), and has been shown to cause mortality in numerous fish species worldwide, among them is the Atlantic cod (Gadus morhua L.). In this study, heritability of VNN resistance in Atlantic cod was estimated through challenge testing of 50 large full sib families (∼ 94 fish per family) comprising two genetically distinct groups of Atlantic cod (Norwegian coastal cod and northeast Arctic cod) and their F1 crossbreds. The overall survival (dead/alive) at end of test was 30%, but coastal cod had considerably higher survival (56%) than northeast Arctic cod (10%), while the F1 cross was intermediate (31%). Furthermore, enormous variation in family survival was observed within each group (17 to 82% for coastal cod, 0 to 42% for northeast Arctic cod and 0 to 92% for the F1 cross). As a consequence, the estimated within-strain heritability of survival under challenge testing was extremely high (0.75 ± 0.11 on the underlying scale and 0.43 ± 0.07 on the observable scale). Common environmental effects of full-sib families were not significant in addition to additive genetic effects, but the data structure was not optimal for distinguishing these effects.