Genetic variation and genotype by location interaction in body weight, spinal deformity and sexual maturity in Atlantic cod ( Gadus morhua) reared at different locations off Norway

Body weight, spinal deformity and sexual maturity were recorded at 2 years of age and at harvest in 51 full-sib families of Coastal and Arctic cod, Gadus morhua, produced from 40 sires and 34 dams. The family-groups were reared at four locations off the coast of Norway in Hordaland, Møre and Romsdal (M&R), Nordland and Troms. Heritability estimates for body weight (0.64 ± 0.12) at harvest indicate promising potential for improvement by selective breeding. Low and non-significant estimates of heritabilities were found for sexual maturity at harvest. All traits showed a significant interaction effect of family group by location. The genetic correlations between the same traits recorded at the different locations ranged from 0.82 to 0.95 for body weight, and from 0.58 to 0.82 for spinal deformity. The high correlations for body weight indicate no important genotype by environment interaction, while spinal deformity shows a higher degree of environmental sensitivity. This should be taken into account in a breeding program. A high genetic correlation was found between body weight recorded at 2 years of age and at harvest (0.89), while weight recorded at tagging was only moderately correlated to weight at 2 years of age and at harvest (0.54 and 0.48). Weight at 2 years of age may thus be used as a selection criterion for growth in Atlantic cod. The degree of sexual maturity was higher in the Coastal than in the Arctic cod at harvest, while no significant differences were found between Coastal and Arctic cod for body weight and spinal deformity at any location. Consequently, separate breeding programs for the two strains in the breeding population may not be needed.