GENETIC-PARAMETERS AND GENOTYPE X ENVIRONMENT INTERACTION FOR EARLY SEXUAL MATURITY IN ATLANTIC SALMON (SALMO-SALAR)

Two year-classes of the breeding stock of Atlantic salmon of the Intit ute of Aquaculture Research Ltd. (AKVAFORSK) in Norway were available for this study. In the year-class 1983 (1987), a hierarchical mating s cheme with 24 (30) sires mated to 119 dams resulted in 119 full-sib gr oups with a total of about 25 000 individuals. Fifteen months after ha tching, random samples of marked fish were distributed to six differen t net cages at different sites in Norway. After 15 to 16 months in the sea, all individuals were classified for indications of maturation. I t was the objective to estimate genetic variance components for the tr ait ''early sexual maturity'' and to assess whether this trait is affe cted by genotype x environment interaction (GEI). Several models were fitted, including fixed cage effects and random sire and dam within si re effects as well as random sire by cage and dam by cage interactions . Since the observations were of categorical nature (mature/not mature ), the threshold concept was applied to project results to an underlyi ng conceptual liability scale. With the full model, the sire component accounted for 3.0 to 4.0% and the dam component accounted fore 3.8 to 6.0% of the total variance on the underlying scale. The sire by cage interaction accounted for 23 to 54% of the sire variance and the dam b y cage interaction accounted for 61 to 105% of the dam variance. The e stimated heritability of the trait was in the range of 0.10 to 0.17. A ll variance components were highly significantly different from zero. It is concluded that GEI plays an important role for the trait early s exual maturity and therefore selection programs should be based on rec ords of this trait at different sites.