Two year-classes of the breeding stock of Atlantic salmon of the Intitute of Aquaculture Research Ltd. (AKVAFORSK) in Norway were available for this study. In the year-class 1983 (1987), a hierarchical mating scheme with 24 (30) sires mated to 119 dams resulted in 119 full-sib groups with a total of about 25 000 individuals. Fifteen months after hatching, random samples of marked fish were distributed to six different net cages at different sites in Norway. After 15 to 16 months in the sea, all individuals were classified for indications of maturation. It was the objective to estimate genetic variance components for the trait “early sexual maturity” and to assess whether this trait is affected by genotype × environment interaction (GEI). Several models were fitted, including fixed cage effects and random sire and dam within sire effects as well as random sire by cage and dam by cage interactions. Since the observations were of categorical nature (mature/not mature), the thresh-old concept was applied to project results to an underlying conceptual liability scale. With the full model, the sire component accounted for 3.0 to 4.0% and the dam component accounted for 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 by cage interaction accounted for 61 to 105% of the dam variance. The estimated heritability of the trait was in the range of 0.10 to 0.17. All variance components were highly significantly different from zero. It is concluded that GEI plays an important role for the trait early sexual maturity and therefore selection program should be based on records of this trait at different sites.
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