Genotypic and environmental effects on the incidence of sexual precocity in coho salmon ( Oncorhynchus kisutch)

The relative effects of genotype and initial freshwater rearing on the incidence of sexual precocity in coho salmon males were examined. Eggs from normally maturing females were fertilized with milt from both normal and precociously maturing males (jacks) in a partially nested factorial mating design. Progeny from each of the resulting full- and half-sib families were subsequently reared under two rearing temperature treatments (ambient and 15°C) during part of the hatchery phase of the life cycle. Mean growth of progeny from the jack and normal male-sired groups was equivalent during the majority of the initial freshwater rearing period. Of the 4980 survivors at the termination of the experiment, 175 individuals or 3.75% of the population had matured precociously. These jacks were distributed disproportionately among jack-sired and normal male-sired families, with jack-sired families contributing a significantly higher 4.6 times as many jacks. The incidence of jacks did not appear to be temperature related.