Effect of triploidy on paternal and maternal variance components in brown trout, Salmo trutta L.

The covariation between diploid and triploid progenies from common breeders and the effect of triploidy on the parental variances were investigated in brown trout (Salmo trutta L.) using two progeny testing experiments, sampling, sires and dams respectively, from the same population. The traits studied were body weight, growth, condition factor and red spotting of the skin. Triploidization generated some interactions with the parental breeding value, but their effect was minor (less than 20% of the genetic variance, in most cases) as compared with the amount of variation common to both ploidy levels. These interactions were mainly caused by a scale effect, triploidy reducing the variance attributable to sires and increasing the variance attributable to dams. Actual lack of correlation (genetic correlation significantly less than 1) between diploid and triploid familial performances was observed in a single instance out of 18. The modification of respective parental variance components by triploidy, already observed in the rainbow trout Oncorhynchus mykiss (Walbaum), appears as a logical consequence of the genetic make-up of triploids, and should be taken into account in selective breeding.