Complete diallele cross between six inbred groups of rainbow trout, Salmo gairdneri

Abstract

Estimates of heterosis, additive and maternal effects were obtained from a complete diallele cross among six inbred groups ( F=0.50) of rainbow trout. Total heterosis was broken down into average, general and specific heterotic effects. Random-bred controls reared parallel to the inbred ( F=0.59) and crossbred groups made it possible to estimate the inbreeding effects on the traits studied. These were: body weight and condition factor of fingerlings, smolts, adults and at slaughter; abdominal fat score; sexual maturity; and survival and relative growth rate in four different periods. The genetic effects studied fit the data well and each effect had, with few exceptions, a significant effect on all traits. Of the heterotic effects, the specific effect was the most important for nearly all traits. The average heterosis effects and the inbreeding effects were all low and quite similar for a given trait. Total heterosis for weight at slaughter ranged from 9% below to 36% above the parental mean for additive effects, and from 17% below to 18% above the control. In total performance for weight at slaughter only one cross was significantly heavier (21%) than the control. The coefficients of correlation between the additive and total performance of the crosses were in general low and estimated as 0.33 for weight at slaughter. The maternal effects were important but were probably sampling effects caused by the low number of females and males used to form the diallele. It was concluded that the costs and time delay in developing and test-crossing inbred lines would only be justified by larger heterotic effects in crossbred stocks than found in this study.