| Summary: | Intra-strain inheritance of growth and survival in rainbow trout (Salmo gairdneri), reared for 8-10 months in 2 hatchery and 2 prairie winterkill lake environments, was studied by means of a hierarchal mating design. Statistical determinations were made on both individual values and full sib family means. The implications for the genetic improvement of rainbow trout for extensive aquacultural purposes are discussed. Individual heritability values for fork length and weight were respectively, 0.09 and 0.06 in the non-competitive hatchery environment, 0.27 and 0.23 in the competitive hatchery environment, 0.09 and 0.00 in lake 971 and 0.27 and 0.04 in lake 506. Fork length and weight heritability estimates determined from full sib family means were much larger in all environments and were respectively, 0.58 and 0.42 in the non-competitive hatchery environment, 0.99 and 0.94 in the competitive hatchery environment, 1.08 and 0.50 in lake 971, and 0.78 and 0.74 in lake 506. In lakes 971 and 506 heritability estimates for individual survival were 0.18 and 0.02 respectively and for full sib family means they were 1.07 and 0.53 respectively. Inter-family competition caused a magnification of genetic differences between hatchery environments and was unimportant in the lake environments. Family selection is expected to produce a more rapid response in growth and survival than individual or mass selection. Genotype-environment interactions were important in all environments. Artificial selection would be more effective in the intended environment than in the hatchery. Additive genetic, environmental, and phenotypic correlations between fork length and weight were large and positive in all environments. Simultaneous selection for these traits would be effective.
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