Contribution of Genetic and Environmental Variance Components to Increasing Body Length in Juvenile Brown Trout Salmo trutta

Genetic and environmental components of variance of body length in juvenile brown trout Sabno trutta were estimated from the results of three experiments. The additive genetic variance increased in the first months posthatch, but was gradually overwhelmed by environmental and residual variances, so that heritability, after going through a maximum (about 0.45) at 3 mo, decreased later on. However, constancy of genetic factors was indicated by high genetic correlations (0.8-1.0) observed between successive measurements. Maternal effects were visible, but not statistically significant. There was no evidence of non-additive genetic variation. These results suggest that selection for precocious growth among separate families should be performed at the time when heritability is about maximum. Accounting for the importance of the within-lot variation (80-90% of the total variation), individual selection should be considered, as compared to more expensive methods.