Estimation of genetic parameters for body weights of Nile tilapia Oreochromis niloticus using random regression models

Abstract

The accuracy of predicted breeding values used for selection in animal breeding programs is dependent upon the amount and quality of information, the adequacy of statistical models and the analytical methodology employed. Random regression models more adequately describe growth than repeatability and multitrait models; because they account for continuous changes in phenotype and for related genetic and environment effects while using all available information without pre-adjustment of the data. In this experiment, longitudinal genetic studies of body weight of Nile tilapia Oreochromis niloticus recorded between 106 and 245days of age were conducted by fitting random regression models. Four models, inclusion or exclusion of a family effect and the assumption of homogeneity vs. heterogeneity of residual variance, were compared by Bayesian Information Criteria (BIC). The lowest BIC (best fit) was observed for the model considering heterogeneous residual variance and including a family effect. Heritability estimates for live body weight ranged from .02 to .52 during the age interval examined, and all estimates beyond 190days of age were greater than .30. Part of the variance among families was attributable to direct additive genetic, common environmental, maternal and other heritable genetic effects. Thus, the inclusion of a family effect in the model would result in lower estimates of additive genetic variance, particularly at the beginning of the growth period, close to when fish were individually identified. Until that point, fish within family groups were kept in a common environment, which may explain the low heritability estimates obtained at the beginning of the experiment. Genetic correlations between body weights at different ages all were greater than .60, suggesting correlated response in body weight at older ages (245days) could be achieved by selecting fish at earlier ages (106days).