Genetic sensitivity of Chitralada Nile Tilapia (Oreochromis niloticus) body weight to dietetic lysine levels

Abstract

Genetic sensitivity of body weight, daily and total weight gains to different levels of dietetic lysine were evaluated on Chitralada Nile tilapia strain at 150 days of age via reaction norms. The diets used in this experiment had fixed 32% of crude protein and 3190 kcal/kg of digestible energy with increasing levels of dietetic lysine (1.43, 1.53, 1.63, 1.73, 1.83%). In this study, data from 700 fish produced by mating a broodstock of 21 males and 29 females were used. Each fish was uniquely identified with a microchip tag and randomly distributed in the 5 different levels of dietetic lysine, with 7 replicates each. The results show homogeneity of the residual variance across the levels of dietetic lysine in this study. Nevertheless, the additive genetic effects presented estimated variances that changed across the levels of lysine, thus so did the heritability (but always above 0.5). These results indicate that the estimated breeding values (EBV's) can vary across lysine levels. Despite the changes in EBVs, the estimated genetic and rank correlations were high (above 0,9), showing that EBVs at different levels of lysine are strongly correlated. Thus, the effect of genotype x environment interaction is minimal and does not affect fish classification and selection can be done for any of the evaluated levels of dietetic lysine.