Genetic variance for uniformity of harvest weight in Nile tilapia (Oreochromis niloticus)

Competition for resources is common in aquaculture, which inflates the variability of fish body weight. Selective breeding is one of the effective approaches that may enable a reduction of size variability (or increase in uniformity) for body weight by genetic means. The genetic variance of uniformity is commonly known as genetic heterogeneity of environmental variance for particular traits. The data collected from a social interaction experiment were used to investigate the presence of genetic variation in heterogeneity of environmental variance for harvest weight in the GIFT strain. A total of 944 records pooled (by family-group) from 6330 individual harvest weights were used in the analysis. For the estimation of genetic parameters we fitted a bivariate sire-dam model to harvest weight and its standard deviation. To normalize the residuals, individual harvest weight was Box-Cox transformed. The heritability (at the family by group level) and genetic coefficient of variation for standard deviation of Box-Cox transformed harvest weight (0.23 and 0.17, respectively) indicated that uniformity of harvest weight was partly under genetic control. In addition, we found a very low genetic relationship between Box-Cox transformed harvest weight and its standard deviation, rA=0.095±0.183. Hence, these two traits are unrelated and can be selected in different directions using index selection, namely, aiming to increase growth rate while decreasing size variation. We conclude that there is potential to increase harvest weight and its uniformity by selective breeding in the GIFT strain of farmed tilapia. Statement of relevance: Uniformity will help to increase aquaculture productio