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
weightswere used in the analysis. For the estimation of genetic parameters we fitted a bivariate sire–dammodel
to harvest weight and its standard deviation. To normalize the residuals, individual harvestweight 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 harvestweight and its uniformity
by selective breeding in the GIFT strain of farmed tilapia.
Statement of relevance: Uniformity will help to increase aquaculture production.