Log-transformed variance from individual growth curves as a potential indicator of resilience in Nile tilapia Oreochromis niloticus

The ability of the animal to cope with environmental changes may be measured by log-transformed variance of deviations from expected weights (LnVar). We calculate LnVar by fitting the expected individual growth curve based on longitudinal weights (LnVar_ind) of Nile tilapia that were grown in either an aerated or a non-aerated freshwater pond. We estimated genetic parameters for LnVar_ind in Nile tilapia, the genetic correlation between LnVar_ind and growth and the genetic correlation for LnVar_ind between aerated and non-aerated pond. The heritability estimate for LnVar_ind (0.28) in the non-aerated pond was higher than in aerated pond (0.06). In the aerated pond, genetic correlations of LnVar_ind were - 0.44 ± 0.23 with daily growth coefficient (DGC) and - 0.45 ± 0.24 with harvest weight (W₅). In the non-aerated pond, genetic correlations with DGC and W₅ were - 0.68 ± 0.12 and - 0.52 ± 0.17, respectively. These values suggest that selection for fish with high growth rate will reduce LnVar_ind. However, genetic correlation of LnVar_ind between aerated and non-aerated pond was 0.50, suggesting that genetic improvement in the aerated environment will reduce LnVar_ind in the non-aerated environment. Therefore, incorporating records from relatives in non-aerated pond is beneficial for breeding programs targeting this environment.