Effect of harvest weight and its uniformity on survival in Litopenaeus vannamei reared in different systems
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A new goal in animal breeding programs is to improve not only trait means, but also to decrease the level of phenotypic variation. One way to achieve uniformity is through selection for reduced residual (environmental) variance, if this is a trait under genetic control. The objective of our study was to evaluate the opportunity of selection for uniformity of harvest weight (HW) and to investigate whether HW and its uniformity (HWv) may affect survival (SUR) in shrimp reared in different production systems. A total of 149,919 and 164,023 records of HW and SUR, respectively, were obtained from a commercial shrimp hatchery and used in this study. Data was grouped into three sets based on the analyses: low density earthen ponds (S1), high density concrete recirculation tanks (S2) and S1 + S2 for joint analyses. A sire-dam double hierarchical generalized linear model (DHGLM) was applied to estimate (co)variance components for HW-HWv, while a bivariate mixed animal model was applied for HW-SUR, using the three datasets. Genetic correlations among these traits were then estimated, in addition to the correlation coefficient between estimated breeding values (EBV) for HWv and SUR. The results revealed a significant proportion of genetic variance in the environmental variance of HW and, consequently, the opportunity to select for uniformity (genetic coefficient of variation ranging from 17 to 35%). The genetic correlations between HW and SUR were different in sign and magnitude based on the production system, being equal to 0.36, −0.59 and − 0.02 for S1, S2 and S1 + S2, respectively. Correlation coefficients between EBV for HWv and SUR were significant only for S1 (−0.32), suggesting that selection for more uniform families may also increase survival rates in a less intensive environment. In conclusion, we found substantial genetic variation in the uniformity of harvest weight in Litopenaeus vannamei and this trait could be improved through selection. Harvest weight and its uniformity have a genetic correlation with survival affected by the production system and environmental condition.