Heritability estimates for male proportion in the GIFT Nile tilapia ( Oreochromis niloticus L.)

The main goal of this study was to estimate the heritability of the proportion of phenotypic males in progeny of Nile tilapia broodstock based on visually scored sex from six consecutive pedigreed generations from the GIFT project. Mean male proportion was 0.44 across all generations, ranging from 0.37 to 0.56 across generations and environments. Across all generations there was a low but significant “additive” genetic component for male proportion with heritability estimates of 0.12±0.02 (observed scale) and 0.22±0.04 (underlying liability scale). The within generation heritability estimates varied from 0.00±0.03 to 0.25±0.07 on the observed scale, and from 0.11±0.02 to 0.32±0.07 on the underlying liability scale. As expected, genetic correlations between male proportion in the different post-nursery test environments were in 16 out of 17 cases not significantly different from unity (P>0.05) since sex was determined before fish were stocked in the different test environments, indicating no or the same degree of sex dependent mortality among the families in the different environments.