Genetic analysis of the Pacific white shrimp (Litopenaeus vannamei): heterosis and heritability for harvest body weight

The aim of this study was to estimate heterosis and heritability for harvest body weight of the Pacific white shrimp (Litopenaeus vannamei) measured at commercial farm conditions. Heterosis and heritability were estimated using a base population from diallel crosses of eight introduced strains. The base population included 9936 shrimp from 207 families that were produced with 188 sires and 172 dams using a nested mating design by artificial insemination. Heterosis was calculated basing on the least squares means (LSM) of harvest body weight. The results showed that most of the hybrids (75%) have positive heterosis for harvest body weight, which ranged from -13.36% (UA2 x UA5) to 13.80% (UA6 x UA5) with a mean of 2.41%. The high amount of heterosis manifested in the hybrids indicated the usefulness of these hybrids for improving the growth. Variance components and heritability for harvest body weight were estimated using an animal model. The heritability estimate for harvest body weight was 0.092 +/- 0.082 (h(2)) when genetic groups were excluded from the pedigree, but it was decreased when genetic groups were included in the pedigree (h(group)(2) = 0.066 +/- 0.050), implying that there are strain additive genetic effect and heterosis in the base population. However, the heritability estimates for harvest body weight were significantly different from zero (P < 0.05) and there was no significant difference between h(2) and h(group)(2) (P > 0.05). The results from this study indicated that significant improvement for growth is possible through crossbreeding and selective breeding in L. vannamei.