Evaluation of the growth, salt tolerance and parents’ heterosis contribution in reciprocal hybrids F₂ between Oreochromis niloticus and Sarotherodon melanotheron

In order to select a good breed both with ideal culture performance and high salt tolerance, taking Nile tilapia (O. niloticus) and black-chip tilapia (S. melanotheron) as compared groups, two reciprocal hybrids, e.g., O. n. ♀×S. m. ♂ (F₂) and S. m.♀×O. n. ♂ (F₂) as trial groups, a comparisons were conducted under 4 salinities (0, 15, 20 and 25 ppt). The major results were: (1) Both O. n. ♀×S. m. ♂ (F₂) and S. m.♀×O. n.♂ (F₂) showed a better growth under 20 and 25 salinities, equal to about 75% of growth of O. niloticus under 0 salinity, and 4 times of growth of S. m. under 25 salinity. It indicated that the growth of hybrids close to O. n., but much better than S. m. Under 25 salinity, O. n. ♀×S. m. ♂ (F₂) showed 7% faster growth than S. m. ♀×O. n. ♂ (F₂). (2) under 15 and 20 salinity, the heterosis showed higher in growth rate and coefficient variation of body weight, and It was found that 0、15、20、25 salinity could not cause a significant difference in survival of two hybrids.（3）It is founded that, the superior traits from different parent fish species, such as the fast growth of Nile tilapia, and the high salt tolerance of black-chip tilapia, are of different contribution for different traits of hybrids under different salinities. Estimated by the formula F1a1P1+a2P2，the contribution for growth of hybrids from Nile tilapia is 3～4 times higher than that from black-chip in 15-25 salinity, and the contribution for survival of hybrids in 25 salinity is almost 0 from Nile tilapia, but 100% from black-chip.