Effects of Temperature, Salinity and Stocking Density on Larval Survival and Growth of Reciprocal Crosses Between Two Strains of Pacific Oysters, Crassostrea gigas

The Pacific oyster Crassostrea gigas is one of the most widely cultivated aquaculture species and contributes significantly to total seafood production for human beings. However, mass mortality occurred frequently, and in some regions almost all oysters died during seed production and grow-out stage. In order to explore whether hybridization breeding can improve its growth and survival, a complete diallel cross between a selected strain ‘Haida No. 1’ (S) and an orange shell variant (O) of C. gigas was carried out. The larval growth and survival were compared among hybrids and purebred strains at temperatures of 16, 20, 24, 28 and 32°C; salinities of 15, 20, 25, 30 and 35; and stocking densities of 0.5, 1, 2, 4 and 8 larvae mL−1. Under different environments, the hybridization between two strains of C. gigas showed the heterosis of growth and survival. The mean shell height and survival rate of the two reciprocal crosses (OS, SO) were significantly higher than those of the two purebred strains (SS, OO) under all environmental conditions. In particular, OS showed greater heterosis than the purebred strains and SO progeny. The results showed that the productive traits of the ‘Haida No. 1’ could be improved by crossing with the orange shell line. Meanwhile, the results from this study also indicated that hybridization between the two strains of C. gigas may be a promising way for breeding new variety with high survival rate.