Survival and growth of reciprocal crosses between two stocks of the Hong Kong oyster Crassostrea hongkongensis (Lam & Morton, 2003) in southern China

The Hong Kong oyster, Crassostrea hongkongensis, is one of the most economically important and well-known oyster species in southern China. To explore the possibility of improving the performance of the Hong Kong oyster, complete diallel crosses between two oyster stocks, the Zhuhai stock (Z: fast growth line F4) and the Maowei Sea stock (M: resistant line F3), were conducted using pooled gametes. Three replicates, each consisting of two pure stocks (ZZ and MM) and two reciprocal crosses (ZM and MZ), were successfully generated. High fertilization rate and hatching level were observed among all the experimental groups, suggesting that there was no sperm-egg recognition barrier between geographic populations. Reciprocal crosses had higher survival rate compared to the pure stock crosses and the rate of survival increased with progeny growth. Growth heterosis became obvious both in larval and adult stages, and was primarily influenced by the egg origin and mating strategy at the larval stage. Also, the phenotypic traits of all progeny differed amongst the culture sites, suggesting a significant environmental effect. The Zhuhai site was more suitable for oyster aquaculture than the Maowei Sea site. Thus, our results demonstrated that crossbreeding between Zhuhai and Maowei Sea stocks of Hong Kong oyster to produce superior heterosis represents a promising means to improve the fishery yield of this species in southern China.