Trait segregation and growth characteristics of the F2 generation hybrids between Crassostrea dianbaiensis and C. iredalei

Crassostrea dianbaiensis, a recently identified species with significant commercial potential, has been successfully hybridized with Crassostrea iredalei, demonstrating that fertilization can be bidirectional. Notably, only the DI hybrid lineage (C. dianbaiensis♀ × C. iredalei♂) achieves maturity. These DI hybrids display remarkable growth vigor and survival advantages over their parental strains. To further investigate the trait segregation patterns in the F₂ generation and the stable inheritance of heterosis, an intraspecific-crossing experiment was conducted with mature DI individuals, and place the juvenile shellfish in natural sea areas and artificial ponds for comparative aquaculture. The study involved crossing within C. dianbaiensis, C. iredalei, and mature DI individuals. The results indicated that F₂ hybrids could fertilize successfully and develop normally, but exhibited signs of outbreeding depression during the planktonic larval stage compared to the grandparental species. Genetic analysis using ITS1 markers classified F₂ individuals into three distinct categories: F₂-I, F₂-D, and F₂-H. Water temperature fluctuations during the growth phase in Oushi’s ponds were more extreme than those observed in the Sanbaimen sea. On day 360, the ratio of F₂-I, F₂-D, and F₂-H in Oushi’s ponds was approximately 1:1:4, contrasting with a 1:1:2 ratio in the Sanbaimen sea. This indicates that F₂-H has a higher survival rate in Oushi’s ponds with drastic temperature changes. In addition, nearly all F₂-D individuals showed phenotypic traits surpassing the F₂ average. Histological examination of gonads indicated that all three F₂ types were capable of gamete production, albeit with delayed gonadal development relative to age-matched grandparental species. In conclusion, both F₂-H and F₂-D exhibited heat tolerance and enhanced growth rates, respectively, suggesting their potential as new foundational breeding stocks for targeted development of strains adapted to large-scale aquaculture in southern China.