Aquaculture performance of artificial interspecific backcross groups between the hybrid of Crassostrea hongkongensis × C. ariakensis and the two parental species

Crassostrea hongkongensis is popular in southern China for its white flesh color, unique flavor, and delicious taste. However, the disadvantages of slow growth, poor tolerance, and high mortality limit its production and market sales. The application of genetic breeding techniques to breed new breeding lines with fast growth and low mortality is an important approach to solve these industrial challenges, including interspecific backcross breeding. In this study, we established eight experimental groups (HH- C. hongkonggensis ♀ × C. hongkonggensis ♂; HA- C. hongkonggensis ♀ × C. ariakensis ♂; AA- C. ariakensis ♂ × C. ariakensis ; A/HA- C. ariakensis ♀ × HA ♂; HA/HA-HA ♀ × HA ♂; H/HA- C. hongkonggensis ♀ × HA ♂; HA/H- HA ♀ × C. hongkonggensis ♂ and HA/A-HA ♀ × C. ariakensis ♂), tracked and compared their phenotypic traits. The results confirmed that the hatching parameters of the interspecific backcross groups (HA/H, HA/A, H/HA and A/HA) were significantly lower than those of the pure parental progeny groups (HH and AA). Although HA/A did not always show a significant growth advantage in the larval stage, it exhibited the largest shell height during the marine culture period (except on the 210th day), and showed a significant shell height advantage on the 360th day ( P < 0.05). Moreover, there were obvious backcross advantages during the marine culture period, with backcross advantages (BAs) in shell height of 7.30 %, 17.66 %, 16.44 % and 10.95 % from the 90th to the 360th days, respectively. In addition, HA/A consistently ranked in the top three in terms of the incremental survival rate, being significantly higher than the grandparental offsprings (HH and AA), with HA/A showing the highest survival rates on the 210th and 360th days. Similarly, backcross advantages were observed at all time points, with BAs of 3.42 %, 5.96 %, 6.29 % and 0.43 %, respectively. Gonad development statistics and paraffin section results showed that all backcross groups were fertile and produced many normal gametes, with little difference in the ratios of males to females among the eight groups. In summary, the HA/A group showed significant backcross advantages in both growth and survival, with the best overall performance. This makes it a promising new strain that could help address the industrial problems of C. hongkongensis and has the potential for large-scale application. • The phenotypic characters of interspecific backcross between C. hongkongensis and C. ariakensis were reported systematically. • F 1 hybrids could be bidirectionally fertilized with both parents, and all backcross offspring could survive. • All backcross groups were fertile and with no significant difference in sex ratio. • F 2 hybrids showed outbreeding depression, but was still better than HH. • HA/A showed significant growth and survival advantages over other groups.