Comparative analysis on growth performance, survival and harvest traits between offspring from wild and mass-selected populations of Crassostrea nippona

Crassostrea nippona has recently been recognized as a preferred alternative to C. gigas in summer due to its firm flesh and high glycogen content. To promote industrial development, the mass selective breeding program was initiated to improve growth performance of C. nippona in 2014. Although a steady genetic gain of approximately 10% for growth traits was achieved in each of the first three generations of the selected strains, little is known about the cumulative genetic progress in desired traits contributed by the selective breeding in the genetic improvement program. In this study, the aquaculture performance of the selected population was comprehensively evaluated by comparing the production performance and reproductive traits of the progeny (WF1 and SF4) from the wild population and the third-generation selected line in commercial farming environments. The results showed that the diameters of eggs from both populations were at similar levels, but the fertilization and hatching rates of the progeny from the selected lines were significantly higher than those of the wild population (P < 0.05). At larval stages, the shell height and cumulative survival rate (CSR) of individuals from SF4 were consistently superior to that of WF1, especially on day 6 post-fertilization, in which CSR of the improved C. nippona was increased by 25.08% compared to that of wild oysters. Meanwhile, a significant 12.10% enhancement in the metamorphosis rate was observed in SF4 when compared with WF1. During the grow-out stage, SF4 displayed distinct advantages in growth performance and survival compared to the wild strain, with 23.19, 33.48, 34.18 and 79.11% improvement in shell height, body weight, CSR and final yield at harvest on day 800, respectively. Meanwhile, relative brood amount (RBA) associated with initial development of offspring was found to be significantly higher in SF4 compared with WF1 (P < 0.05). Remarkably, the gonadal development, sex ratios and biochemical composition of oysters from both populations were at similar levels at final harvest, implying that high-intensity artificial selection had no significant effect on reproductive characteristics and nutritional quality of C. nippona. The encouraging results in the present study suggest that the overall genetic progress contributed by genetic breeding is considerable in the fast-growing strain of C. nippona, and such gains are expected to continue to increase with further selective breeding.