To investigate the tetraploid induction effect between two allotetraploid oysters (GGAG—GGA ♀×GG ♂ and AAGG—AAG ♀×GG ♂) under varying cytochalasin B (CB) concentration (0.2, 0.4, 0.6, 0.8 mg/L), salinity gradient (6, 8, 10, 12) and induction duration (10, 15, 20, 25 min), we analyzed the cleavage rate, hatching rate, tetraploidy rate and induction efficiency. At the same time, the growth and survival of the early larvae were analyzed. The results showed that the optimal method of inducing tetraploid of GGAG was 0.6 mg/L of CB and 15 min. The tetraploidy rate of (42.75± 2.89)% was obtained with the method. The salinity 8 and 15 min was also the optimal method, with which the tetraploidy rate of (32.28±1.97)% was obtained. For AAGG, 0.6 mg/L of CB and 20 min was optimal, with which the tetraploidy rate of (47.03±2.66)% was obtained. The salinity 10 and 15 min was the optimal method, with which the tetraploidy rate of (33.06±1.18)% was obtained.

To explore the optimal conditions for inducing triploid oyster (Crassostrea nippona), the effects of different induction methods (cytochalasin B and hypotonic treatment), induction durations, and induction times on cleavage rate, hatching rate, triploid rate and comprehensive evaluation index were examined in this study. Additionally, the impact of the two induction methods on larval growth and survival was analyzed. When cytochalasin B(CB) concentration was 0.5 mg/L, the induction duration was 16 min, and the induction was initiated when 30% of the first polar body(PB1) was released, the triploid rate reached (69.71±2.59)% at which the comprehensive evaluation index was the highest (42.39%). For the hypotonic treatment, at salinity 7, with the same induction duration and time (30% PB1 release), the triploid rate was (41.82±1.79)% with a comprehensive evaluation index of 24.82%. Regarding survival rate, both CB and hypotonic groups exhibited significantly lower survival rates than the control. The survival rate of the hypotonic group was higher than that of the CB group within the first 6 days but dropped below it after 8 days. In summary, the optimal condition for inducing triploid C.nippona is 0.5 mg/L CB concentration, initiating induction at 30% PB1 release, and maintaining treatment for 16 min. With the optimized method, the highest triploid rate, survival rate and comprehensive evaluation index were observed.