Triploidy induction by CB and their survival rate and triploidy rate in Kumamoto oyster (Crossostrea sikamea)

In order to induce triploid using cytochalasin B (CB) in Crossostrea sikamea, three effecting factors, including CB concentration, initial time of induction, and duration time of induction, were optimized by the cleavage rate, D larvae rate, and triploidy rate. In addition, the variations of survival rate and triploidy rate were also compared for larvae and adults. The results suggested that the optimal method of triploid induction were 0.5 mg/L CB, 40% first polar body releasing for initial time of induction, and 20 min for duration time of induction. The triploidy rate of 87% was obtained by the optimal method. The first effecting factor for cleavage rate, D larvae rate, and triploidy rate was CB concentration, duration time of induction and initial time of induction, and duration time of induction, respectively. Furthermore, there was insignificant negative relationship between triploidy rate and cleavage rate. Whereas, the positive relationship was significant between triploidy rate and D larvae rate. As a result, high triploidy rate and high larvae production could be obtained by decreasing both CB concentration and duration time of induction. The survival rates were 71.27% and 96.09% at 3 days, and 34.14% and 58.80% at 15 days for triploid and control groups, respectively. Comparatively, the survival rate were 53.62% and 44.67% for adults at 450 days (September) in triploid and control groups, respectively. The triploidy rate declined from 87% to 77% during the period of 3 to 9 days. Whereas, the triploidy rate was 59.21%±4.99% on average from 90 to 450 days, suggesting that there was no correlativity between triploidy rate and survival rate, with a small variation of triploidy rate for adults. This study provides valuable data for further exploration into triploidy of C. sikamea.