Comparative study on tetraploid induction of the Fujian oyster Crassostrea angulata utilizing three typical methods

Abstract

The sterility advantages of triploids make them paramount for oyster aquaculture. Current hatcheries for triploid industrial breeding utilize tetraploids as male parents, and thus tetraploids are a core asset for triploid oyster culture. The oyster Crassostrea angulata is the most productive oyster species in China, however, the optimal conditions for tetraploid induction have never been examined. In this study, we investigated the effectiveness of three induction methods (Method Ⅰ, 2n ♀ × 2n ♂ + inducer abbreviated as DD + ind; Method Ⅱ, 3n ♀ × 2n ♂ + inducer abbreviated as TrD + ind; Method Ⅲ, 2n ♀ × 4n ♂ + inducer abbreviated as DT + ind) and three inducers (salinity; cytochalasin B, CB; and 6-dimethylaminopurine, 6-DMAP) for tetraploid induction in C. angulata. The optimal induction conditions for the three induction methods were a CB concentration of 0.5 mg/L treated for 20 min, 0.75 mg/L CB for a constant induction treatment of 20 min and 6-DMAP at a concentration of 100 mg/L for 20 min, respectively. When the optimal induction conditions were applied to a single pair of oysters, the D-larval tetraploid rate for the three methods were 18.93%, 58.32% and 51.61%, respectively. The survival rates of the experimental groups were only 10.36%, 28.07% and 21.99%, respectively, at day 30. The tetraploid rates for Method Ⅰ and Method Ⅲ, although decreased significantly over time, still reached 11.81% and 21.99% at 30 days, and 8% and 16% at 180 days of age, respectively. Tetraploid rates for Method Ⅱ were 58.32% − 71.28% at the larval stage and 80% at day 180. In summary, in spite of very different induction rates, viable tetraploid C. angulata can be harvested in all three methods. Method Ⅱ (TrD + inducer) was regarded as the optimal method to induce C. angulata tetraploids, and the optimal induction condition was a CB concentration of 0.75 mg/L and treated for 20 min under this method.