The induction of metamorphosis in Iwagaki oyster (Crassostrea nippona)

The Iwagaki oyster Crassostrea nippona, is a large sessile oyster inhabiting intertidal hard grounds and reefs along the coast of East Asian. Because of its unique flavor, delicious taste and edibility during summer when other oyster species are unavailable, C. nippona is highly valued and has a broad market prospect. To obtain cultchless oyster with a regular shell shape and uniform size, epinephrine (EPI) was applied to C. nippona eye-spot larvae to induce cultchless metamorphosis. To determine optimum levels for C. nippona, the effect of EPI concentration, exposure time to EPI, and larval density were examined. The results demonstrate that EPI can significantly facilitate larval metamorphosis. 0.05 mmol/L and 1 h treatment were the optimum for single oyster seed production, and shell height and survival rates of cultchless spats showed a curve of descending with increasing EPI concentration and exposure time. However, there was no significant difference between EPI treatments at larval densities <8 larvae/mL. The growth of C. nippona was also examined in the following days, which showed that shell height and spat survival rates were higher in 0.5-4 larvae/mL than those in 8 larvae/mL. Therefore, 8 larvae/mL was the optimum for single oyster seed production, while a density of no more than 4 larvae/ml was the best for cultchless spats cultivation.