Growth, survival and reproductive traits of chemical induced and tetraploid-derived triploid Hong Kong oysters (Crassostrea hongkongensis )

Chemical induction (inhibition of polar body II release) and crossing between tetraploid and diploid oysters (mating triploids) are 2 distinct and typical methods for obtaining triploids, and systematic comparative analysis on the phenotypic traits of these two triploids is rare. We tracked and compared the growth, survival, reproductive characteristics and ploidy composition of diploids, induced triploids, and mating triploids, and conducted interaction analysis between genotypes and sites. The results showed that the shell height of larvae showed a significant decrease trend of 3 NTD > 3 NCB > 2 N, while the D larval rate and survival rate of 3 NCB were the lowest, which may be related to the long-term effects of CB toxicity. During offshore farming, from the 180th to 700th day, the shell heights of the three groups followed a significantly decreasing order at both sites, namely 3 NTD > 3 NCB > 2 N (except on the 270th day at Beihai site), and the triploid advantage of shell height in 3 NTD was generally higher than that in 3 NCB, with the same trend in the whole weight. Genotypes and sites always had significant effects on shell height, but their interactions were not significant. The incremental survival rates of the 2 triploid groups were higher than that of the diploid at both sites on the 270th and 700th day, while that of the 3 NTD was significantly higher than the 3 NCB only on the 270th day. In addition, both triploids had some individuals fertile and could produce mature gametes, but the proportion was much lower than that of diploids. Triploid gonadal development is characterized by feminization and a high proportion of hermaphroditism. The fertility ratio and gamete production of 3 NTD were higher than that of 3 NCB, but the relatively high fertility of 3 NTD had no significant effect on its growth and survival. Ploidy composition tracking found that the ploidy composition of 2 N and 3 NTD groups was stable, but the ploidy composition of 3 NCB varied over time. These results indicate that 3 NTD has better performance and higher triploid advantages than 3 NCB, making it more suitable for the commercial production and promotion of triploid C. hongkongensis .