Comparative analysis of growth, survival and sex proportion among tetraploid-based autotriploid (Crassostrea gigas and C. angulata) and their allotriploid oysters

Triploid is widely cultivated in China and many other oyster-producing countries for the advantages of fast growth, favorable infertility and better meat quality. However, triploid Crassostrea gigas is found to have disadvantages of slow growth in later grow-out stage and high summer mortality, while the triploid C. angulata has the disadvantages of fragile shells and a relatively high ratio of developed gonads in population, and therefore, both of them have space for further improvement. Due to the limitations of poor fertility and low survival of offspring, triploid genetic improvement cannot be carried out directly. Hybridization between species is a useful method for indirect genetic improvement of triploids, and natural crosses between tetraploid males and diploid females have proven to be the best method for commercial promotion of triploids. The growth, survival and gonad development of autotriploids (DGTG-diploid C. gigas ♀ × tetraploid C. gigas ♂, DATA-diploid C. angulata ♀ × tetraploid C. angulata ♂) and allotriploids (DATG-diploid C. angulata ♀ × tetraploid C. gigas ♂, DGTA-diploid C. gigas ♀ × tetraploid C. angulata ♂) were investigated in this study. It is showed that the fertilization rates of autotriploids were significantly higher than that of allotriploids, and DATG larvae grew significantly faster than the other three groups (P < 0.05). DGTA had significant shell height, whole weight and survival advantages at Laizhou site (P < 0.05), while DATG exhibited significantly fastest growth and highest survival at Zhangpu site (P < 0.05), but both DATG and DATA showed significantly faster growth and higher survival at Beihai site (P < 0.05), with no significant difference between them (P > 0.05). Sites, genotypes and their interaction always presented significant effects on shell height and whole weight from the 90th to 360th day, but not on survival with the 180th day as an exception. Gonad examination confirmed that the proportions of fertile individuals in the groups with maternal C. gigas (DGTG and DGTA) were lower than that in the groups with maternal C. angulata (DATA and DATG), and DATA always had the highest rate of developed gonad at three sites. These results indicate that DGTA has advantages in growth, survival and infertility in northern China while DATG performs best in southern China, which exhibits that there is a significant maternal effect of hybridization in allotriploids, and promise a guidance for their commercial production.