Comparative histological analysis of gonad development between autotriploid (Crassostrea gigas and C. angulata) and allotriploid oysters.

China has the highest oyster yield in the world, with Crassostrea gigas and C. angulata being the two most productive oysters species. The hybrid triploid of Crassostrea gigas and C. angulata exhibits good heat resistance and can mitigate the plight of mass mortality of Crassostrea gigas in northern China caused by high temperature and spawning during the summer. Additionally, triploid oysters have reduced fecundity, which allows the energy typically used for gonad development to be redirected to somatic cell growth, resulting in better taste and lower mortality during the reproductive season. Therefore, it is essential to study the detailed gonad development of hybrid triploid oysters. This study compared the gonad development between autotriploids (TGG-diploid C. gigas ♀ × tetraploid C. gigas ♂) and allotriploids (TAG-diploid C. angulata ♀ × tetraploid C. gigas ♂) during the breeding season. Results showed that the female proportion of TGG increased gradually with rising temperature, reaching a peak of 57.1% in August, whereas the proportion of females in TAG was lower, with males accounting for >50% from June to August 2023. Histological analysis revealed that the proportion of female α (producing many oocytes) increased with gonad development, peaking for TGG female α in July and for TAG female α in September. Moreover, the number of sperm in male TAG gonadal tubules was less than in male TGG, and more apoptotic cells were observed in the ultrastructure of male TAG gonad, which was confirmed by apoptosis experiment. Based on these results, it is suggested that the gonad development of female and hermaphrodite TAG were delayed compared with TGG, and the level of sterility in male TAG should be higher than in male TGG. • First comparative histological analysis of gonad development of triploid Crassostrea gigas and hybrid triploid of C. gigas and C. angulata (TAG). • TAG had higher male proportion during the breeding season. • Gonad development of female and hermaphrodite TAG were delayed compared with triploid C. gigas. • Male TAG sterility was higher compared with male triploid C. gigas. [ABSTRACT FROM AUTHOR]