Histochemical study of glycogen and lipid of different fertility Pacific oyster (Crassostrea gigas) during gonadal development

Shellfish culture is one of the pillar industries of China's mariculture industry, and oyster is the species with the highest yield and output value. Crassostrea gigas, also known as Pacific oyster, is one of the leading species of oyster culture in China, which is characterized by high fertility, strong adaptability, rapid growth and rich nutrition. In order to solve the problem of diploid oysters with reduced meat quality due to spawning in summer, triploid oysters were successfully cultivated. Because of their poor fertility and high quality in breeding season, the market vacancy of diploid oysters in summer was made up for. The study of the regulatory mechanism of gonadal development has always been one of the hot research fields in developmental biology. Gonad development is accompanied by energy storage and utilization. Analysis of energy storage and consumption during gonadal development helps to reveal the regulation mechanism of gonadal development. Therefore, to carry out research on energy changes and related regulation mechanisms in the development of gonads of different fertility oysters has important scientific significance and important application value. In order to investigate the utilization and change of the main energy supply substances during the gonadal development of different fertility C. gigas, the gonadal tissues of triploid and diploid C. gigas were observed and analyzed by using the methods of PAS staining and oil red O staining. The results showed that a large amount of glycogen and lipid are accumulated in the gonadal connective tissue of both diploid and triploid C. gigas during the proliferation stage. With the development of gonad, the content of glycogen in the gonadal connective tissue of diploid and fertile triploid (3nα type) C. gigas decrease significantly, and almost no glycogen is detected at maturity stage, indicating that the glycogen in the gonadal connective tissue provides energy for gametogenesis. Lipids mainly existed in the connective tissue and cytoplasm of oocytes in the female diploid and 3nα gonad of C. gigas, indicating that lipids were an important component of oocyte development. The content of lipids in gonadal connective tissue of female diploid and 3nα type C. gigas does not decrease significantly with gonadal development, so it is speculated that glycogen may be converted into lipids to meet the material needs of gonad development. Lipids are significantly reduced during the gonadal development in diploid male C. gigas, indicating that the main function of lipids in the gonadal development of male C. gigas may be energy supply rather than structural composition. As important energy supply and components in the gonadal development of C. gigas, their content shows no significant change during the gonadal development of sterile triploid (3nβ type) C. gigas, and this is closely related to the locked gametogenesis of the 3nβ. It is speculated that glycogen and lipid accumulated at the early stage of gonadal development of 3nβ can not be transported to germ cells, but remain in connective tissue due to the blocked gametogenesis, so that the sterile triploid C. gigas can still grow rapidly during the reproductive season. The results of this study provide important information for the regulation mechanism of oyster reproductive development and fertility control breeding.