Impact of reproductive activity on physiological metabolism and molecular regulation in the Yesso scallops ( <i>Mizuhopecten yessoensis</i> )

Yesso scallops ( Mizuhopecten yessoensis ), a commercially important shellfish species in China, suffer a persistently high post-spawning mortality rate, which seriously restricts the sustainable development of the Yesso scallop aquaculture industry. To address this phenomenon, this study explored the mechanism by which reproductive activities affect Yesso scallops at both physiological and molecular levels. Fifty sexually mature female and fifty male scallops were selected for the experiment. Artificial spawning induction was performed using the shade-drying and temperature-elevating stimulation method. A comparative analysis was conducted on the nutritional components (crude protein, crude fat, glycogen) in the gonads, histological structures, and activities of enzymes related to immunity and energy metabolism (SOD, LDH, ATP, etc.) of the scallops before and after reproduction. Additionally, LC-MS/MS-based metabolomics technology was employed to analyze changes in differential metabolites and their associated pathways. There were significant decreases in nutritional components (crude protein, crude lipid, and glycogen content) within the gonads before and after spawning, with a particularly pronounced reduction in crude lipids. Histological examination showed that, post-spawning, lumens formed within the gonadal follicles of both sexes following gamete release, accompanied by decreased germ cell numbers. Enzyme activity assays indicated significant changes in enzyme activities post-spawning. Superoxide dismutase and lactate dehydrogenase exhibited significant differences in the female mantle. ATPase content displayed a decreasing trend in all tissues of both male and female scallops. Alanine aminotransferase showed significant differences in the gonads and adductor muscles, and aspartate aminotransferase activity increased significantly in the adductor muscles, of both male and female scallops. Gonadal metabolomics analysis identified 1,644 differential metabolites between pre- and post-spawning periods, primarily enriched in lipid and amino acid metabolic pathways. Female metabolic changes were concentrated in lipid and amino acid metabolism, whereas males showed alterations in sulfur-containing compound metabolism. In summary, the reproductive process significantly impacts the physiological status and metabolic patterns of M. yessoensis , with distinct variations between sexes. This study provides fundamental data for in-depth analysis of energy allocation during bivalve reproduction and lays a theoretical foundation for exploring the regulatory networks of reproductive metabolism in M. yessoensis at the molecular level.