Temporal dynamics of gonadal development and reproduction of wild Manila clam (Ruditapes philippinarum) in the Xiaoqing River estuary, Laizhou Bay

The Manila clam (Ruditapes philippinarum) is one of the main mudflat shellfish aquaculture species, and their wild population is widely distributed in Chinese coastal areas. However, environmental change and human activities have led to the destruction of the clam's natural habitat, resulting in a gradual decline in production. To better conserve and sustainably utilize R. philippinarum resources, the study presents the first comprehensive investigation of gonadal development and reproductive dynamics of a natural R. philippinarum population in the Xiaoqing River Estuary, Laizhou Bay, from February 2023 to January 2024. The condition index (CI) and histological examinations were used to assess the development of gametogenesis and spawning activities. The findings revealed that the CI of R. philippinarum varied seasonally, reaching its maximum at first maturation in April 2023 (22.49%) and decreasing sharply when spawning activity first appeared in May. Annual sexual changes in gonadal development were essentially the same for both males and females. Additionally, the gonads of R. philippinarum were capable of forming complete developmental stages (the proliferating, growing, maturing, spawning, and resting stages). As temperatures increased, R. philippinarum matured in successive batches, and the breeding season was observed from May to October. The RDA revealed that seawater temperature (R² = 0.7095, p = 0.003) and chlorophyll-a (Chl-a) (R² = 0.7293, p = 0.002) were the primary environmental drivers, exhibiting strong positive associations with the CI and gonadal development (growing and maturing stages). These findings provide valuable insights into the reproductive cycle of wild R. philippinarum and lay a foundation for exploring the mechanisms of natural seedling formation in the Xiaoqing River Estuary, Laizhou Bay. This study contributes to the conservation and sustainable utilization of this important shellfish resource in the river estuary.