A comparative histological study of the reproductive structure of dominant Bivalvia species in Karkheh River in a year. (English)

Despite the economic and environmental importance of freshwater mussels, there is limited information available regarding their biology. Considering the significance of bivalve gonads as vital reproductive organs, this study aimed to identify and investigate the histological structure of reproductive organs of dominant bivalve species throughout one year, from April 2021 to February 2022, in the Karkeh River. For this purpose, bivalves were seasonally collected, identified, and then dissected. Subsequently, the gonads underwent histomorphometric examination following tissue processing stages. The results indicated that Unio tigridis and Pseudodopsis euphratica were the predominant species in the Karkeh River, both belonging to the Unionidae family. The ovaries in both species exhibited asynchronous development. The reproductive cycle throughout the year comprised three stages: undeveloped, developing, and mature. Considering gonadal maturity in spring and spawning in summer, it appears that the primary gonadal activity of both species in the Karkeh River in the study area occurs in spring, while peak reproductive activity takes place in summer. [ABSTRACT FROM AUTHOR]

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