Synchrony between Reproductive Phase and Flood Period: A Dispersion Mechanism for the Freshwater Clam Corbicula fluminea (Bivalvia: Corbiculidae) in a Brazilian Neotropical Floodplain.

This study evaluates the gonadal histology of Corbicula fluminea present in the upper Paraná River floodplain and samples of limnological variables to understand its reproductive cycle. Corbicula fluminea was monitored monthly from December 2013 to February 2015. Spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa were identified in the male follicles of the hermaphrodites. Oogonia, oogonial nests, previtellogenic oocytes, early vitellogenic oocytes, middle vitellogenic oocytes and full-grown vitellogenic oocytes were identified in the female follicles of the hermaphrodites and females. The reproductive phases were described as developing, active spawning/sperm releasing, regression and regeneration. Higher values of temperature, dissolved oxygen, total nitrogen and total phosphorous were identified during flood periods, while higher values of pH and conductivity were obtained during dry periods. The species either does not reproduce or reduces the intensity of reproduction in cold months, with the sex ratio not differing significantly between hermaphrodites and females with regard to month and reproductive phase. Thus, reproduction is synchronized with the flood period and its limnological characteristics and when the increase in connectivity between floodplain environments facilitates the larval dispersion of this non-native species into other environments.