Salinity and rainfall as inducers of cell proliferation and apoptosis in mangrove oyster Crassostrea gasar spermatogenesis

Abstract The present study investigated the influence of physical–chemical​ variables on the development of male gonads, providing information on cell proliferation and apoptosis in cells of the spermatogenic lineage throughout the reproductive cycle. Seeds of oysters of the species Crassostrea gasar from the same population were grown in two cultivation areas with different seawater influences. The area I, located in the municipality of Nova Olinda and area II, in the municipality of Curuca. The two areas are part of the mangrove coast of the Amazon region and are located approximately 5 and 25 km away from the Atlantic Ocean, respectively. A sample containing 20 specimens of oysters was collected monthly in each of the two areas, and the abiotic parameters were also measured in situ during the collections. Routine histological techniques were used for cell characterization, as well as the classification of gonadal stages and morphometric measurements. Immunohistochemistry was used to access cell proliferation and apoptosis. The abiotic parameters varied constantly during the study, however, precipitation and salinity were the variables that most differed between periods in both areas. The cells of the spermatogenic lineage of C. gasar did not differ from the morphological point of view, however, the analysis of the morphometric parameters showed significant differences both in the cell diameters between maturation periods and between the study areas. Proliferative and apoptotic activities also varied throughout the study, and the quantification of positively labeled cells showed statistically significant differences between the study areas. The animals in the area I showed greater proliferative activity in relation to individuals in area II and using a regression model, we demonstrated that both cell proliferation and apoptosis are related to environmental conditions. It seems likely that animals in area I, exposed to a salinity of ∼ 25–35, find more favorable environmental conditions for their reproduction since the reduction in cell proliferation observed in area II was negatively related to the salinity of this environment ( ∼ 15– 25). Changes in the dynamics of mangrove interstitial waters contribute to changes in the salinity of the environment and can directly impact the physiology of oysters. These findings indicate that oyster farming systems in estuarine environments should be in areas as close to the ocean as possible.