Osmotic stress as a modulator of spermatogenesis in the Neotropical tetra Astyanax bimaculatus (Linnaeus, 1758)

The salinization of aquatic environments, driven by natural processes and human activities such as agricultural irrigation and industrial waste disposal, poses a growing threat to freshwater ecosystems. Astyanax bimaculatus, a fish species native to the Amazon basin, is known for its resilience to environmental variations, including salinity changes. However, the effects of this stressor on its reproductive function, especially spermatogenesis, remained unknown. This study evaluated these impacts by exposing sexually mature males of the species to different salinity concentrations (0, 5, 10, and 15 g/L of NaCl) for 7 days. Histological evidence suggests that the animals maintained active spermatogenesis up to 10 g/L, as indicated by the presence of residual spermatozoa in the seminiferous tubules. This suggests spontaneous gamete release occurred until the third day of exposure. However, increased salinity was associated with histological signs consistent with forced spermiation and reduction in sperm head diameter, suggesting harmful effects during prolonged experiments. Despite the tolerance of A. bimaculatus to moderate salinities in the short-term, long-term salinization may affect its reproductive traits.