Evolution of cadmium effects in the testis and sperm of the tropical fish Gymnotus carapo

•The present study shows the Cd effects in the testes and sperm of Gymnotus carapo.•Testis morphology was altered after exposure to progressive doses and exposure times.•Cd affected the germ cells in different stages of differentiation.•Alterations in sperm count and morphology were also observed.•The work characterizes the Cd-induced pathogenesis in the male reproductive system.

The present study investigated the testis and sperm morphology of the tropical fish Gymnotus carapo after exposure to increasing CdCl2 concentrations (5–40 μM) for 24 and 96 h. The treatments induced Cd accumulation in the testis and a decrease in the gonadosomatic index from a 10 μM. Cd induced alterations in testis since 24 h; however the extension and severity of damages increased after 96 h in all tested concentrations. Marked variations in the cysts size, proliferation of the interstitial tissue, infiltration of inflammatory cells, necrosis, reduction of germ cells and sperm aggregation was observed in 96 h treated fishes. In this time, there was a complete absence of germ cells in the testis of fish treated with 40 μM. The ultrastructural analysis allowed for the visualization of the initial damages over germ cells, such as the presence of vacuoles in the cytoplasm of spermatogonia, spermatocytes, and spermatids. Exposed fish (20 μM for 24 and 96 h) had alterations in sperm number and morphology. These results are important for establishing a direct correlation between the Cd accumulation and incidence of damages and can help characterize the mechanism of Cd-induced pathogenesis in the male reproductive system.