Histopathological Effects of Mercury on Male Gonad and Sperm of Tropical Fish Gymnotus carapo in vitro

Abstract

Hg is toxic metal mostly due to adverse effects on structure and function of tissues and organs in humans and animals. Male reproductive systems of fish species are also sensitive to Hg action. However, the histological alterations in tropical fish testis are less known and little information is available concerning the underlying mechanisms of metal pathogenesis in reproductive functions. Further investigations dealing with Hg direct effects on tissue and organs of tropical species are a need. The present study investigated HgCl2 toxic effects in testes and sperms of tropical fish Gymnotus carapo. The histopathology, germ cell structure and number were analysed to elucidate the pathological process during exposure to increasing metal concentrations (1 μM - 30 μM). Fishes exposed to 20μM and 30μM reached testicular Hg concentrations of 5.1 μg.g-1 and 5.2 μg.g-1, respectively. No significant alterations in gonadosomatic index (GSI) occurred between control, and Hg exposed fishes. Untreated fishes showed characteristic organization of testicular tissue, with germ epithelium organized in cysts where spermatogenesis occurs. Germ cells and spermatozoa are seen an inner the cysts. HgCl2 induced severe damages characterized by complete disorganization of seminiferous lobules, proliferation of interstitial tissue, congestion of blood vessels, reduction of germ cells and sperm aggregation. Exposed fishes showed a decrease in the sperm's number. Initial reduction of a sperm's number (36,8%) was observed after 20 μM/24h treatment and subsequent decrease (48,7%) was observed after 20μM/96h. Hg (20μM) also altered sperm morphology in 24h and 96h where sperm head abnormalities were present. In conclusion, the present study showed HgCl2 progressive damages in testicular tissue, sperm count and morphology of tropical species Gymnotus carapo. The effects in testicular tissues were observed since low Hg concentrations. These results are important to establish a direct correlation between the mercury accumulation and severity of lesions.