Cadmium (Cd) is one of the most toxic environmental heavy metals to organisms. The prominent toxic effects of Cd on reproductive organs are very well known. Gonad histopathology is a valuable tool for the assessment of endocrine disruption compounds EDCs effects on fish. The aim of this study was to evaluate the reproductive toxicity of cadmium chloride (CdCl2) on histopathology of Zebrafish (Danio rerio) testis under sub-lethal conditions. Male Zebrafish were exposed to four concentrations of CdCl2 (0.002,0.02, 2, and 20 mg/L) for 21 days in semi-static conditions. Histopathological changes in testis and Gonad Somatic Index (GSI) were studied. Treatment at 0.002 to 20 mg/L cadmium had no significant effect on the survival and condition factor. GSI decreased in a dose- dependent manner and the decrease was significant (P < 0.001) in the group that received the highest dose. Testis histological alteration consisted of reduced testicular size, blood–testis barrier (BTB) disruption, germ cell loss, testicular edema, hemorrhage, blood cell leakage, interstitial fibrosis, reduced sperm count, degenerated seminiferous tubules and abnormal Leydig cells. These data show that, Cd-induced treatment has an adverse effect on GSI decrease and can disrupt the histology of reproductive target tissues, highlighting the disruption of the blood–testis barrier (BTB), which is a major target of Cd toxicity in testis. Even a low dose Cd pollution may become a problem in the future, because Cd accumulates in the male reproductive organs and disturbs spermatogenesis and population stability.
