Background: Histological studies in organs like hepatopancreas and gill of the freshwater fish, Cyprinus carpio, were made to assess tissue damage due to sub-lethal concentration of cadmium after a long exposure period. Methods: This study was conducted in University of Tehran, in 2013. The fish were divided into two groups in 1000 litre fiberglass tanks supplied with dechlorinated water [hardness 302.6 mg CaCo3/l, pH 7, O2 7.8 mg/L and temperature 15 ± 2 ºC] and continuous aeration. Group 1 was without any cadmium considered as control group. Group 2 was exposed to 30 ppb CdCl2 (Merck) containing 7.8 ppb cadmium. The tissue samples from: hepatopancreas, gill were collected 30 days post exposure and processed by histological procedures. Results: The main lesions in cadmium exposed groups were: (a) pancreatitis necrosis in endocrine part of pancreas (b) cholangitis and necrosis in liver parenchyma (c) hypertrophy, fusion and telangiectasia in secondary lamellae Conclusion: Cadmium chloride at low concentration can induce pathological alterations in hepatopancreas and gill of common carp. .
