Aquatic environments received huge amount of pollutants such as heavy metals, hydrocarbons, pesticides and organic materials every day. In this study, the effect of dissolved cadmium chloride on some hematological parameters and histopathological change of gill in Chondrostoma regium was investigated. For this purpose, one hundred fishes were caught by sein net from one of the branches of Zayandeh Roud and transferred to the laboratory. The Fish randomly were allocated to four glass tank. The experiment consist of four treatments including: control group (without cadmium), 0.5, 2.5 and 7.5 µg/l cadmium concentration. There were 15 fishes in each experimental groups. The experiment run for 14 days period. Some Physicochemical parameters of water were measured during the experiment such as dissolved oxygen, pH, EC, alkalinity and hardness. At the end of experiment, blood samples were taken of caudal region and prevalent hematology indices were evaluated. For histopathological studies liver and gill were performed at the end of experiment the samples were fixed in 10% formalin. To assess the cadmium concentrations in gill tissue were determinate with flame atomic absorption spectrometry. The highest rate of RBC, Hematocrit and hemoglobin were observed 0.5 µg/l cadmium which were significantly differentiated from the control group (p 0/05). Expect the mean corpuscular hematological concentration (MCHC) other secondary hematological indices showed significantly decrease at 7.5 µg/l of cadmium compared to the control group. The highest rate of cadmium concentration was observed in gill at 7.5 µg/l of cadmium equivalent 2.8±0.136 µg/g. Hyperplasia, clubbing and fusion were the main gill histopathological changes. Congestion, nuclear psychosis and necrosis were the main liver histopathological signs. Intensity of gill and liver damages showed increased trend in a dose dependent manner. As a whole results showed among the secondary hematology indices only MCHC wasn not affected. These results show that cadmium can effect on histopathological and hematological parameters in Chondrostoma regium even in sublethal concentration. Key words : Chondrostoma regium , cadmium, hematology parameter, accumulation, gill, liver
