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 liver and 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 experiments consist of four treatments including: control group (without cadmium), 0.5, 2.5 and 7.5 µg/l cadmium concentrations. For histopathological studies liver and gill were performed at the end of experiment the samples were fixed in 10% formalin.The highest rate of cadmium concentration was observed in gill at 7.5 µg/l of cadmium equivalent. 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.

Parasitic infestation of two native fish species in Behesht-Abad River were investigated at spring 2013. In this study 52 Chondrostoma regium and Aphanius vladykovi (26 from each species) were sampled and transferred to the laboratory. Then the weight and total length of fish were measured and investigated their infestation to parasites by microscope and stereomicrpscope. Some of the observed parasites are reported for the first time as new host records of: Philometra sp on the abdominal cavity of C. regium, Moreover, some external and internal parasites identified to the species and genus level including: Ichthyophthirius multifiliis in skin and gill of C. regium and A. vladykovi, one immature digenean; Allocreadium isoporum on the intestine of A. vladykovi and Trichodina sp on gill and skin of C. regium and A. vladykovi. The highest frequency of I. multifiliis (96.15%) was observed in gill of A. vladykovi and the lowest frequency  was related to Tricodina sp in skin of C. regium (23.07%). A. isoporum Infestation was only observed in the intestine of A. vladykovi (mean±SD; 5.42±3.73) and philometra sp infection was only observed in the abdominal cavity of C. regium (mean±SD; 3.25±.82). The maximum average (±SD) infection intensity belonged to I. multifiliis in skin of C. regium (69.9±72.07, range: 12-196).