study of histopathological changes on gill of aphanius sophiae in arsenic and cadmium toxicity in saltwater and freshwater

in aquatic ecosystems, pollutants including heavy metals cause pathological alternations in fishes. as, the impacts of pollutants are affected by chemical properties of water, this study was conducted to compare the histopathological effects of two heavy metals as and cd on gill structure of aphanius sophiae. a total of 350 specimens were collected from the shoor river of eshtehard during the spring and summer of 2011. for saltwater experiments seven treatments including 5, 10 and 20 ppm of as and 5, 10 and 20 ppm of cd plus a control one were prepared in 30-l glass aquariums with three replicates. twenty five fish specimens were introduced into each aquarium. similar experiments were designed for freshwater treatments using dechlorinated tap water. after 18 days of exposure, three specimens were sampled from each treatment and fixed into boein fixative solution and left gill were removed for histological preparation. the observations of prepared histological sections showed alterations including epithelial lifting, increasing goblet cells and fusion of secondary lamellae in both treatments. result revealed that the severity of these changes in freshwater was more than saltwater treatment. necrosis, hyperplasia, fusion of first and secondary lamellae had been intensively occurred in freshwater treatments. data were analyzed by multivariate analysis two-way npmanova in past software. it was concluded that decreasing salinity, which led to a decrease in water hardness can proliferate the losses rate of 11/4 times and histopathological effects as a result of as and cd pollution.