The concentrations of Cd, Pb, Ni and Hg were determined in gill, liver and muscle of Barbus xanthopterus in down streams of Karoon and Dez Rivers during summer 2009. Heavy metal concentrations varied significantly, depending on the types of the tissue in fish species. The levels of heavy metals such as Cd, Pb, Ni and Hg in the Barbus xanthopterus of Karoon River were higher than in Barbus xanthopterus of Dez River (Pliver>muscle. The concentration of Hg in Karoon River was in the sequence liver>gill>muscle but, in Dez River, it was in the sequence liver>muscle>gill. Among heavy metals (Cd, Pb, Ni and Hg), the accumulation of Pb was more than other heavy metals in fish (P<0.05). In both rivers, the accumulation of heavy metals in muscle of fish was higher than the world health organization (WHO) standard
