Background: In Anzali Lagoon, there are some endemic and exotic fishes. The present study was conducted to compare the parasitic fauna of Blicca bjeorkna, as an endemic fish and Hemiculter leucisculus, as an introduced fish to the lagoon.Methods: A parasitological investigation was done on 78 specimens of B. bjoerkna and 114 of H. leucisculus. The fishes were collected from August 2009 to April 2010 by the electro fishing from Anzali Lagoon.Results: Eleven parasites species were found in 192 fish samples. The prevalence and mean intensity of parasites in each host were as follows: Parasites from B. bjorkna were Trichodina perforata (53.85%); Myxobolus musayevi (27.19%, 1±0.79); Dactylogyrus difformis (88.05%, 8±7.24) and D. sphyrna (5.18%, 0.95±0.51), Diplostomum spataceum (98.72%, 9.51±9.01), Posthodiplostomum cuticula (15.38%, 4.25±2.5), Ripidocotyle sp. (1.28%, 2±0.74); Contracaecum osculatum (17.95%, 1.64±0.79), Philometra rischta (12.8%, 1.4±0.54), and Raphidascaris acus (1.04%, 0.03±0.26). The H. leucisculus were infected with T. perforata (27.19%), D. spataceum (7.89%, 1.33±0.54), Ps. tomentosa (7.02%, 1.62±0.49) and R. acus (0.88%, 3±0.28). B. bjoerkna was presented as a new host for M. musayevi and C. osculatum, while H. leucisculus was introduced as a new host for T. perforata and Ps. tomentosa.Conclusion: The prevalence of parasites was significantly more in native fish than that of exotic fish (P<0.05). This reduction in parasitic infection in H. leucisculus may be due to its immune system resistance, well adaptation to the new environment, host-specific limitation for endemic parasites and disability of introduced parasite to complete its life cycle in the new host as well
