parasitic infection of an endemic fish (blicca bjoerkna) and an exotic fish (hemiculter beucisculus) in anzali lagoon, caspian sea, iran

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.