This investigation was performed in order to identify and introduce common parasite of freshwater crayfish present in the rearing condition of Sefidrood fishery research station, Astaneh (Astaneh bridge station). during the study, from August date, 80.5.24 till September 82.6.11, between years 2001- 2003, more than 80 freshwater crayfish specimen with scientific name “Astacus leptodactylus” were captured by beach-seine from culture earth ponds and transported to laboratory of the station, and carried on an exact parasitological examination. In the lab processing, each crayfish were accomplished biometry and sex determination. After word, the animal’s external and internal organs, according to routine parasitological procedures, were taken sampled. To this way, first, parasite specimen seen through microscope, after separation, prepared on wet mount smear. Second, washed in physiological serum, then fixed in %10 buffered formalin and stained with carmine acid. The parasites were exactly identified with the view of genus and species by credit diagnosis keys. by the result, a total range of 35 crayfish specimen (Prevalence equal to %43.2) with mean infection intensity of 4.6, were affected by a kind of parasite called, Branchiobdella hexodonta ( Phylum : Annelida ). This parasite is separated from carapace and gills of the crustacean. by increasing the length range of crayfish, prevalence rate was increased too. The highest number range of parasite (1-23) was seen in length range of 10.6-12.6cm and the lowest number range of parasite (1-11) observed in length range between 12.7-14.9cm. Maximum mean intensity (6.3) was in length range of 10.6-12.6 cm and minimum mean intensity (3.1) was in 12.7-14.9. Maximum average abundance (3.6) was in length range 10.6-12.6, while minimum average abundance (0.88), calculated in length range 8.1-10.5cm. Prevalence rate (%32) and mean intensity (4.3) in carapace was higher, in comparison to gills, with prevalence and mean intensity of %20.9 and 2.8, respectively. Also in female crayfish, prevalence (%47) was higher than male one (%36.6). Spring season, with prevalence of %62.5 and mean intensity of 7.8 has allocated the most infection rate among other seasons, while no infection has seen in winter. It’s worthy of mention that, this worm only parasitism freshwater crayfish, and crayfish is specific host for the parasite.
Meanwhile Annelida Branchiobdella hexodonta, which known as “brunch worm” is reported for the first time from rearing freshwater crayfish in Iran culture system.