Aras dam reservoir situated in the northwest of Iran, west Azarbaijan province, is the only water resource of Astacus leptodactylus harvest in the country that more than 250tons of this species were exported to different countries all over the world, annually. On the other hand, one of the polices of Iranian Science Fisheries Institute is the release of this species into other water resources in the country and for this purpose, the study of risky diseases such as Crayfish pest (Aphanomysis astasi) and other zoonotic diseases are considered as the research priorities of aquaculture development of the country. This study was carried out to health screening of Astacus leptodactylus at Aras dam reservoir from winter 2013 to fall 2014. In this regard, A total of 394 harvested livefreshwater crayfish Astacus leptodactylus (255males, 139females) weretested. 9 epibionts and parasites peritrich protozoans were identified. From Metazoan parasites group, Branchiobdella kozarovi with incidence rate of (100%) in obtained samples was the only isolated organism from this group that identified up to species level. There was a heavy damage in gills of samples with Aeolosoma hemprichi (Annelid) in winter with90% prevalence. Furthermore, Other Epibiont fouling organisms such as Rotatoria; free living nematods and suctoria were observed in this survey. The fungi study of the lesions and melanized spots of mentioned samples revealed their infection to Penicillium expansum; Aspergillus flavus; Alternaria sp. ; Fusarium sp. and Saprolegnia sp. The results of bacterial study confirmed the presence of pathogen bacteria in Astacus leptodactylus. The most frequency percentage (15.16%) in hepatopancrease were related to Aeromonas hydrophila and the least one (1.37%) were due to Yersinia bacteria. Also, only Aeromonas hydrophila and Staphylococcus aureus were isolated and identified from heamolymph, respectively. The results revealed that the combination of Salmonella typhi, Escherichia coli and Staphylococcus sp. has caused the most infection rate while. Yersinia ruckeri and Salmonella typhi has caused the least infections in Astacus leptodactylus. According to the isolation of 6 bacteria species from hepatopancreas and 2 species from heamplymph , it can be concluded that hepatopancreas enjoyed the higher infection rate compared to haemolymph in the obtained samples
