L. Yazdanpanah-Goharrizi - Department of Microbiology, Kerman Branch, Islamic Azad University, Kerman, Iran.
F. Rokhbakhsh-Zamin - Department of Microbiology, Kerman Branch, Islamic Azad University, Kerman, Iran.
M.J. Zorriehzahra - Department of Aquatic Animal Health and Diseases, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research Education and Extension Organization (AREEO), Tehran, I.R. Iran.
N. Kazemipour - Department of Microbiology, Kerman Branch, Islamic Azad University, Kerman, Iran.
B. Kheirkhah - Department of Veterinary Medicine, Baft Branch, Islamic Azad University, Baft, Iran

The isolation of Aeromonas hydrophila from Oncorhynchus mykiss reared in the farms was the aim of the present study. Ninety samples were collected aseptically from the infected fish with signs of hemorrhagic septicemia in gill and skin, exophthalmia, dropsy and ۳۶ water samples were sub-cultured on Tryptic Soya Agar (TSA), as well as kidney. The genotyping by PCR method was used to amplify the gene of ۱۶ SrDNA using primers ۲۷F and ۱۴۹۲R as primer pairs to achieve an approximate length of ۱۵۰۰ bp. The identified motile Aeromonas species were sequenced with electrogram chromas format in chrome version ۱/۴۱ software and a phylogenetic tree was drowned by MEGA۵.۱ software. The results showed that ۱۹% of ۲۴ isolated from gram-negative bacteria were detected as Aeromonas, which the sequencing results revealed that all the isolated bacteria had ۹۹% similarities with the standard A. hydrophila. The results of environmental factors showed when the levels of dissolved oxygen have decreased and the levels of nitrite and ammonia have increased throughout the year, Aeromonasias is increased. Also, when the water has gone alkaline due to increased ammonia, the disease has increased. It may be concluded that fish farmers should take proper management practices to avoid such disease in cultured fishes especially rainbow trout and to get rid of the infection by such serious bacterial pathogen like Aeromonas hydrophila by improving their culture strategy and culture ecosystem.

Aeromonas hydrophila, Environmental factors, Kerman province, Oncorhynchus mykiss, PCR.