Iranian Journal of Veterinary Medicine 209 IJVM (2016), 10 (3): Isolation, phenotypic and molecular characterization of motile Aeromonas species, the cause of bacterial hemorrhagic septice- mia in affected farmed carp in Iran Soltani, M. 1* , Moghimi, S.M. 1 , Ebrahimzade Mousavi, H. 1 , Abdi, K. 2 , Soltani, E. 3 1 Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran 2 Aquatic Animal Health Expert, Offce of Health and Control of Aquatic Animal Diseases, Iranian Veterinary Organization, Tehran, Iran 3 Department of Microbiology, Faculty of Science, University of Tehran, Tehran, Iran Abstract: BACKGROUND: Motile Aeromonas species cause heavy mor- talities in carp farms during spring and summer in Iran. OBJEC- TIVES: The aim of this study was to detect phenotypic and ge- notypic characterization of motile Aeromonas species isolated from diseased carps in some northern and southern provinces of Iran. METHODS: A number of 40 samples from 22 fsh farms were collected. The identifed motile Aeromonas species were sequenced and phylogenetic tree was drawn by MEGA6 using UPGMA analysis. RESULTS: A number of 19 bacterial isolates were identifed as motile Aeromonas sp. by biochemical tests, and the DNA segments of 16S rRNA gene of all these strains gave 1200 bp after running on 1% agarose electrophorus gel. Also, the sequencing results showed that the bacterial samples were determined as A. hydrophila and A. veronii biovar veronii. CONCLUSIONS: Phylogenetic analysis revealed that motile Aer- omonas strains in this study were separated in two clusters and four genogroups with high similarities. Key words: Farmed carp, Motile Aeromonas septicemia, 16S rRNA gene Correspondence Soltani, M. Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran Tel: +98(21) 61117094 Fax: +98(21) 66933222 Email: msoltani@ut.ac.ir Received: 27 January 2016 Accepted: 11 May 2016 Introduction Aeromonas hydrophila and other motile Aeromonas species which cause motile Aer- omonas septicemia are known as the most common bacterial infections in freshwater aquaculture worldwide (Borrell et al., 1997; Leblanc, et al., 1981; Woo et al., 2011; Hen- ebry et al., 1988). The species of A. hydroph- ila, A. sobria, A. caviae and A. veronii are the cause of carp mortalities (Popoff and VéEron, 1976; Garrity et al., 2004). Motile Aeromonas species cause some pathologic conditions in- cluding acute, chronic and latent infections with different clinical signs (Soltani, 2002). The disease occurrence is common in spring and summer in farmed carp that is related to high temperature, fsh metabolism and organic loading rate (Soltani, 2002). According to the Iranian veterinary organization, the most epi- zootics occur in the north and south regions of Iran where the carp aquaculture is located (Iranian Veterinary Organization, unpublished data, 2011). So far, some epizootics of the dis- ease have occurred in various species of carp in the north and south provinces (Peyghan and Esmaili, 1997; Soltani et al., 1998; Alishahi et al., 2009). Although the morphological and biochemical approaches have been applied to identify the genus Aeromonas in Iran, there is no adequate data on the phylogenetic position of the Aeromonas species involved in morbid- 209-216