RESUMO
Samples from the kidney of 100 diseased fish with signs of haemorrhagic septicemiaand50 samples from outlet water of fish farms were taken aseptically and cultured. In the laboratory, 75 colonies of gram-negative bacteria were biochemically diagnosed as motile aeromonads in our Bacteriology Laboratory Unit using API 20E rapid identification system. The genotype identification using specific primers for 16S rDNA by PCR and direct sequencing of 28 Iranian motile aeromonads isolates were as follow: in diseased fish, Aeromonas hydrophila [3 isolates, 15%], A. veronii bv. sobria [8 isolates, 40%], A. bestiarum/piscicola [5 isolates, 25%], A. media [3 isolates, 15%], A. j and aei [1 isolate, 5%], A. aquariorum [0 isolate, 0%] and in water, Aeromonas hydrophila [0 isolate, 0%], A. veronii bv. sobria [6 isolates, 75%], A. bestiarum/piscicola [0 isolate, 0%], A. media [1 isolate, 12.5%], A. j and aei [0 isolate, 0%] and A. aquariorum [1 isolate, 12.5%]. Results of this study suggest that the incidence of motile aeromonads septicemia due to A. veronii bv. sobria is the most prevalent motile aeromonads. Nucleotide polymorphisms on the sequencing results of the 16S rDNA were detected as noticeable inter and intra-specific variation within the population of different aeromonads isolates. In total, 10-20 variant nucleotide positions in this region were observed among Aeromonas spp. Key words: Phenotype, Genotype, Motile aeromonads, Diseased fish, Fish farms