The study was conducted on 225 diseased fish samples, 125 Nile tilapia (Oreochromis niloticus) and 100 Catfish(Claris gariepinus) , collected from different fish markets at Qalubia Governorate during the period from January (2016) to May (2017) for detection of Aeromonas species. The samples were taken from apparently pathognomic lesions in muscle, kidney, liver, intestine and spleen after clinical and postmortem examination for bacteriological examination. The results revealed that, 125 Aeromonas species were isolated from the examined samples where A. hydrophila and A. caviae were identified..Accurately 114 (91.2 %) A. hydrophila strains, 63 (50.4%) and 51 (40.8%) were isolated from C. gariepinus and O. niloticus fishes respectively. Meanwhile, 11(8.8 %) A. caviae strains, 7 (5.6%) and 4 (3.2%) from C. garicpinus and O. niloticus fishes respectively.further PCR results for virulence genes in isolated Aeromonas strains indicated that, aero gene was detected in 9 out of 10 A .hydrophila studied strains and in 3 out of 6 A. caviae ; hly gene in 7 out of 10 A .hydrophila and in 2 out of 6 A. caviae; Ahcytoen gene in 6 out of 10 A .hydrophila and in 1 out of 6 A. caviae ; act gene in 6 out of 10 A .hydrophila and in 3 out of 6 A. caviae and ast gene in 7 out of 10 A .hydrophila and in 3 out of 6 A. caviae studied strains. Finally, the production of a wide array of virulence factors by isolated strains is indicative of their potential to cause diseases in fishes and humans.
Key words: Fish, bacteriological, Aeromonas, virulence genes