Abstract
Aeromonas hydrophila is an opportunistic pathogen that is highly important for freshwater fish. In the present study, two freshwater fish species Nile tilapia (Oreochromis niloticus) and Mullet (Mugil cephalus) collected from various fish farms in Kafrelsheikh Governorate, Egypt. The fish samples were examined to determine Aeromonas hydrophila presence (A. hydrophila). In addition, a treatment trial was conducted involving four groups of Nile tilapia fish, which treated with florfenicol (FFC) and oxytetracycline (OTC) based on the antimicrobial susceptibility test results. According to the findings, 12 (20%) A. hydrophila strains were isolated from a total of 60 collected fish samples (30 of Nile tilapia and Mullet with percentages of 30% and 10%, respectively). Based on species-specific 16 S rRNA genes, six (6) isolates were identified as A. hydrophila and carried aerolysin (aerA) and hemolysin (hylA) virulence genes, with percentages of 83.3% and 50%, respectively. Whereas, the antimicrobial resistance gene results were blaTEM with percent (100%) and aadA1 (83.3%). Histopathological changes were significantly reduced in all assessed organs (liver, spleen, kidney, and gills) in the FFC group compared to the OTC-treated group. The prevalence of virulent and multidrug-resistant A. hydrophila in aquaculture poses significant risks to fish health, economic productivity, and public health.