Molecular Detection of Aeromonas hydrophila in Farmed Rainbow Trout (Oncorhynchus mykiss) from Zanjan Province, Iran

Background: Rainbow trout (Oncorhynchus mykiss), an economically important fish in Iran, is valued for its nutritional potential.Aeromonas hydrophila causes infections that lead to motile septicaemia in fish and humans worldwide.Given the rapid expansion of fish farming in Iran, particularly in Zanjan Province, and the associated losses due to bacterial infections, this study aimed to detect A. hydrophila in farmed rainbow trout using molecular methods.Methods: A total of 103 fish samples were collected from ponds across five cities in Zanjan Province.Cultured specimens were subsequently analyzed, and A. hydrophila isolates were confirmed through standard biochemical tests.Genomic DNA was extracted from the isolates, and the aerA and lip genes were identified as markers for confirmation of A. hydrophila using the Polymerase Chain Reaction method.Results: Overall, 72 (69.90%) samples were positive for A. hydrophila, as determined by both culture and biochemical tests.However, molecular analysis confirmed the aerA gene in 66 (64.07%) of the isolates, while only 3 (2.91%)samples carried both the lip and aerA genes. Conclusion:The high prevalence of A. hydrophila in rainbow trout poses a threat to public health and results in significant economic losses in aquaculture.Collaboration among epidemiologists, microbiologists, veterinarians, and food safety experts is essential to reduce these impacts.