Abstract

Aquaculture sector in Egypt has demonstrated a remarkable development; however, it has also faced challenges with respect to disease outbreaks. Nile tilapia is the most widely cultured species in Egypt. Under stress conditions, tilapia is vulnerable to a variety of bacterial diseases that tend to be ubiquitous in the freshwater environment. Semi-intensive Nile tilapia farms in Kafr El-Sheikh Governorate, Egypt are experiencing acute mortality especially during summer months. The samples from these farms were collected and subjected to investigations to identify the etiological agent(s) behind these mortalities. Bacteriological examination revealed that the dominant bacteria were Gram-negative rods and identified as Aeromonas spp. through biochemical tests. PCR, restriction fragment length polymorphism (RFLP) assays, and sequencing confirmed the presence of Aeromonas hydrophila. In addition, the aerA gene, a virulence factor in A. hydrophila, was detected by PCR in all identified A. hydrophila isolates. In order to confirm that the isolated A. hydrophila was the causative agent of tilapia mortality, healthy Nile tilapia were challenged with the isolated strains, which produced the same clinical picture of the collected samples. This study implicates that A. hydrophila could be the causative agent of the summer mortality in Nile tilapia farms in Kafr El-Sheikh Governorate, Egypt.