Molecular identification and epizootiology of Aeromonas veronii infection among farmed Oreochromis niloticus in Eastern Province, KSA

Nile tilapia, Oreochromis niloticus , is the main cultured freshwater fish species of Saudi Arabia, KSA. Earlier studies have reported Aeromonas hydrophila to be the most predominant Aeromonas spp seen in tilapia aquaculture so, 560 Nile tilapia were randomly collected from two private freshwater farms at Al-Qatif, Eastern province, Saudi Arabia, during a period of January 2015 until December 2015. Bacterial isolates were recovered and biochemically identified using the API-rapid-identification system as A. hydrophila and A. sobria and confirmed genetically by sequencing of targets in the 16S rDNA and gyr B gene regions as A. veronii . A phylogenetic tree was also constructed and placed isolates of the present study in the A. veronii group. To evaluate the pathogenicity of isolated strains to Nile tilapia, an experimental infection challenge was done and histopathological alteration in both naturally and experimentally challenged fish were investigated and resulted in prominent clinical signs, gross pathological lesions and 78% mortality. The Antibiogram profiling for the strains isolated were also, done. Our results suggest that A. veronii is the predominant Aeromonas spp. in cultured O. niloticus in Eastern Province of Saudi Arabia.