ISOLATION AND CHARACTERIZATION OF AEROMONAS VERONII FROM NATURALLY INFECTED NILE TILAPIA

Aeromonas species are common pathogens that induce significant economic losses in aquaculture. This study investigated Aeromonas infection in cultured Nile tilapia (Oreochromis niloticus) in Qena Province, Egypt, with fifty fish were sampled. Bacteriological examinations as well as a molecular-based approach with 16S ribosomal DNA sequences were used. Moreover, a challenge experiment was conducted to assess the pathogenicity of the isolated Aeromonas. Clinical findings of the naturally infected fish were characterized by generalized septicemic signs of hemorrhagic ulcerations, ascites, and exophthalmia. Based on morphological, biochemical, and molecular characterization, 30 isolates (60% prevalence) of Aeromonas were identified in internal organs. The 16S rDNA gene sequencing and phylogenetic analysis confirmed the identity of the isolated Aeromonas as A. veronii. Four sequenced A. veronii displayed 99.92% and 99.84% identity with the 16S rDNA gene of A. veronii species available in the GenBank database, accession numbers MT302825 and KC633849, respectively. The phylogenetic position of the nucleotide sequences identified here were clustered with other fish-infecting A. veronii. Results of the waterborne challenge experiment revealed that the A. veronii (accession number PV495274) produced mortality rate of 75.6 % with the same clinical picture as the naturally infected fish. Findings herein concluded that A. veronii is a predominant pathogen in tilapia aquaculture in Qena Province and the biochemical and genomic characterization providing critical data for disease management. The study highlights the need for targeted surveillance and control measures against Aeromonas infections in this economically vital sector.