Characterization of Aeromonas jandaei Associated with Climbing Perch (Anabas testudineus) Mortalities in Assam, India: Identification, Pathogenicity, Antibiotic Susceptibility and Histopathology

The Climbing perch, Anabas testudineus is a hardy fish due to its ability to survive even in waters with depleted oxygen levels. However, in the past few years, several reports of infections and mortality in cultured A. testudineus from Assam have been reported but studies on characterizing the pathogen are limited. In the present study, diseased A. testudineus fishes exhibiting symptoms of hemorrhages and ulcerative lesions were collected from a fish farm in the Nalbari district, Assam to isolate and characterize the causative pathogen. The isolate, designated as ZOO-GH01, was subsequently identified as Aeromonas jandaei through morphological, biochemical and molecular (16S rRNA and rpo B gene sequencing) characterization. Pathogenicity tests confirmed the isolate’s ability to cause disease in healthy climbing perch, with an LD50 of 2.6 × 104 CFU/mL. Virulence gene profiling revealed the presence of aerolysin, hemolysin, cytotoxic enterotoxin, cytotonic enterotoxin, and lipase. Antibiotic susceptibility testing showed resistance to eight antibiotics including vancomycin, amoxycillin, methicillin, erythromycin, amikacin, clindamycin, ampicillin and penicillin.