An Outbreak of Aeromoniasis in an Organized Composite Carp Culture Farm in India: Experimental Pathogenicity and Antibiogram Study

Abstract

High incidence of mortality in carps was noticed in a polyculture fish farm situated in Orissa, India during March 2009 accounting for cumulative mortality of nearly 2% per day. The infected fish revealed gross ulcerative lesions on skin with erosion of scales and fin- and tail-rot. Acute tubular and diffused interstitial necrosis was observed in kidney tissue along with increased melanomacrophage reactions on histopathological examination. Hepatic and muscular necrosis was also noticed in most of the fish examined. The bacteria isolated from kidney, liver and blood samples were identified as Aeromonas hydrophila after biochemical characterization. This isolate was found to possess aerolysin, lipase, extracellular haemolysin and P-haemolysin genes contributing to its virulence. It was found sensitive to antibiotics amikacin, aztreonam, ceftazidime, ceftazidime, cefuroxime, cephotaxime, ciprofloxacin, co-trimoxazole, gentamicin, levofloxacin, nalidixic acid, netillin, nitrofurantoin, ofloxacin, streptomycin, tetracycline, tobramycin and trimethoprim. Experimental infection of Laheo rohita with this isolate resulted in similar clinical signs as those of collected from the farm. The LD50 dose was ccdculated to be 1.15 • 10^ CFU/fish. This study suggests that A. hydrophila still remains an important bacterial pathogen from aquaculture point of view and regular examination of cultured fish is required to resist unexpected loss.