Aeromonas veronii Causes Hemorrhagic Septicemia in Cultured Nile tilapia in Qena Governorate

Document Type : Research article

Authors

Department of Fish Diseases, Faculty of Veterinary Medicine, South Valley University, Qena 83523, Egypt

Abstract

In summer 2021, acute mortalities occurred in Nile tilapia farm in Qena governorate. Different
hypothesis including the implication of environmental factors, and/or pathogens have been
explored. Clinical, parasitological and bacteriological examinations have been performed. In
addition, the water quality parameters were assessed. The clinical investigation of the moribund
and recently dead fish demonstrated generalized septicaemia. The phenotypic and biochemical
characterization of the pure bacterial colonies that isolated from 60 moribund fish revealed
Gram-negative rods and identified as Aeromonas species. The identity of the isolates was
identified as Aeromonas species by amplification of Aeromonas 16S rDNA gene fragment by
PCR and confirmed as Aeromonas veronii by amplification and sequencing the Aeromonas
gyrB-gene. The water quality parameters showed an increase in the pH and ammonia levels
over the permissible levels. Experimental infections were performed to confirm the virulence of
the isolated bacteria. Results revealed that A. veronii isolate produced the same clinical picture
of the collected samples with mortality rate 80 %. The present study implicates that A. veronii
could be the causative agent of the Nile tilapia mortality in Qena, without neglecting the role of
water quality in worsening this outbreak

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