DAO 94:29-39 (2011)  -  DOI: https://doi.org/10.3354/dao02304

Isolation and characterization of virulent Aeromonas veronii from ascitic fluid of oscar Astronotus ocellatus showing signs of infectious dropsy

K. Sreedharan1, R. Philip2, I. S. Bright Singh1,*

1National Centre for Aquatic Animal Health, and 2Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology, Fine Arts Avenue, Cochin 682 016, Kerala, India
*Corresponding author. Email:

ABSTRACT: The cichlid oscar Astronotus ocellatus has worldwide commercial value in the pet fish industry because of its early maturation, relatively high fecundity, ability to identify its caretaker and also to alter colouration amongst conspecifics. Pathogenic strains of Aeromonas veronii resistant to multiple antibiotics were isolated from A. ocellatus individuals showing signs of infectious abdominal dropsy. The moribund fish showed haemorrhage in all internal organs, and pure cultures could be obtained from the abdominal fluid. The isolates recovered were biochemically identified as A. veronii biovar sobria and genetically confirmed as A. veronii based on 16S rRNA gene sequence analysis (GenBank accession no. FJ573179). The RAPD profile using 3 primers (OPA-3, OPA-4 and OPD-20) generated similar banding patterns for all isolates. They displayed cytotoxic and haemolytic activity and produced several exoenzymes which were responsible for the pathogenic potential of the isolates. In the representative isolate MCCB 137, virulence genes such as enterotoxin act, haemolytic toxin aerA, type 3 secretion genes such as aexT, ascV and ascF-ascG, and gcat (glycerophospholipid-cholesterol acyltransferase) could be amplified. MCCB 137 exhibited a 50% lethal dose (LD50) of 105.071 colony-forming units ml–1 in goldfish and could be subsequently recovered from lesions as well as from the internal organs. This is the first description of a virulent A. veronii from oscar.


KEY WORDS: Aeromonas veronii · Oscar · Astronotus ocellatus · Virulence · Ornamental fishes


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Cite this article as: Sreedharan K, Philip R, Bright Singh IS (2011) Isolation and characterization of virulent Aeromonas veronii from ascitic fluid of oscar Astronotus ocellatus showing signs of infectious dropsy. Dis Aquat Org 94:29-39. https://doi.org/10.3354/dao02304

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