Aeromonas veronii biovar veronii infection in European seabass (Dicentrarchus labrax) cultured in Turkey

Fish in aquaculture systems are susceptible to infectious agents as they are kept in a densely populated and often physically restricted environment. Genus Aeromonas include well-known pathogens, and the member Aeromonas veronii has been reported to cause diseases in both humans and animals, either as primary infection or as mixed infection with other pathogens. This study describes a low mortality epizootic caused by Aeromonas veronii biovar veronii in European seabass (Dicentrarchus labrax) farmed in the Aegean Sea. The gills, kidneys and livers of moribund fish were pale. Erythema, haemorrhage and superficial ulcerative lesions were detected on the skin. In addition, petechial haemorrhage was observed on the tongue, maxilla, and operculum. The spleen was enlarged and multiple granulomas were detected in both the kidney and the spleen. Some fish had skin depigmentation, ecchymosis in the liver, and a bloody exudate in the abdominal cavity. The intestinal walls were lined with a clear yellowish fluid. Twenty-nine motile, Gram-negative bacterial isolates were obtained from the internal organs of diseased fish. According to morphology, biochemical properties and 16S rRNA gene sequencing results, all isolates were identified as Aeromonas veronii bv. veronii. All isolates were resistant to amoxicillin and ampicillin, and sensitive to oxytetracycline, enrofloxacin, ciprofloxacin, florfenicol, and flumequine.