Similarities and differences between vibriosis in European sea bass caused by Vibrio anguillarum and Vibrio harveyi

Vibrioses caused by different members of the genus Vibrio are common diseases in aquaculture characterised by systemic infections, high mortalities, and economic losses of fish and shellfish. Farming of European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) has rapidly grown over the last decade in Croatia but its economic efficacy is significantly jeopardized by losses due to Vibrio anguillarum and Vibrio harveyi infection Therefore, we studied and compared the most prominent similarities and differences in the environmental conditions, clinical signs and conventional and molecular diagnostic methods of vibriosis caused by both bacterial pathogens. Outbreaks in sea bass and sea bream caused by V. anguillarum mostly occur during the spring and autumn, following a fast increase or decrease in the sea temperature, whereas infections with V. harveyi occur during the summer months at a temperature above 20 degrees C. They have a similar clinical appearance in the acute form but in subacute forms they differ. V. anguillarum infection is characterized by massive haemorrhages in the abdominal wall, while during infection with V. harveyi keratitis, corneal opacity and uncoordinated swimming behaviour are noticed. Necropsy disclosed haemorrhages in the liver, intestine and stomach during infection with V. anguillarum, and sera-catarrhal enteritis with distension of the intestine and ascites in the case of V. harveyi. Although molecular tools enable correct identification, in this study we defined the main differences capable of distinguishing V. anguillarum from V. harveyi based on traditional bacteriological identification such as sensitivity to O/129 (10 mu g) and novobiocin, and the enzymatic activity of beta-galactosidase, arginine dihydrolase and amygdalin fermentation.