Characterization of Vibrio Populations from Cultured European Seabass and the Surrounding Marine Environment with Emphasis on V . anguillarum .

Vibrio species are widely distributed and can be potentially pathogenic to aquatic organisms. In this study, we isolated Vibrio spp. from environmental samples (seawater, sediment, and fish swabs) collected over a three-year period from a fish farm in Mali Ston Bay in the Adriatic Sea, Croatia, and assess their distribution. A total of 48 seawater samples and 12 sediment samples, as well as gill and skin swabs from 110 farmed European seabass, were analysed for the presence of Vibrio . Vibrio strains were identified to the species level by MALDI TOF MS. The analysis revealed that V . alginolyticus was the predominant species in European seabass, followed by V . anguillarum . V . alginolyticus was isolated from the sediments, along with V . gigantis and V . pomeroyi , while V . chagasii , V . cyclitrophicus , V . fortis , V . gigantis , V . harveyi , V . pelagius , and V . pomeroyi were isolated from seawater. V . anguillarum was isolated only twice during two different spring seasons, once from a diseased sea bass and the second time from a healthy sea bass. We analysed these two isolates and found that they differ both genetically and in terms of resistance to antibiotics. Our results confirm the seasonality of vibriosis incidence and the presence of the pathogenic V . anguillarum , which increases the risk of vibriosis.