To determine occurrence, diversity and frequency of bacterial pathogens in cultured sea bass (Dicentrarchus labrax) using 16S rDNA and biochemical tests. Four hundred seventy-seven sea bass from two distinct farms in the Black Sea were submitted to bacteriological profiling. We often isolated multiple bacterial species in fish, cages and farms during the testing period. Using 16S rDNA sequences and biochemical profiles, 6 species of bacteria were identified and all had different susceptibility to a range of antibiotics. Aeromonas veronii biovar sobria (65.2%) and Photobacterium damselae subsp. damselae (19.1%) were the most frequently isolated species, followed by Vibrio vulnificus (6.7%), V. harveyi (6.7%) and V. rotiferianus (3.3%). Furthermore, elevated monogenean ectoparasite (Diplectanum aequans) load correlated with a higher incidence of bacterial infection. These results are in accordance with the hypothesis that the highly eutrophic environment of the Black Sea supports rich diversity of bacteria in fish and the environment. To our knowledge, this is the first report of A. veronii and V. rotiferianus in sea bass. Our findings also suggest that D. aequans increases the susceptibility of sea bass to bacterial infection. The accurate identification and profiling of bacterial species are essential to manage the mortality of cultured sea bass. Using bacteriological profiling we have identified the most common bacteria found in fish and their susceptibility to a range of antibiotics. These results will help guide the selection and use of antibiotics and vaccines to manage disease outbreaks in cultured fish. (C) 2014 Elsevier B.V. All rights reserved.