Bacterial pathogens and flora isolated from farm-cultured eels (Anguilla japonica) and their environmental waters in Korean eel farms

The purpose of this study was to investigate bacterial pathogens and flora in both sick and clinically healthy eels, Anguilla japonica, and the environmental rearing waters of Korean eel farms. Between 2003 and 2010, a total of 621 sick eels were submitted for diagnosis, while 216 healthy eels and 87 environmental water samples were collected during a survey of 26 eel farms in Korea. Seven different bacterial species were obtained from 183 isolates, which were recovered from the internal organs of the 621 sick eels. The most frequently isolated bacterium was Edwardsiella tarda (71.0%), followed by Aeromonas hydrophila (9.3%), Citrobacter freundii (7.7%), Aeromonas veronii (6.0%), Listonella anguillarum (2.7%), Plesiomonas shigelloides (2.2%), and Pseudomonas anguilliseptica (1.1%). From the eel and water samples of the survey, a total of 472 isolates from 34 different species belonging to 15 genera of bacteria were isolated. The most prevalent genus of bacteria was Aeromonas spp. (141/472, 29.8%). Among the 34 types of bacterial species, C. freundii (20.1%) and A. hydrophila (19.9%) were the most frequently isolated. The results of this study indicate that a wide range of bacterial species, which can act as primary or opportunistic pathogens, may be recovered from clinically healthy eels and rearing waters. This study provides baseline information about bacterial pathogens and floral contamination for the control and treatment of bacteria in Korean eel farms.