Identification and pathogenic significance of Shewanella sp from pond fish

Four Gram negative, H2S-producing, pigmented bacterial strains isolated in Belgium from the internal organs of pond fish were identified. Biochemical characteristics and results of fatty acid analysis demonstrated that the isolates belonged to the genus Shewanella. Goldfish were experimentally infected with three of these isolates. For each isolate ten fish were used. These animals were inoculated intramuscularly with 10(6) colony forming units of the isolate. Ten other fish were inoculated intramuscularly with phosphate buffered saline solution and used as controls. None of the inoculated fish showed clinical symptoms. Macroscopic lesions were not detected at post-mortem examination performed three weeks after inoculation. In all fish inoculated with the Shewanella isolates bacteria were isolated from the spleen and kidney with the same characteristics as the inoculated strain. These results may indicate that the pathogenicity for goldfish of the strains used in these studies is low if not totally absent. Results of bacteriological examination of dead fish have to be interpreted with care.