Identification and characterization of pathogen to bacterial septicaemia in cultured turbot, Scophthalmus maximus

Bacteria-infected turbots Scophthalmus maximus with septicaemia were examined between 2001 and 2004 in aspects of the conditions of disease occurrence, clinical syndromes and pathological changes. The phenotypic information of pathogenic bacteria was studied, including morphology, physiological and biochemical characteristics, and the mol% G＋C of the DNA. In addition, representative strains （S010623-1, LH031120-1） were selected for molecular identification by partial 16S rRNA gene sequencing. The results show that the isolates （LH031120-1 to LH031120-6, HT040308-1 to HT040308-6, HT040620-1 to HT040620-6） from three farms were identified as Edwardsiella tarda. The isolates （S010610-1 to S010610-10, S010623-1 to S010623-20） from one farm were identified as Listonella anguillarum. We conducted studies on the pathogenicity of isolates by artificial infection, and revealed all infected groups in morbidity and mortality. The septicaemia infected turbot showed a syndrome similar to that of the naturally infected fish. Antibiotic sensitivity showed that of 37 antimicrobial agents, E. tarda was sensitive to 27 agents, and L. anguillarum was sensitive to 21 agents.