Causative pathogen of dark-thin syndrome in cultured Scophthalmus maximus and Chinese herbal medicine screening for the bactericidal effect

Dark-thin syndrome often occurred at stages of larval turbot Scophthalmus rnaximus, causing lower metamorphosis and more than 80% of mortality. One bacterial strain was isolated from the diseased larvae, and it was confirmed to be the pathogen causing the disease through artificial infection tests. The pathogenic bacterium was identified as Vibrio splendidus by conventional physiological and biochemical tests as well as 16S rDNA sequence analysis. In addition, histopathological studies demonstrated that the bacterium could cause infectious changes in the liver, kidney, spleen, intestine and brain. The effective components of 11 Chinese herbs were extracted respectively by the methond of decoction, and they were tested for the susceptibility against V. splendidus. The results showed that Galla chinensis and Radiz pulsatillae had the best inhibitory effect on the bacterium, with minimal bactericidal concentration (MBC) of 25mg/ml. MBC for both Phellodendron chinense and Herba andrographitis was 50mg/ml. While C