Identification and Detection of the Pathogenic Bacteria Responsible for Swollen Abdomen Disease in Cultured Turbot, Scophthalmus maximus, and Flounder, Paralichthys olivaceus

Abstract

Swollen abdomen disease (SAD) seriously threatens the aquaculture of turbots and flounders. Two dominant bacterial strains, FS1 and FS2, were isolated from the livers and kidneys of fish with diagnosed SAD. Applications of biochemical analyses, sequence analyses of 16S ribosomal RNA gene and heat shock protein 60 gene revealed two distinct pathogenic bacterial species, Edwardsiella tarda and Vibrio alginolyticus. These two hypothesized SAD‐causing pathogens were validated by challenge trials on flounder, Paralichthys olivaceus. Challenges with E. tarda and V. alginolyticus demonstrated lethal dose 50 (LD50) values at 1.51 × 105 colony‐forming units (CFU) and 1.05 × 105 CFU, respectively. To develop a rapid SAD diagnosis method in flounders and turbots, a multiplex polymerase chain reaction (PCR) assay method was developed to simultaneously detect E. tarda and V. alginolyticus. Our multiplex PCR assay successfully detected as low as 105 CFU/mL E. tarda and V. alginolyticus in flounders and turbots. No other common fish pathogens were detected with the multiplex PCR, suggesting a high specificity of this assay. The multiplex PCR assay developed in this study showed a great reliability in detecting SAD‐causing bacterial pathogens. Further optimization of this assay may contribute to the development of a novel SAD diagnosis tool in aquaculture.

Identification and characterization of pathogens associated with fin erubescence and ulceration of culturedScophthalmus maximus

“…Vibrio alginolyticus is the largest group of Gram‐negative bacteria that can infect humans and marine animals (Kaneko & Colwell ). As an opportunistic pathogen, it is extremely harmful to the seawater and freshwater fishery industry including aquaculture production of Pseudosicaena crocea (Zheng, Wang, Huang, Jin, He & Lin ), Epinephelus (Lee ), Lutjanus erythropterus (Li, Jian & Wu ), Sparuslatus (Ding & Xu ), Rachycentron canadum (Liu, Lin, Hsian & Lee ), S. maximus and Paralichthys olivaceus (Xue, Feng & Sheng ; Zhang, Zhou, Xing & Zhan ), causing huge economic losses and seriously threatening the development of China's aquaculture industry.…”