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Title: Microbiological characteristics of Vibrio scophthalmi isolates from diseased olive flounder Paralichthys olivaceus

Author
item QIAO, GUO - Pukyoung National University
item LEE, DEOK CHAN - Pukyoung National University
item WOO, SUNG HO - Pukyoung National University
item LI, HUA - Dalian University Of Technology
item Xu, Dehai
item PARK, SOO II - Pukyoung National University

Submitted to: Fisheries Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2012
Publication Date: 5/8/2012
Citation: Qiao, G., Lee, D., Woo, S., Li, H., Xu, D., Park, S. 2012. Microbiological characteristics of Vibrio scophthalmi isolates from diseased olive flounder Paralichthys olivaceus. Fisheries Sciences. 78(4):853-863.

Interpretive Summary: Olive flounder is one of the most important commercial food fishes and commonly cultured through flatfish aquaculture in inland Korea. Massive mortality occurred in olive flounder farms in 2005 and five bacterial isolates were collected from the diseased fish to study their phenotypic characteristics, genetic characteristics and pathogenicity to olive flounders. According to genetic analysis, 16S rRNA gene sequences showed 98–100 % identity with Vibrio scophthalmi and V. ichthyoenteri. The dnaJ gene sequences presented a higher identity with V. scophthalmi than with V. ichthyoenteri. Thus, the isolates were identified as V. scophthalmi. In pathogenicity test of the five isolates in olive flounder, LD50 values ranged from 10^6 to 10^8 CFU/g of fish. Symptoms included darkening of skin, hemorrhage of liver and intestine, ascites, and distended abdomen. Histopathological changes included hemopoiesis dilatation and epithelial hyaline droplets in kidney, macrophage infiltration and ellipsoid dilatation in spleen, and serosa inflammation of intestine. Cumulative mortality was 25 % for fish singly infected by isolate A19008 and increased to 87.5 % in super-infection group with two pathogens. These results will be benefit to animal health managers and fish producers for understanding pathogenic characteristics of the infected bacteria, preventing fish disease, and minimizing loss in aquaculture.

Technical Abstract: In 2005, massive mortality occurred in olive flounder Paralichthys olivaceus farms in Korea, and five isolates were collected from diseased fish. In this study, microbiological and pathogenic characteristics of these isolates were studied. The isolates gave negative results in lysine and ornithine decarboxylase, ortho-nitrophenyl-bgalactoside, and citrate tests, and positive results in urease, esculinase, and nitrate reduction tests. The isolates produced acid from adipate, fructose, D-glucose, and maltose, and gave positive results in alkaline phosphatase, esterase lipase, leucine arylamidase, and naphthol-AS-BI phosphohydrolase. According to genetic analysis, 16S rRNA gene sequences showed 98–100 % identity with both Vibrio scophthalmi and V. ichthyoenteri. The dnaJ gene sequences presented a higher identity with V. scophthalmi than with V. ichthyoenteri. Thus, the isolates were identified as V. scophthalmi. Pathogenicity of the five isolates in olive flounder was different and LD50 values were from 10^6 to 10^8 CFU/g fish. Symptoms included darkening of skin, hemorrhage of liver and intestine, ascites, and distended abdomen. Histopathological changes included hemopoiesis dilatation and epithelial hyaline droplets in kidney, macrophage infiltration and ellipsoid dilatation in spleen, vascular dilatation, submucosal edema, and serosa inflammation of intestine. Cumulative mortality was 25 % for fish singly infected by isolate A19008 or Streptococcus parauberis, and increased to 87.5 % in super-infection group with these two pathogens.