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Diseases of Aquatic Organisms

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DAO 37:121-126 (1999)  -  doi:10.3354/dao037121

The protective immune response of yellowtail Seriola quinqueradiata to the bacterial fish pathogen Lactococcus garvieae

Tsuyoshi Ooyama1, Akio Kera1, Toshiaki Okada2, Valerie Inglis3, Terutoyo Yoshida2,*

1Miyazaki Fisheries Station, Miyazaki Prefecture, Aoshima 6-16-3, Miyazaki, Japan
2Department of Fisheries, Faculty of Agriculture, Miyazaki University, Miyazaki 889-2192, Japan
3Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, UK
*Addressee for correspondence. E-mail:

ABSTRACT: Yellowtail Seriola quinqueradiata were immunized with 2 different Lactococcus garvieae bacterin, formalin-killed KG- phenotype cells (capsulated phenotype) and formalin-killed KG+ phenotype cells (unencapsulated phenotype). These 2 injected vaccines conferred long-term protection to yellowtail against an artificial infection of an encapsulated Lactococcus garvieae strain with long-lasting agglutinating titres against KG+ phenotype cells. However, no agglutinating titres or low agglutinating titres against KG- phenotype cells were detected in fish given each of these bacterin. These results suggested that a capsule in KG- phenotype cells apparently affects their immunogenicity, but the antigens which conferred protection to fish against lactococcal infection may be located on the surface of KG+ phenotype cells, and are not cell capsules in KG- phenotype cells. The protection offered by a formalin-killed KG+ phenotype cell vaccine would not appear to be strain specific. Encapsulated L. garvieae cells were well phagocytosed, and fimbrie-like appendages were seen in KG- phenotype cells after treatment with yellowtail immune serum.

KEY WORDS: Vaccines · Lactococcus garvieae · Seriola quinqueradiata · Phenotypic variation · Immune response

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