• Journal of fish pathology
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• v.22 no.3
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• pp.263-273
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• 2009

There is an increasing number of reports describing Streptococcus parauberis as an important pathogen of cultured olive flounder Paralichthys olivaceus and starry flounder Platichthys stellatus in Korea. We tried to determine the effects of water temperature (14${^{\circ}C}$ and 21${^{\circ}C}$) on the pathogenicity in Streptococcal disease caused by S. parauberis. We have challenged 180 olive flounder by i.p injection to $2.0{\times}10^{7}$ live cells/fish. Mortality was monitored for 21 days post challenge. And histopathological characterizations as infection degree, tissue degeneration and/or bacterial distribution were investigated with H&E stain and in situ hybridization technique. Fifty percent and 16.7% of mortality occurred within 21 days at 21${^{\circ}C}$ and 14${^{\circ}C}$ water temperature, respectively. In most cases, the typical symptoms of olive flounder infected with S. parauberis were darkness of the skin, lethargy, mild abdominal distension cause by ascites, splenomegaly, congested liver and internal organs paleness. The pericardial sac contained large amounts of cloudy fluid. Numerous whitish nodules, which were variable in size and often confluent, were randomly scattered throughout the myocardium. Especially, pericarditis and/or myocarditis was observed in all tested fishes after death. Positive in reaction with S. parauberis were found in all tissues in situ hybridization analysis. The relative numbers of S. parauberis in heart were much more than in liver, spleen, kidney and stomach. We evaluated that S. parauberis strain causes serious damage in the pericardium, shortness of breath and the blood disorder. Therefore, pericarditis and myocarditis caused by S. parauberis were closely related to mortality of olive flounder.