Fish Pathology
Online ISSN : 1881-7335
Print ISSN : 0388-788X
ISSN-L : 0388-788X
Research Articles
Prevalence of Infection with Nocardia seriolae in Juvenile of Yellowtail Seriola quinqueradiata Cultured in Owase Bay, Japan
Goshi KatoKensuke OkaMegumi MatsumotoMotohisa KanemaruMasato YamamotoMotohiko Sano
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2020 Volume 55 Issue 1 Pages 1-7


Nocardiosis caused by Nocardia seriolae makes severe losses of fish production of Seriola spp. in Japan. ​In this study, we investigated prevalence of N. seriolae infection in yellowtail Seriola quinqueradiata cultured in an open sea net-cage in Owase Bay, Japan. ​The gills, serum and spleen were sampled from juvenile fish (n = 5) on May, June, July, August, November 2017 and January 2018. ​Serum antibody titer against N. seriolae were significantly increased on November 2017 and January 2018. ​N. seriolae 16S rRNA gene were detected by PCR in the spleen and/or gills of 1–4 individuals sampled on May, July, August, November 2017 and January 2018, while the bacterium was not isolated from any individuals on Ogawa medium. ​Granulomatous inflammation which is the typical characteristic of pathological feature of nocardiosis was not observed in any spleen sections examined. ​However, fluorescent immunohistochemistry with anti-N. seriolae rabbit serum detected the long- and short-rod shaped bacteria in the spleen of all fish examined in this study. ​These data suggest that the juvenile yellowtail cultured in Owase Bay had been already infected with N. seriolae even in May. ​In addition, N. seriolae may be in viable but non-culturable state (VBNC), resulting in latent infection in cultured yellowtail.

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© 2020 The Japanese Society of Fish Pathology
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