魚病研究
Online ISSN : 1881-7335
Print ISSN : 0388-788X
ISSN-L : 0388-788X
最新号
選択された号の論文の3件中1~3を表示しています
論文
  • Goshi Kato, Kensuke Oka, Megumi Matsumoto, Motohisa Kanemaru, Masato Y ...
    原稿種別: Research Article
    2020 年 55 巻 1 号 p. 1-7
    発行日: 2020/03/15
    公開日: 2020/04/02
    ジャーナル 認証あり

    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.

  • Shinya Mizuno, Shigehiko Urawa, Yoshitomo Katsumata, Takumi Morishita, ...
    原稿種別: Research Article
    2020 年 55 巻 1 号 p. 8-17
    発行日: 2020/03/15
    公開日: 2020/04/02
    ジャーナル 認証あり

    Systemic infections caused by diplomonad flagellates belonging to the genus Spironucleus commonly result in heavy mortalities in salmonids. ​Diplomonad flagellates were found in the intestinal lumen of hatchery-reared juvenile chum Oncorhynchus keta and masu salmon O. masou in Hokkaido. ​We performed ultrastructural observation and molecular phylogenetic analysis using the small subunit ribosomal RNA gene (SSUrDNA) of the flagellates to clarify their taxonomy. ​The flagellates showed elongated and tapered nuclei, and sub-apical location of the kinetosomes relative to the nuclei: which are the distinguishing characters of the genus Spironucleus among three genera of parasitic diplomonads. ​In addition, the flagellates had electron dense plaques at their posterior end, a posterior sac of dense free ribosomes, an electron dense body, and bowl-shaped membranous structures, identifying them as S. salmonis among four Spironucleus species that affect fish. ​The ultrastructure of the flagellates showed no variations between the two host species of salmon. ​All the isolated flagellate SSUrDNAs had the same 1,031 bp sequence, and no difference in the sequence. ​The SSUrDNA showed the highest homology (99%) with S. salmonis among 11 diplomonad flagellates. ​Thus, this study successfully used ultrastructure diagnosis and molecular phylogenetic analysis to confirm S. salmonis as the diplomonad flagellate that has infected hatchery-reared chum and masu salmon in Hokkaido.

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