魚病研究
Online ISSN : 1881-7335
Print ISSN : 0388-788X
ISSN-L : 0388-788X
55 巻 , 2 号
選択された号の論文の4件中1~4を表示しています
総説
  • 高野 倫一, 松山 知正
    原稿種別: 総説
    2020 年 55 巻 2 号 p. 25-30
    発行日: 2020/06/15
    公開日: 2020/07/28
    ジャーナル フリー

    Bacterial hemolytic jaundice (BHJ) was first described in populations of cultured yellowtail, Seriola quinqueradiata in 1980 in Japan. ​BHJ is now one of the most important diseases of farmed yellowtail. ​The taxonomic position of the causative agent, Ichthyobacterium seriolicida, was recently determined as a single clade within the order Flavobacteriales and was distinct from the known clades of the family Flavobacteriaceae, Blattabacteriaceae and Cryomorphaceae. ​Whole genome analysis of the type strain JBKA-6T revealed that this bacterium harbors a single circular chromosome. ​Polymorphic analyses of I. seriolicida identified four major clusters among I. seriolicida isolates, and all belonged to clonal complexes; thus, this bacterium is considered to be recently introduced in Japan. ​In passive immunization tests, significantly lower mortality was observed in fish that received the serum from a convalescent fish, indicating I. seriolicida is neutralized by the humoral component of the immune system. ​However, since this bacterium does not grow vigorously in vitro, control measures such as the production of an inactivated vaccine is under development.

論文
  • Yuzo Takada, Kosei Taguchi, Kyuma Suzuki, Akihiko Ashizawa, Koichi Kaj ...
    原稿種別: Research Article
    2020 年 55 巻 2 号 p. 31-37
    発行日: 2020/06/15
    公開日: 2020/07/28
    ジャーナル フリー

    The temperature of water used to rear juvenile stages of ayu affects the development of the thymus. ​However, subsequent differences in the thymus in adults after rearing juveniles at different temperatures are unclear. ​We analyzed thymus development of ayu grown at a constant water temperature of 15°C from juveniles reared at different water temperatures. ​Juvenile ayu weighed at 0.6 g and 1.4 g were reared at different temperatures (10°C, 12°C, 15°C, 18°C and 22°C) for 64 days and 54 days, respectively, and then held at 15°C for analysis of the thymus development. ​Thymus volume was measured by computed tomography and thymus development of experimental fish was evaluated as the ratio of thymus volume to body length. ​The thymus volume ratios of juveniles immediately after rearing at lower water temperatures (10°C, 12°C) were higher than in those reared at the higher temperatures (18°C, 22°C). ​These levels of thymus volume ratio were preserved in grown ayu continuously reared at 15°C. ​After the summer solstice, the thymus began to atrophy and no longer exhibited differences among the experimental groups. ​Thus the thymus formed at the juvenile stage retains its morphological properties until the summer solstice.

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