魚病研究
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45 巻 , 2 号
選択された号の論文の10件中1~10を表示しています
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論文
  • Sho Shirakashi, Shuya Nakatsuka, Akihisa Udagawa, Kazuo Ogawa
    45 巻 (2010) 2 号 p. 51-57
    公開日: 2010/07/13
    ジャーナル フリー
    We conducted a series of experiments to understand the behavioral characteristics of oncomiracidium of the monogenean Heterobothrium okamotoi and compared them with those of two other monogenean species, Heteraxine heterocerca and Neobenedenia girellae. Behavior of H. okamotoi oncomiracidium consisted of two alternate phases: a swimming phase with strong ciliary beatings and a stationary phase with ciliary beatings too weak to generate any movements. The duration of one swimming-stationary cycle considerably varied among individuals but tended to increase with larval age. During the 5-day monitoring, length of the swimming phase decreased while that of the stationary phase tended to increase as the larva became older. The locomotion patterns differed significantly among individuals, but as a whole, larvae showed random horizontal movement and no phototactic reaction. The oncomiracidium tended to move downward because it was heavier than seawater and also swam downward at the start of the swimming phase because its anterior part pointed downward when the larva was not swimming. Those behavioral characteristics of larval H. okamotoi are likely to have evolved in order to maximize the chance of encountering its benthic fish host, tiger puffer Takifugu rubripes.
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  • Kazuhiro Sugahara, Erina Fujiwara-Nagata, Mitsuru Eguchi
    45 巻 (2010) 2 号 p. 58-65
    公開日: 2010/07/13
    ジャーナル フリー
    Bacterial cold-water disease (BCWD) causes heavy mortality of ayu Plecoglossus altivelis in Japan. To control BCWD of ayu, warmed water treatment at 28°C has been used. However, the mechanism of this treatment is unknown. Hence, we investigated the growth/survival of Flavobacterium psychrophilum at 15-28°C under two nutritional conditions: in modified cytophaga (MCY) broth and sterilized underground water. Within 2 days at 28°C in both the conditions, F. psychrophilum totally lost its colony-forming ability. We also studied distributions of F. psychrophilum in infected fish organs and in rearing water after various treatments. For bacteria detection, the colony-counting method and loop-mediated isothermal amplification (LAMP) method were used. For warmed water treatment, the rearing water was warmed from 18°C to 23°C or 28°C for 3 days. The treatments were started 1 day after immersion infection. In the experimentally infected fish, F. psychrophilum was detected neither in any fish organs nor in the rearing water after the 28°C treatment for 3 days. These results indicate the effectiveness of the warmed water treatment at 28°C against BCWD of ayu.
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