魚病研究
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50 巻 , 3 号
選択された号の論文の6件中1~6を表示しています
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論文
  • Michitaka Yamamoto, Kazuhiro Sugahara, Makoto Endo, Katsuya Ishimaru, ...
    50 巻 (2015) 3 号 p. 97-104
    公開日: 2015/09/29
    ジャーナル フリー
    We studied the epidemiology of Flavobacterium psychrophilum in ayu from Lake Biwa for establishing control measures to bacterial cold water disease (BCWD). During 1998-2011, 12,743 wild ayu were collected from coastal (set net and gill net), offshore (offshore scoop net) and inflow river (fishing weir) areas of Lake Biwa. We employed a nested-PCR technique targeting 16S rRNA gene for the detection of F. psychrophilum in the gills and kidney of ayu. Prevalence of the bacterium was greatest when the water temperature of Lake Biwa was 18-21°C, which coincides with the optimum temperature for multiplication of F. psychrophilum. The prevalence of F. psychrophilum in the gills was higher in fish from fishing weirs and set nets maintained in net cages than in fish just after catch with the other fishing techniques. This suggests that rearing ayu in net cages at high densities following catch by fishing weirs and set nets can advance infection with the bacterium among the captured fish which will be used for seedlings in aquaculture or releasing in rivers. Control measures for the captured ayu must be conducted in reliable ways to prevent spread of the disease after release and in aquaculture.
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  • Yukitaka Sugihara, Toshiyuki Yamada, Kazuo Ogawa, Fumihiko Yokoyama, K ...
    50 巻 (2015) 3 号 p. 105-111
    公開日: 2015/09/29
    ジャーナル フリー
    The blood fluke Cardicola opisthorchis (Trematoda: Aporocotylidae) is a significant pathogen of cultured Pacific bluefin tuna Thunnus orientalis in Japan. We conducted monthly surveys of the intermediate polychaete host Terebella sp. (Polychaeta: Terebellidae) for one year in 2014 to elucidate seasonality in the C. opisthorchis infection at a tuna farm in Tsushima Island, Nagasaki Prefecture, Japan. The intermediate host, collected from ropes and floats attached to culture cages, was abundant from January to March and in November and December but quite scarce from April to October. The sporocysts of C. opisthorchis were found from January to March and from September to December, with the prevalence of infection ranging from 2.0% to 18.4%. Development of sporocysts was observed in the body of the intermediate host Terebella sp. Sporocystogenous sporocysts and cercariogenous sporocysts co-occurred in the body cavities of the polychaete host. This is the first detailed description of asexual multiplication process of sporocysts among marine aporocotylid species. Additionally, sporocystogenous sporocysts and released daughter sporocysts survived in L-15 medium for up to 63 and 66 days, respectively. The highest number of sporocysts in one polychaete host was about 1,800 and the highest number of cercariae in one sporocyst was 75, suggesting that as many as >105 cercariae can be released from one infected polychaete.
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