魚病研究
Online ISSN : 1881-7335
Print ISSN : 0388-788X
43 巻 , 4 号
選択された号の論文の7件中1~7を表示しています
論文
  • Hiroshi Yokoyama, Fumihiko Yokoyama, Jin-Yong Zhang, Kouta Tsuruoka, K ...
    2008 年 43 巻 4 号 p. 137-143
    発行日: 2008年
    公開日: 2008/12/28
    ジャーナル フリー
    Recently, a microsporidian infection was found in the trunk muscle of hatchery-bred juvenile spotted halibut Verasper variegatus. The disease occurred from mid-July to the end of September 2007 and the cumulative mortality reached approximately 20%. Infected fish showed the external sign of a concave body surface on the eyed side, and the microsporidian parasite formed numerous ‘cysts’ in the muscle. These characteristics resembled ‘beko’ disease caused by Microsporidium seriolae from cultured yellowtail Seriola quinqueradiata, Microsporidium sp. from red sea bream Pagrus major (RSB) and Microsporidium sp. from gilthead sea bream Sparus aurata (GSB), but several differences were observed in associated pathological findings such as internal hemorrhage around the ‘cysts’. Average dimensions of spores from spotted halibut (SH) were 3.07 × 2.13 μm, which were relatively smaller than those of M. seriolae, Microsporidium sp. RSB and Microsporidium sp. GSB, but the ranges of measurements overlapped among them. Molecular analysis of rDNA sequences suggested that the present parasite, provisionally named as Microsporidium sp. SH, was distinct from the other known species.
  • Jianping Fang, Sho Shirakashi, Kazuo Ogawa
    2008 年 43 巻 4 号 p. 144-151
    発行日: 2008年
    公開日: 2008/12/28
    ジャーナル フリー
    Japanese eel Anguilla japonica and European eel A. anguilla, 65 individuals each, were exposed in a tank to 8,600 oncomiracidia of Pseudodactylogyrus bini and P. anguillae, monogeneans originally recorded on Japanese eel from Asia. Infection was monitored weekly for 6 weeks to compare susceptibility to these monogenean infections between the two eel species. Approximately 40% of the oncomiracidia infected the eels. In the six samplings, both P. bini and P. anguillae were always found in greater numbers on the gills of European eel than on Japanese eel. The first generation of parasites matured within 2 weeks, laying eggs in the tank, and the second generation appeared on the gills of the eels on the third week. European eel was more susceptible not only to the first but also to the second and later generations of parasites than Japanese eel. Besides, both parasites grew faster on European eel than on Japanese eel. This is the first experimental evidence that there are substantial differences in the susceptibility to P. spp. infection between European eel, an unnatural host in Japan, and Japanese eel, the natural host in this country.
  • Takamitsu Sakai, Takashi Kamaishi, Motohiko Sano, Kozue Tensha, Taeko ...
    2008 年 43 巻 4 号 p. 152-157
    発行日: 2008年
    公開日: 2008/12/28
    ジャーナル フリー
    From middle August to early October in 2007, mortalities in wild ayu Plecoglossus altivelis occurred in the rivers of Tokyo Metropolis, Yamaguchi Prefecture and Hiroshima Prefecture, Japan. Hemorrhagic ascites was observed in almost all the examined fish. Some fish showed reddening of body surface, anus or bases of fins and exophthalmos. A single species of bacteria was isolated from the kidney, spleen and ascites of all the examined fish and identified as Edwardsiella ictaluri. Pathogenicity against ayu of the bacterial isolates was demonstrated by experimental infections, with the LD50 being approximately 104 CFU/fish. The dead fish exhibited similar disease signs to those of naturally affected fish. From these results, it was concluded that the present mortality of wild ayu was caused by E. ictaluri infection. This is the first report on E. ictaluri infection of fish in Japan.
  • Takahiro Nagai, Emi Iwamoto, Takamitsu Sakai, Taeko Arima, Kozue Tensh ...
    2008 年 43 巻 4 号 p. 158-163
    発行日: 2008年
    公開日: 2008/12/28
    ジャーナル フリー
    A Gram-negative bacterium was isolated from diseased wild ayu Plecoglossus altivelis, which were caught in rivers in Japan from August to October in 2007. All four isolates examined showed the same morphological, physiological and biochemical characteristics and were classified into the genus Edwardsiella. The isolates were differentiated from E. tarda in respect of its negative production of indole and no growth at 37°C, and different from a reference strain of E. ictaluri (JCM1680) in its positive production of hydrogen sulfide. All isolates were completely identical in the partial nucleotide sequences of 16S rDNA, a type 1 fimbrial gene (etfA) and a heat shock protein gene (dnaJ), and these sequences showed high similarity (100%, 99.7% and 100%, respectively) with E. ictaluri but low similarity (99.7%, 92.5% and 87.3%, respectively) with E. tarda. Based on these phenotypic and genetic characteristics, the present isolates from ayu were identified as E. ictaluri.
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