魚病研究
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44 巻 , 4 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
  • Mamiko Mochizuki, Hyoung Jun Kim, Hisae Kasai, Toyohiko Nishizawa, Mam ...
    44 巻 (2009) 4 号 p. 159-165
    公開日: 2009/12/30
    ジャーナル フリー
    Infectious hematopoietic necrosis virus (IHNV) is the causative agent of IHN, one of the most serious viral diseases of salmonid fish. A total of five major genogroups including JRt for Asian isolates were confirmed among worldwide isolates based on glycoprotein (G) gene nucleotide (nt) sequences. The present study revealed existence of new two lineages, JRt Shizuoka and JRt Nagano, in the genogroup JRt by addition of new isolates obtained in 2006. The maximum nt diversity of G gene within JRt Shizuoka or JRt Nagano lineage was 6.3% or 3.5%, while that between JRt Shizuoka and JRt Nagano lineages was 7.0%. To evaluate influence of the evolutional divergence to virulence of IHNV, experimental challenges to rainbow trout Oncorhynchus mykiss were conducted by bath exposure at 104 TCID50/mL of RtShiz06s and RtShiz06a (JRt Shizuoka lineage), RtNag96 and RtNag06a (JRt Nagano lineage), and ChAb76 (a representative of the genogroup U). Distinct difference was observed in IHNV virulence to rainbow trout, i.e. the highest virulence was in RtShiz06s and RtShiz06a (≥ 76% of mortalities), and subsequently in RtNag96 and RtNag06a (20-40%), but scarcely any virulence in ChAb76 (≤ 10%). Thus it was suggested that nt diversity of Japanese IHNV continued rapidly with changing its virulence in rainbow trout farm environments.
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  • Masayuki Miura, Kishio Hatai, Heisuke Oono, Nana Kaji, Jun Nagura
    44 巻 (2009) 4 号 p. 166-171
    公開日: 2009/12/30
    ジャーナル フリー
    The antifungal effects of potassium chloride (KCl) against Saprolenia diclina, S. parasitica and Achlya sp. and fungal infection in ayu Plecogrossus altivelis eggs were evaluated. Zoospore motility of the fungi was greatly inhibited within 1 min in 0.03% KCl, although hyphal growth and zoospore germination of the fungi were not inhibited at a concentration of 0.24% KCl. When fertilized ayu eggs were continuously kept in 0.03%, 0.06% and 0.12% KCl until the eyed-egg stage, treatment at concentrations of 0.06% and 0.12% apparently decreased the rate of fungal infection in three separate experiments. These concentrations showed no effect on the egg-eyed ratio, the subsequent hatching and the larval deformity rates. It was confirmed that KCl was a useful chemical to prevent mold infection in ayu eggs.
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  • Hiroshi Yokoyama, Masahiro Kageyama, Tetsuya Yanagida, Kazuo Ogawa
    44 巻 (2009) 4 号 p. 172-177
    公開日: 2009/12/30
    ジャーナル フリー
    A vital staining assay using Hoechst 33342 and propidium iodide was developed for the determination of viability of Enteromyxum leei (Myxozoa), a causative agent of myxosporean emaciation disease. Using this in vitro viability assay combined with in vivo infectivity test, the survival of developmental stages of E. leei in seawater was evaluated. Developmental stages of E. leei were freshly isolated from infected tiger puffer Takifugu rubripes and incubated in filtered natural seawater at 20ºC for 0, 6, 12 and 24 h. The in vitro staining assay showed a time-dependent decrease in viability, and no viable stages were detected at 24 h. In the first trial of in vivo infectivity, naïve tiger puffer were exposed to E. leei suspensions which were incubated in seawater for 0-48 h. In the second trial, naïve grass puffer T. niphobles were fed E. leei incubated for 0-24 h. After rearing for 3-4 weeks, infection with E. leei was detected in fish challenged with the parasite incubated for 24 and 6 h in the first and second trials, respectively. Results of the in vitro and in vivo assays showed that the survival time of developmental stages of E. leei in seawater was variable but estimated less than 24 h.
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