Morphological and Molecular Comparisons of Myxobolus spp. in the Nerve Tissues of Salmonid Fishes with the Description of Myxobolus murakamii n. sp., the Causative Agent of Myxosporean Sleeping Disease

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  • Urawa Shigehiko
    Research Division, National Salmon Resources Center, Fisheries Research Agency North Pacific Anadromous Fish Commission
  • Iida Yoshisuke
    Fisheries and Marine Technology Center, Hiroshima Prefectural Technology Research Institute
  • Freeman Mark A.
    Institute of Biological Sciences, University of Malaya
  • Yanagida Tetsuya
    Department of Parasitology, Asahikawa Medical College
  • Karlsbakk Egil
    Department of Biology, University of Bergen
  • Yokoyama Hiroshi
    Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo

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Other Title
  • サケ科魚類の粘液胞子虫性眠り病 : 神経組織寄生Myxobolus属の新種M. murakamiiの記載

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Abstract

Myxosporean sleeping disease is known to cause severe mortality of masu salmon Oncorhynchus masou masou and amago salmon O. masou ishikawae farmed in Hiroshima, western Japan. Diseased fish become unable to swim, and shortly afterwards die on the bottom of the pond. The causative agent is Myxobolus sp. which infects the peripheral nerves of salmon, but its definitive identity and taxonomic status have been unresolved for years. We investigated interspecific relationships among Myxobolus spp. infecting the nerve tissues of salmonid fishes from Japan, Europe and North America. Our morphological comparisons revealed that myxospores varied in spore shape, and separated into two types: spherical (typically M. neurobius, M. kisutchi and M. neurotropus) or pyriform (typically M. arcticus and M. fryeri). Molecular analysis based on small subunit ribosomal DNA (SSU rDNA) demonstrated that Myxobolus sp. from the lateral line nerve of amago salmon with sleeping disease in Hiroshima was genetically distinct from other myxosporean species, but had 99.5% sequence similarity to Myxobolus sp. from the lateral line nerve of subclinical masu salmon in the Mena River, Hokkaido. Both myxosporeans had similar spherical-type spores. Consequently, Myxobolus sp. from the lateral line nerve of both amago and masu salmon in Hiroshima and Hokkaido are considered to be a new species, and described as M. murakamii n. sp.

Journal

  • Fish Pathology

    Fish Pathology 44 (2), 72-80, 2009

    The Japanese Society of Fish Pathology

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