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<p>The Manila clam is a commercially important bivalve species inhabiting tidal flats. Since the 1980s, Manila clam populations have declined significantly, partly due to parasitic infections. While the protist <i>Perkinsus olseni</i> has been extensively studied as a major parasite of Manila clams, less is known about other potentially parasitic protists affecting this species. Using a PCR method, we detected small subunit ribosomal RNA (SSU rRNA) gene fragments of protists from the gill tissues of Manila clams collected from the Tsuyazaki tidal flat, located within a semi-enclosed inlet. Phylogenetic analyses of the SSU rRNA gene sequences revealed that the detected DNA belonged to the Ciliophora (<i>Ancistrum crassum</i>, <i>Trichodina sinonovaculae</i>, <i>Plagiocampa</i> sp., and a species belonging to either <i>Planeticovorticella</i> or <i>Zoothamnium</i>), Ichthyosporea (<i>Sphaeroforma tapetis</i>), and Haplosporida (<i>Urosporidium tapetis</i>). Although <i>Perkinsus</i>-derived sequences were not detected by PCR, incubation in Ray’s Fluid Thioglycollate Medium (RFTM) resulted in the enlargement of <i>Perkinsus</i>-like cells. This discrepancy suggests either that <i>Perkinsus</i> was present at very low infection levels below the PCR detection threshold, or that morphologically similar organisms (e.g., <i>Sphaeroforma tapetis</i>) were detected in the RFTM assay. This study revealed the possibility of the existence of diverse protists associated with the Manila clams on the Tsuyazaki tidal flats.</p>

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Diversity of protists associated with the Manila clam Ruditapes philippinarum inhabiting the Tsuyazaki tidal flat in northern Kyushu, Japan

  • 期刊论文

  • 发表日期：

    2025年11月5日

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  • Kiyotaka Takishita,
  • Saya Kunisaki,
  • Honoka Hyakutake,
  • Mayuko Otsubo,
  • Yuqi Liu,
  • Naoki Itoh

摘要

The Manila clam is a commercially important bivalve species inhabiting tidal flats. Since the 1980s, Manila clam populations have declined significantly, partly due to parasitic infections. While the protist Perkinsus olseni has been extensively studied as a major parasite of Manila clams, less is known about other potentially parasitic protists affecting this species. Using a PCR method, we detected small subunit ribosomal RNA (SSU rRNA) gene fragments of protists from the gill tissues of Manila clams collected from the Tsuyazaki tidal flat, located within a semi-enclosed inlet. Phylogenetic analyses of the SSU rRNA gene sequences revealed that the detected DNA belonged to the Ciliophora (Ancistrum crassum, Trichodina sinonovaculae, Plagiocampa sp., and a species belonging to either Planeticovorticella or Zoothamnium), Ichthyosporea (Sphaeroforma tapetis), and Haplosporida (Urosporidium tapetis). Although Perkinsus-derived sequences were not detected by PCR, incubation in Ray’s Fluid Thioglycollate Medium (RFTM) resulted in the enlargement of Perkinsus-like cells. This discrepancy suggests either that Perkinsus was present at very low infection levels below the PCR detection threshold, or that morphologically similar organisms (e.g., Sphaeroforma tapetis) were detected in the RFTM assay. This study revealed the possibility of the existence of diverse protists associated with the Manila clams on the Tsuyazaki tidal flats.