Abstract
Infections by ectoparasitic trichodinid ciliates cause epidermal damages to artificially reared juvenile barfin flounder Verasper moseri of mariculture fisheries in Hokkaido, northern Japan. In the present study, morphological observation and molecular phylogenetic analysis using the small subunit ribosomal RNA gene (SSU rDNA) were performed to identify the trichodinid ciliates. Morphological analysis of denticles and adoral ciliary spiral demonstrated that the trichodinid ciliate belongs to the genus Trichodina within ten genera of Trichodinidae. Denticles of the trichodinid ciliate were clearly distinguishable from those of other Trichodina species by small denticle span, and extensive elongation of the central conical part and anterior ray apophysis. All the isolated ciliate had the same 1,699 base pair SSU rDNA nucleotide sequences, which revealed that the trichodinid ciliates comprised a single species. The SSU rDNA of the trichodinid ciliate showed the highest homology with that of T. pectenis (98.5%) among 30 species of trichodinid ciliates, and the two species formed a single clade in the phylogenetic tree. However, no identical sequence with the present trichodinid ciliate was found in the database. We propose Trichodina hokkaidoensis n. sp. for the ciliate infecting artificially reared juvenile barfin flounder, based on both morphological and molecular phylogenetic analyses.
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