Trichodinids are ciliated protozoan parasites or symbionts of marine and freshwater organisms. During a parasitic ciliate survey in Hubei, China, two Trichodina species, T. acutaLom, 1961 and T. hyperparasitis Chen & Hsish, 1984, were isolated from body surface of loach Misgurnus anguillicaudatus and gills of yellow catfish Pelteobagrus fulvidraco, respectively. The two species were investigated morphologically, based on silver-strained specimens, and their small subunit ribosomal RNA gene (SSU rDNA) sequences were sequenced. Morphologically, T. acuta is distinguished mainly by the acute sickle-shaped blade with well-developed sharp blade apophysis, the irregular circular granule, and the robust ray. Trichodina hyperparasitis is mainly characterized by the broad blade and the inconspicuous round ray apophysis. Phylogenetic analyses revealed that the two Trichodina species investigated were nested within a clade including several freshwater Trichodina species. This indicates that the central granule is a useful taxonomic feature, but it may not be an important phylogenetic characteristic. Histopathological analysis revealed that T. hyperparasitis firmly colonized gills, which resulted in discrete hyperplasia and injuries of the gill filaments.
Keywords: Histopathology; Morphological taxonomy; SSU rRNA gene sequence; Trichodina acuta; Trichodina hyperparasitis.
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