Renal Trichodinosis in the Japanese Rice Fish, Oryzias latipes: First Report and Phylogenetic Classification.

Investigation of a disease outbreak in a hobbyist's medaka (Oryzias latipes) collection led to the detection of Trichodina sp. in the kidney tubuli of individual fish. Based on this observation, a thorough clinical workup, including native microscopy, histopathology and molecular genetics, was conducted. Besides the trichodinids, Ichtyobodo necator and microsporidian gill infection were found in one out of the eight fish, and all of them were infected with Mycobacterium sp. Morphological description of the renal Trichodina sp. was based on the parasites found in renal tubules. For molecular genetic characterization and phylogenetic analysis, primers targeting the 18S rRNA gene of all members of the order Mobilida were designed. The phylogenetic analysis of the 18S rRNA sequences showed a close relationship to Trichodina ruditapicis (FJ499385), Trichodina glossogobae (ON042773) and Trichodina sinonovaculae (FJ499386) sampled from fish and mussels in China, differing by 2.2%-2.5%. Here we report for the first time renal trichodinosis of O. latipes and molecular data of a fish-endozoic Trichodina sp.