PCR-based Discrimination and Scanning Electron Microscopy o Genotypically Differentiated Ectoparasitic Flagellates Ichthyobodo spp. Infecting Salmonid Species Cultured in Freshwater in Hokkaido, Japan

The present study investigated the genotype of Ichthyobodo spp. that caused six cases of ichthyobodosis in various salmonid species cultured in freshwater, in Hokkaido, Japan, through molecular phylogenetic analysis of the parasite ribosomal RNA gene (rDNA). Polymerase chain reaction (PCR) and scanning electron microscopy (SEM) were performed to distinguish the genotypically differentiated Ichthyobodo spp. The parasites were identified as genotypes I (I. necator sensu stricto), II (I. salmonis), or III (Ichthyobodo sp.). The present PCR method could completely distinguish between genotypes I, II and III using the electrophoresis pattern of PCR products from the parasite rDNA. Our SEM observations were able to SEM observations were able to morphologically distinguish genotype I from other two genotypes, but not between genotype II and III.