A REVIEW OF ICHTHYOBODO INFECTION IN MARINE FISHES

The ectoparasitic flagellate Ichthyobodo has been recorded from 25 spe cies of marine fishes and 3 species of anadromous salmon in the Pacifi c Ocean, Atlantic Ocean, and adjacent seas ranging from the subarctic to tropical zones. With an increasing number of reports on the occurre nce of Ichthyobodo in the marine environment, its origin and taxonomic status have been confused. The parasite from marine fishes is morphol ogically comparable to the freshwater parasite I. necator, which can s urvive and reproduce on anadromous salmon in seawater. It was assumed that the parasite on marine fish was transmitted from freshwater hosts . However, the marine parasite from Japanese flounder (Paralichthys ol ivaceus) and I. necator from freshwater chum salmon (Oncorhynchus keta ) were differentiated by their host specificity. The parasite has been found on pure marine fishes in offshore waters. Thus, Ichthyobodo on marine fishes may be regarded as a separate species from freshwater I. necator. The parasite infects the skin and gills of host fishes, caus ing severe epidermal hyperplasia and necrosis. Ichthyobodo infections caused moderate deaths in yearling Japanese flounders and tiger puffer (Takifugu rubripes), while the infections induced high mortalities am ong larvae of marine fishes such as Japanese flounders, gilthead sea b ream (Sparus aurata), and rockfish (Sebastes schlegli). The most effec tive treatment for Ichthyobodo infections is a formalin bath, but alte rnative safe control methods should be established by future studies.