Morphological and molecular characterization of four Ceratomyxa species parasitizing marine fish in Japan including descriptions of three new species

A parasitological survey in western Japan identified the myxosporean parasites in the bile and gallbladders of four marine fish species: farmed white trevally Pseudocaranx dentex (Bloch & Schneider), Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel), and red seabream Pagrus major (Temminck & Schlegel), as well as wild false kelpfish Sebastiscus marmoratus (Cuvier). Morphological characterization and molecular analysis of the small subunit rDNA confirmed that these parasites belong to the genus Ceratomyxa. Three novel species were identified: Ceratomyxa shimaaji n. sp. from P. dentex (prevalence 100 %, n = 8 fish), Ceratomyxa kuromaguro n. sp. from T. orientalis (prevalence 100 %, n = 1 fish), and Ceratomyxa gashira n. sp. from S. marmoratus (prevalence 100 %, n = 1 fish). Additionally, Ceratomyxa cf. barnesi, was detected in P. major (prevalence 10 %, n = 10 fish). While the pathological effects of these Ceratomyxa species on their hosts remain to be investigated, this study contributes to a broader understanding of the diversity and geographic distribution of Ceratomyxa spp. in marine fish.