Abstract / Introduction / Summary:
Six adult specimens of Ceratothoa oxyrrhynchaena Koelbel, 1878, were collected from the buccal cavity of three individuals of blackthroat seaperch, Doederleinia berycoides (Hilgendorf, 1879), at 150 m deep on the continental shelf of Toyama Bay, an inlet of the southern Sea of Japan, Ishikawa Prefecture, central Japan, in August 2022. Each fish was found to harbor two (female and male) isopods. Although there is a record published in 2002 of a specimen of C. oxyrrhynchaena from Toyama Bay off Ishikawa Prefecture, no information was given about its morphology and host. The present collection represents the second record of C. oxyrrhynchaena from Ishikawa Prefecture and the first record of its host in this prefecture. Toyama Bay is the northernmost collection locality of C. oxyrrhynchaena in the Sea of Japan off the Japanese Archipelago.