The caligid copepod Caligus bonito Wilson, 1905 is reported based on adult females from the inner surface of the operculum of skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758) (Perciformes: Scombridae), caught on 10 July 2018 in the East China Sea (33° 04′N, 128°23′E) off the Goto Islands, Nagasaki Prefecture, Kyushu, Japan. Four of the 10 individuals of K. pelamis examined (46.0–55.2 cm in fork length) hosted each one or two females of C. bonito. The copepod is known to parasitize primarily scombrids in the tropical, subtropical, and temperate waters throughout the world, and the present collection extends its distribution range in the western North Pacific north to the East China Sea. The host and collection locality records of C. bonito from the western North Pacific and its adjacent seas, including the waters around Japan, Taiwan, China, and Vietnam, are also tabulated.

東シナ海から初記録の魚類寄生虫,カツオウオジラミ Caligus bonito (カイアシ亜綱:管口目:ウオジラミ科) (長澤和也・大橋慎平・田中文也)