養殖ブリ幼魚における大型吸虫の寄生

高知県沿岸で養殖されていたブリSeriola quinqueradiata 幼魚2尾の筋肉に大型吸虫の寄生を認めた。この吸虫は各尾に1個体が寄生し，生時の体長約7–15mm で，わが国の養殖カンパチから報告されている「ヒルディネラ類吸虫」によく似ていた。寄生魚が見出されたのは2015年5月中旬で，養殖種苗はその約1か月前に高知県沖の北西太平洋で漁獲された。寄生魚の皮膚は寄生部位付近で凹凸を有し，筋肉には吸虫から排泄されたと考えられる黒色異物が見られた。

Two big trematodes, provisionally identified as a hirudinellid, were found individually in the muscle of two juveniles (ca. 150 mm fork length) of Japanese amberjack, Seriola quinqueradiata Temminck and Schlegel, 1845, cultured in mid-May 2015 in coastal waters of Tosa Bay off Kochi Prefecture, Shikoku, western Japan. The trematodes were 7-15 mm long in fresh conditions. The juveniles were caught in the western North Pacific Ocean off Kochi Prefecture around 10 April 2015 and then cultured in net pens. The body surface of the infected juveniles was uneven in the affected area, and black substances, probably excreted by the trematodes, were found in the host’s muscle.