Argulus coregoni Thorell, 1864 was found to parasitize the body surface of Ayu, Plecoglossus altivelis altivelis (Temminck and Schlegel, 1846), in the middle reaches of the Ôuchiyama River, a tributary of the Miya River, Mie Prefecture, central Japan. This represents the second record of A. coregoni from the prefecture. Based on this and other studies in Japan, Ayu is regarded as an important riverine host of A. coregoni, and Ayu and salmonids are considered to serve as the hosts for A. coregoni in the middle and upper reaches of rivers, respectively.

三重県大内山川産アユに寄生していたチョウモドキと 宿主である河川アユの重要性に関する考察(長澤和也・森川学)