Abstract / Introduction / Summary:
Argulus coregoni Thorell, 1864 was collected from the body surface of ayu, Plecoglossus altivelis altivelis (Temminck and Schlegel, 1846), in the Asuwa River, a tributary of the Hino River, one of the major Kuzuryu River tributaries, in Fukui Prefecture, central Japan in July 2022. Four (14.8%) of the 27 ayu examined were each infected by a single female of A. coregoni. Regarding this species from Fukui Prefecture, there is only a short report published in 1964 about its occurrence on masu salmon, Oncorhynchus masou masou (Brevoort, 1856), in an unknown stream. The present collection represents the second record of A. coregoni from Fukui Prefecture and its first record from ayu in the prefecture.