Abstract / Introduction / Summary:
An adult female specimen of Argulus coregoni Thorell, 1864 was collected from the body surface of ayu Plecoglossus altivelis altivelis (Temminck and Schlegel, 1846) at 295 m elevation in the middle reaches of the Ohmata River at Asukacho-kozaka in Kumano, Mie Prefecture, central Japan, on 13 August 2025. Prevalence and intensity of infection were as low as 1.2% (31 fish examined) and one, respectively. The specimen is characterized by eight plumose setae near the posterior margin of the first leg coxa and 69 and 72 supporting rods each in the marginal membranes of the first maxillae. The second leg coxa of this specimen does not bear any protuberance but has one plumose seta near the posterior margin. The Ohmata River represents a new locality record for A. coregoni.
