Abstract / Introduction / Summary:
A free-swimming ovigerous female of Argulus japonicus Thiele, 1900 was collected from a bucket of water which contained three live freshwater fishes caught by electrofishing in a small lake, Lake Shimo-Ezu (32º46′15″N, 130º45′06″E), Kumamoto City, Kyushu, western Japan on 4 July 2016. The fishes were individually identified as ayu Plecoglossus altivelis altivelis (Temminck and Schlegel, 1846) (Osmeriformes: Plecoglossidae), river higai gudgeon Sarcocheilichthys variegatus variegatus (Temminck and Schlegel, 1846) (Cypriniformes: Gobionidae), and spined sleeper Eleotris oxycephala Temminck and Schlegel, 1845 (Gobiiformes: Eleotridae). The collected female of A. japonicus was most likely detached from one of these fishes in a bucket of water. It is briefly described here and characterized by a single plumose seta on the posterior margin of the coxa of the first leg and about 50 supporting rods in the sucker membrane of the first maxilla. Lake Shimo-Ezu belongs to the Midori River system, and the present collection represents the second record for A. japonicus from this river system: the species was previously recorded from a rosy bitterling Rhodeus ocellatus (Kner, 1866) (Cypriniformes: Acheilognathidae) in an irrigation canal near the lake.
