Abstract / Introduction / Summary:
Argulus japonicus Thiele, 1900 was collected in late September 2019 from the body surface of both common carp and koi carp, Cyprinus carpio Linnaeus, 1758 (Cyprinidae), reared in different raceways at the Ishikawa Prefecture Fisheries Research Center in Kaga, Ishikawa Prefecture, central Japan. This represents the first record of A. japonicus from Ishikawa Prefecture. The species was found near the base of ventral fins. The specimens of A. japonicus from the common carp are mostly small individuals (1–4 mm in body length), which were produced from the first generation of the species appearing in spring and summer 2019. The koi carp were treated with trichlorfon in early June 2019 and the specimens of A. japonicus from the koi carp were mostly survivors from the first generation.