Adults of both sexes of Argulus coregoni Thorell, 1864 were collected from the body surface of bester a hybrid of beluga Huso huso (Linnaeus, 1758) × sterlet sturgeon H. ruthenus (Linnaeus, 1758), common carp Cyprinus carpio Linnaeus, 1758, and rainbow trout Oncorhynchus mykiss (Walbaum, 1792) at a governmental fish hatchery in Hyogo Prefecture, central Japan. There was a marked difference in the number of A. coregoni per infected fish between these host species: rainbow trout were more heavily infected (151–224 individuals) than bester and common carp (25 and seven individuals, respectively). The parasite is described and characterized by possessing four to six plumose setae near the posterior margin of the coxa of the first leg, 59–66 supporting rods in the marginal membrane of the first maxilla, and two protrusions adorned with small spines and a digitiform projection on the ventro- and dorsoposterior margins, respectively, of the coxa of the male second leg. The collection of A. coregoni from bester represents a new host and the second record from sturgeons (the family Acipenseridae) worldwide. Common carp is reported as a host of this parasite for the first time in Japan.
Nagasawa et al. (Wed,) studied this question.