<i>Argulus coregoni</i> (Crustacea: Branchiura: Argulidae) Parasitic on a Dark Chub <i>Nipponocypris temminckii</i> (Cypriniformes: Xenocyprididae) in a Stream, Central Japan, with a List of Its Known Hosts in East Asia

Abstract

An adult male specimen of Argulus coregoni Thorell, 1864 was collected from the body surface of a dark chub Nipponocypris temminckii (Temminck and Schlegel, 1846) at 15 m elevation in a small stream in central Japan. The specimen collected is herein described and corresponds well to the descriptions of A. coregoni from European and East Asian countries. This represents the first record for A. coregoni from a fish of the cypriniform family Xenocyprididae in Japan, where this species usually occurs in higher-elevation mountain streams and infects fishes in two salmoniform families (Salmonidae and Plecoglossidae). The male of A. coregoni is characterized by the presence of two protrusions adorned with small spines and a digitiform projection on the ventro-and dorsoposterior margins, respectively, of the coxa of the second leg and the abdominal lobes have pointed posterior ends. In addition to these morphological characters, the number of plumose setae on the posterior margin of the coxa of the first leg and the number of supporting rods in the sucker membrane of the first maxilla are useful for distinguishing A. coregoni from a morphologically similar congeneric species, A. japonicus Thiele, 1900, which parasitizes cypriniform fishes in Japan. Based on literature published between 1936 and 2023, this paper also gives a list of the hosts of A. coregoni reported from East Asia, including the Russian Far East, China, Malaysia, and Japan. To date, 31 species and three subspecies of fishes are known as hosts of this parasite in East Asia, and these fishes belong to 16 families and eight orders, which indicates that the species is not a host-specific parasite. In order to further understand the host utilization of A. coregoni in Japan, it is necessary to study its occurrence on fishes of various taxonomic groups in rivers of different lengths.