Distribution of Fish Parasites Argulus japonicus and Argulus coregoni (Crustacea: Branchiura: Argulidae) in the Lake Biwa Basin, Central Japan

Abstract

Argulus japonicus Thiele, 1900 and Argulus coregoni Thorell, 1864 are ectoparasites of freshwater fishes and are known to occur in Lake Biwa and its adjacent inland waters in Shiga Prefecture, central Japan. Since these parasites are not common in the wild in Japan, this study examined the specimens loaned from the Lake Biwa Museum and those previously reported from this prefecture in order to clarify their distributional patterns. The specimens of A. japonicus were obtained in Lake Biwa and a nearby pond, whereas those of A. coregoni were almost exclusively collected in the large rivers flowing into the lake and most of them were from mountain streams which are higher-elevated than the lake or pond. These results indicate both A. japonicus and A. coregoni has its own habitat preference dependent on different environmental conditions: A. japonicus inhabits the still or slow-flowing waters, but A. coregoni occurs in the running waters, especially in the colder, well oxygenated mountain streams.