Abstract
A hitherto unknown leech has been found infected on crucian carps Carassius auratus langsdorfii and C. cuvieri in the Yodo River system since 2000. From the morphological characteristics, the parasite was identified as Limnotrachelobdella sinensis (Piscicolidae). Parasitological surveys on 16 species of wild fish (n = 1,661) caught from October 2000 until March 2005 revealed that the leech was found only from moribund crucian carps. It has a one-year life cycle, in which the leeches were found from December until April next year. Because of its recovery only from moribund fish, large size (up to 4.9 cm in body length) and frequent heavy infection (highest number of parasites/fish: 62), its pathological effects on the hosts were suspected. However, such effects were not made clear except for the hemorrhages and erosion on and near the inner surface of operculum, the attachment site. This is the first record of this parasite from Japanese waters. Since the geographical distribution of the leech in Japan is still restricted to the Yodo River system, the potential risk of spread of the parasite to other water bodies is discussed.
