Host and seasonal distribution of fish acanthocephalans from the Lake Biwa basin, Japan

Six species of acanthocephalans were collected from 30 of 62 surveyed species of fish in Lake Biwa, the most ancient lake in Japan, and from various water bodies in the lake's drainage basin including the Seta and Daido Rivers. The 3 most common species were Acanthocephalus opsariichthydis Yamaguti, 1935 (8 new host records), Echinorhynchus cotti Yamaguti, 1935 (7 new host records), and Pseudorhadinorhynchus samegaiensis Nakajima and Egusa, 1975 (7 new host records; perhaps endemic to Lake Biwa and its basin). The latter 2 species were found only in the spring. Specimens of both species were also found in Gymnogobius isaza (Tanaka, 1916) in the autumn. Gravid females of all 3 species were found in the spring. Developed cystacanths of Southwellina hispida (Van Cleave, 1925) Witenberg, 1932 were also collected (5 new host records). Anatomical similarities between these species and the original descriptions are clearly evident, but differences in certain key characteristics are noted. Two recently described species of Acanthogyrus (Acanthosentis) Verma and Datta, 1929, Acanthogyrus (Acanthosentis) alternatspinus Amin, 2005, and Acanthogyrus (Acanthosentis) parareceptaclis Amin, 2005 were also first collected in the course of this survey. Three species previously recorded in the 1920s and 1930s from Lake Biwa were not found in the present survey: Acanthocephalus aculeatus Van Cleave, 1931, Acanthocephalus gotoi Van Cleave, 1925, and Echinorhynchus parasiluri Fukui, 1929.