Species Diversity 20: 73–81 25 May 2015 DOI: 10.12782/sd.20.1.073 Rediscovery of a Fish Acanthocephalan, Acanthocephalus minor (Echinorhynchida: Echinorhynchidae), in the Lake Biwa Basin, Central Japan, with a Review of the Fish Acanthocephalan Fauna of the Basin Kazuya Nagasawa1,2 and Masato Nitta1 1 Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8528, Japan E-mail: [email protected] (KN); [email protected] (MN) 2 Corresponding author (Received 28 January 2015; Accepted 30 April 2015) Specimens of the echinorhynchid acanthocephalan Acanthocephalus minor Yamaguti, 1935 were collected from the rectum of a dark sleeper, Odontobutis obscura (Temminck and Schlegel, 1845), in an irrigation canal near Lake Biwa, Shiga Prefecture, west-central Japan. This represents a rediscovery of A. minor in the Lake Biwa basin after a gap of nearly 80 years. It appears not to be distributed in Lake Biwa proper, but to occur rarely in rivers and irrigation canals of a limited coastal area around the lake. To date, 10 nominal species of acanthocephalan in four families and three orders have been re- ported from fish in the Lake Biwa basin. Among these, striking morphological similarities between Acanthocephalus aculea- tus Van Cleave, 1931 and its congener A. opsariichthydis Yamaguti, 1935 are noted. It is furthermore suggested that A. gotoi Van Cleave, 1925 could not maintain its population after the basin’s wild population of its major host, Anguilla japonica Temminck and Schlegel, 1846, disappeared in the mid-1960s. Key Words: Acanthocephalus minor, Acanthocephala, Odontobutis obscura, fish parasite, faunistic review, Lake Biwa basin, Japan. rigation canal near the Ado River, one of the rivers flow- Introduction ing into Lake Biwa. Here we report on this find which rep- resents a rediscovery of the species in the Lake Biwa basin Lake Biwa is located in west-central Honshu, being the after a gap of nearly 80 years. We also take this opportunity largest (670 km2) and oldest (over four million years old) to review the fish acanthocephalan fauna of the Lake Biwa lake in Japan (Horie 1984). The fauna of this lake and its basin based on the literature published between 1918 and watershed has been intensively studied and includes many 2014. endemic species (Timoshkin et al. 2011; Kawanabe et al. 2012). The acanthocephalan fauna of fish in the Lake Biwa basin is also well studied: to date, 10 nominal species in Materials and Methods four families and three orders have been reported (Table 1). Among these species, the extent of occurrence of Acan- One specimen of O. obscura was collected using a hand thocephalus minor Yamaguti, 1935 in Lake Biwa and the net on 14 July 2014 in an irrigation canal (35°19′54″N, lake’s drainage basin remains poorly understood. This spe- 136°2′44″E) along the lower reaches of the Ado River at cies has not been reported since 1936, when it was collected Adogawacho-Kawashima, Takashima city, Shiga Prefec- from the dark sleeper Odontobutis obscura (Temminck and ture, Honshu, west-central Japan. The fish was transported Schlegel, 1845) caught in Lake Biwa (Fukui and Morisita alive to the laboratory at Hiroshima University, Higashi- 1936). Amin (2005) and Amin et al. (2007) examined the Hiroshima city, Hiroshima Prefecture, where it was mea- acanthocephalans isolated from more than 500 inspected sured for standard length (SL) in millimeters and examined fish belonging to 30 species in 12 families collected in Lake for metazoan parasites. Of the 10 acanthocephalans found, Biwa and its tributaries between 1997 and 2002 as part of a eight individuals were flattened between slides and cover large-scale survey involving 62 fish species in total from the glasses with slight pressure, fixed in 70% ethanol, stained region, but did not recover A. minor from them; moreover, in Heidenhain’s iron hematoxylin, dehydrated through a they did not mention A. minor in their discussion of the fish graded ethanol series, cleared in xylene, and mounted in acanthocephalan fauna of the Lake Biwa basin. Canada balsam, while the remaining two individuals were Recently, we found 10 individuals of A. minor infecting preserved in 100% ethanol for future molecular study. The the rectum of a specimen of O. obscura collected in an ir- stained specimens were used for measurements and counts. © 2015 The Japanese Society of Systematic Zoology 74 Table 1. Acanathocephalans reported from fish in the Lake Biwa basin, Shiga Prefecture, Japan. Order Family Genus and species Fish species (family) Reference Gyracanthocephala Quadrigyridae Acanthosentis (Acanthosentis) alternatspinus Rhodeus ocellatus ocellatus (Cyprinidae) Amin (2005), Amin et al. (2007), Nagasawa Amin, 2005 and Grygier (2011, as Neoechinorhynchus sp.)a Acanthosentis (Acanthosentis) parareceptacilis Cobitis biwae (Cobitidae) Amin (2005), Amin et al. (2007) Amin, 2005 Echinorhynchida Echinorhynchidae Acanthocephalus aculeatus Van Cleave, 1931b Plecoglossus altivelis altivelis (as P. altiv eli s ) (Plecoglossidae) Kataoka and Momma (1933, 1934) Acanthocephalus gotoi Van Cleave, 1925 Gymnogobius urotaenia (as Chaenogobius annularis urotaenia) (Gobiidae) Yamaguti (1939) Acanthocephalus minor Yamaguti, 1935 Odontobutis obscura (Odontobutidae) Fukui and Morisita (1936), this study Acanthocephalus opsariichthydis Yamaguti, 1935 Cobitis biwae (Cobitidae); Gnathopogon elongatus elongatus, Hemibarbus barbus, Hemibarbus Yamaguti (1935)c, Ito (1959, as Acantho- labeo, Hemibarbus longirostris, Opsariichthys platypus (as Zacco platypus), Phoxinus oxycephalus cepharus [sic] sp.), Nakajima et al. (1975), jouyi (as Rhynchocypris o. jouyi), Pseudogobio esocinus esocinus, Pseudorasbora parva, Pungtungia Nakajima and Egusa (1975a), Amin et al. herzi (Cyprinidae); Gasterosteus aculeatus subsp. 2 (as G. microcephalus) (Gasterosteidae); (2007) Oncorhynchus masou ishikawae, Oncorhynchus mykiss (as Salmo gairdnerii irideus), Oncorhynchus sp. (Salmonidae); Silurus asotus (as Parasilurus asotus) (Siluridae) Echinorhynchus cotti Yamaguti, 1935d Anguilla japonica (Anguillidae); Tachysurus nudiceps (as Pelteobagrus nudiceps) (Bagridae); Kataoka and Momma (1933, 1934, as e Channa argus (Channidae); Cottus pollux , Cottus reinii (Cottidae); Cyprinus carpio, Gnathopogon Echinorhynchus sp.), Yamaguti (1935, 1939), M.Nitta and K. Nagasawa caerulescens, Hemibarbus barbus, Opsariicthys uncirostris uncirostris, Sarcocheilichthys variegatus Fukui and Morisita (1937), Shimazu (1999), microoculus (Cyprinidae); Gymnogobius isaza, Rhinogobius sp., Tridentiger brevispinis (Gobiidae); Amin et al.(2007) Hypomesus nipponensis (as H. transpacificus nipponensis) (Osmeridae); Plecoglossus altivelis altivelis (as P. altivelis) (Plecoglossidae); Silurus biwaensis (Siluridae) Echinorhynchus parasiluri Fukui, 1929 Silrus asotus (as Parasilurus asotus) (Siluridae) Fukui (1929) Echinorhynchus sp. Anguilla japonica (Anguillidae); Cyprinus carpio (Cyprinidae) Kawamura (1918) Illiosentidae Pseudorhadinorhynchus samegaiensis Nakajima Anguilla japonica (Anguillidae); Hemibarbus barbus, Opsariichthys uncirostris uncirostris, Nakajima et al. (1975), Nakajima and Egusa and Egusa, 1975 Tribolodon hakonensis (Cyprinidae); Gasterosteus aculeatus subsp. 2 (as G. microcephalus) (1975b), Grygier (2004), Amin et al. (2007), (Gasterosteidae); Gymnogobius isaza (Gobiidae); Oncorhynchus mykiss (as Salmo gairdnerii Nagasawa and Grygier (2011) irideus), Oncorhynchus masou ishikawae (Salmonidae) Polymorphida Polymorphidae Southwellina hispida (Van Cleave, 1925) Micropterus salmoides (Centrarchidae); Lefua echigonia (Cobitidae); Cottus reinii (Cottidae); Amin et al. (2007), Nagasawa and Grygier Candidia sieboldii (as Zacco sieboldii), Tanakia lanceolata, Tanakia limbata (Cyprinidae); (2011) Coreoperca kawamebari (Sinipercidae) Unidentified Tachysurus nudiceps (as Fluvidraco nudiceps) (Bagridae); Misgurnus anguillicaudatus Fujita (1927), Amin et al. (2007) Acanthocephala (Cobitidae); Candidia platypus (as Zacco platypus), Gnathopogon caerulescens (as Leucogobio mayedae), Sarcocheilichthys sp. (as S. variegatus)f, Opsariichthys uncirostris uncirostris (as Opsarichthys [sic] uncirostris) (Cyprinidae); Gymnogobius isaza (as Chloea castanea) (Gobiidae); Salvelinus leucomaenis japonicus (as S. pluvius) (Salmonidae) aThe manuscript of Nagasawa and Grygier’s report, including information on Neoechinorhynchus sp., was first prepared in 1998 but was not published until 2011. This acanthocephalan was described as Acanthosentis (Acanthosentis) alternatspinus by Amin (2005). bAcanthocephalus aculeatus had been synonymized with Acanthocephalus echigoensis by Harada (1935), but Petrochenko (1956) and Yamaguti (1963) listed the former spe- cies as valid. cYamaguti (1935) described Acanthocephalus opsariichthydis using specimens from seven species of fish (P. curta, C. carpio, H. barbus, O. uncirostris uncirostris, O. platypus, P. parva, and P. asotus) caught in three localities, Lake Biwa (Shiga Prefecture), Lake Ogura (Kyoto Prefecture), and the Yodo River (Osaka Prefecture), all of which belong to the same river system, but he did not differentiate these localities from each other in his description of the species. However, according to Amin et al. (2007), only P. parva was collected in Lake Biwa. Thus, this fish is cited here from Yamaguti (1935).d Golvan (1969) described a new species, Echi- norhynchus oblitus, by citing Kataoka and Momma (1937), but Nagasawa et al. (2007) relegated E. oblitus to a junior