Hirotaka Katahira

Heliconema anguillae Yamaguti, 1935, a physalopterid nematode found in Japanese eels: taxonomic resurrection with a note on the third-stage larva from intertidal crabs in western Japan

A parasitic nematode from the stomach of Japanese eel Anguilla japonica Temminck et Schlegel in western Japan, previously identified as Heliconema longissimum (Ortlepp, 1922), was morphologically re-examined and compared with the previous descriptions. In addition, the third-stage larva of this nematode is described, based on the specimens of encapsuled larvae found in musculature of two crabs, Hemigrapsus sp. and Perisesarma bidens (De Haan), caught from the upper-intertidal zone of the same locality. As a result of the morphological observation, seven pairs of postcloacal papillae in adult males are confirmed. This matches with the character of H. longissimum, but the shape of the fifth postcloacal papillae differs between the present material and H. longissimum; the former possesses pedunculate papillae in the fifth pair whereas the latter has sessile papillae. Since the pedunculate papillae can be found in the original description and the syntype specimens of H. anguillae Yamaguti, 1935 that has been synonymised with H. longissimum, we thus here resurrect H. anguillae as an accepted species. For the life-cycle of the present nematode, littoral crabs, including the two infected species, are likely to be the source of infections for Japanese eels, acting as intermediate hosts.

Influence of host habitat on the occurrence of gill monogeneans Pseudodactylogyrus spp. on wild Japanese eels Anguilla japonica

With technological improvements in otolith microchemical analysis, the flexible use of habitat from coastal marine to fresh waters has been discovered in Japanese eels Anguilla japonica. We examined the occurrence of 3 congeneric gill monogeneans-Pseudodactylogyrus anguillae, P. bini, and P. kamegaii-on wild Japanese eels, in relation to the hosts flexibility. From April 2008 to October 2009, 114 eels were collected from a brackish-water cove and 2 rivers flowing into the cove in Ehime Prefecture, western Japan. Based on otolith microchemical analysis, the eels were discriminated according to the following 4 types of habitat use: freshwater residents (Type I), individuals utilizing low-salinity habitats (Type II), downstream habitat-shifters (Type III), and cove residents (Type IV). P. anguillae occurred mainly on Type I and II eels, while P. bini was primarily found on Type I eels. In contrast, P. kamegaii occurred mainly on Type III and IV eels. Thus, we conclude that species composition and infection levels of Pseudodactylogyrus spp. clearly differed with habitat-use patterns of Japanese eels. Also, since P. anguillae was scarcely found on either Type III or IV eels, this study suggests that previous identifications of monogeneans collected from European brackish-water localities as P. anguillae may require verification.

Temporal change in the distribution and composition of native, introduced, and hybrid charrs in northern Japan

Introductions of non-native species have caused various negative impacts on native species and their ecosystems. Hybridization is particularly prevalent among closely related species, and can result in displacement, hybrid swarms, or the disruption of a locally adapted gene complex. Although hybridization between native and non-native species is widespread, long-term monitoring is generally lacking. In this study, we compared the distribution and composition of native white-spotted charr (Salvelinus leucomaenis), introduced brook trout (Salvelinus fontinalis), and their hybrids in the upper Sorachi River, Hokkaido, Japan in 2003 and 2013, especially focusing on (1) if genetic introgression or hybrid swarm has occurred and (2) if white-spotted charr have declined, since a previous study indicated a potentially harmful asymmetric hybridization with the mothers of hybrids being all white-spotted charr. We found no evidence of decline in native white-spotted charr; rather, the distribution and abundance of introduced brook trout had decreased. Of 142 charr (i.e., genus Salvelinus) collected, 18 individuals (13%) were hybrids but no unidirectional hybridization was observed. However, most of the hybrids were post-F1 individuals with biased mating with white-spotted charr. The effects of long-term introgression on native white-spotted charr should be further examined.

Euryphorus brachypterus (Copepoda: Caligidae) on wild pacific bluefin tuna from the Tsugaru Strait, northern Japan.

Parasitic copepods infecting large scombrid fishes have been known for a long time because their hosts are economically important. Most studies, however, have focused on their morphology or their infection status in aquaculture from pathological viewpoints, and very few quantitative surveys have been conducted under conditions in the wild. This study therefore investigated the prevalence of Euryphorus brachypterus (Caligidae) in wild Pacific bluefin tuna (PBF). Results of sampling from August to September 2014 at the western area of the Tsugaru Strait, Japan showed that 13.2% of the PBF individuals (n = 1978) were infected with this copepod. The prevalence of infections was highest in larger fish but varied among landing dates, which were classified into three clusters and in all smaller fish, the prevalence of infections was zero. This suggests that E. brachypterus mainly uses the larger PBF, which becomes sources of further infections in other seas, and that at least two host populations with different infection statuses at the strait.

Human infection by acanthocephalan parasites belonging to the genus Corynosoma found from small bowel endoscopy.

A 73-year-old man with a suspected ileus in January 2013 and subsequently suffered melena in February 2014 was endoscopically examined. As a result of the examinations, unidentified species of Corynosoma sp. and Corynosoma villosum were recovered from the small intestine, further endoscopic diagnosis suggested relevance between abdominal pain and the present infections in the small intestine. The recovered worms were composed of gravid females with developed eggs, suggesting that these parasites can survive for a long time in the intestine after infection. In this case, the short interval between infections appears to be due to the individuals eating habits which consist of regularly consuming uncooked seafood.

Host characteristics and infection level of an intestinal parasite Corynosoma strumosum (Acanthocephala) in the Kuril harbor seal of Erimo Cape, Hokkaido, Japan

The Kuril harbor seal around Hokkaido is presently recovering from a resource crisis while conflicts with local fisheries have become a concern. However, its feeding habits, which are fundamental information for taking proper preventive measures, are still poorly understood. We thus examined the infection status of a trophically-transmitted parasite, Corynosoma strumosum in the seals of Erimo Cape, to assess the hosts feeding habits with a practical view of the parasite as a biological indicator. A total of 2802 worms were found from 20 male and 20 female by-caught animals in salmon set nets within local fisheries during August to November 2014. The parasite abundance was explained mainly by the hosts developmental stage and intestinal length while weakly affected by gender and body size, through an estimation of generalized linear models combined with hierarchical partitioning. Considering the past records that demersal fishes are the probable main sources of infection, the infection level may owe to individual host differences regarding these sources and/or feeding grounds with relating the host characteristics. This supports that the resource management of Kuril harbor seals requires careful consideration of the individual differences in feeding behavior.

A revised and updated checklist of the parasites of eels (Anguilla spp.) (Anguilliformes: Anguillidae) in Japan (1915-2017)

1915-2017年の103年間に出版された文献に基づき，日本産ウナギ属魚類3種（ニホンウナギ Anguilla japonica，オオウナギ Anguilla marmorata，ヨーロッパウナギ Anguilla anguilla）と日本に輸入されたAnguilla australis の寄生虫に関する情報を2つのリスト（寄生虫－宿主リスト，宿主－寄生虫リスト）に整理して目録を作成した。宿主のニホンウナギとオオウナギは在来種であり，ヨーロッパウナギはシラスウナギとして輸入され養殖された個体，Anguilla australis はオーストラリアから輸入された個体である。本目録は2007年に出版した同名目録の追補改定版である。本目録には，54名義種の寄生虫（繊毛虫類6種，微胞子虫類1種，ミクソゾア類6種，吸虫類12種，単生類8種，条虫類3種，線虫類7種，鉤頭虫類6種，ヒル類3種，二枚貝類1種，カイアシ類1種）に加えて，学名がまだ決定していない寄生虫の情報が含まれる。寄生虫－宿主リストでは，各寄生虫は高位分類群ごとに配列され，最新の学名，シノニム，寄生部位，地理的分布および報告者の情報が示されている。上記54名義種のうち，ニホンウナギから50種，オオウナギから6種，ヨーロッパウナギから9種，Anguilla australis から1種の寄生虫が報告されていた。単生類のGyrodactylus anguillae，Gyrodactylus nipponensisおよびPseudodactylorgyrus mundayi，条虫類のBothriocephalus claviceps，線虫類のRaphidascaris acus は海外から持ち込まれたと推察されており，残りの49名義種が日本にもともと分布するものである。ニホンウナギから報告された寄生虫のうち，9名義種（Lecithochrium musculus, Proctotrematoides pisodontophidis, Tubulovesicula anguillae［ 吸虫類］, Gyrodactylus nipponensis, Pseudodactylogyrus kamegaii［ 単生類］, Nybelinia angullicola［ 条虫類］, Cucullanus filiformis, Heliconema anguillae［ 線虫類］, Limnotrachelobdella okae［ ヒル類］）は海産または汽水産であり，海ウナギや河口ウナギとして知られる個体がそれら寄生虫の宿主になっていると考えられる。

A synopsis of the parasites from cyprinid fishes of the genus Tribolodon in Japan: A 2016 update and supplement

1908年以降に出版された文献に基づき，2013年に日本産ウグイ属魚類4種（ウグイTribolodon hakonensis，エゾウグイT. sachalinensis，マルタT. brandtii，ウケクチウグイT. nakamuraii）の寄生虫に関する情報を整理した目録を出版した。今回，その後に出版された情報と2013年の目録に収録されなかった情報を加えて，この目録を補足した。宿主に関して，従来のマルタは2015年に2亜種（マルタT. brandtii maruta，ジュウサンウグイT. brandtii brandtii）に分けられたので，各亜種における寄生虫の情報を整理した。本目録では，新たに追加した6種の寄生虫（吸虫類2種，単生類1種，線虫類2種，鉤頭虫類1種）を含む15種の寄生虫に関する情報を寄生虫－宿主リストに整理して示した。今回の作業により，1908～2015年の108年間にわが国のウグイ属魚類からは48名義種の寄生虫（繊毛虫類2種，ミクソゾア類1種，吸虫類20種，単生類1種，条虫類3種，線虫類9種，鉤頭動物3種，ヒル類1種，軟体動物1種，カイアシ類6種，ワラジムシ類1種）が報告されていたことが分かった。種まで同定された寄生虫の種数を魚種別に示すと，ウグイから48種，エゾウグイから8種，マルタから4種，ジュウサングイから3種で，ウグイから最も多くの寄生虫が報告されていた。ウケクチウグイからは1未同定種のみが記録されていた。

A synopsis of the parasites from cyprinid fishes of the genus Tribolodon in Japan (1908-2013)

1908～2013年の106年間に出版された文献に基づき,日本産ウグイ属魚類4種(ウグイTribolodon hakonensis,エゾウグイTribolodon sachalinensis,マルタTribolodon brandtii,ウケクチウグイTribolodon nakamuraii)の寄生虫に関する情報を2つのリスト(寄生虫-宿主リスト,宿主-寄生虫リスト)に整理して目録を作成した。寄生虫-宿主リストでは,44種の寄生虫と学名がまだ決定していない寄生虫の情報を,下記の高位分類群ごとに配列し,最新の学名,シノニム,寄生部位,地理的分布および報告者の情報を示した:繊毛虫類(2種:種小名まで決定している種数),ミクソゾア類(1種),吸虫類(18種),単生類(0種),条虫類(3種),線虫類(9種),鉤頭動物(2種),ヒル類(1種),軟体動物(1種),エラオ類(0種),カイアシ類(6種),ワラジムシ類(1種)。宿主-寄生虫リストでは,ウグイ属魚類4種の種ごとに,各寄生虫の学名と地理的分布を示した。魚種ごとに寄生虫の種数を示すと,ウグイ43種,エゾウグイ7種,マルタ6種,ウケクチウグイ1種で,ウグイから報告されている寄生虫数が最も多かった。