Studies on the origin of the monogenean Neoheterobothrium hirame, the causative agent of parasitic anemia of Japanese flounder

20世纪90年代中期，在日本附近海域突然出现单殖吸虫新异博氏菌，引起野生比目鱼寄生性贫血。寄生虫对日本比目鱼野生种群的影响是非常令人担忧的。为了阐明这种寄生虫的来源，本研究采集了分布于美国大西洋水域的南方比目鱼和分布于智利的大眼比目鱼Hippoglossina macps以及分布于美国大西洋水域的夏季比目鱼P.dentatus中的几种新异博氏菌，并与N.hirame进行了比较。在18S rRNA区、ITS1-5.8S rRNA-ITS2区和线虫COI区的形态和序列上与N.hirame一致。根据前人报道的南方比目鱼感染拟步甲虫的报道，认为该鱼可能与拟步甲鱼同义。本研究在形态和分子生物学两个方面对两种牙鲆标本进行了比较研究。结果表明，这两个种属于不同的种，但由于本研究使用的标本数量较少，因此还需要进一步的研究才能得出结论。采集自大叶海棠的新异博氏菌在形态和ITS1和28S rRNA的序列上与海南新种和拟新种有很大的不同。结果表明，该属与这两个种不同。

The monogenean Neoheterobothrium hirame suddenly appeared in Japanese flounder in the waters adjacent to Japan in mid-1990s, causing parasitic anemia in wild flounder. The impact of the parasite on the wild stocks of Japanese flounder is much apprehended. In this study, in order to clarify the origin of the parasite, several species of genus Neoheterobothrium were collected from southern flounder, Paralichthys lethostigma, and summer flounder, P.dentatus, distributed in the Atlantic waters of USA and bigeye flounder, Hippoglossina macrops distributed in Chile and compared with N.hirame.Worms collected from southern flounder were virtually identical to N.hirame in the morphology and sequences of 18S rRNA region, ITS1-5.8S rRNA- ITS2 region, and mitcondrial COI region. From the results, it is concluded that N.hirame recently invaded Japanese waters and settled there using Japanese founder as its host.According to a previous report that southern flounder was infected with N.affine originally reported from summer flounder, there was a possibility that N. hirame was synonymous to N.affine. In this study, two specimens of N.affine were obtained from summer flounder and compared with N.himame morphologically and molecular biologically. The present results indicate that the two species belong to different species, although further studies are needed for reaching a conclusion because of the small number of the specimens used in this study.Neoheterobothrium chilensis collected fom H.macrops was greatly different from N.hirame and N.affine in the morphology and the sequences of ITS1 and 28S rRNA resions. The results suggest that N.chilensis is not congeneric to the two species.