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，在日本邻近海域的日本比目鱼中突然出现了一种单系新异芽孢菌，引起了野生比目鱼的寄生性贫血。这种寄生虫对野生日本比目鱼种群的影响是非常令人担忧的。为了明确该寄生虫的起源，本研究从美国大西洋海域的南部比目鱼（parichthys lethostigma）、夏季比目鱼（p.d dentatus）和智利海域的大眼比目鱼（Hippoglossina macrops）中采集了几种新异虫属（Neoheterobothrium），并与hirame进行了比较。结果表明，从南部比目鱼中采集的线虫在形态和18S rRNA区、its1 - 58s rRNA- ITS2区、和中部COI区。根据研究结果，可以得出平名是近期入侵日本海域并以日本创建者为宿主定居的结论。根据先前的报道，南方比目鱼感染了原报道自夏季比目鱼的N.affine，有可能N. hirame与N.affine同义。本研究从夏比目鱼身上采集了2个仿射体标本，并与夏比目鱼进行了形态和分子生物学的比较。目前的研究结果表明，这两个物种属于不同的物种，但由于本研究使用的标本数量较少，需要进一步的研究才能得出结论。在形态、ITS1和28S rRNA序列分析上，大鼠新异芽孢菌与hirame新异芽孢菌和仿射新异芽孢菌存在较大差异。结果表明，智利北蝽与这两个物种不具有同属关系。

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.