Establishment of Experimental Infection of Marine Philometrid Nematodes Using Surrogate Copepod Intermediate Host

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K05735
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 40030:Aquatic bioproduction science-related
• Research Institution: Meguro Parasitological Museum
• Principal Investigator: Ogawa Kazuo 公益財団法人目黒寄生虫館, その他部局等, 名誉館長 (20092174)
• Co-Investigator(Kenkyū-buntansha): 白樫 正 近畿大学, 水産研究所, 准教授 (70565936)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: ブリ筋肉線虫 / 代理宿主 / シオダマリミジンコ / 生活環 / フィロメトラ類

Outline of Final Research Achievements

We used the copepod Tigriopus japonicus as a surrogate host to experimentally complete the life cycle of Philometoides seriolae, a nematode infecting the skeletal muscle of Japanese amberjack Seriola quinqueradiata. P. seriolae developed to the third stage larvae which are infective to the final host, within the copepod fed with freshly hatched larvae. Eleven months after given infected copepods, two out of seven amberjacks were found infected with a mature female nematode in the skeletal muscle. It would take more than a year for P. seriolae females to produce and disseminate larvae, as those recovered from the experimental fish only contained developing eggs in the uterus. Most larvae retrieved from fully mature females had an exuvium, suggesting that they were already at the second stage. In addition, we found a hitherto undescribed male worm in the skeletal muscle of wild Japanese amberjack.

Free Research Field

魚病学

Academic Significance and Societal Importance of the Research Achievements

ブリ筋肉線虫は宿主のブリに対して強い害作用は示さず、人体寄生虫でもない。しかし体側筋に寄生している雌成虫は最大体長が50 cmにも達する大型寄生虫のため、目につきやすく、ブリの商品価値を落とす水産上重要な寄生虫である。一方、本線虫の生物学的知見はきわめて乏しく、生活環も解明されていない。本研究によってシオダマリミジンコを代理の中間宿主とすることで実験的にふ化幼生を成虫にまで発育させることに成功し、本線虫の生活環が回るのに少なくとも1年を要することが明らかになった。この実験系は本線虫のみならず、他のフィロメトラ科線虫の寄生生態解明の研究に有用な手段といえる