A Parasite Introduced from Mainland China Invades Parts of the Tone River System

Clarifying Its Life Cycle and Infection of Native Fish via Invasive Species

A collaborative research team from Toho University, the Japan Fisheries Research and Education Agency, Nihon University, the Global Environmental Forum, and the Museum Park Ibaraki Nature Museum has revealed that a newly introduced parasite is infecting native fish in the Tone River system. Their study also confirms that the golden mussel, an invasive species, acts as the infection source, while non-native fish such as bluegill and channel catfish help sustain the parasite’s life cycle.
This study was published in the Journal of Helminthology on January 20, 2025.

Fig. 1 Life cycle of the introduced trematode Dollfustrema invadens in Japan. Illustration: Iwata Sho, Makito Hayashi and Tsukasa Waki

Key Findings of the Study

A newly introduced bucephalid trematode, originating from Mainland China, infects native freshwater fish in the Tone River system, Japan.
Although previously reported in China, this parasite lacked a valid scientific name. It has now been described as Dollfustrema invadens, marking the second case of an introduced bucephalid trematode in the Tone River system, following Prosorhynchoides ozakii.
Dollfustrema invadens uses the invasive golden mussel (Limnoperna fortune) as its infection source. It parasitizes native freshwater fish, such as Tridentiger brevispinis and Tridentiger obscurus,, as well as non-native freshwater fish, including both domestically and internationally introduced species.
Yellow-colored parasites were observed in the fins and their bases of infected native fish. Notably, high parasite loads were found in infected individuals of the channel catfish (Ictalurus punctatus) and bluegill (Lepomis macrochirus), both of which are designated as invasive species. These findings suggest that these three invasive species play a crucial role in sustaining the life cycle of the parasite and facilitating its transmission to native fish.
This parasite is estimated to have been introduced into the Tone River system around 2020, though its exact introduction route remains unknown. To date, no cases of human infection have been reported.

Fig. 2 Dollfustrema invadens. A. adult. B. metacercaria. C. D. invadens infecting a fin of a host. Photographed by Sho Iwata, Yoshiki Saito and Makito Hayashi

Fig. 3 Golden mussels, the first intermediate host. A. golden mussels. B. uninfected mussel. C. infected mussel. Arrows indicate sporocysts. Photographed by Yoshiki Saito and Makito Hayashi

Journal:
Journal of Helminthology, January 20, 2025 issue

Title:
Lifecycle of an introduced Dollfustrema (Bucephalidae) trematode in the Tone River system, Japan

Authors:
Yoshiki Saito, Sho Iwata, Makito Hayashi, Masato Nitta, Takanori Ishikawa, Tomiji Hagiwara, Hiromi Ikezawa, Nobuhiro Mano, Tsukasa Waki

DOI No.
10.1017/S0022149X24000932

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