November 18, 2022
November 18, 2022

Exotic parasite infection in native fishes in parts of the Tone River system

Life history of infection of native fishes from the invasive alien species like the golden mussel Limnoperna fortune has been revealed in this study.

A research group led by Toho University has revealed that Prosorhynchoides ozakii, a non-native species of parasite, has been infecting native fishes and other aquatic organisms in the Tone River system. The source of infection was the specified invasive alien species, namely the golden mussel Limnoperna fortune, and it was found that non-native fishes such as the Rhodeus ocellatus ocellatus and channel catfish (a specified alien species) also contributed to the life history of this trematode. This study was published in the online edition of Diseases of Aquatic Organisms on November 17, 2022

Dr. Tsukasa Waki
Key Points:
  • Prosorhynchoides ozakii (Trematoda: Budephalidae), is a non-native species of parasite of the continental origin, with no reports of parasitism in humans. This species was already known to have invaded the Yodogawa River system along with the Specified Invasive Alien Species, the golden mussel Limnoperna fortunei, but the status of its invasion into other water systems is unknown. In this study, the research group found that this parasite has also invaded the Tone River system, far from the Yodogawa River system.

  • In the Tone River system, the parasite was found to infect the golden mussel Limnoperna fortune, which in turn infects native fishes, such as Tribolodon hakonensis, as well as non-native freshwater fishes of foreign and domestic origin. The main parasite sites of infected fish were the fins and their bases, and bleeding symptoms were also observed at the parasite sites of severely infected fish. When these infected fishes are consumed by channel catfish (a specified invasive species) or catfish, the Trematoda become adults in the host’s intestines. The eggs laid by the adults are released into the water along with the catfishes’ feces, again infecting the mussel. Thus, it was found that the non-native species of parasite, Prosorhynchoides ozakii was using many non-native species of fishes of the Tone River system as a host. In this context, this parasitic infection spreads to native fishes, which continue to show disease potential.

  • Since the Yodogawa River system and the Tone River system are separated by land, the invasion of this Trematoda into the Tone River system was thought to be anthropogenic, but the specific route of transfer remains unknown.

Fig. 1 Life cycle of the invasive parasite Prosorhynchoides ozakii, in Tone River system, Japan.

Fig. 2 The golden mussels and sporocysts of the invasive parasite Prosorhynchoides ozakii. A. The golden mussels in Tone River system. B. Sporocysts of Prosorhynchoides ozakii detected in the golden mussels. C. Uninfected mussel. D. Infected mussel.

Diseases of Aquatic Organisms: Online Edition November 17, 2022 issue

Invasion of the fish parasite Prosorhynchoides ozakii (Trematoda:Bucephalidae) into Lake Kasumigaura and the surrounding rivers of eastern Japan

Makito Hayashi, Yoshihiko Sano, Takanori Ishikawa, Tomiji Hagiwara, Mizuki Sasaki, Minoru Nakao, Misako Urabe, Tsukasa Waki



@ Toho University