Foreign parasites penetrate Japan’s waterways

The newly identified parasites from mainland China have established themselves in Japan’s tone river system, using complex networks of local and invasive species to complete their life cycle, the researchers said. Their findings show how introduced species carry hitchhiking parasites, ultimately affecting native wildlife.

A collaborative research team from Toho University, Japan Fisheries Research and Education Bureau, Nihon University, Global Environment Forum and Museum Park Ibaraki Nature Museum, identified the parasite as a new species and named it Dollfustrema invasion In their research, it was published in the Journal of Worms on January 20, 2025.

While studying fish and mussels collected between 2021 and 2023, researchers found unique yellow parasites in the fin and fin alkalis of several species of fish. The parasite belongs to a group called Bucephalid Trematodes and appears to have entered Japan’s ecosystem around 2020, although its exact introduction route is unclear.

“We found that gold mussels are an invasive species that act as a source of infection,” explained lead researcher Yoshiki Saito. “Then the parasite uses two native freshwater fish, for example, Tridentiger Brevispinis and Tridentiger obscurusand non-native species to complete their life cycle. ”

What stands out about this particular parasite is its extraordinary ability to adapt to new environments by leveraging available host species. The researchers found that catfish and blue g parasite loads were particularly high, and both were designated as invasive species in Japan. These findings suggest that these three invasive species (gold mussels, cath fish and blue g) play a crucial role in maintaining the life cycle of the parasite and allowing it to spread to native fish.

A complex life cycle

The team conducted extensive DNA analysis to track the different stages of the development of the parasite in various host species. Their work reveals how parasites travel through ecosystems in a different way than typical patterns.

Like other members of the family D. Invasion Typically, three different hosts are required to complete their life cycle. The parasite begins with golden mussels, where it develops into a stage called sporangia. These sporangia release cercariae (ammunition-free larvae) and then infect small freshwater fish, encapsulated in their tissues and contained in their tissues.

Usually, predatory fish need to eat these palm c in order to develop into adults. However, the researchers made a surprising discovery: In some cases, palmistry can develop directly into adults while still within the second host tissue.

“We found adult eggs in fins, bottoms and g, both adults and metacercariae can occur together,” the researchers noted in publication. “This suggests that Metacercariae can develop directly into adults within the second intermediate host tissue.”

This unusual flexibility may help explain how parasites build themselves so quickly in new environments.

Connection of invasive species

What makes this particularly interesting is that most of the hosts involved are themselves non-native species. Of the eight species of fish that have been found, six are from western Japan, China or North America.

The golden mussels, which are the main source of infection, are native to East Asia and are likely introduced to Japan around 2005, with Asian clam seeds used in aquaculture. The researchers believe that the parasite may be linked to specific fish by repeatedly introducing these mussels.

Dr. Tsukasa Waki, one of the authors of the study, expressed concern about the potential focus: “Given that an adult may produce eggs through self-administration, D. Invasion It can be expanded rapidly when newly introduced water systems. ”

Potential impact

Despite no human infection, the presence of brown or yellow worms visible in fish muscles reduces the commercial value of affected freshwater fish. The team noted that strong meningeal infections have been reported to have negative effects on the host fish in other cases, which can lead to bleeding, swimming abnormalities and sometimes the host’s death.

This is not the first parasite to build its own in the Japanese freshwater system. The study also detected another introduced Bucephalid trematode, i.e. prosorhynchoides ozakiithis has been reported in the Tone River System. In some cases, researchers found that fish were co-infected with the two parasites.

Golden mussels with these parasites have now spread to at least eight river systems in Japan. Potential fish hosts are also becoming more common in these river systems, creating conditions that can further expand the parasites.

To prevent the spread of the species, the researchers recommend avoiding the introduction of potential hosts from the tonal river system into other water systems.

This study illustrates how invasive species produce complex ecological chain reactions, sometimes facilitating the establishment of other non-native organisms that might otherwise not gain a foothold in new environments. As climate change and global trade continue to promote global species movement, understanding these ecological relationships has become increasingly important for the protection and management of freshwater ecosystems.

The study was published in the Journal of Worms on January 20, 2025.