Precautions when consuming freshwater fish sashimi: Even scaleless Mandarin fish can pose parasite risks

Among those who enjoy eating freshwater fish as sashimi, myths such as "fish living in clear water are safe" or "scaleless fish like Mandarin fish have no parasites and are fine to eat as sashimi" are often passed around. However, according to recent experimental results, these common beliefs may differ from the truth, requiring caution.

Encysted larvae found in wild sweetfish

According to a video from the YouTube channel 'TV Saengmul Dogam', the cast conducted an experiment to check for the presence of parasites in freshwater fish alongside experts from the Korea Association of Health Promotion MEDICHECK Research Institute and the Parasite Museum. The subjects used in the experiment included wild sweetfish, farmed sweetfish, Mandarin fish, large mudfish, catfish, small crabs, and Dongjak crabs.

During the experimental process, the fish muscle was decomposed with digestive fluids and observed under a microscope, resulting in the discovery of round-shaped encysted larvae in the wild sweetfish. According to the expert in the video, these larvae are 100–200 micrometers in size, making them difficult to identify with the naked eye, and they were in a living larval stage where movement was confirmed through microscopic observation. The larvae are presumed to be trematodes, suggesting the possibility that multiple individuals exist in wild sweetfish.

Why even scaleless fish cannot be trusted

Many believe that species with few or no scales, such as Mandarin fish and catfish, are safe to eat as sashimi, but experts warn that this cannot be fully guaranteed. In the experimental results, larvae were not found in the other species surveyed (Mandarin fish, catfish, etc.) except for the wild sweetfish, but this is because results can vary depending on the region or individual.

In fact, a nematode called *Acanthocephala* has been reported in Mandarin fish, and there are records of liver flukes being found in catfish in research cases from China. Furthermore, in the case of the scaleless Dongjak crab, there have been instances where parasite encysted larvae were discovered in past investigations. Parasites can be found not only under the scales but also within the muscle of the fish, so the presence or absence of scales cannot serve as a measure to guarantee safety.

Liver flukes (distoma) can be dangerous enough to be classified as a Group 1 carcinogen in South Korea. While there may be no immediate pain upon infection, repeated infections that lead to parasitism in the bile duct can cause diseases by blocking the bile duct. Experts explain that it is difficult to remove trematodes with general antiparasitic drugs available at pharmacies, so a doctor's prescription is necessary. The most certain preventive measure is to ensure that wild freshwater fish are cooked before consumption.