1,600 Parasites Found in Skipjack Tuna: Caution Issued for Brazilian Imports

Penetrating Deep into Organs and Muscle
Survey Conducted on 53 Skipjack Tunas from Southern Brazil

A significant number of Brazilian skipjack tuna have been found to be heavily infested with parasitic worms such as anisakis. Notably, a large quantity of parasites was detected not only in the internal organs but also in the muscle tissue, raising concerns about the safety of eating raw tuna and calling for extreme caution among consumers.

Parasites Penetrating into the Flesh

On September 3 (local time), the New York Post reported that a research team from the Federal University of Santa Catarina in Brazil had published in the international journal Marine and Coastal Research the findings of their examination of 53 locally caught skipjack tuna. According to the research, parasites—including anisakis (commonly known as whale worms)—were found in as many as 96% of the fish.

Dissected Brazilian skipjack tuna (A) and internal organs (B), infected tissues (C, D, E). Captured from the international journal Marine and Coastal Research

The total number of parasites identified in this study reached approximately 1,600. The majority were discovered in the internal organs (596), but large numbers were also found in the muscle tissue (441) and the stomach (408). The researchers stated, "Except for the kidneys and heart, virtually every part of the fish was infected with parasites."

Skipjack tuna is a popular species with a global annual catch reaching 3 million tons, and it is consumed in various forms such as sashimi and canned goods. While the appearance of parasites in fish is not uncommon, experts note that this level of infection rate within a single species is highly unusual.

Hard to Spot with the Naked Eye... Recommendation for Freezing or Cooking

Consuming raw fish containing live parasite larvae can lead to anisakiasis, a condition in which the parasites burrow into the stomach lining and cause severe abdominal pain and vomiting. The research team emphasized that to prevent parasites from moving from the internal organs into the flesh, it is imperative that the fish are quickly gutted and processed immediately after being caught.

However, even with careful inspection during processing, it is practically impossible to remove all microscopic parasites. In fact, according to a study by the University of Washington, cases of parasitic nematodes in raw fish have increased by several hundred times over the past few decades.

Experts recommend, "Since it is virtually impossible to detect larvae that have penetrated deep into the muscle with the naked eye, raw fish should be thoroughly frozen at a temperature below minus 20 degrees Celsius or fully cooked, making sure the center reaches at least 60 degrees Celsius for over one minute, to ensure it is safe for consumption."

Cold Weather Still Brings No Relief from Anisakis

Parasites are commonly thought to be found only in summer, but anisakis can also be detected in winter, meaning there is no season for complacency. In particular, from July, when sea temperatures are high, to October, when warm currents arrive, domestic fish such as squid and conger eel are frequently infected with anisakis in Korea as well.

Anisakis is the most well-known fish parasite, drifting in egg form before being eaten by shrimp, which in turn are eaten by fish such as mackerel, and eventually reaching whales at the top of the food chain—hence the name "whale worm." Before reaching the final whale host, if an infected fish is consumed raw by a human, the parasite can also infect people.

Parasitic worms cannot reproduce in the highly acidic environment of the human stomach. However, as anisakis larvae pierce the stomach wall, they may cause abdominal pain, vomiting, and stomach cramps. A medical industry source warned, "If infected with anisakis, standard anthelmintic medications may offer little effect and symptoms may persist for an extended period. In severe cases, endoscopy may be required to extract the parasite."

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