A group of five men in their 40s and 50s were hospitalized this weekend after eating the liver of pufferfish served in a hot pot at a restaurant in Wakayama prefecture.

Pufferfish, also called blowfish and known as fugu in Japanese, contains deadly toxins in parts of its body. Serving its liver is prohibited under Japan’s food safety law, but some gourmands consider it an exquisite delicacy.

According to an official at the Wakayama city office, the five men pleaded with the restaurant owner to serve them fugu liver. About five hours after the meal, the diners began showing symptoms of nausea, dizziness and difficulty breathing. All five were hospitalized but are recovering, the official said.

Wakayama city shut down the restaurant that served the fugu liver for five days beginning Sunday. The restaurant didn’t immediately respond to a message seeking comment.

The U.S. Food and Drug Administration advises on its website that consumers should only eat imported blowfish that are prepared by specially trained and certified fish cutters in Shimonoseki, Japan, or those that are caught in the mid-Atlantic coastal waters of the U.S.

The toxins in fugu are “more deadly than the poison cyanide and can affect a person’s central nervous system. There are no known antidotes for these toxins. Puffer fish must be cleaned and prepared properly so the organs containing the toxins are carefully removed and do not cross-contaminate the flesh of the fish,” the FDA states on its website.

Those who succumbed to the deadly delicacy include kabuki actor Bando Mitsugoro VIII, who died in January 1975 after enjoying plates of fugu liver at a restaurant in Kyoto.