Five men have been poisoned in Japan after allegedly asking a restaurant to serve them banned parts of the world 's most toxic fish . The men were having dinner on Friday night in the western city of Wakayama when they ate puffer fish liver , which prompted vomiting and breathing difficulties early the next morning . Puffer fish - also called blowfish or fugu in Japanese - are the world 's most toxic group of fish and their livers , ovaries and skin contain tetrodotoxin , 100 times more lethal than cyanide . Dicing with death : Five Japanese men were poisoned after eating banned parts of the puffer fish ( file photo ) Yet eating the fish 's flesh is a tradition in Japan , where wealthy diners play the Russian roulette of the restaurant world by dining on sashimi slivers so thin they are almost transparent . According to a city health official , the men asked to eat a banned , toxic part of the fish - which the most foolhardy fugu aficionados are said to enjoy for the tingling it produces on the lips . Popular : The tradition of eating thin slices of 'fugu ' persists despite dozens of poisonings a year . The tingling is only the first symptom of tetrodotoxin poisoning , and is seen as part of the thrill for lovers of the fish . But if the toxin is served in any significant quantity it then paralyses the muscles , suffocating victims as it reaches their chests and diaphragms while they are still conscious . The health official said the men were in their 40s and 50s and the restaurant was shut down for five days from yesterday amid an investigation . 'They consumed a dinner that included liver , which is regarded as toxic material , ' she told AFP , reading from a statement . Calls to the restaurant went unanswered . Chefs who want to serve puffer fish must train for two years before taking a rigorous test which a third of applicants fail . The most prized species is the tiger puffer , takifugu rubripes , whose flesh is safe to eat but whose liver , ovaries and intestine can all kill . It is not clear which species of puffer fish the men ate . Puffer fish account for the majority of Japan 's food poisoning deaths but the delicacy shows no sign of dying out , although it is heavily regulated . Government figures show 30 to 50 people are hospitalised every year , with a few of those cases leading to death .
Men in their 40s and Friday ate at restaurant in Wakayama , Japan , on 50s . They fell ill the next morning with breathing difficulties and vomiting . Health official claimed they asked to eat highly poisonous fish 's liver . Restaurant has been shut down for five days as investigation continues . Puffer fish toxins kill - but aficionados eat just enough for tingling on lips .