One of the more, uh, interesting culinary experiences I have had in Asia was ordering fugu (pufferfish) sushi at a Japanese restaurant in China. A few moments after my order, a plate was sat in front of me that contained lots of fresh, white sushi slices…positioned just below the still-gasping decapitated fugu head. My dad was so disturbed that he asked the waitress to take the fugu head away while I happily chomped away at the delicious sushi. Well, at least I knew it was fresh!
The fugu, or pufferfish, is a delicacy in Asia (and particularly Japan) due to the dangers inherent in consuming it. Fugu liver and ovaries, and the flesh to a much lesser degree, contain a potent neurotoxin called tetrodotoxin. For this reason, sushi chefs in Japan must be specially trained and licensed to prepare fugu for consumption, with only 30% passing an extremely rigorous test (go here for a video of the test).
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Consuming fugu in Japan is relatively safe, however there are still dozens of deaths per year related to tetrodotoxin poisoning from fugu. The proper preparation of fugu is shown in the video below.
Tetrodotoxin (TTX) is a sodium channel blocker with no antidote, although several Japanese biotech companies are working on one. It binds to the pores of the voltage-gated, fast sodium channels in nerve cell membranes. TTX is not unique to fugu–it is also found in some newts, parrotfish, toads, several starfish, an angelfish, etc. The first recorded incident of fugu poisoning was from Captain Cook’s log in the 1770s. His men caught and ate several ‘spiny tropical fish’ and fed the leftovers to the pigs kept on board. While the crew who ate the fugu felt ill and weak, all the pigs died, suggesting that the crew received a mild dose of TTX while the pigs ate the livers and ovaries and received a lethal dose.
Those poisoned gradually lose muscle control, although not consciousness, and eventually suffocate to death when the diaphragm becomes paralyzed. However, in very small amounts, approximately the amount found in fugu sushi, TTX gives a funny tingly sensation on the tongue and lips. Interestingly, the fugu itself is not affected by the toxin due to a mutation in the protein sequence of the sodium channel pump on its nerve cell membranes, and there is a Fugu Genome Project (Sydney Brenner’s idea). The source of the fugu’s TTX is hypothesized to be a bacteria called Psuedoalteromonas tetraodonia.
Just last month, a handful of deaths due to fugu poisoning occurred in Thailand when some unscrupulous fishmongers sold fugu as salmon. I actually saw a very large fugu, which was slow-moving but very wary of people, when I was snorkeling in Malaysia in June. And what does it feel like to be poisoned by fugu? A firsthand account describes it thusly:
Approximately four hours had passed after the fugu meal – I was not the only person who felt numb on finger tips. “Probably we ate poison today,” someone said. “My finger tips won’t hold a piece of mah-jong ,” someone else joined. We all felt something out of ordinary but nobody took the matter seriously.
The mah-jong was over and I tried to rise for the guest’s belongings upstairs. I fell on my hip before I knew. “What on earth is the matter?” I wondered, but managed, while feeling ny body numb, to go upstairs and get back to my guests.
“I feel dizzy, ” someone said. “Something is strange, ” others uttered and they all left. I felt too sick to put things away. “Sorry but let me go to bed,” I excused myself and rose to go to my bedroom upstairs, then I suddenly felt like vomiting. My stomach by then was empty and left me in sheer agony. I felt dizzy and crawled on all fours to the bed…
I felt my whole body.in sickening rotation whether I opened or closed my eyes. I felt pressures on the breast and hard to breathe….
I remember joking under all such agonies, “If I should die, take 48 hours before you bury me. You may come to life again when poisoned by fugu.”
My poisoned sickness lasted for good three days and nights. The Doctor came for camphor injections and said that I would have to wait for natural recovery. After all, none of us died or appeared in the newspapers.
TTX also has a scientific use– it has been used in neural and tissue preparations to block certain types of sodium channels while leaving others (those resistant to TTX, such as cardiac tissue) unhampered. This allowed a scientist to measure and isolate certain populations of sodium channels.
Fore more info, as well as an example of a dinner of fugu, check out this podcast on fugu by National Geographic.