Puffer fish & Tetrodotoxin

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Pufferfish: kind of cute, right? Also kind of poisonous. They hit the news this week after a Japanese supermarket accidentally sold five packages of fugu (as it’s known in Japan) without removing the highly poisonous livers. This post looks at what makes them so poisonous.

Pufferfish are poisonous due to the presence of tetrodotoxin. Several other aquatic animals also contain this toxin, such as the blue-ringed octopus. In all cases, it’s not produced by the animals themselves, but by symbiotic bacteria.
In pufferfish, high levels of tetrodotoxin occur in the liver, skin, and reproductive organs. Before it is eaten these must be skillfully removed. If even the tiniest amount of liver (for example) remains, it could prove a deadly final meal for whoever eats it.
Because of these high stakes, chefs must complete years of rigorous training before they can prepare the fish for eating. Japanese government figures state that, since 2000, 23 people have died as a result of eating incorrectly prepared fugu, though the majority of these were due to attempts to prepare the fish at home. This is a significant improvement on past figures: in 1958 alone, 176 people died from fugu poisoning.
Tetrodotoxin kills because it can interfere with our nervous systems. It blocks sodium channels, which carry messages between the brain and our muscles. As a result, those suffering from tetrodotoxin poisoning initially lose sensation. This is rapidly followed by paralysis of muscles. This paralysis extends to the diaphragm and the muscles which help move the ribs, ultimately stopping breathing.
Only small amount of tetrodotoxin is needed for poisoning to occur. This is why it’s so important to prepare the fish correctly. It’s estimated that just 25 milligrams of tetrodotoxin is enough to kill a 75kg human, and other estimates suggest that it’s up to 1200 more toxic than the infamous poison, cyanide.
There is no known antidote for tetrodotoxin poisoning. In cases where the poisoning is spotted quickly, pumping the patient’s stomach can remove the some of the poison. Even if this approach isn’t taken, some patients are lucky enough to recover from serious poisoning, as was the case for 11 diners in Brazil in 2014.
Three of the five fugu packets sold in Gamagori, Japan, have been located, but two still remain at large. Loudspeakers have broadcast the news across the city in the hope that the information will reach those who purchased the packets.
If you wanted to try your luck with fugu, there might be a safer way: scientists claim to have succeeded in creating a non-toxic variety. Their theory is that by controlling the diet of the fish, they can prevent the production of tetrodotoxin. Will it one day replace poisonous fugu? That depends – for some, the lure of the dish is undoubtedly the thrill of its potential lethality.