If we use pufferfish toxin to poison pufferfish, will the pufferfish be killed by the pufferfish toxin?

"When the ground is covered with mugwort and the reed shoots are short, it is the time when puffer fish are about to come up." It was March, and schools of puffer fish were swimming upstream from the river mouth. In ancient China, this was the time to taste puffer fish meat.

But eating this stuff requires a strong mental preparation because pufferfish contains tetrodotoxin (TTX).

This is one of the most toxic non-protein neurotoxins currently available . Even in ancient times when medical and health conditions were underdeveloped, people were well aware of the dangers of puffer fish. There has been a saying among the people since ancient times that "eating puffer fish is risking your life", meaning that eating puffer fish meat is risking your life.

0 1

Sources of tetrodotoxin

Pufferfish, also known as bubble fish or angry fish, are so called because their bodies will quickly swell into a "little ball" when touched.

Biologists believe that pufferfish developed their famous inflation ability because their slow and clumsy swimming style makes them vulnerable to predators.

Pufferfish can inflate into a spherical shape to hide from predators

Image source: nationalgeographickids

To escape, pufferfish use their highly elastic stomachs and the ability to quickly take in large amounts of water (or even air if necessary) to transform themselves into a ball several times larger than normal size, making them nearly inedible to predators, and some species even have spikes on their skin to make them look less appetizing.

However, appearance is just a small means for pufferfish to adapt to the environment. The real killer comes from the pufferfish toxin they carry.

In my country and Japan, there are countless records of poisoning caused by eating pufferfish. The first person to conduct modern research on pufferfish was Japanese scholar Yoshi-zumi Tahara, who analyzed the physical and chemical properties of pufferfish toxin and named the toxin in pufferfish tetrodotoxin.

Schematic diagram of the distribution of tetrodotoxin levels in adult pufferfish

Image source: MDPI

For a long time, tetrodotoxin was believed to be a toxin that only existed in pufferfish. It was not until 1964 that the toxin in salamanders was also identified as tetrodotoxin. Since then, tetrodotoxin has been detected in many organisms, including bacteria, algae, mollusks such as blue-ringed octopus, bivalves and gastropods.

Based on these findings, Nagashima Y et al. proposed that tetrodotoxin in pufferfish is enriched through the food chain and the storage location is in the liver.

Experiments have also proven that artificially farmed pufferfish do not contain tetrodotoxin , but if the livers of toxic pufferfish are added to their feed, toxins will accumulate in the bodies of the originally non-toxic pufferfish.

The accumulation process of tetrodotoxin in pufferfish

Image source: researchgate

In addition, some scientists believe that the toxin is produced by bacteria in the pufferfish's body. By isolating bacteria in the pufferfish's body, such as actinomycetes, Vibrio, Pseudomonas, etc., and culturing them, they all detected the presence of pufferfish toxin. At the same time, scientists also detected that the toxin content in the pufferfish embryo was constantly increasing during the incubation process, which indicates that pufferfish toxin is a product of the embryo.

In general, most scientists currently agree that the tetrodotoxin in pufferfish is the result of the dual influence of the food chain and microorganisms.

02

Will pufferfish toxin kill pufferfish?

Tetrodotoxin is a marine neurotoxin, so its selection for sodium ion channels is very high priority.

When tetrodotoxin binds to the sodium ion channel, the α-subunit of the sodium ion channel contains tetrodotoxin receptors, which prevent sodium ions from entering the cell, thereby blocking the excitatory activity of nerves and muscles, causing paralysis, and in severe cases, breathing difficulties and death.

The cell structure in the pufferfish has undergone genetic mutation, and a site on the sodium ion channel in their bodies has been replaced with a receptor that does not bind to pufferfish toxin. At the same time, the pufferfish's body still retains specific proteins that can bind to pufferfish toxin, reducing the toxic effects and making the pufferfish extremely tolerant to pufferfish toxin in the body .

However, everything has a limit. Pufferfish of the family Tetrapodidae can distribute pufferfish toxin on their body surface or in their mucus to warn or deter predators.

However, if these pufferfish are overly nervous or strongly stimulated, they will produce more pufferfish toxin on their body surface . In this case, even the pufferfish themselves cannot resist it and may even die of poisoning.

03

The correct way to eat pufferfish

In ancient my country, many people dared to eat poisonous pufferfish, and even formed a regional eating custom in Jiangsu and Zhejiang. Therefore, in the Yangtze River Basin, every spring, there are always a large number of fishermen going to catch pufferfish.

Image source: lostplate

However, the toxins in pufferfish's body have always been a hurdle that cannot be avoided when eating pufferfish. In order to solve the problem that pufferfish is delicious but highly poisonous, the ancients tried every means to collect detoxification remedies.

Some methods can be started before eating, such as adding reed roots and olive branches to cook with puffer fish to remove toxins from the puffer fish's body. Other methods can be used to detoxify after eating, such as grinding gallnut, alum, etc. into fine powder and taking it with water. If these materials are not available at hand, you can take clear oil and drink it to expel the toxins.

After reading these methods, I said: Don’t learn them!!!

In fact, pufferfish toxin is very toxic, and its chemical and thermal properties are very stable. It cannot be fundamentally eliminated by cooking or adding herbal remedies. Therefore, after ancient scholars realized this, they could only physically remove pufferfish toxin.

Because the toxins of pufferfish are mainly concentrated in the internal organs, blood and head , as long as these parts are removed and the residual blood is washed away, and only pure fish meat is used for cooking, poisoning will not occur. Through this scientific processing method, the safety of eating pufferfish by the ancients has made a qualitative leap.

Image source: VICE

At present, the modern way of processing pufferfish is the same. According to the "Yangzhong Yearbook", pufferfish are slaughtered by cutting along their back from top to bottom, and then the liver, heart, kidneys, stomach, intestines, gills, air sacs, ovaries of female pufferfish and spermatocysts of male pufferfish are removed in turn, and the eyes are dug out with scissors. The key point is that the removed parts should not be thrown away first, but need to be placed one by one for subsequent inventory to see if they are clean.

In addition, based on the research on the pathway of pufferfish toxin, there is theoretical support for the artificial breeding of pufferfish, so that low-toxic or even non-toxic pufferfish can be bred , especially the dark-striped pufferfish. There are relatively mature toxin control technology and breeding yields. Perhaps in the near future, everyone will be able to eat "pufferfish freely."

References:

[1] Wang Xiaojie, Yu Rencheng, Zhou Mingjiang. Research progress on the ecological effects of tetrodotoxin[J]. Acta Ecologica Sinica, 2009, 29(9):8.

[2] Wang Liya, Tao Ningping, Gong Xi. Research progress on food safety and nutritional value of pufferfish[J]. Shanghai Journal of Agriculture, 2012, 28(2):6.

[3] Wang Saishi. Investigation of ancient Chinese pufferfish[J]. Ancient and Modern Agriculture, 2001(3):8.

[4] Ye Jingqin, Xiao Ye, Lu Yikuan, et al. Overview of research on processing of cultured puffer fish and reduction of tetrodotoxin[J]. Food and Fermentation Industries, 2021, 47(7):6.

Puffer Fish https://www.sciencedirect.com/topics/immunology-and-microbiology/puffer-fish

Author: Fish

Winner of the Silver Award for Outstanding Science Popularization Works of China Science Writers Association

For those who love steamed fish head, spicy fish head and other fish head

Editor: Guru