Where does pufferfish's toxicity come from, and how can we eat them safely?

Hilsa shad, razor fish and puffer fish are collectively known as the "Three Fresh Fishes of the Yangtze River" and have been a delicacy sought after by gourmets since ancient times.

Su Shi, a scholar in the Song Dynasty, wrote in his poem "Evening Scene on the Spring River by Hui Chong": "Beyond the bamboos, there are three or two branches of peach blossoms. The ducks know first when the spring river water warms up. The ground is full of mugwort and the reed buds are short. It is the time when the pufferfish are about to come up."

Puffer fish is known as the "king of fish". Its high nutritional value is well known. It is extremely rich in nutrients such as protein, unsaturated fatty acids, DHA, EPA, etc., but has a very low fat content. Now is the season for puffer fish, with Artemisia selengensis all over the ground. Although puffer fish tastes delicious, it is poisonous. Every year, there are several news reports that diners risk eating puffer fish to try it out, resulting in poisoning, hospitalization, and death. This also makes many people "talk about puffer fish with fear". However, what kind of fish is puffer fish? Why does eating it cause poisoning? How can you eat puffer fish safely without being poisoned? Today, let's talk about puffer fish.

Although most people have heard of the name of pufferfish, you may not know whether the correct spelling is pufferfish or pufferfish. I used to think that the correct spelling should be pufferfish, with the character "fish" on the left and the character "tun" on the right. However, I later discovered that pufferfish is the real name!

Because pufferfish has a special skill, when it is frightened or angry it will quickly swallow a large amount of water or air, making itself round. When it floats on the water, it looks like a fat pig floating on the water. Therefore, the ancients called it "pufferfish", and the word "貀" was created by later generations and is mainly used in taxonomy to name this type of fish.

In a broad sense, fish in the order Tetraodontiformes in taxonomy, including the largest bony fish - the sunfish, the ill-tempered pufferfish, the horse-faced pufferfish commonly known as the rat fish, and the thorny pufferfish covered with thorns, can all be said to be a kind of pufferfish, but in a narrow sense, only pufferfish living in freshwater, especially several species of "Oriental pufferfish" that we often eat as food fish can be called "pufferfish". The most common one on the dining table is the "Dark-striped Oriental pufferfish", and the pufferfish in Su Xue Shi's poems is most likely it.

The picture comes from Tuchong.com

Why is pufferfish poisonous? The toxin in pufferfish is called "tetrodotoxin", which is a very strong neurotoxin. Only about 2 mg is enough to kill a person. The amount of tetrodotoxin in an adult female pufferfish can kill you more than 30 times. After poisoning, you will experience numbness of the mouth, tongue, fingertips, dizziness, vomiting, diarrhea and other symptoms. In severe cases, the limbs will be numb, consciousness will be unclear, blood pressure will drop, fainting and even death will occur. At present, there is no antidote invented. It is said that the ancients would feed feces to induce vomiting after discovering poisoning, while modern people mainly remove toxins left in the body by gastric lavage. Tetrodotoxin is not only powerful, but also extremely stable, and it cannot be destroyed by ordinary cooking methods. This makes many diners stop at pufferfish.

The good news is that pufferfish toxin is not present in the pufferfish itself, nor is it poisonous throughout the body. The current mainstream research view is that pufferfish toxin is produced by some bacteria in the body, and these bacteria are enriched and gradually accumulated in the body through food, and the toxin is mainly found in organs such as the ovaries, liver, blood, eyes and skin. Pufferfish muscles are almost non-toxic. In Japan, only specialized restaurants can sell pufferfish dishes, and chefs who handle pufferfish must undergo years of professional training before they can prepare pufferfish dishes for guests. In addition, there are very complicated and delicate steps in handling pufferfish:

1. Wash the pufferfish under running water, remove the mucus from its body, and cut off its fins.

2. Use a sharp knife to carefully insert it between the fish skin and the fish meat to separate them and peel off the fish skin without damaging the skin or the fish meat.

3. Use a towel to dry the moisture on the surface of the fish meat, and then remove the fish eyes.

4. Remove all the internal organs carefully without breaking them, otherwise toxins may contaminate the fish meat.

5. Open the fish's skull and remove the fish's brain.

6. Wash the fish repeatedly with running water to remove all blood and body fluids.

7. Check at least twice before cooking to make sure all poisonous organs have been removed and properly destroyed.

Even with such careful observation, we still occasionally hear about people being poisoned from eating puffer fish, especially in spring, when such news is most frequent. Why is that?

There are two reasons. First, spring is the traditional season for eating pufferfish. Second, pufferfish are most toxic in spring. Take the dark-striped pufferfish as an example. They usually migrate to freshwater to lay eggs in spring. During the breeding season, they need to accumulate a lot of fat in their bodies. The fish meat is the most plump at this time. Not only is the production large, but more people will eat pufferfish, and the number of poisoning reports will also increase. Moreover, the ovaries of pufferfish are the organs with the highest toxins. At this time, in order to lay eggs, the ovaries of female pufferfish will mature, increase in size and mass, and increase the chance of poisoning.

So is it possible for us to eat pufferfish safely? The answer is yes. After years of hard work, scientists in my country who are engaged in fishery technology have achieved artificial breeding of four types of pufferfish, namely, dark-striped pufferfish, red-fin pufferfish, two-spotted pufferfish and chrysanthemum-yellow pufferfish, and have bred drug-free strains. By completely isolating the pufferfish from the outside world in an artificial environment and feeding them with artificial feed, the pufferfish cannot obtain toxin-producing bacteria, and multiple generations of breeding are carried out to select pufferfish individuals with lower toxin content in their bodies, so that the toxins in their offspring gradually decrease, and finally a stable non-toxic pufferfish is obtained.

In 2016, the former Ministry of Agriculture of my country issued the "Notice on the Registration of Farmed Puffer Fish Source Bases", and the former Ministry of Agriculture and the State Food and Drug Administration jointly issued the "Notice on the Conditional Opening of Farmed Redfin Pufferfish and Farmed Obscure Pufferfish Processing and Operation". Since then, my country's pufferfish has been officially included in the conditional opening. The document has made very strict management requirements for the opening of pufferfish, including: the registration of farmed puffer fish source bases, the assessment of farmed puffer fish processing, the safety processing process of puffer fish, and the quality standards of puffer fish products.

It is important to emphasize that if you want to eat puffer fish safely, you must choose artificially farmed fish that meet the above requirements, and find a restaurant that specializes in puffer fish to ensure that you will not be in danger of poisoning while enjoying the delicious food.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Li Weiyang

Reviewer: Liu Yadan (Researcher of Chinese Society of Fisheries)

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.