The eel in eel rice hides a secret that has troubled humans for thousands of years

Produced by: Science Popularization China

Author: Tian Dawei (popular science creator)

Producer: China Science Expo

Speaking of eels, does eel rice come to your mind? But did you know that the tiny eel actually hides a secret that has troubled humans for thousands of years?

Eel Rice

(Photo source: veer photo gallery)

The mystery of the eel's origin

The eels we often talk about are a type of fish called eels , but for convenience, we will still use the more familiar name eel in the following text.

Given their delicious taste, eels have been considered a delicacy for thousands of years, but for a long time people didn't know how eels were created.

It may sound strange to describe a fish by saying "how it was created". Don't all fish hatch from an egg?

In fact, to this day, people have never seen eel eggs in the wild. And thousands of years ago, people had never seen eel fry, let alone eggs.

Therefore, scholars at that time gave their own explanations for the "origin" of eels.

For example, Aristotle believed that eels were transformed from river mud, while the ancient Roman naturalist Pliny the Elder believed that adult eels did not need to reproduce, they rubbed their bodies against rocks in the river, and the debris that fell off could turn into baby eels.

Such a statement certainly seems unreliable today, but in the past two thousand years, people have not found any young eels, and have not been able to give a more reasonable explanation, so they can only accept it reluctantly.

It was not until the end of the 19th century that the mystery of the eel's life history was finally solved when young eels were found. The clue came from a small fish called the "willow leaf eel".

Willow Leaf Eel

(Image source: wikimedia)

In fact, people have discovered the lanceolate eel a long time ago, but no one has ever thought about the relationship between this fish and the eel. After all, the lanceolate eel is flat and transparent, while the eel is round and yellow-brown. They have almost no similarities. Moreover, the lanceolate eel lives in seawater, while the eel lives in rivers, and their living environments are also different.

But in 1896, Italian scientists kept the eel in an aquarium and found that it gradually became thinner and longer, and took on the shape of a glass eel. This eel is also transparent all over, but it no longer looks flat, and has taken on the initial appearance of an eel.

Glass Eel

(Image source: wikimedia)

After a while, the glass eel's body is no longer transparent and turns into a black-lined juvenile eel . As the juvenile eel grows up, it becomes the familiar yellow-brown eel.

Elvish eel

(Image source: wikimedia)

Now the truth is clear, whether it is the willow leaf eel or the glass eel, they are actually the young forms of eels. When they grow up, they become the familiar eels.

Scientists now have a complete understanding of the eel's life history.

The life of an eel can be roughly divided into five stages: willow leaf eel → glass eel → young eel → yellow eel → silver eel. Among them, the silver eel is the last stage of the eel's life history. At this time, the eel will return to the sea to lay eggs and finally die.

Several forms of eels

(Image source: Reference [1])

Of course, the reason why the origin of eels has puzzled people for thousands of years is not only because the morphology of small eels and large eels is very different, but also has a lot to do with another habit of eels, which is migration .

Eel migration

Eels lay their eggs in the ocean, often thousands of kilometers away from rivers on land. After hatching, the young fish will swim along the ocean current to the river estuary, then swim upstream into the river. After living in the river for several years to decades, they return to the deep sea thousands of kilometers away to lay eggs. The offspring repeat this life cycle again and again.

This is why humans often find willow eels in the ocean, and they think of them as some kind of marine fish. When willow eels swim all the way to the estuary, they have basically become glass eels and juvenile eels.

Of course, at the end of the 19th century, after people figured out the "past and present life" of eels, some scientists wanted to find the eel's spawning grounds. After all, in the past few thousand years, no one has ever seen how eels reproduce, and no one knows where they go to complete this life cycle.

In the early 20th century, a scientist named Johannes Schmidt decided to uncover this secret. But the ocean is so big, where can he find it?

The method Schmidt came up with was simple and effective, which was to go to the sea and see where there were more and smaller glass eels. Because the more and smaller the glass eels were, the closer it was to the eel's spawning grounds.

After more than ten years of searching, Schmidt finally located the eel's spawning grounds in the Sargasso Sea on the western Atlantic Ocean .

The size of eels near the Sargasso Sea

(Image source: wikimedia)

This was also confirmed by a study published in 2022. The study captured some eels preparing to migrate for spawning, marked them, and tracked them. It was found that after migrating for 40-366 days, they arrived in the Sargasso Sea.

Eel crisis

Humans have only truly understood eels for about 100 years, but in this period of time, some species of eels have been pushed to the brink of extinction.

For example, the Japanese eel, which used to be common in the western Pacific, has become an endangered species.

Japanese eel

(Image source: wikimedia)

The European eel , which was once common in continental Europe, has even become a critically endangered species . If we don't protect them, we may never be able to eat these eels again.

There are two main reasons why eels have become endangered.

On the one hand, it is overfishing . Because eels with migratory characteristics cannot be fully cultivated artificially, currently artificially cultivated eels can only be caught from wild glass eels in estuaries and then brought back to farms for breeding, and they cannot achieve "self-sufficiency" in farms. Therefore, people need to catch a large number of glass eels from estuaries every year, which has a great impact on the population of wild eels. There was even news that the price of glass eels was comparable to gold.

On the other hand, eels migrate to specific river sections to live, and the dams built on large rivers will block the small eels that have traveled thousands of kilometers outside their homes . This has also caused great trouble for the eel population. Fortunately, in the construction of some dams, people have begun to introduce fish ladder designs to protect migratory fish such as eels and salmon.

But it may take a long time for the eel population to return to a non-threatening status.

Fish ladder for migratory fish

(Image source: wikimedia)

Since many species of eels are already endangered, is it still possible to eat eel rice?

Eel rice sold by regular merchants on the market is still edible.

Eels belong to a large family, and there are other eels that can be used as food, such as the conger eel shown below.

Star Conger Eel

(Image source: wikimedia)

Of course, while looking for other alternatives to eels, what we should do more is to protect the eel's habitat and protect this magical and delicious animal.

Conclusion

The mysteries of many living things, including eels, have undergone a long and tortuous exploration process, and even many of the mysteries of these organisms have yet to be solved.

The past and present life of the eel makes us realize that exploring the mysteries of biology is vital to human civilization, and protecting the long-term survival of biology is the top priority for the sustainable development of the entire ecosystem.

References:

[1] Danielle Hall. The Origin of Eels

[2] Cresci A, Durif CM, Paris CB, et al. Glass eels (Anguilla anguilla) imprint the magnetic direction of tidal currents from their juvenile estuaries[J]. Communications biology, 2019, 2(1): 366.

[3] Bruijs MCM, Durif CM F. Silver eel migration and behavior[M]//Spawning Migration of the European Eel: Reproduction index, a useful tool for conservation management. Dordrecht: Springer Netherlands, 2009: 65-95.

[4] Wright RM, Piper AT, Aarestrup K, et al. First direct evidence of adult European eels migrating to their breeding place in the Sargasso Sea[J]. Scientific Reports, 2022, 12(1): 15362.

[5] Tsukamoto K. Discovery of the spawning area for Japanese eel[J]. Nature, 1992, 356(6372): 789-791.