There’s a fish that mates only once in its life…and you eat it!

In the book “The Chronicle of the Emerald Isle” that oceanographers should like, I saw “Ode to the Ocean Current” written by the Irish poet, and my mind was full of eels after that.

Not eel rice. What the Irish call eel is not the same eel that is used in eel rice – the former is European eel ( Anguilla anguilla ), the latter is Japanese eel ( Anguilla japonica ). There is also the American eel ( Anguilla rostrata ) that lives on the east coast of North America. They all have the same strange problem: they like to travel thousands of miles to mate in strange places. European eels and American eels run to the Sargasso Sea in the middle of the Atlantic Ocean, and Japanese eels are also very strange. They have to go near the Suruga seamount in the middle of the Pacific Ocean—if you don’t know where this is, it’s in the deepest Mali in the world West of the Yana Trench.

Eels are said to mate only once in their lives.

When decades of eating and sleeping single dog

then go home and get married

The evocative life of European eels is roughly like this: when they were still little translucent dolls, they had to take advantage of ocean currents to embark on a journey of finding their roots in Europe thousands of miles away. Then, as long as you successfully migrate to your hometown in Europe, you can breathe a sigh of relief. Apart from worrying about being caught cooking, you don’t have to be busy looking for a partner for the time being. In the fresh water of Europe, I ate, slept, and ate carefree. I ate everything from annelids to fish. Europeans also opened their minds and said that eels can be used to prevent and control the invasive species of crayfish, which shows that their combat effectiveness is terrible. than the Chinese people.


There are two things that European eels often do when they are young: one, hide in the sand (left), and two, eat small bugs (right). |

During this period, no one urged them to get married, so they lived alone for a few years or even decades-until they suddenly became enlightened one day (sexual maturity is about the same as the time of death), and now foodies become lovers, that is, It is said that they reserve the energy for the road and mating (paste the autumn fat), and then go to the Sargasso Sea, their birthplace, without eating or drinking, with the only purpose of “falling in love and then dying”. This journey will take about six months, starting in autumn and arriving in the spring of the following year. In the second half of the journey, the eel gradually fills its body with reproductive organs, reaches its destination, reproduces, and then dies.


The life of an eel can be divided into six stages with different shapes: ① the egg stage (Egg), ② the willow eel stage (Leptocephalus) that cannot swim and can only drift along the ocean current, ③ the transparent glass eel that comes near the mainland (Glass eel), ④ came to the Tamsui estuary, the eel line stage (Elver) with melanin in the body, ⑤ the growth stage of the yellow eel (Yellow eel), which can reach 8-20 years, ⑥ eyes become bigger and the belly is silvery In the Silver eel period (Silver eel), I plan to go back to my hometown to get married (so, where is my hometown, the mainland or the sea?). |

The one who told us this story was the professor of environmental genomics who had read “One Hundred Years of Solitude” four times. I don’t know if it is because he has read too many novels, but the legendary story is particularly contagious. He says no one knows why European eels (and American eels for that matter) are breeding in the Sargasso Sea – in such barren waters! The seawater lacks nutrients, and the sargassum is not tasty . Could it be that the admission score for the college entrance examination is low?

The love stories of American eels and Japanese eels are similar. So here comes the question: both American eels and European eels breed in the Sargasso Sea in spring. Will they simply hybridize widely and become the same species? not at all.

Morphologically, American and European eels differ in the number of vertebrae, as do various molecular markers. That is to say, at least in most cases, the eels only look for the other half from the same direction. “Two eels, one male and one female, swim from both sides of the Atlantic Ocean, and they meet and mate in a touching magpie bridge on the Sargassum Sea.” This scenario didn’t happen. Not only that, those translucent, flat little eels like willow leaves were born in the same place, but as if they were called by different people, they firmly walked on different paths —American eels headed west, European eels headed east, Embark on a journey that may last for years by means of ocean currents. It is really remarkable that the little eel is so clear about “the whereabouts of its own species” without being accidentally swept away by another ocean current, and the reason has not been explained clearly.


Schematic illustration of the routes of the three species of eels described in this paper to their breeding grounds. Yellow arrow: American eel. Black arrow: European eel. Red arrow: Japanese eel. Baby eels migrate home in the opposite direction. |By Strebe (Own work) via Wikimedia Commons (Note: This picture is highly abstract. It is a “soul painting” made with a brush tool by the author who failed in elementary school art. It does not represent the actual migration path. In fact, the rivers where eels live are all over North America , Europe, North Africa, and the coasts of East Asia, the migration paths are also more complicated.)

Japanese eels endangered, European eels critically endangered

However, they refuse to breed in farms

Next, let’s talk about eel rice. What is the relationship between eel rice and the love story of eel? Let’s put it this way, it is impossible for the fastidious Japanese to ignore the issue of eel reproduction in such an important matter as eel rice. Japanese eels in autumn are supposed to be the most plump. At this time, sexually mature eels are fattened and ready to go, with the highest body fat content. However, the Japanese people, who have always had strange aesthetics, are not interested in these things. It is fashionable to eat eel in summer , and there is a special eel eating day every summer. It seems that there is another saying in a certain article, saying that compared with the plumpness of autumn eels, I appreciate the thinness of wild eels in summer. Compared with guys who are high-spirited and always ready to sacrifice for love, they prefer young teenagers who have not yet got rid of the single dog mentality-this kind of explanation immediately shows the Japanese aesthetic style… (No, in fact, maybe they are just Supplementary food in summer, or thinking of a trick to sell eels that are not fat in summer…)


So the eel rice we eat…is all virgins? |Pixabay

It’s just that it seems a little out of date to pursue the food supplement of eating wild eel now: Japanese eel has been listed on the IUCN Endangered List (EN) in recent years, and the popularity of eel rice probably has a lot to do with it. So the next best thing is to eat farmed eel? There are indeed many people raising eels. In the past, there were eels in Xiamen, which were directly made into grilled eels and exported to Japan. The eel calcium that I ate when I was a child was probably a by-product of eel bones—but it was from glass eels or small eels that had migrated to the vicinity of the mainland. When the eels started to be raised, no one had a way to let them lay eggs in a farm and raise them from scratch. There was no way to achieve “closing the life cycle” under artificial conditions. So even if you farm eels, you usually have to rely on the supply of (endangered) wild fry. No wonder the eel farming business is difficult to do, and the price of eel rice is also rising every year.

However, there are many difficulties in getting eels to reproduce completely under artificial conditions. For example , first of all, you don’t know when they will be sexually mature , and having a pair of sexually mature ones at the same time is even more extravagant; what’s more, the sex ratio is prone to imbalance under artificial breeding conditions (yes, the sex of eels is not determined at birth, and many other The same is true for fish), raising a bunch of bachelors – the eels in the pond are really rough.


Female (left) and male (right) Japanese eels caught in a Pacific eel breeding area|Tsukamoto et al., 2011.

Although a few freshwater eels also have sex chromosomes, the actual sex of development is not determined by the sex chromosomes, but is mainly affected by the surrounding environment. At low population densities, eels develop primarily as females. At high population densities, eels develop primarily as males. This mechanism is conducive to the automatic adjustment of the wild population, but it is easy to produce a large number of good genes in crowded farms. ♂ friend.

Even if successful mating is achieved, it is difficult to raise the next generation. It turns out that the little eels that can complete the long journey back home are not idle people. They are cold by nature , and they don’t eat plankton like other larvae, but eat a food that sounds like poetry— marine snow (marine snow). snow) . This beautifully named sea snow is actually a group of metabolites of plankton and other debris that stick together and slowly fall in the sea—that is to say, it is basically feces and corpses . There is no way, the little eel with an awkward personality has to eat it, and it is hard enough to raise at birth. The teacher said in the class that the Japanese have actually raised eels in the laboratory through a series of extraordinary methods such as hormone injections, artificial sea snow, etc., but they definitely want to keep the eel rice for themselves and never disclose the technology.

Europeans love eels as much as Japanese, and their eating methods are even more cruel. Eating young eels is like eating whitebait. Grab a lot of them and stir fry them . It seems to be a famous Spanish dish. You finally just came back from swimming in the Sargasso Sea? Actually eat a lot. There is not even a fattening process.


I can’t find the picture of the juvenile eel, so I put a small whitebait dry, everyone understands… | pixabay

In recent years, the reproductive rate of European eels has dropped significantly (it is said that it is mainly due to the famine in European freshwater basins, and they have no enough food and strength to swim to breed). Level, if you insist on eating authentic fried eel now, I’m afraid not only the way of eating is cruel, but also the whole species. What puzzles me is that some food that looks like frozen juvenile eels are still being sold in Spanish supermarkets, and they are sold so cheaply that I can be sure that it is not a critically endangered authentic European eel. So I bought some and made it according to the method of whitebait omelette, and it really tasted like whitebait omelette. According to people familiar with the aquatic industry, these eel-like things may be high-quality imitations made of fish meat, similar to a university cafeteria selling two crab sticks wrapped in crab meat as fried crab claws.

I originally wanted to write that (like all migratory fish) vigorous and slightly nostalgic love stories, but I accidentally wrote about how good it can be. So it is really eel rice that is in the mind.


[1] Ocean lovers/sea phobia patients (often the same thing) read this article: Harry Clifton’s “Ode to the Ocean Current” translated by Bao Huiyi

[2]Katsumi Tsukamoto et al., Seamounts, new moon and eel spawning: The search for the spawning site of the Japanese eel, Environmental Biology of Fishes 66: 221–229, 2003. Seamounts, new moon and eel spawning: The Japanese eel Exploring the breeding grounds (approaching science, you). The new moon means that Japanese eels may prefer to mate on a moonless night.

[3]Katsumi Tsukamoto, Spawning of eels near a seamount, Nature 439: 929, 2006. (Japan) Eels breed near a seamount (see how normal this title is)

[4]Katsumi Tsukamoto et al., Oceanic spawning ecology of freshwater eels in the western North Pacific, Nature Communications 2, Article number: 179, 2011. Are all articles about Japanese eels written by this Tsukamoto…

[5]Vincent JT van Ginneken & Gregory E. Maes, The European eel (Anguilla anguilla, Linnaeus), its lifecycle, evolution and reproduction: a literature review, Rev Fish Biol Fisheries 15:367–398, 2005. European eel life history , A Review of Evolution and Reproduction (which also mentions reproduction in American eels). It is necessary to explain that, as a moral love story, this article does not detail the process of eel mating. Attention students who want to watch teaching videos: There are pictures in this document.

[6]Laura Aquiloni et al. Biological control of invasive populations of crayfish: The European eel (Anguilla anguilla) as a predator of Procambarus clarkii, Biological Invasions. 12(11):3817-3824, 2010. European eels prey on invasive crayfish species

[7] Classroom story of Professor Ibon Cancio

[8] Curious whether American eels have hybridized with European eels, read this article: Jacobsen, MW et al., Genomic footprints of specification in Atlantic eels (Anguilla anguilla and A. rostrata), Molecular Ecology 23, 4785–4798, 2014.

[9] Sex determination in eels: Davey, AJH & Jellyman, DJ, Sex determination in freshwater eels and management options for manipulation of sex, Reviews in Fish Biology and Fisheries, 15: 37–52, 2005.

[10] If you are concerned about the prospect of eel rice, please read this article: Artificial breeding of Japanese eel

Author: grass hydrochloride

Original title: “Eel Love Story: Once in a Lifetime, Migrating Thousands of Miles”

Cover image source: Pixabay

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