The river eel is a very interesting fish, because outwardly it looks more like a snake, and besides, it can cover a distance of several kilometers by land. And it is also appreciated by gourmets: its meat is considered very tasty. Not least because of this, the population of the species has greatly decreased, so that in many countries measures are being taken to protect it.
Origin of the species and description
Photo: River eel
The proto-fish is considered to be a small chordate pikaya that lived on Earth 530 million years ago. They were small in size – only a few cm, but at the same time, the eels are very similar to them in the way they move – they move in the same way, bending the body. But this similarity should not deceive: unlike lampreys, eels are ray-finned fish, that is, they did not occur until many millions of years later. Although they looked like eels in appearance, conodonts were one of the first jawless fish that lived in the late Cambrian.
Jaws appeared in the Silurian period: it, as well as the next two, Devonian and Carboniferous, is considered the time of the highest flowering of fish, when they were the most diverse and largest animals on the planet. But there is little left of the species that lived on the planet then – most of the current diversity of fish arose much later.
Video: River eel
Bony fish, which include eels, arose at the beginning of the Jurassic period or at the end of the Triassic. At the same time, the first representatives of the eel order could also have arisen, although researchers have no consensus on this issue: some believe that they occurred later, at the beginning of the Paleogene.
Others, on the contrary, relying on the finds of fossil creatures similar in structure, attribute the origin of their ancestors to more ancient times. For example, such an extinct fish as Tarrasius is known, belonging to the Carboniferous period and very similar to the eel in structure. But the prevailing point of view is that this similarity does not mean their relationship. The river eel was described by C. Linnaeus in 1758, the Latin name is Anguilla anguilla.
Interesting fact: The oldest eel, his name was Putt, lived in an aquarium in Sweden for 85 years. He was caught very young in 1863 and survived both world wars.
Appearance and Features
Photo: What a river eel looks like
Eels have a very long body, which makes them look much more like snakes than fish – because of this, they were not eaten in some countries because they were not considered fish. In fact, this is not just a fish, but also very tasty: eels are considered a delicacy, although their appearance may indeed seem repulsive.
The color of an eel can be different: the back is olive, dark green or brown with a green sheen It depends on where he lives. As a result, it is difficult to see the fish when looking at the water from above. Its sides and belly can be from yellow to white – usually the eel brightens as it matures.
The scales are very small, and its skin is covered with a layer of mucus, which is why it is smooth and slippery – the eel can easily wriggle right out of the hands, so it should be handled very carefully. The maximum fish can grow up to 1.6-2 m, and weigh 3-5 kg.
The head of the eel is apparently flattened from above, its body near the head is cylindrical, gradually flattening as it approaches the tail. When moving, the eel bends with its whole body, but primarily uses the tail. His eyes are pale yellow and very small even for a fish, which also gives originality.
The teeth are small, but sharp, arranged in rows. The fins, except for the pectorals, are fused and very long: they begin at some distance from the pectorals and continue to the very tail of the fish. The lateral line is clearly visible. The eel is very tenacious: it may seem that his wounds are so severe that he should die, but if he still manages to escape, most likely in a few months he will already be almost healthy, unless he has a broken spine.
Where does the river eel live?
Photo: River eel in water
River eel is also sometimes called European eel, because it lives almost exclusively in Europe: outside it is found only in North Africa and a small area in Asia Minor. In Europe, it is easier to say where it is not: in the Black Sea basin. It is found in the rivers flowing into all the other seas washing Europe.
Of course, this does not mean that it is found in all rivers: it prefers rather calm rivers with still water, so you can meet it in fast mountain streams can be quite rare. The largest populations live in rivers flowing into the Mediterranean and Baltic Seas.
River eel is distributed throughout Western and Northern Europe, but the border of its distribution to the east is very complicated: it is found on the Balkan Peninsula up to the south of Bulgaria inclusive, but further this border sharply goes west and goes near the western coast of the Balkans. River eel is not found in Austria.
In Eastern Europe, it lives:
- in most of the Czech Republic;
- almost everywhere in Poland and Belarus;
- in Ukraine it can be found only in a small area in the north-west;
- throughout the Baltics;
- in the north of Russia up to the Arkhangelsk and Murmansk regions inclusive.
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Its range also includes all of Scandinavia and the islands near Europe: Great Britain, Ireland, Iceland. From the area of its distribution, it can be seen that it is undemanding to the temperature of the water: it can be warm, as in the rivers of the Mediterranean Sea, and cold, as in those that flow into the White Sea.
Eels are also notable for the fact that they are able to crawl out of a reservoir and move along wet grass and earth – for example, after rain. Thus, they are able to overcome up to several kilometers, as a result of which they may end up in a drainless lake. Without water, 12 hours can easily be done, more difficult, but also possible – up to two days. They spawn in the sea, but spend only the first time and the end of their lives there, the rest of the time they live in rivers.
Now you know where the river eel is found. Let's see what this fish eats.
What does the river eel eat?
Photo: River eel fish
In the diet of eel includes:
- amphibians;
- small fish;
- roe;
- mollusks;
- larvae insects;
- worms;
- snails;
- chicks.
They hunt at night, and the young usually in shallow water very close to the shore, and adults, on the contrary, in deep water away from it. You can catch them during the day, although at this time they are less active. They mainly hunt for small fish that live near the bottom, such as sculpins. If it is not possible to find it, they can rise to the surface.
Eel, especially young one, is one of the main fighters of eggs of other fish, especially cyprinids. He loves her very much, and during the period of active spawning in May-June, it is caviar that becomes the basis of his menu. Toward the end of summer, he switches to eating crustaceans, eats a lot of fry.
They specialize in fry of pike and tench, so in those rivers where there is a lot of this fish, eels are usually also found. It is noteworthy that they can eat not only in water, but also on land: they crawl out onto the shore to catch an amphibian or a snail. A large eel can intercept a waterfowl chick.
Although they hunt in the dark, and their eyesight is poor, they are able to accurately determine the location of the victim if they are at a distance of 2 meters or closer to it, and they also have an excellent sense of smell, thanks to which they can smell it from afar. Glass eels mainly eat larvae and crustaceans – they themselves are too small and weak to catch amphibians, small fish or even fry.
Peculiarities of character and lifestyle
Photo: River eel in Russia
Eels are active at night, but spend their days resting in burrows, or generally just lie at the bottom, buried in silt – sometimes to a depth of up to a meter. Eel burrows always have two exits, usually hidden under some kind of stone. They can also rest near the shore, in the roots of trees: the main thing is that the place is calm and cool.
Most of the time they spend near the bottom or on it, they like to hide in shelters, which are various snags, boulders or thickets. At the same time, great depth is not necessary: it can be either the middle of the river or a not too deep place near the coast. But sometimes they appear on the surface, especially if the water rises: at this time they are found in thickets of sedge or reeds near the shore, in pools nearby. They prefer when the bottom is covered with mud or clay, but in places where it is rocky or sandy, it is unlikely to meet this fish.
From the end of spring and all summer, the eel moves: they go downstream and then swim to the spawning grounds, overcoming very long distances. But eels spawn only once (after that they die), and they live 8-15 years, and in some cases much longer, up to 40 years, therefore only a small part of them participate in the course. In winter, eels hibernate by burrowing into the river bottom or hiding in their burrow. They practically do not react to external stimuli, all processes in their body slow down greatly, which allows them to almost not consume energy and not eat at this time.
But by the spring they still lose weight significantly, so after waking up they begin to actively feed . Most eels go into hibernation, but not all: some remain active even in winter, this mainly applies to the inhabitants of warm rivers and lakes.
Social structure and reproduction
Photo: Giant river eel
Eels from all rivers swim to the Sargasso Sea to spawn. To do this, they have to travel long distances: those fish that live in Russian rivers, up to 7,000 – 9,000 km. But they swim exactly there – to the place where they themselves were once born. It is in this sea that the conditions are ideal for eel larvae, called leptocephali. Spawning takes place at a great depth – 350-400 m. The female eel spawns 350-500 thousand small eggs, each about 1 mm in diameter, after which it dies.
After hatching, the larvae are almost transparent – this provides them with good protection from predators. Only their black eyes are visible in the water. They are so unlike their parents that they were previously considered to be a different species altogether – scientists have long been occupied with the mystery of the reproduction of eels, and the name leptocephaly has stuck to their larvae.
After the leptocephalus is born, it emerges and is picked up by the Gulf Stream. Together with this current, leptocephali gradually swim towards Europe. At the stage when the fish is already close to the coast of Europe, and then enters the mouths of the rivers, it is called the glass eel. By this moment, the fish grows up to 7-10 cm, but immediately on the approach to the river it stops feeding for a long time and decreases in size by one and a half times. Her body changes, and she becomes outwardly similar to an adult eel, and not like a leptocephalus, but still remains transparent – hence the association with glass.
And already when rising up the river, the eel acquires the color of an adult, after which it spends almost the rest of its life there: these fish remain in the river for 8-12 years, and constantly grow, so that by the end of their life they can grow up to 2 meters.
Natural enemies of the river eel
Photo: River eel
No specialized predators hunting basically just for the eel. Adult individuals in nature are practically not threatened at all while they remain in the river: they are large enough not to be afraid of river fish or birds of prey. But in the sea they can have lunch with a shark or tuna.
Juvenile eels that have not yet matured to large sizes can be threatened by predatory fish like pike, or birds like cormorants, gulls, and so on. And yet it cannot be said that even for a young eel there are many threats in the river. Of course, it is more difficult for very fry, not to mention leptocephals: many predators feed on them.
But the main enemies of the eel are people. This fish is considered a delicacy, because it has very tender and tasty meat, so it is actively hunted. Not only fishing, but also other human activities have a negative impact on the eel population. Pollution of the waters does not affect their population in the best way, as does the construction of dams that prevent them from spawning.
Interesting fact: Why eels swim so far to spawn has not yet been established, there are different theories about this. The most common one explains this by continental drift: before, eels were close to swimming to the Atlantic Ocean, and even now, when the distance has greatly increased, they continue to do so.
Population and species status
Photo: How looks like a river eel
Previously, the population of eels in European countries was very large. In some places, they were not caught at all, considering them inedible, or they were fed to livestock at all, since, nevertheless, many eels came across as bycatch. This is especially true of the Iberian Peninsula, where a lot of eel fry were caught.
In other countries, they have long been actively consumed for food and loved, there they were caught even more. This led to the fact that the population of this fish was significantly reduced by the second half of the 20th century. Fishing for eels is still carried out, however, its scale has noticeably decreased due to a decrease in the number of fish.
Back in the late 1990s, 8-11 thousand tons were caught annually, but by that time it had become It is noticeable that the population has declined. It continued to fall in recent decades, as a result of which the scale of fishing has become much more modest. Now river eel has become much more valuable.
His fry are now sold in Spain for 1,000 euros per kilogram as a delicacy for the rich. The river eel is listed in the Red Book as a species on the verge of extinction, however, its fishing has not been banned – at least not in all countries. The recommendation of the International Union for Conservation of Nature is to limit its catch.
Protection of river eels
Photo: Red Book eel
Due to the decline in the number of European eel and its inclusion in the Red Book, measures have been taken to protect it in many countries. Despite the fact that its catch has not yet been completely banned, it is often quite strictly regulated. So, in Finland, the following restrictions are set: eels can only be caught when they reach a certain size (less fish need to be released) and only in season. If these rules are violated, large fines are imposed on fishermen.
In Russia and Belarus, measures are being taken to stock reservoirs with fish: earlier, back in Soviet times, glass eels were purchased in Western Europe for this, now their sale outside the EU is limited, which greatly complicates matters. Purchases have to be made in Morocco, and since this is a different population, more thermophilic, it has to be more difficult.
In Europe, to preserve the populations of migrating larvae, they are caught and raised on farms where they are not threatened by any danger. Already adult eels are released into the rivers: so much more of them survive. But it's not possible to breed eels in captivity, because they simply do not breed.
An interesting fact: When eels swim from the ocean to European shores, they swim into the first river that comes across , so it all depends on where exactly they turn to the shore. Rivers with wide mouths are much more likely to become their target, therefore, there are more eels in their pools.
And once an eel has chosen a target, it is difficult to stop him: he can get out onto land and continue on like this, crawl over an obstacle, climb onto another eel.
The river eel is one example of how excessive exploitation undermines the population of a very valuable commercial fish. It now takes many years of painstaking work to protect and breed eels in order for the numbers to recover – the latter is especially difficult due to the fact that they do not breed in captivity.
