Eel

European river eels are fascinating fish. They swim up to 5000 kilometers to reproduce: from the rivers of Europe across the Atlantic to the Sargasso Sea.

Characteristics

What does the European river eel look like?

European river eels belong to the eel family and are unmistakable with their long, slender bodies. The head is narrow and does not stand out from the body, which is round in cross-section. The mouth is superior, that is, the lower jaw is slightly longer than the upper jaw. At first glance, the eel resembles a snake. The pectoral fins sit behind the head, the pelvic fins are missing. The dorsal, anal and caudal fins do not resemble typical fish fins. They are narrow and fringe-like and run along almost the entire body.

The back is black to dark green, the belly yellow or silvery. Males and females of river eels are different in size: the males are only 46 to 48 centimeters long, while the females are 125 to 130 centimeters and weigh up to six kilograms.

Where do eels live?

The European river eel is found throughout Europe from the Atlantic coast across the Mediterranean to North Africa and Asia Minor. Eels are among the fish that can live in saltwater, freshwater and brackish water.

What types of eels are there?

In addition to the European, there is also the American river eel, both species are very similar. There are other species in Asia and Africa. Around 150 species of conger eels also belong to the same family. They are found in the oceans from the tropics to temperate zones, but never go to freshwater.

How old do eels get?

Eels that migrate to the Sargasso Sea to reproduce die after spawning. The males are then about twelve, the females a maximum of 30 years old. However, if the animals are prevented from migrating to the sea and reproducing, they start eating again and can then live up to 50 years.

Behavior

How do river eels live?

River eels are nocturnal animals. During the day they hide in caves or between stones. There are two variants of the European river eel: the black eel, which mainly eats tiny crabs, and the white eel, which mainly feeds on fish. But both occur together.

Eels are very robust animals. They can survive on land for long periods of time and can even crawl across land from one body of water to another. This is because they only have small gill openings and can close them. They can also absorb oxygen through the skin.

When winter comes, they move into the deeper water layers of the rivers and bury themselves in the muddy bottom. This is how they survive the winter. European river eels are so-called catadromous migratory fish: they migrate from rivers and lakes to the sea to reproduce. The opposite is the case with the so-called anadromous migratory fish such as salmon: they migrate from the sea to the rivers to reproduce.

Friends and foes of the eel

Eels – especially juveniles – are the main victims of other predatory fish.

How do eels reproduce?

Between March and May, the five to seven millimeter larvae hatch in the Sargasso Sea. They are ribbon-shaped and transparent. They are called “willow leaf larvae” or leptocephalus, which means “narrow head”. For a long time, they were thought to be a separate species of fish because they don’t look anything like adult eels.

The tiny larvae live in the upper water layer and drift east in the Atlantic with the Gulf Stream. After one to three years, they finally reach the shallow, coastal sea off the European continent and off North Africa. Here the larvae transform into so-called glass eels, which are about 65 millimeters long and also transparent. For some time they live in brackish water, for example in estuaries where fresh and saltwater mix.

During the summer, the glass eels darken and grow vigorously. Some of them stay in the brackish water, others migrate up the rivers. Depending on the food supply and the temperature, the eels grow at different speeds: on the North Sea coast, the animals are about eight centimeters long in the first autumn after they have reached the coast, and up to 20 centimeters a year later. They are now called yellow eels because their bellies are yellowish and their backs are grey-brown.

After a few years, the eels begin to transform. This begins at the age of six to nine years for males and between 10 and 15 years for females. The eel’s head then becomes more pointed, the eyes larger, and the body firm and muscular. The back becomes darker and the belly silvery.

Gradually the digestive system recedes and the eels stop eating. This transformation takes about four weeks and they are now called silver eels or silver eels – because of their silvery belly coloration.