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Dieren en planten

Fish   Eel family   Eel   Conger   Fish biology   Reproduction of fish   Nurseries   

Eel

size:

maximum 150 centimeters

gewicht:

maximum 10 kilograms

color:

Larva: transparent
young eel:olive green to brown and yellow-white belly
adult eel: dark gray, lighter by the belly

age:

up to around 30 years

food:

larva: zooplankton
young eel: water fleas, small crustaceans, worms and insect larva
large eel: also fish

enemies:

birds such as cormorants and herons; humans

reproduction:

lays eggs
maturity: between 8-13 years old
number: millions of eggs

  • Dut: Paling (aal, bamisaal, blankaal, biezenbijter, blinker, breedbek, dikkop, happer, koppe, platkop, robber, schieraal, schoenveter, slokker, spitskop, zilverpaling, tetting (juveniel), tochtaal (juveniel), gele aal (juveniel), rode aal (juveniel), glasaal (larve))
  • Lat: Anguilla anguilla
  • Eng: European eel
  • Ger: Flussaal
  • Fren: Anguille
  • Dan: Ål
print print
Eel, foto fitis, sytske dijksen

Eel

Eels are mysterious fish. For the longest time, it was unknown as to where they spawned. Juvenile eels look very different than adults so that people also used to think that they were two different species of fish. Eel can live in fresh as well as salt water. As long as the ground is wet enough, they can move on land. Eels are momentarily threatened by overfishing. Obstacles between fresh and salt water also form a problem. In 2007, the eel was declared as a protected animal species. A European recovery plan has been developed.

  • Life cycle

    The very young eel larvae have been found in the Sargasso Sea, in the western Atlantic Ocean. However, adults have never been seen there. No one has ever witnessed how eel spawn. In general, it is assumed that they die after performing the act.

    The larvae in the Sargasso Sea drift with the sea current towards the European coast. That is a 6000-kilometer long voyage, which takes 1 to 3 years. When the larvae arrive, they are 7 centimeters long and are referred to as glass eel.

    In the winter and spring, the glass eel gather by river mouths. When the water is cold, large groups of glass eel can be found 'hanging out' around the river mouth or sluis doors. Glass eels are quite tasty. In England and several countries around the Mediterranean Sea, these fish are professionally fished in such 'hangouts'. Eventually, the glass eel spread out in rivers, ditches and lakes. Some remain in the sea.

    Eel grow very slowly because it is so cold here. A 30-centimeter long eel that you buy at the market can be 8 to 10 years old. They only reach puberty when obtaining a length of 35 to 45 centimeters. This is when thoughts of reproducing begin and they start on the long voyage back to the Sargasso Sea. The trip commences in late spring and summer.

    At this stage, the eels change in color and appearance. They are then referred to as silver eels. The color of the back changes from green-brown to black. The belly changes from yellow into a metallic silver color. Even the eyes grow larger, their pectoral fins grow longer and their head narrower. All these changes make them look more and more like a deep sea fish. They also stop eating.

    Their urge to return to the Sargasso Sea is so great that they will even move over land. It is known that during migration, eels can crawl out of ditches and through (damp) fields. The eel has gills that can close and then makes use of breathing through its skin. In the autumn migration, millions of silver eels migrate through the North Sea.

  • Studies of migration and reproduction

    An experimental situation has been built at the University of Leiden to study the migration habit of the eel. It is possible to simulate the entire migration route from the Netherlands to the Sargasso Sea in a complex of aquaria and tunnels. Light, air pressure, temperature and water currents are imitated as closely as possible. In December 1997, 22 adult eels from the Grevelingen began their trip in this system to the Sargasso Sea. The researchers hope to learn more about the migration of eel and the mystery behind their reproduction.
    The study in Leiden showed that the eel contain sufficient fat reserves to make the long trip to the Sargasso Sea. This is clarified by their very efficient manner of swimming whereby little fat is burned. These reserves are necessary since they don't eat during the trip. There is a danger hidden in the fat: fatty eel contain relatively extra amounts of PCBs, which can have a disastrous effect on the reproduction. There are also indications that eel in recent years contain less fat.

  • High tech eel

    There have even been experiments with supplying eel with transmitters. Eel that were ready to depart Germany for the North Sea were implanted with a small glass tube in their belly. The tube was around 6 centimeters long and contained the transmitter and a battery. A signal was transmitted every time this high tech eel passed by a special registration station. In that way, the researchers knew precisely which eel it was.

    In total, 130 eel were supplied with a transmitter. The starting point was by the main stream of the Rhine by Cologne. After four days, the fastest fish had reached the North Sea while it took more than a year for the slowest one to arrive!

  • Threatened eel

    The eel stock in the Netherlands has declined drastically. The exact cause of the decline is unknown. Overfishing, land reclamation and the closure of river mouths with sluices and dams can be a reason. However climate changes, hormone-disrupting materials and pollution may also play a role. According to IMARES biologist Dekker, also chairman of the ICES eel workgroup, it is possible that the real cause is the release of French eel after the war. This could have changed the ecology of the indigenous eel too much. According to him, a general ban on catching eel is the only solution, and even then it could take two hundred years before the population has recovered.

  • Eel plans

    In 2004, the European Commission announced regulations to limit fishing eel. The idea was that every European country must present a plan of their own, the goal being a recovery of the eel stock. The Dutch government developed a plan to allow more eel to return to the Sargasso Sea in order to reproduce. Part of the plan was a ban on catching eel in the months of September and October, when the majority of the eel migrate to sea.

    The fishermen did not agree with the plan and made an alternative plan. In order to help the eel, they want to release part of their catch from the rivers and lakes into the sea themselves. In December 2008, fishermen released 2000 'teenage' eel into the sea.

  • Golden eel
    Partially golden eel from Lake Grevelingen, Jaap de Ronde, Visserijnieuws

    Sometimes, very unusually colored eel are found. In 2004, the Bout brothers caught a bright yellow eel with black spots in Lake Grevelingen. They brought it to biologist Dekker at IMARES in IJmuiden, who identified it as a 'golden eel', a kind of albino. Due to the lack of dark colors, the yellow color becomes clearly visible. Biologists have a name for this phenomenon: xanthochromatism.

  • Distribution of the eel
    Distribution of eel, Ecomare

    Dutch eel are found from the Sargasso Sea to Morocco, including the entire Mediterranean Sea, the Baltic Sea and all the way up to northern Norway. Eel is found in the entire Benelux region in just about all surface water.

  • Farmed eel

    The eel nurseries in Europe are suffering from a shortage on eel. This has to do with the natural migration of glass eel, which has declined greatly in the past 20 years. That is why fishermen release glass eel themselves. They were doing the same even a century ago. The glass eel were released in the polders where they grew into the size of an eel within 4 to 10 years.

    The price for glass eel has risen from 10 euro per kilo in 1980 to 250 euro per kilo. Chinese eel farms will pay up to 600 euro per kilo!

    In England and several countries around the Mediterranean Sea fish eel professionally. They fish in the winter and spring, trying to catch the glass eel in the fresh-salt transition zones such as estuaries, river mouths and by dams. A large part of the catch is cultivated further in eel farms. There is also a portion kept for European farms. The farms need glass eel since it is not yet possible for eel to reproduce artificially. Some of the caught glass eel is also released or eaten, particularly in Spain.