European Eel (Anguilla anguilla): Life Cycle and Decline

What does a European eel look like?

The European eel has a long, cylindrical body that is round in front and slightly flattened toward the tail. A single long fin, formed by the dorsal, tail and anal fins joined together, runs around the rear half of the body. The dorsal fin begins well behind the head, and there are no pelvic fins at all. Small pectoral fins sit just behind the gill openings.

The scales are tiny and buried in thick, slimy skin, so the eel feels smooth. The lower jaw juts slightly beyond the upper one. Growing eels, called yellow eels, are dark brown, olive or greenish on the back and yellowish on the belly. When they mature they become silver eels, with a dark back, silvery sides, a white belly and much larger eyes.

Two forms are often found in the same river. Broad-headed eels have wide jaws and feed on larger prey such as fish and crayfish, while narrow-headed eels mostly eat small invertebrates. This difference seems to depend partly on diet and growth rather than on separate types of eel.

How big do European eels get?

Female European eels grow much bigger than males. Males usually mature and leave for the sea at about 30–45 cm (12–18 in) long. Females typically reach 50–100 cm (20–39 in) before migrating, and the largest recorded female measured 1.33 m (4.4 ft). Most eels weigh well under 2 kg (4.4 lb), and the heaviest on record weighed about 6.6 kg (14.5 lb).

Whether a young eel becomes male or female seems to depend partly on its surroundings. Crowded waters, such as estuaries and lower rivers, tend to produce more males, while eels growing at low density far upstream are more likely to become females.

Where do European eels live?

European eels live in almost every kind of water connected to the Atlantic, Baltic and Mediterranean: rivers and streams, lakes and ponds, canals, estuaries, coastal lagoons and shallow seas. Their range stretches from Iceland and northern Norway to Morocco and the Atlantic islands, and east through the Mediterranean to the Black Sea coasts. Some eels never enter fresh water and spend their whole growing life in the sea or in brackish lagoons, while others move back and forth.

Eels are catadromous, the opposite of salmon. They grow up in fresh or coastal water but return to the ocean to breed, whereas fish such as the Atlantic salmon grow at sea and breed in rivers. Eels are also remarkable climbers. Young eels can wriggle up damp walls and weirs, and on wet nights older eels can cross fields to reach isolated ponds.

The European eel life cycle

The European eel’s life has five stages, which early naturalists thought were different animals:

1. Leptocephalus: a flat, transparent, leaf-shaped larva that hatches in the Sargasso Sea and drifts toward Europe on the Gulf Stream and North Atlantic Drift.
2. Glass eel: near the continental shelf the larva changes into a tiny, see-through eel that swims into estuaries.
3. Elver: the young eel turns dark and moves into rivers and lakes.
4. Yellow eel: the long growing stage, lasting years or decades.
5. Silver eel: the mature eel stops feeding and swims back to the Sargasso Sea to spawn once and die.

Silver eels usually leave their rivers in autumn and early winter, traveling mostly on dark, moonless nights when rain has raised the water level. They then face an ocean journey of roughly 5,000–10,000 km (3,000–6,000 mi), depending on where they start, without eating. Spawning has never been seen in the wild, but each female is thought to release millions of tiny eggs before dying.

Each stage is explained in What are glass eels?, and the centuries-long hunt for the eel’s birthplace is told in Where do eels come from?

What do European eels eat?

European eels are carnivores and opportunistic feeders. Young eels eat insect larvae, small crustaceans and worms. Larger eels add snails, mussels, crayfish, fish, frogs and fish eggs, and they will scavenge dead animals. Big broad-headed eels can tackle fish too large to swallow whole, tearing off pieces by spinning their bodies.

Eels feed mainly at night and find food largely by smell, which is extremely keen. In cold weather they become inactive, often burying themselves in mud until the water warms again. Once an eel turns silver and begins its migration, its digestive system shrinks and it stops eating altogether, living on stored fat for the rest of its life.

Behavior and senses

European eels are mostly solitary and nocturnal, hiding by day under stones, among roots or in burrows in the mud. They are adaptable fish that can tolerate warm, poorly oxygenated water better than many others, and their skin can take up some oxygen directly from the water or damp air.

Their navigation abilities are still being uncovered. Experiments suggest that eels can sense Earth’s magnetic field, and in a 2017 study young glass eels responded to magnetic conditions matching different points of their ocean journey in ways that would help them reach the Gulf Stream. Silver eels heading for the Sargasso Sea make daily vertical migrations, swimming in deep water by day and rising nearer the surface at night.

How long do European eels live?

An eel’s lifespan depends mostly on how long it takes to mature. In the wild, males usually spend about 6–12 years growing before they migrate, and females about 9–20 years, longer in cold northern waters where growth is slow. Because eels breed only once and then die, most never live much beyond 20 years.

Eels that are kept from migrating, for example in landlocked ponds, wells or aquariums, can live far longer. Ages of up to 85 years have been reported, and an eel kept in a well in Brantevik, Sweden, was claimed to be over 150 years old, although that claim has never been verified.

Predators and threats

Glass eels and elvers are eaten by many fish and birds, including gulls. Adult eels are hunted by herons, cormorants, otters, pike and larger eels. Their slimy skin, burrowing habits and nighttime activity help them avoid many predators.

Human pressures are far more serious. Dams, weirs and hydropower turbines block migration routes or kill eels on their way to the sea. For centuries eels have been caught at every life stage, from glass eels in estuaries to silver eels on their way out. A swim bladder parasite introduced from Asia in the 1980s, pollution, wetland drainage and changes in ocean conditions add to the pressure. These causes are explained in Why are European eels endangered?

Conservation status

The IUCN Red List has classified the European eel as Critically Endangered since 2008, and reassessments in 2014 and 2020 confirmed that status. According to the joint ICES working group on eels, the number of glass eels arriving in 2024 was about 1 percent of the 1960–1979 average in the North Sea region and about 7 percent elsewhere in Europe.

International trade has been controlled under Appendix II of CITES since 2009, and the European Union has banned exports and imports of European eels across its borders since 2010. A 2007 EU regulation requires member countries to run eel management plans designed to let more silver eels escape to the sea, and scientists at ICES have repeatedly advised that no eels should be caught at all until the stock recovers. Across Europe, eel passes are being built at dams and weirs, and some young eels are moved past barriers into rivers and lakes where they can grow.

Eels and people

Eels have been part of European life and food for thousands of years. Jellied eels became a classic street food in London’s East End, smoked eel is a delicacy in the Netherlands, Germany and Scandinavia, and young glass eels, called angulas, are a traditional luxury in the Basque Country. Angulas are now so expensive that imitation versions made from fish paste are widely sold instead.

Eel farms in Europe and Asia still depend entirely on young eels caught in the wild, because the species has never been bred through its full life cycle in captivity, despite decades of research. The eel also puzzled scholars for more than 2,000 years. Aristotle believed eels arose from mud, and as a young student in 1876 Sigmund Freud dissected hundreds of eels in Trieste in a fruitless search for their testes. Only in the early 20th century did the Danish biologist Johannes Schmidt trace the smallest larvae to the Sargasso Sea.

The European eel is a true eel of the order Anguilliformes, unlike the South American electric eel, which only shares its long shape.