← Back to Fauna
Fish Critically Endangered

European Eel

Anguilla anguilla

European Eel

Overview

The European carp is one of the most fascinating and mysterious fish in the world, with an extraordinary and unique life cycle that has baffled scientists for millennia - their maturation in nature has never been directly observed, and their five stages of development were originally considered to be different species. It is a catadromous fish with a characteristic serpentiform (snake-shaped), cylindrical, very elongated body, perfectly adapted for moving through narrow places and for swimming efficiently over huge distances. Unlike most migratory fish that breed in freshwater and live in the ocean (anadromous), the grayling does the opposite: it breeds in the ocean (the Sargasso Sea near Bermuda) and lives in continental freshwater. In the Danube Delta and Romania, the European grayling is present historically and sporadically, being quite rare - it enters the coastal lakes and the Danube from the Black Sea, where it spends the growth phase of life (6-18 years) before migrating back to the ocean for reproduction. Since the 1970s, the European cheetah population has declined dramatically by over 90%, leading to the classification of the species as "Critically Endangered" (CR) - critically endangered. The main factors are: overfishing (especially of juvenile "glass eel"), parasites (the nematode *Anguillicola crassus*), barriers to migration (dams), pollution and climate change. For the fishermen of the Danube Delta, the grayling was historically a valuable fish with white meat, very fatty and tasty, eaten smoked, but today it is extremely rarely caught.

Physical Characteristics

The European eel has a unique and immediately recognisable body — serpentine (snake-like), very elongated, cylindrical at the front and slightly compressed laterally at the rear, extraordinarily flexible and muscular. The head is conical and slightly flattened dorso-ventrally. The mouth is terminal, relatively large, with the lower jaw slightly longer than the upper. It is equipped with fine, tiny teeth arranged in bands on both jaws and the vomer. The eyes vary dramatically with developmental stage: small in juveniles and "yellow eels", very large in mature "silver eels" preparing for reproductive migration. The body is covered with extremely tiny, elliptical scales deeply embedded in the skin and nearly invisible — the skin is thick, slippery, covered with abundant mucus. The dorsal and anal fins are continuous, confluent with the caudal, forming a single long fin that surrounds the posterior part of the body. Coloration varies dramatically with developmental stage: larvae and "glass eels" are completely transparent; "yellow eels" (adults in freshwater) are greenish-brown or blackish on the back, yellow on the belly; "silver eels" (adults preparing for migration) become blackish on the back, brilliantly silver on the flanks and belly, with greatly enlarged eyes. Males reach 0.5 metres, females can reach 1.0 metres, rarely 1.5 metres.

Habitat & Distribution

Reproduction (never directly observed) takes place exclusively in the Sargasso Sea (western Atlantic Ocean, near Bermuda) at depths of 600 metres. The transparent larvae (leptocephali) are carried by the Gulf Stream toward European coasts in a migration of 200–300 days. As they approach the European coast, the larvae metamorphose into "glass eels" — transparent, cylindrical, miniature — which enter estuaries. In Romania and the Danube Delta, the eel enters from the Black Sea into coastal lakes (Razim, Sinoe, Mangalia, Siutghiol) and the Danube, ascending the Prut, Siret, Olt and other tributaries. Adults live 6–18 years in freshwater or brackish water, occupying extremely diverse habitats: rivers, lakes, ponds, canals, estuaries. They prefer muddy bottoms where they can burrow, vegetated banks, and structures under which they can hide. They are predominantly nocturnal, finding hiding places during the day and emerging at night in search of food. They spend winter in torpor, hidden in the mud at the bottom of waterways. Eels are remarkably mobile — they can cross short distances on wet ground at night and can survive hours out of water thanks to their moist skin and small gill openings. In the final year of life in freshwater, they become sexually mature and migrate back to the ocean to reproduce, not feeding at all during the entire migration. After reproduction, adults die.

Behavior and Feeding

The European eel is a nocturnal opportunistic carnivore with an extremely varied and adaptable diet. The diet includes benthic invertebrates (insect larvae, crustaceans, molluscs), small fish and fry, amphibians (frogs, newts), carrion and decomposing organic matter — eels are efficient scavengers. The feeding mode is characteristically nocturnal: during the day they remain hidden, buried in mud or under structures; at night they actively emerge in search of food, using their well-developed sense of smell to detect prey. Eels have an extremely well-developed chemical sense — they can detect water from great distances and move toward it in a straight line. During reproductive migration, adults do not feed at all, living exclusively from accumulated fat reserves. Behavior is solitary, avoiding interactions with other individuals outside the reproductive period. They have a remarkable ability to move overland — they can cross short distances on moist ground at night, allowing them to bypass obstacles and colonise isolated waters.

Life Cycle & Reproduction

The European eel has one of the most complex, lengthy and mysterious reproductive cycles in the fish world. Reproduction takes place exclusively in the Sargasso Sea (western Atlantic, near Bermuda) at depths of ~600 metres, in March–June. When they reach sexual maturity (males at 6–12 years, females at 9–18 years), "yellow eels" transform into "silver eels": their eyes enlarge dramatically, body fat content increases, coloration becomes brilliantly silver. The reproductive migration occurs in the second half of the year. "Silver" adults cross the Atlantic Ocean (5,000–6,500 km!), not feeding at all throughout the journey. After reproducing at depth, adults die — they reproduce only once in their lives. From pelagic eggs, transparent larvae (leptocephali) emerge, carried by the Gulf Stream toward Europe. Before reaching coastal waters, leptocephali undergo metamorphosis into "glass eels" — transparent, cylindrical, ~6–8 cm. "Glass eels" enter estuaries and gain pigmentation, transforming into "elvers" which migrate upstream. Growth is slow: 10–15 cm in the first year, then 5–10 cm/year. The "yellow eel" stage lasts 6–18 years before the final transformation. The complete cycle takes 15–25 years.

Conservation Status

The European eel is classified as Critically Endangered (CR) by IUCN — representing one of the most severe conservation crises for fish in Europe. Since the 1970s, the European population has declined dramatically by over 90%. In Romania and the Danube Delta, the species is extremely rare, with sporadic and continuously declining presence. It benefits from strict protection: commercial fishing is prohibited or severely regulated throughout Europe, and trade in "glass eels" is strictly controlled. Threats are multiple and severe: overfishing of "glass eels" to supply aquaculture farms in Asia; the nematode parasite Anguillicola crassus infecting the swim bladder, causing severe damage (fibrosis, ruptures) preventing successful migration; dams and hydropower plants blocking upstream juvenile migration and downstream migration of "silver" adults; pollution with polychlorinated biphenyls (PCBs); climate change affecting the oceanic currents that carry larvae toward Europe; and habitat loss. Sustainable management requires stopping commercial fishing, strictly protecting glass eels, eliminating migration barriers or constructing fish passes, reducing pollution, restoring natural habitats, and developing artificial reproduction.