Overview
The European eel (Anguilla anguilla) is one of the most extraordinary — and most threatened — fish in the world. Capable of crossing entire ocean basins, surviving in both freshwater and saltwater, and living for decades, this serpentine creature has fascinated naturalists for centuries. Yet despite centuries of study, it still guards many of its deepest secrets.
Physical Characteristics
European eels have a long, cylindrical body that tapers toward the tail — a shape perfectly adapted for navigating dense vegetation, crevices, and muddy river beds. Key identifying features include:
- Length: Females commonly reach 60–100 cm; males are typically smaller at 30–50 cm
- Coloration: Juveniles ("yellow eels") display a yellow-brown underbelly; adults transitioning to the sea ("silver eels") develop a silvery sheen on their flanks
- Fins: A continuous dorsal-anal fin runs most of the body's length, giving the eel its characteristic undulating swimming motion
- Eyes: Silver eels develop enlarged eyes before their oceanic migration — an adaptation for deep, low-light waters
Range & Habitat
True to their name, European eels are found across Europe and parts of North Africa — from Iceland and Scandinavia in the north to the Mediterranean and Morocco in the south. They inhabit a remarkable diversity of freshwater environments including rivers, lakes, marshes, estuaries, and coastal lagoons. Some individuals are even found far inland, suggesting impressive overland movement capabilities in wet conditions.
Life Stages
The European eel passes through several distinct life stages, each with a different name:
- Leptocephalus larvae: Transparent, leaf-shaped larvae that drift across the Atlantic from the Sargasso Sea spawning grounds
- Glass eel: Near-transparent juvenile eels that arrive at European coasts and begin moving into estuaries
- Elver: Small, pigmenting juveniles moving upstream into freshwater
- Yellow eel: The long freshwater growth phase, lasting anywhere from 6 to 20+ years
- Silver eel: The sexually maturing adult that migrates back to the sea
Diet & Behavior
European eels are opportunistic, largely nocturnal predators. During their yellow eel phase in freshwater, they feed on invertebrates, small fish, crustaceans, frogs, and carrion. They are known to bury themselves in mud during cold winter months, entering a semi-dormant state — a key reason they survive in a wide variety of habitats.
Conservation Status
The European eel is currently classified as Critically Endangered by the IUCN. Populations have declined dramatically over recent decades due to habitat loss, river barriers, overfishing, pollution, and the impact of introduced parasites. European Union regulations now restrict eel fishing in many member states, and restocking programs are underway across several river systems.
Why the European Eel Still Mystifies Scientists
No one has ever observed European eels spawning in the wild. Scientists believe they travel thousands of kilometers to the Sargasso Sea — a region of the North Atlantic — but the precise spawning location and the mechanism by which eels navigate there remain unknown. It is one of the great unsolved mysteries in marine biology.