The eel life cycle
Explainer · Last reviewed 2026-08-14
One of the most extraordinary life histories in the animal kingdom, and one of the least understood: a transparent leaf drifting across an ocean, a glass eel entering a river, decades in fresh water, and a one-way return nobody has observed.
THE EUROPEAN EEL'S LIFE RUNS IN STAGES THAT LOOK LIKE DIFFERENT ANIMALS, and for a long time were classified as such.
THE LEPTOCEPHALUS is a transparent, leaf-shaped larva, a few centimetres long, drifting in the open ocean. It was described as a separate species entirely before anybody connected it to eels. It drifts with ocean currents for a period measured in months to years, crossing an ocean.
THE GLASS EEL is what it becomes on approaching the continental shelf: a small, transparent, recognisably eel-shaped fish that arrives at coasts and estuaries in vast numbers, historically in runs so dense they were harvested by the ton.
THE ELVER is a glass eel that has begun to pigment and is moving into fresh water, ascending rivers with a remarkable capacity to climb wet surfaces and cross damp ground.
THE YELLOW EEL is the long freshwater growth phase, and it is long: years to decades, in rivers, lakes, ditches and drains, feeding and growing, and — extraordinarily — with the duration apparently plastic rather than fixed.
THE SILVER EEL is the migratory adult. The eye enlarges, the flanks silver, the gut regresses, and the fish stops feeding and leaves for the sea on a one-way journey to spawn.
WHAT MAKES THIS SO STRANGE, stated plainly. The animal is CATADROMOUS — the opposite of a salmon — feeding in fresh water and breeding at sea. It changes body plan several times. It stops feeding for the final migration. It spawns once and dies. And its sex is not determined at fertilisation but influenced by conditions during the freshwater phase, including density, which is a mechanism almost unknown in fish that people fish for.
AND ITS SPAWNING HAS NEVER BEEN DIRECTLY OBSERVED, which has its own record because the fact that a species this well known and this heavily exploited has a reproductive event nobody has watched is itself remarkable.
WHY THIS MATTERS NOW. The European eel is assessed as critically endangered following a recruitment collapse of very large magnitude, and the fisheries built on the glass eel and yellow eel stages are now prohibited or tightly restricted almost everywhere. A life history this long, this dependent on ocean conditions and this reliant on free passage through rivers is exposed at every stage, and the collapse has its own record too.
Where to go next
Fish this applies to
What these connections rest on (1)
Scientific evidence — 1 connection
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
European eel
A mechanism edge between a record and the biology beneath it. The underlying claims are documented in the fisheries science and reference literature cited rather than restated from practice.
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Scientific advice on the European eel including recruitment trends, the state of the stock and the basis for management advice.States this directlyCitation checked — the work exists and is described correctly
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: Global extinction-risk assessment, population trend and the threats identified for the species concerned.States this directlyCitation checked — the work exists and is described correctly
Where this applies
What these connections rest on (1)
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Lough Neagh
A place joined to the mechanism that explains what is distinctive about fishing there, which is what makes a location record transferable rather than local colour.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, habitat association, life history and depth range recorded for the species concerned.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: Biology, distribution and conservation status of British and Irish freshwater and diadromous fishes.States this directlyCitation checked — the work exists and is described correctly
- The Fishes of the British Isles and North-West Europe — Macmillan, 1969 (Reference work)Relied on for: Distribution, habitat and biology of the fishes of the British Isles and north-west Europe.States this directlyCitation checked — the work exists and is described correctly
Related reading
- Catadromy, anadromy, and crossing the salinity lineThe eel's life is the catadromous case in its most extreme form, with the salinity crossing made twice and the second one on a one-way journey with no feeding.
- Eel and elver fisheriesA fishery that takes glass eels arriving from an ocean spawning ground cannot be understood without the life cycle that produces them, and the reason the fishery is now restricted almost everywhere is a recruitment collapse in exactly that stage.
- Why European eel populations collapsedA life history this long, this dependent on ocean conditions and this reliant on free passage through rivers is exposed at every stage, which is why the causes are plural rather than singular.
What these connections rest on (3)
Scientific evidence — 2 connections
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
Catadromy, anadromy, and crossing the salinity line
A mechanism edge between a record and the biology beneath it. The underlying claims are documented in the fisheries science and reference literature cited rather than restated from practice.
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Scientific advice on the European eel including recruitment trends, the state of the stock and the basis for management advice.States this directlyCitation checked — the work exists and is described correctly
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: Global extinction-risk assessment, population trend and the threats identified for the species concerned.States this directlyCitation checked — the work exists and is described correctly
Why European eel populations collapsed
A mechanism edge between a record and the biology beneath it. The underlying claims are documented in the fisheries science and reference literature cited rather than restated from practice.
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Scientific advice on the European eel including recruitment trends, the state of the stock and the basis for management advice.States this directlyCitation checked — the work exists and is described correctly
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: Global extinction-risk assessment, population trend and the threats identified for the species concerned.States this directlyCitation checked — the work exists and is described correctly
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Eel and elver fisheries
A mechanism edge between a record and the explanation beneath it. The link rests on established practitioner knowledge rather than on experiment, and the support level says so rather than borrowing an authority it does not have.
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: Global extinction-risk assessment, population trend and the threats identified for the species concerned.States this directlyCitation checked — the work exists and is described correctly
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Scientific advice on the state of north-east Atlantic stocks, including recruitment trends and the basis for management advice.States this directlyCitation checked — the work exists and is described correctly
How this compares
What these connections rest on (1)
Scientific evidence — 1 connection
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
Where eels spawn, and why nobody has watched
Two biological records a reader will hold together, joined where the contrast between them is the informative part.
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Scientific advice on the European eel including recruitment trends, the state of the stock and the basis for management advice.States this directlyCitation checked — the work exists and is described correctly
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: Global extinction-risk assessment, population trend and the threats identified for the species concerned.States this directlyCitation checked — the work exists and is described correctly
Sources for this page
- ICES Advice on fishing opportunities, catch and effort — International Council for the Exploration of the Sea (Scientific institute)Relied on for: Scientific advice on the state of north-east Atlantic stocks, including recruitment trends and the basis for management advice.States this directlyCitation checked — the work exists and is described correctly
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: Global extinction-risk assessment, population trend and the threats identified for the species concerned.States this directlyCitation checked — the work exists and is described correctly
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: Biology, life history, distribution and conservation status of British and Irish freshwater and diadromous fishes.States this directlyCitation checked — the work exists and is described correctly
How FishingHQ labels evidence is explained in the evidence policy.