Sea lamprey

Fish · Last reviewed 2026-08-19

A jawless, boneless, parasitic fish with a rasping sucker for a mouth — a delicacy in Iberia, an invasion that broke the Great Lakes, and a strictly protected species across much of its native range.

Safety

Biosecurity and disease transfer — Can cause injury needing treatment

Sea lamprey in the Great Lakes is the clearest demonstration anywhere of what a migratory parasite does when it reaches a fish community with no evolved defence against it, and the route it took was a man-made waterway. Moving live fish, water or unwashed equipment between catchments is the same mechanism operating at a smaller scale.

What reduces it: Check, clean and dry equipment between waters, never move live fish or water between catchments, and treat larval-bearing silt on waders and nets as a transport risk rather than as dirt.

Worse when:

Where a canal, transfer scheme or navigation joins two catchments that were previously separate.
Where equipment goes between a river with a lamprey population and one without in the same season.

Fish welfare — Can cause injury needing treatment

Adults die after a single spawning, so every fish removed or killed on the spawning run is a whole reproductive event lost, and the larval phase lasting several years means a population knocked back recovers slowly. In much of the native range the species is additionally protected.

What reduces it: Return any lamprey encountered immediately and without handling, do not disturb gravel nests or silt beds during the spring run, and establish the position with the responsible authority before assuming anything may be taken.

A lamprey is not a fish in the sense the rest of this catalogue uses the word. It has no jaw, no paired fins, no bone and no scales. Its mouth is a circular sucker lined with rings of horny teeth and a rasping tongue, and its skeleton is cartilage. The lineage it belongs to separated from everything else with a backbone several hundred million years ago, and it is the reason `jawless_fish` had to be added to this catalogue's taxonomy before the record could be written.

Its life history is stranger than its anatomy. Adults run from the sea into rivers to spawn and die. The larvae — ammocoetes — are blind, toothless filter-feeders that burrow into silt beds and stay there for several years, looking so unlike the adult that they were long described as a separate genus. They then transform, go to sea, and become parasites: attaching to a host fish, rasping through the body wall and feeding on blood and tissue.

The same animal is therefore three completely different things depending on where a reader meets it. In Portugal, Spain and south-west France it is a prized and expensive traditional food with a genuine seasonal fishery. In the North American Great Lakes it is a catastrophic invader that reached above Niagara Falls through canal construction and collapsed a fishery. In British and Irish rivers it is a native species in long decline and strictly protected, alongside two smaller relatives.

Identification

FishingHQ holds no photograph of this species whose identity and licensing it can vouch for, so it is not showing one. Misidentified fish photographs teach identification wrongly, and a picture with an unchecked caption would be worse than none. The identification points below are what to look at instead.

Scientific name: Petromyzon marinus
Family: Petromyzontidae
Water: Moves between fresh and salt water
Conservation status: Varies by population
Regions: Britain & Ireland, Western Europe, Northern Europe, Mediterranean, North America

No jaw. The mouth is a circular sucking disc lined with concentric rows of horny teeth — the single feature that separates any lamprey from every other animal an angler will encounter.
No paired fins. There are no pectorals and no pelvics, only fin folds along the back and tail, which is why a lamprey swims like an eel but does not look like one on close inspection.
Seven circular gill openings in a row behind the eye on each side, which is the origin of the folk name 'nine-eyed eel' — the eye and the nostril making up the other two.
Adult sea lamprey are large, commonly over half a metre, with a marbled dark-on-olive pattern; river lamprey are much smaller and plainer, and brook lamprey smaller again.
Brook lamprey never parasitise anything and never go to sea: adults do not feed at all. A small lamprey in a stream is far more likely to be this harmless species than a sea lamprey.
Larvae (ammocoetes) are blind, toothless and worm-like, buried in silt, and are frequently mistaken for worms or eel fry rather than for lampreys at all.

Size

Typical: 30–60 cm as returning adults
Large: 70–90 cm

Exceptional: FishBase records a maximum around 120 cm

Lifecycle and reproduction

Several years — commonly three to seven, sometimes longer — spent as a blind filter-feeding larva buried in river silt, then metamorphosis into the toothed adult form, a marine parasitic phase of one to two years, and a single spawning migration back into fresh water after which the adult dies. The long silt-dwelling larval phase is the part that matters for conservation, because it means river bed condition over many years determines whether a population survives at all.

Adults run into rivers in spring, excavate a shallow nest in gravel by moving stones with the sucker — the behaviour behind the genus name, which means 'stone sucker' — spawn, and die. The whole adult phase ends at spawning, so every returning adult is a one-time event and a run that fails is not repeated by the same fish.

Feeding and senses

Larvae filter organic particles from silt and feed on nothing else. Adults at sea attach to a host fish with the sucker, rasp through the skin with the tongue, and feed on blood and body fluid, secreting an anticoagulant. A host may survive the attachment or may not, and the scarring is distinctive enough to be used as evidence of lamprey pressure on a stock.

Larvae are blind and function entirely by chemoreception in the dark of the silt. Adults have functional eyes but are strongly driven by smell: migrating adults locate spawning rivers by detecting a pheromone released by the larvae already living in them, which means a river with no larvae gives off no signal and is not recolonised easily once lost.

Through the year

The spawning run into rivers is the only phase most people ever see, and it is concentrated in spring and early summer. Outside it the adults are at sea attached to hosts and the larvae are invisible in the silt, which is why a species that can be locally abundant appears to be absent for most of the year.

Distribution

Native to the North Atlantic on both sides: western Europe from Scandinavia to the Mediterranean, and eastern North America. Landlocked populations exist in the North American Great Lakes, where the species is not native above Niagara Falls and arrived through canal construction in the nineteenth and twentieth centuries.

This is a biological range — where the species occurs, not a prediction that you will catch one. To browse the fishing geography FishingHQ holds, start at fishing places.

Why anglers care

Not an angling quarry in any ordinary sense — a lamprey has no jaw and cannot be hooked in the usual way, and where it is taken it is taken in traps and nets under specific arrangements rather than on rod and line. Its significance to anglers is threefold and entirely indirect. It is a well-established DEADBAIT for pike, catfish and other large predators, sold frozen and valued because it bleeds heavily and holds scent. It is the animal behind the scarring anglers find on salmon, shad and other hosts. And it is one of the species whose presence or absence is used as evidence of river condition, which puts it at the centre of the migratory-fish restoration work now running on many European rivers.

Handling and returning

A lamprey caught or found incidentally should be handled as little as possible and returned immediately, wet-handed, without attempting to detach a sucker by pulling. In much of its native range it is a protected species and handling may itself be restricted — FishingHQ does not state what any current rule is, and the responsible authority holds the position. The sucker can grip a hand and the sensation is alarming rather than dangerous; the teeth are horny rasping structures rather than cutting ones and a lamprey cannot bite in the way its mouth suggests.

Where to go next

Where you will find it

What these connections rest on (5)

Scientific evidence — 5 connections

Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.

France
That the species occurs in these waters, drawn from distribution science and stock literature.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly
Portugal
That the species occurs in these waters. The cultural note describes a fishery that exists; it states no rule about it and no permission to participate in one.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly
The Bay of Biscay
That the species occurs in these waters, drawn from distribution science. It is not a statement that anybody will encounter one.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly
The Great Lakes
That the species occurs in these waters, and that its occurrence there is an introduction rather than a native range. Both are statements about where the animal is, not about anybody fishing for it.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly
The Severn Estuary
That the species occurs in these waters, drawn from distribution science and from the conservation literature on the system.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly

Understanding this fish

Catadromy, anadromy, and crossing the salinity lineThe record uses lampreys as a worked example of anadromy and could not point at one. Feed at sea, breed in fresh water, and die at the end of a single spawning run.

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.

Catadromy, anadromy, and crossing the salinity line
A link from the animal to the mechanism that explains its life history, closing a reference the concept record was already making.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly

Told apart from

European eelThe two animals a reader most often confuses, and they are not close relatives at all — an eel is a bony fish with jaws and paired fins, a lamprey has none of the three. Both are long, both are diadromous, and both are in trouble, which is where the resemblance ends.

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 navigational link between two records a reader genuinely confuses, offered as orientation and as a correction rather than as a ranking.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Distribution, environment and diadromous parasitic life history of Petromyzon marinus.States this directlyPassage read and verified
- Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The lampreys of the British Isles and north-west Europe: identification, the ammocoete larval phase, spawning behaviour and population status.States this directlyCitation checked — the work exists and is described correctly

Rules and access

Protected species, and why some fish may not be takenThe same animal is strictly protected in some rivers, a legally taken traditional food in others, and a control target in a third. FishingHQ states none of those positions — it states the biology that explains why they differ, and routes the question to the authority.

What these connections rest on (1)

Authoritative guidance — 1 connection

Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.

Protected species, and why some fish may not be taken
A link to a rule CONCEPT rather than to a rule. It exists to force the page to say that the answer is held elsewhere and differs by jurisdiction, which for this species is unusually true.
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: The conservation assessment of the species concerned and the basis for treating population status as varying rather than uniform.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: The decline of migratory fishes in European rivers and the habitat requirements — including long-duration silt beds for larvae — that explain it.States this directlyCitation checked — the work exists and is described correctly

Environment and conservation

Invasive species and biosecurityThe clearest demonstration anywhere of an introduction routed through a man-made waterway, and the reason canal and transfer schemes are treated as biosecurity events rather than as engineering.

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.

Invasive species and biosecurity
An environmental claim resting on the documented history of the introduction and its consequences, attached to the species that caused it.
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: The conservation assessment of the species concerned and the basis for treating population status as varying rather than uniform.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: The decline of migratory fishes in European rivers and the habitat requirements — including long-duration silt beds for larvae — that explain it.States this directlyCitation checked — the work exists and is described correctly

Check the rules before you fish

Fishing laws, bylaws, access rules, seasons, bait restrictions and permitted methods vary by location and can change. Check the current rules from the relevant authority and the water you intend to fish before fishing.

Check with:

Current national or regional law for where you are fishing
Current local bylaws
The relevant fisheries authority
The landowner, club or fishery whose water it is
Any restrictions specific to the species or the method you intend to use

Sources for this page

FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Family placement, maximum size, environment and distribution of Petromyzon marinus, and its diadromous parasitic life history.States this directlyPassage read and verified
Freshwater Fishes of the British Isles — HarperCollins (New Naturalist 75), 1992 (Reference work)Relied on for: The three British lamprey species, their identification, the ammocoete larval phase and its duration, spawning behaviour and the status of lamprey populations in British and Irish rivers.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: Morphological description and identification of the lampreys of north-west Europe, including the gill openings, the absence of paired fins and the structure of the oral disc.Background and mechanism onlyCitation 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: The conservation assessment of Petromyzon marinus and the basis for treating its status as varying between populations rather than uniform.States this directlyCitation checked — the work exists and is described correctly

How FishingHQ labels evidence is explained in the evidence policy.

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