Sea Lamprey

Sea Lamprey
    • Scientific name: Petromyzon marinus
    • Also know as: Lamprey Eel, Eelsucker, Nine Eyed Eel, Vampire Eel
    • Size: up to 3ft. Typically 1ft to 18inches.
    • UK minimum size: N/a
    • UK shore caught record: N/a
    • IUCN Status
      • Global: LC (Least Concern)
      • Europe: LC (Least Concern)
    • Distribution: Widespread but patchy distribution throughout the UK. Found along coastlines and will also travel up rivers meaning it can be found far inland.
    • Feeds on: Parasite which feeds on the blood of other fish.
    • Description: Long and slender eel-like body, which can be black or a mottled dark green to yellow in colour. The underside is pale. Eyes are located on either side of the head and the gills are made up of seven holes either side of the body, rather than gill slits. There is a single nostril at the top of the head. Dorsal fins are set back on the body and no pectoral, pelvic or anal fins are present. The mouth consists of a disc full of circular rows of very sharp small teeth.

The sea lamprey is a parasitic creature which is found around much of the United Kingdom and Ireland. An anadromous species (able to live in both marine and freshwater environments) the sea lamprey feeds primarily on the blood of other species, and its biological makeup means that this species is extremely difficult to classify.


Lamprey are found in both European and North American waters. In Europe they are present in the North Sea, the Baltic Sea and off the coast of Norway, with their range extending into the Bay of Biscay. They are also found in the Mediterranean. In North America they are found from Nova Scotia to Florida and are also found in the Great Lakes of the USA and Canada. In all areas where they are present lamprey will travel up rivers meaning they can be found very far inland, and lamprey can also be found in landlocked lakes where they have been inadvertently introduced.

Life Cycle and Reproduction

Lamprey hatch in freshwater. The adults travel up rivers from the sea and seek out soft sandy or muddy ground to lay their eggs on. The distance they travel along rivers varies – sometimes they are still in tidal saltwater when they spawn, whereas in some areas they have been found laying eggs many miles inland.

Sea lamprey attached to a trout
Two lampreys attached to an American lake trout.

Once they have found their spawning ground the lamprey will dig a hole into the riverbed to lay their eggs in. They are capable of moving fairly large stones out of the way with their mouths in order to create the right sized depression in the seabed. The eggs will be laid here and shortly after spawning the lampreys will begin to weaken and will die a short time later. The eggs hatch and the lamprey larvae look very different to the adults, having a flat tadpole-like appearance, no eyes and lacking the circular mouth. The young lamprey live in the freshwater environment for a long time – usually three or four years, but sometimes as long as six years – and filter feed on passing microscopic matter. This long larval stage originally led to the immature lampreys being classed as a separate species, although it was eventually discovered that they were in fact juvenile lamprey. Once the lamprey reaches around six inches in length they transform into an adult appearance and head back to the sea to live and feed in their parasitic adult form. After living in the sea for several years they head back along the rivers to spawn and die, repeating the process.


Lamprey Mouth
A view of the rows of sharp teeth in a lamprey’s mouth.

When fully grown and living in the sea the lampreys only aim is to feed. They do this by hunting down a fish and clamping themselves onto the flank of the fish with their powerful, flat circular mouth. Once attached they will use their sharp teeth and abrasive tongue to chew through the skin and/or scales of the host fish and the begin feeding on the blood. They also emit a mucus which prevents the wound they have inflicted on the host from healing. Lampreys are very aggressive when hunting a suitable fish and attaching themselves to the host. They are unfussy about which species they choose to feed on, with pretty much any fish from mackerel, cod and haddock to rays, conger eels and even massive basking sharks all being found with lampreys attached. Sometimes a single fish can be found with several lampreys attached to their body. Eventually, through a combination of blood loss and infection, the host fish will become weak and will eventually die. The lamprey will detach itself and search for a new host. Occasionally lampreys will be found attached to rocks, driftwood or even the underside of boats. The reason for this is unknown as the lamprey will obviously not be getting any form of sustenance from this. One theory is that lampreys attach themselves to inanimate objects to rest while they are searching for a new host.

Other Species of Lamprey

There are two other species of lamprey found in British waters. The river lamprey (Lampetra fluviatilis) has a similar life cycle to the sea lamprey but grows to a smaller size of around 40cm and spends less of its lifetime in marine waters. The other species is the brook lamprey (Lampetra planeri). This is a smaller species, only growing to 15cm which lives its entire life in freshwater. This species is not parasitic and is instead a filter feeder for its whole life.

Difficulty in Classification

Lampreys are an ancient species and do not appear to have evolved at all in several million years. They have primitive features such as gill holes, rather than slits, and a mouth which is incapable of opening or closing. These unique feature makes the lamprey very difficult to classify as they do not fit into any of the existing animal groups.

Lamprey Gills
A picture showing the primitive gill holes of the sea lamprey. The row of seven gill holes, along with the eye and single nostril at the top of the head has led to the ancient name of nine-eyed eel being used to describe the lamprey.

Despite their appearance, they cannot be classed as either eels or fish as they lack features such as scales and opposing fins. They also have a skeleton made out of cartilage (like sharks and rays) whereas fish and eels have skeletons made of bone. Some scientific literature classes them in the subgroup of Agnatha (jawless fishes which include the hagfish), whereas other literature places lampreys in the unique but disputed group of Hyperoartia which consists of only lampreys and their extinct relatives (which have been identified only through fossils). At the time of writing, there is still no scientific consensus on how to classify lampreys and they fall between recognised classifications.

Human Interactions with Lamprey

Tacuinum Sanitatis Lamprey Fishing
People fishing for lamprey to eat. This picture is taken from Tacuinum Sanitatis, a fifteenth century book on health and wellbeing.

Despite their gruesome way of life lamprey have long been a source of food for humans and have been considered a delicacy in many cultures. The ancient Greeks and Romans ate lamprey, and King Henry I of England was said to have died of food poison after eating many lampreys in a short amount of time. Lampreys are still eaten throughout much of Europe. In Britain, lampreys are not popular as a food today. They do, however, have a long association with the Royal Family (despite the death of Henry I) and lamprey pies were specially cooked for the Queen as part of the Diamond Jubilee celebrations in 2012. The number of lampreys in Britain has reduced in recent years, possibly due to freshwater pollution and dams and other barriers blocking the lampreys natural migration routes. In some areas of Britain lamprey are a protected species – in 2015 conservation work on the historic Thornton Bridge which crosses the River Swale near Thirsk, North Yorkshire had to be stopped for thirteen weeks as the construction work would disturb lampreys which were spawning in the river. Despite the reduction in numbers the IUCN (International Union for the Conservation of Nature) classes the sea lamprey as a species of Least Concern on both a global and European basis. Indeed, lamprey numbers appear to be increasing around the British Isles, with recent years seeing lamprey return to rivers which they have been absent from for years, such as the Trent, Wear and Ouse.

Lampreys do not attack humans as they are adapted to attach themselves to cold-blooded fish and not warm-blooded mammals. Occasionally lamprey will attempt to attach themselves to a swimmer but they can be fairly easily removed, and would probably detach themselves anyway when the realise that they are not feeding on a fish. Swimmers in America’s Great Lakes appear to be the most commonly ‘attacked’ by lampreys. The famous Canadian long-distance swimmer Marilyn Bell successfully swam the thirty-two mile width of Lake Ontario in 1954 when she was just sixteen years old. Along with strong winds, high waves and bad weather she listed attacks from lampreys which constantly attached themselves to her swimming suit and attempted to feed on her as one of the biggest challenges of the swim.

Lamprey as a Fishing Bait

Lamprey have long been used as a fishing bait in freshwater fishing. They are available frozen from tackle shops and online bait retailers and are popular for deadbaiting for large predatory freshwater species such as pike. Lamprey have yet to catch on as a mainstream sea fishing bait. However, anglers who have experimented with lamprey as a bait have reported that cod, bass and conger eels have all been caught on lamprey which was bought frozen. It could be the case that if more anglers used lamprey it could become an effective bait for a range of sea fish species.

Invasive Species Status in the United States

Authorities in the United States and Canada take a very different view of the lamprey to the British, and rather than protecting it they considered it to be a dangerous invasive species. Lampreys have been present in the Great Lakes since the late 1950s when artificial canals were cut into the lakes allowing lamprey to enter.

Great Lakes
A photograph of the Great Lakes taken from the International Space Station. Lamprey have become a major issue in the Great Lakes in recent decades.

With no natural predators and perfect conditions for reproduction, the lamprey population in the Great Lakes rapidly increased and the lampreys caused damage to valuable sport fish such as trout and salmon. This situation is made worse by the fact that lampreys will generally attach themselves to the largest – and therefore the most valuable – fish which are present in the lakes.

Sea lamprey damage on a salmon
Sea lamprey damage on a salmon. A fish with wounds like this would almost certainly die through infection.

Over the decades many methods have been employed to try and reduce the lamprey population. These include the use of ‘lampricide’ – a poison which kills lampreys but supposedly leaves all other aquatic life unharmed and the introduction of barriers and traps to stop lamprey travelling into the lakes. Often lamprey will be targeted in creeks and rivers before they reach the Great Lakes as they are much easier to remove before they reach the main bodies of water. In June 2013 there was a major operation to kill sea lampreys in a creek before they could reach leak Michigan. It is thought that the US Fish and Wildlife Service and the Canadian Department of Fisheries and Oceans collectively spend many millions of dollars every year attempting to control lamprey numbers in the Great Lakes and surrounding areas.