The lampreys (family Petromyzonidae) belong to a small but important group known as Agnatha, which literally means ‘jawless’; there are around 45 species worldwide. Three species of lamprey occur in the UK; Brook Lamprey Lampetra planeri, River Lamprey Lampetra fluviatilis and Sea Lamprey Petromyzon marinus. Although it should be noted that almost all authors regard the River and Brook Lamprey as being very closely related, and some consider them to be effectively the same species.

Lampreys are not in fact true fish. True fish exhibit upper jaws fixed closely to the skull and hinged lower jaws. In contrast, the lampreys have no lower jaws, and the mouth is surrounded by a round, sucker-like disc within which, in the adults, are strong rows of teeth. These vary in shape, size, position and number among the species, and are an important aid to identification.

Lampreys are the most primitive of all living vertebrates, having evolved almost 200m years before the dinosaurs. Two of the three species in the UK are parasitic and lack gill covers and paired fins, instead latching on to larger animals to suck their blood and eat their scales.

The Brook Lamprey

The smallest of the British lampreys (up to 14cm), which occurs in streams and occasionally lakes in north-west Europe, is also known locally as the Mud Lamprey or the Pride. It can live for up to eight years and unlike most species of lamprey, the adults do not migrate to the sea and do not have a parasitic phase.

Young Brook Lampreys are blind filter feeders, surviving on detritus and other organic matter for three to five years before maturing. Metamorphosis begins in their third or fourth year when eyes and the suction disk develop, while the digestive tract degenerates and loses its function; this full transformation can take up to a year. These adults do not feed (they develop their teeth precisely when they are no longer able to eat! It is thought that the suction disk is used for gripping stones with their teeth in order to build nests) and in the spring they spawn communally in gravel close to the soft sediment in which they were previously resident, following which they die. The eggs hatch within a few days, and the young larvae bury themselves in soft sediment with only their mouth protruding.

Populations of the Brook Lamprey have declined, although is the most abundant and widespread of the British lampreys and is often found in the absence of the other two species (for example above a barrier that precludes the presence of the migratory species).

The River Lamprey

The River Lamprey, showing its seven gill openings

The River Lamprey, known in various parts of the British Isles as the Juneba, Llamper Eel, Lampern, Nine-eyed Eel, Nine Eyes, Seven eyes, and Stone Grigis, is found only in western Europe, where it has a wide distribution from southern Norway to the Mediterranean. The UK population, which is widespread, is considered important for the conservation of the species at an EU level.  The average adult length is around 0.3m with a corresponding weight of about 60g, but specimens over 0.4m can be found, and the unusual race in Loch Lomond is often less than 0.2m.

After metamorphosis, which occurs at between three and five years of age, the aim of young River Lamprey is to descend downstream to the sea. In the estuaries of major rivers they can be found in some numbers, feeding on a variety of estuarine fish, particularly Herring Clupea harengus, Sprat Sprattus sprattus and Flounder Platichthys flesus. They often inflict considerable damage to these fish by sucking away large amounts of flesh, usually from the back. Mature River Lamprey, having spent one to two years mainly in estuaries, stop feeding in the autumn and move upstream into medium to large rivers. Spawning in British rivers, which commences in March, occurs in flowing water with patches of small stones and gravel beds. After an incubation period of some 15–30 days (depending on water temperatures) the larvae hatch, drift downstream and burrow in suitable silt beds. The larvae are about 7mm long on hatching and grow to about 50mm after one year feeding on fine particulate matter, mainly micro-organisms such as desmids and diatoms.

The Sea Lamprey

The Sea Lamprey is the largest of the British lampreys, reaching up to 1m in length and up to 2.5 kg in weight and is known colloquially as the Marine Lamprey or Lamprey Eel. This species occurs over much of the Atlantic coastal area of western and northern Europe, from northern Norway to the western Mediterranean, as well as eastern North America (where they are considered a pest). It is also found in estuaries and easily accessible rivers in these regions. Occasional specimens are even taken in mid-water in the Atlantic Ocean.

Sea Lampreys feeding

Adults enter estuaries from April onwards, and migrate some distance upstream, providing that there are no obstacles; either natural, such as waterfalls, or manmade, such as dams, weirs or pollution barriers. After hatching, larvae leave the nest and drift downstream, distributing themselves among suitable silt beds. The duration of larval life varies, but averages about five years.

History

Lampreys were a medieval delicacy and are eaten in a scene of Games of Thrones. King Henry I of England was known to be especially fond of the fish but died from food poisoning in 1135 after eating ‘a surfeit of lampreys’ while in France. Lampreys remained, however, a favourite amongst the royals; Henry’s grandson, King John, fined the city of Gloucester 40 marks (around £250,000 in today’s money) for failing to deliver him a Christmas pie filled with them!

Indeed, it was traditional for Gloucester to send a Christmas lamprey pie to the monarch until 1836 when the practice was discontinued, except for coronations and jubilees. In 2012 a pie was sent to the Queen to mark the Diamond Jubilee but numbers of UK lampreys were so low that they had to be imported from the Great Lakes of North America.

Lamprey were once common in British waters, although are now endangered across Europe, after pollution caused by industrialisation and the installation of barriers (such as weirs) in rivers which led to a population crash. However, it now seems lampreys are reappearing in their old habitats, as rivers see their lowest pollution levels for more than 100 years.

Key References

Maitland PS (2003). Ecology of the River, Brook and Sea Lamprey. Conserving Natura 2000 Rivers Ecology Series No. 5. English Nature, Peterborough