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Lamprey

May 28, 2014

Lampreys (aka. lamprey eels) are an order of jawless fish, the adult of which is characterized by a toothed, funnel-like sucking mouth. The common name "lamprey" is probably derived from Latin lampetra, which may mean "stone licker" (lambere "to lick" + petra "stone").
Pacific Lamprey Swimming
Pacific Lamprey Swimming

While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, most species of lampreys are not parasitic and never feed on other fish. The lampreys are a very ancient lineage of vertebrates, though their exact relationship to hagfishes and jawed vertebrates is still a matter of dispute.

Characteristics


Adults physically resemble eels, in that they have no scales, and can range from 13 to 100 cm (5.0 to 40 inches) long. Lacking paired fins, adult lampreys have large eyes, one nostril on the top of the head, and seven gill pores on each side of the head. The unique morphological characteristics of lampreys, such as their cartilaginous skeleton, suggest they are the sister taxon of all living jawed vertebrates (gnathostomes), and are usually considered the most basal group of the Vertebrata. Parasitic lampreys feed on prey as adults by attaching their mouth parts to the target animal's body, then using their teeth to cut through surface tissues until they reach blood and body fluid. Although attacks on humans do occur, they will generally not attack humans unless starved. Non-parasitic lampreys, which are usually freshwater species, do not feed as adults; they live off reserves acquired as larvae, which they obtain through filter feeding.

Painting of Lamprey
Painting of Lamprey

Hagfish, which superficially resemble lampreys, are the sister taxon of the true vertebrates (lampreys and gnathostomes).

Lamprey close-look at rowed teeth
Lamprey close-look at rowed teeth

The pharynx is subdivided; the ventral part forming a respiratory tube that is isolated from the mouth by a valve called the velum. This is an adaptation to how the adults are feeding, which both prevents the prey's body fluids from escaping through the gills or interfering with the gas exchange, which takes place by pumping water in and out of the gill pouches instead of taking it in through the mouth. Near the gills are the eyes, which is poorly developed and buried under skin in the larvae. The eyes' development is completed during metamorphosis, and is in adults covered by a thin and transparent layer of skin that becomes opaque in preservatives.

Pouched lamprey (Geotria australis) larvae also have a very high tolerance for free iron in their bodies, and have well-developed biochemical systems for detoxification of the large quantities of these metal ions.

Research


The lamprey has been extensively studied because its relatively simple brain is thought in many respects to reflect the brain structure of early vertebrate ancestors. In a study of the lamprey tectum published in 2007, researchers found electrical stimulation could elicit eye movements, lateral bending movements, or swimming activity, and the type, amplitude, and direction of movement varied as a function of the location within the tectum that was stimulated. These findings were interpreted as consistent with the idea that the tectum generates goal-directed locomotion in the lamprey as it does in other species.

Lampreys are used as a model organism in biomedical research, where their large reticulospinal axons are used to investigate synaptic transmission. The axons of lamprey are particularly large and allow for microinjection of substances for experimental manipulation.

Distribution

Lamprey biting man's arm
Lamprey biting man's arm

Lampreys live mostly in coastal and fresh waters, although some species (e.g. Geotria australis, Petromyzon marinus, and Entosphenus tridentatus) travel significant distances in the open ocean, as evidenced by their lack of reproductive isolation between populations. Some species are found in land-locked lakes. They are found in most temperate regions except those in Africa. Their larvae (ammocoetes) have a low tolerance for high water temperatures, which may explain why they are not distributed in the tropics.

Lamprey distribution may be adversely affected by overfishing and pollution. In Britain, at the time of the conquest, lampreys were found as far upstream in the River Thames as Petersham. Reduction of pollution in the Thames and River Wear has led to recent sightings in London and Chester-le-Street.

Distribution may also be adversely affected by dams and other construction projects disrupting migration routes, obstructing access to spawning grounds. Conversely, the construction of artificial channels has exposed new habitats for colonisation notably in North America where sea lampreys have become a significant introduced pest in the Great Lakes.

Lifecycle


Adult lampreys spawn in rivers and then die. The young larvae spend several years in the rivers, where they live burrowed in fine sediment, filter feeding on detritus and microorganisms. Then, larvae undergo a metamorphosis lasting several months. Some species do not feed after metamorphosis, while others migrate to the sea or lakes, where they feed on different species of fish and even on marine mammals. Species whose adults migrate to the sea begin preying on other fish soon after metamorphosis, even as they begin swimming downstream.

Fossil record


Lamprey fossils are rare because cartilage does not fossilize as readily as bone. The first fossil lampreys were originally found in Early Carboniferous limestones, marine sediments laid down more than 300 million years ago in North America: Mayomyzon pieckoensis and Hardistiella montanensis, from the Mississippian Mazon Creek lagerst├Ątte and the Bear Gulch limestone sequence..

As food


Lampreys have long been used as food for humans. They were highly appreciated by ancient Romans. During the Middle Ages, they were widely eaten by the upper classes throughout Europe, especially during fasting periods, since their taste is much meatier than that of most other fish. King Henry I of England is said to have died from eating "a surfeit of lampreys."

On 4 March 1953, Queen Elizabeth II's coronation pie was made by the Royal Air Force using lampreys.

Especially in southwestern Europe (Portugal, Spain, and France), and in the northern half in Finland, larger lampreys are still a highly prized delicacy. Sea lamprey is the most sought species in Portugal and one of only two that can legally bear the commercial name "lamprey" (lampreia): the other one being Lampetra fluviatilis, the European river lamprey, both according to Portaria (Government regulation no. 587/2006, from 22 June). Overfishing has reduced their number in those parts. Lampreys are also consumed in Sweden, Finland, Russia, New Zealand, the Baltic countries, Japan, and South Korea.

The mucus and serum of several lamprey species, including the Caspian lamprey, river lampreys , and sea lamprey, are known to be toxic, and require thorough cleaning before cooking and consumption.

In Britain, lampreys are commonly used as bait, normally as dead bait. Northern pike, perch, and chub all can be caught on lampreys. Frozen lampreys can be bought from most bait and tackle shops.

As pests


Lampreys attached on a Lake Trout
Lampreys attached on a Lake Trout
Sea lampreys have become a major pest in the North American Great Lakes after artificial canals allowed their entry during the early 20th century. They are considered an invasive species, have no natural enemies in the lakes, and prey on many species of commercial value, such as lake trout. Lampreys are now found mostly in the streams that feed the lakes, with special barriers to prevent the upstream movement of adults, or by the application of toxicants called lampricides, which are harmless to most other aquatic species. However, those programs are complicated and expensive, and do not eradicate the lampreys from the lakes, but merely keep them in check. New programs are being developed, including the use of chemically sterilized male lampreys in a method akin to the sterile insect technique. Research currently under way on the use of pheromones and how they may be used to disrupt the lifecycle has met with some success. Control of Sea lampreys in the Great Lakes is conducted by the U.S. Fish and Wildlife Service and the Canadian Department of Fisheries and Oceans. The work is coordinated by the Great Lakes Fishery Commission.

Lake Champlain, bordered by New York, Vermont, and Quebec, and New York's Finger Lakes are also home to high populations of sea lampreys that warrant control. Lake Champlain's lamprey control program is managed by the New York State Department of Environmental Conservation, the Vermont Department of Fish and Wildlife, and the U.S. Fish and Wildlife Service. New York's Finger Lakes sea lamprey control program is managed solely by the New York State Department of Environmental Conservation.

Folklore


Lampreys are called "nine-eyed eels" (i.e., per side) from a counting of their seven external gill slits on a side with one eye and the nostril. A German word for lamprey is Neunauge, which means "nine-eye".