Lampreys resemble eels in external appearance and, although not related to the true eels, are sometimes called lamprey eels. When not attached to prey, they swim with undulating movements. The marine lampreys normally migrate into freshwater to spawn, and some populations have become landlocked in freshwater.
The sexes are separate in lampreys and fertilization is external. The parents die shortly after the eggs are deposited in a nest. The larvae, called ammocoetes, are about 1/4 in. (6 mm) long. They are transparent, eyeless filter-feeders and live in muddy river bottoms, eating particles of organic matter. Ammocoetes are used in zoology courses to demonstrate a theoretically primitive vertebrate construction. At about five years of age they metamorphose into the adult, parasitic form. In some species the adult does not feed and remains the size of the larva.
There are 7 genera and about 25 species of lampreys, with 13 species in the United States. The Atlantic lamprey, Petromyzon marinus, found on both sides of the Atlantic, has become well established in the Great Lakes, where it is considered a serious pest by the fishing industry. Lampreys are classified in the phylum Chordata, subphylum Vertebrata, class Agnatha, order Cyclostomata, family Petromyzontidae.
A lamprey (sometimes also called lamprey eel) is a jawless fish with a toothed, funnel-like sucking mouth. While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority. In zoology, lampreys are often not considered to be true fish because of their vastly different morphology and physiology.
Lampreys live mostly in coastal and fresh waters, although at least one species, Geotria australis, probably travels significant distances in the open ocean, as evidenced by the lack of reproductive isolation between Australian and New Zealand populations, and the capture of a specimen in the Southern Ocean between Australia and Antarctica. They are found in most temperate regions except Africa. Their larvae have a low tolerance for high water temperatures, which is probably why they are not found in the tropics.
Outwardly resembling eels, in that they have no scales, an adult lamprey can range anywhere from 13 to 100 centimetres (5 to 40 inches) long. Lampreys have no paired fins, large eyes, one nostril on the top of the head, and seven gills on each side. The unique morphological characteristics of lampreys, such as their cartilaginous skeleton, mean that they are the sister taxon (see cladistics) of all living jawed vertebrates (gnathostomes) and are not classified within the Vertebrata itself. This is disputed by some, who place lampreys within Vertebrata. Hagfish, which superficially resemble lampreys, are the sister taxon of the lampreys and gnathostomes (a clade termed the Craniata).
Studies reported in Nature suggest that lampreys have a unique type of immune system with parts that are unrelated to the antibodies found in mammals. They also have a very high tolerance to iron overload, and have biochemical defenses to detoxify this metal.
Lampreys begin life as burrowing freshwater larvae (ammocoetes). At this stage, they are toothless, have rudimentary eyes, and feed on microorganisms. This larval stage can last five to seven years and so was originally thought to be an independent organism. They transform into adults in a metamorphosis which is at least as radical as that seen in amphibians. It involves a radical rearrangement of internal organs, development of eyes and transformation from a mud-dwelling filter feeder into an efficient swimming parasite/predator that typically moves to the sea. The adult feeds by attaching its mouth to a fish, secreting an anticoagulant to the host, and feeding on the blood and tissues of the host. In most species this phase lasts about 18 months.
Some lampreys are landlocked and remain in fresh water, and some of these stop feeding when they leave the larval stage. The landlocked species are usually rather small. To reproduce, lampreys return to fresh water, build a nest, spawn (that is, females lay eggs, males excrete semen), then invariably die. In Geotria australis, the time from ceasing to feed at sea to spawning can be up to 18 months.
In the 22 June 2006 issue of Nature, Mee-mann Chang and colleagues reported on a fossil lamprey from the same Early Cretaceous lagerstätten that have yielded feathered dinosaurs, in the Yixian Formation of Inner Mongolia. The new species, morphologically similar to Carboniferous and modern forms, was given the name Mesomyzon mengae ("Middle lamprey"). The exceedingly well-preserved fossil showed a well-developed sucking oral disk, a relatively long branchial apparatus showing branchial basket, seven gill pouches, gill arches and even the impressions of gill filaments, and about 80 myomeres of its musculature.
Months later, in the 27 October issue of Nature, an even older fossil lamprey, dated 360 million years ago, was reported from Witteberg Group rocks near Grahamstown, in the Eastern Cape of South Africa. This species, dubbed Priscomyzon riniensis still strongly resembled modern lampreys despite its Devonian age.
Within this family, there are 40 recorded species in nine genera and three subfamilies:
Some taxonomists place lampreys and hagfish in the phylum Chordata under the super-class Agnathostomata (without jaws). The other super-class of the phylum is Gnathostomata (jaw-having) and includes the classes Chondrichthyes, Osteichthyes, Amphibia, Reptila, Aves, and Mammalia.
Lampreys have long been used as food for humans. 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 true fish. King Henry I of England is said to have died from eating "a surfeit of lampreys". On 4th March 1953, the Queen of the United Kingdom's coronation pie was made by the Royal Air Force using lampreys.
Especially in southwestern Europe (Portugal, Spain, and France), larger lampreys are still a highly prized delicacy. Overfishing has reduced their number in those parts. Lampreys are also consumed in Sweden, Finland, the Baltic countries, and South Korea.
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.
Sea lampreys have become a major plague 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. Since the majority of North American consumers, unlike Europeans, refuse to accept lampreys as food, the Great Lakes fishery has been adversely affected by their invasion. 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 lamprey in a method akin to the sterile insect technique. Research is currently under way on the use of pheromones and how they may be used to disrupt the life cycle (Sorensen, et al., 2005). 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 State, Vermont, and Quebec, and New York's Finger Lakes are also home to populations of sea lampreys whose high populations have warranted 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.
Stephen King's novel Dreamcatcher has alien cratures that look and move like Lampreys, which are nicknamed in the novel, "shitweasles"