Lamprey River Iron Works

Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like sucking mouth. The common name "lamprey" is probably derived from Latin , which may mean "stone licker" ( "to lick" + "stone"), though the etymology is uncertain. ''Lamprey'' is sometimes seen for the plural form.

There are about 38 known extant species of lampreys and five known extinct species. Parasitic carnivorous species are the most well-known, and feed by boring into the flesh of other fish to suck their blood; but only 18 species of lampreys engage in this micropredatory lifestyle. Of the 18 carnivorous species, nine migrate from saltwater to freshwater to breed (some of them also have freshwater populations), and nine live exclusively in freshwater. All non-carnivorous forms are freshwater species. Adults of the non-carnivorous species do not feed; they live on reserves acquired as ammocoetes (larvae), which they obtain through filter feeding.

Distribution

Lampreys live mostly in coastal and fresh waters and are found in most temperate regions. 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. Other species are found in land-locked lakes. 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 . The reduction of pollution in the Thames and River Wear has led to recent sightings in London and Chester-le-Street.

Distribution of lampreys may also be adversely affected by dams and other construction projects due to disruption of migration routes and obstruction of 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. Active control programs to control lampreys are undergoing modifications due to concerns of drinking water quality in some areas.

Biology

Anatomy

Adults superficially resemble eels in that they have scaleless, elongated bodies, and can range from in length. Lacking paired fins, adult lampreys have large eyes, one nostril atop the head, and seven gill pores on each side of the head.

The brain of the lamprey is divided into the telencephalon, diencephalon, midbrain, cerebellum, and medulla.

The heart of the lamprey is anterior to the intestines. It contains the sinus, one atrium, and one ventricle protected by the pericardial cartilages.

The pineal gland, a photosensitive organ regulating melatonin production by capturing light signals through the photoreceptor cell converting them into intercellular signals of the lamprey is located in the midline of its body, for lamprey, the pineal eye is accompanied by the parapineal organ.

The buccal cavity, anterior to the gonads, is responsible for attaching the animal, through suction, to either a stone or its prey. This then allows the tongue to make contact with the stone to rasp algae, or tear at the flesh of their prey to yield blood.

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 feed, by preventing the prey's body fluids from escaping through the gills or interfering with gas exchange, which takes place by pumping water in and out of the gill pouches instead of taking it in through the mouth.

One of the key physical components to the lamprey are the intestines, which are located ventral to the notochord. Intestines aid in osmoregulation by intaking water from its environment and desalinating the water they intake to an iso-osmotic state with respect to blood, and are also responsible for digestion.

Near the gills are the eyes, which are poorly developed and buried under skin in the larvae. The eyes consummate their development during metamorphosis, and are covered by a thin and transparent layer of skin that becomes opaque in preservatives.

Morphology

The unique morphological characteristics of lampreys, such as their cartilaginous skeleton, suggest they are the sister taxon (see cladistics) of all living jawed vertebrates (gnathostomes). They are usually considered the most basal group of the Vertebrata. Instead of true vertebrae, they have a series of cartilaginous structures called arcualia arranged above the notochord. Hagfish, which resemble lampreys, have traditionally been considered the sister taxon of the true vertebrates (lampreys and gnathostomes) but DNA evidence suggests that they are in fact the sister taxon of lampreys.

Studies have shown that lampreys are among the most energy-efficient swimmers. Their swimming movements generate low-pressure zones around the body, which pull rather than push their bodies through the water.

Research on sea lampreys has revealed that sexually mature males use a specialized heat-producing tissue in the form of a ridge of fat cells near the anterior dorsal fin to stimulate females. After having attracted a female with pheromones, the heat detected by the female through body contact will encourage spawning.

Due to certain peculiarities in their adaptive immune system, the study of lampreys provides valuable insight into the evolution of vertebrate adaptive immunity. Generated from a somatic recombination of leucine-rich repeat gene segments, lamprey leukocytes express surface variable lymphocyte receptors (VLRs). This convergently evolved characteristic allows them to have lymphocytes that work as the T cells and B cells present in higher vertebrates immune system.

Northern lampreys (Petromyzontidae) have the highest number of chromosomes (164–174) among vertebrates.

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.

Lampreys are the only extant vertebrate to have four eyes. Most lampreys have two additional parietal eyes: a pineal and parapineal one (the exception is members of ''Mordacia'').

Adaptations

Different species of lamprey have many shared physical characteristics. The same anatomical structure can serve different functions in the lamprey depending on whether or not it is carnivorous. For example, non-carnivorous species use their teeth to scrape algae from rocks for food, rather than drilling into the flesh of hosts. The mouth and suction capabilities of the lamprey not only allow it to cling to a fish as a parasite, but provide it with limited climbing ability so that it can travel upstream and up ramps or rocks to breed. This ability has been studied in an attempt to better understand how lampreys battle the current and move forward despite only being able to hold onto the rock at a single point. Some scientists are also hoping to design ramps that will optimize the lamprey's climbing ability, as lampreys are valued as food in the Northwest United States and need to travel upstream to reproduce.

The last common ancestor of lampreys appears to have been specialized to feed on the blood and body fluids of other fish after metamorphosis. They attach their mouthparts to the target animal's body, then use three horny plates (laminae) on the tip of their piston-like tongue, one transversely and two longitudinally placed, to scrape through surface tissues until they reach body fluids. The teeth on their oral disc are primarily used to help the animal attach itself to its prey. Made of keratin and other proteins, lamprey teeth have a hollow core to give room for replacement teeth growing under the old ones. Some of the original blood-feeding forms have evolved into species that feed on both blood and flesh, and some who have become specialized to eat flesh and may even invade the internal organs of the host. Tissue feeders can also involve the teeth on the oral disc in the excision of tissue. As a result, the flesh-feeders have smaller buccal glands as they do not require the production of anticoagulant continuously and mechanisms for preventing solid material entering the branchial pouches, which could otherwise potentially clog the gills. A study of the stomach content of some lampreys has shown the remains of intestines, fins and vertebrae from their prey. Although attacks on humans do occur, they will generally not attack humans unless starved.

Carnivorous forms have given rise to the non-carnivorous species that feed on algae, and "giant" individuals amongst the otherwise small American brook lamprey have occasionally been observed, leading to the hypothesis that sometimes individual members of non-carnivorous forms return to the carnivorous lifestyle of their ancestors.

Another important lamprey adaptation is its countershading, a form of camouflage. Similarly to many other aquatic species, most lampreys have a dark-colored back, which enables them to blend in with the ground below when seen from above by a predator. Their light-colored undersides allow them to blend in with the bright air and water above them if a predator sees them from below.

Lamprey coloration can also vary according to the region and specific environment in which the species is found. Some species can be distinguished by their unique markings – for example, ''Geotria australis'' individuals display two bluish stripes running the length of its body as an adult. These markings can also sometimes be used to determine what stage of the life cycle the lamprey is in; ''G. australis'' individuals lose these stripes when they approach the reproductive phase and begin to travel upstream. Another example is ''Petromyzon marinus'', which shifts to more of an orange color as it reaches the reproductive stage in its life cycle.

Lifecycle

The adults spawn in nests of sand, gravel and pebbles in clear streams. After hatching from the eggs, young larvae—called ammocoetes—will drift downstream with the current till they reach soft and fine sediment in silt beds, where they will burrow in silt, mud and detritus, taking up an existence as filter feeders, collecting detritus, algae, and microorganisms. The eyes of the larvae are underdeveloped, but are capable of discriminating changes in illuminance. Ammocoetes can grow from to about . Many species change color during a diurnal cycle, becoming dark at day and pale at night. The skin also has photoreceptors, light sensitive cells, most of them concentrated in the tail, which helps them to stay buried. Lampreys may spend up to eight years as ammocoetes, while species such as the Arctic lamprey may only spend one to two years as larvae, prior to undergoing a metamorphosis which generally lasts 3–4 months, but can vary between species. While metamorphosing, they do not eat.

The rate of water moving across the ammocoetes' feeding apparatus is the lowest recorded in any suspension feeding animal, and they therefore require water rich in nutrients to fulfill their nutritional needs. While the majority of (invertebrate) suspension feeders thrive in waters containing under 1 mg suspended organic solids per litre (<1 mg/L), ammocoetes demand minimum 4 mg/L, with concentrations in their habitats having been measured up to 40 mg/L.

During metamorphosis the lamprey loses both the gallbladder and the biliary tract, and the endostyle turns into a thyroid gland.

Some species, including those that are not carnivorous and do not feed even following metamorphosis, live in freshwater for their entire lifecycle, spawning and dying shortly after metamorphosing. In contrast, many species are anadromous and migrate to the sea, beginning to prey on other animals while still swimming downstream after their metamorphosis provides them with eyes, teeth, and a sucking mouth. Those that are anadromous are carnivorous, feeding on fishes or marine mammals.

Anadromous lampreys spend up to four years in the sea before migrating back to freshwater, where they spawn. Adults create nests (called redds) by moving rocks, and females release thousands of eggs, sometimes up to 100,000. The male, intertwined with the female, fertilizes the eggs simultaneously. Being semelparous, both adults die after the eggs are fertilized.

Classification

Taxonomists place lampreys and hagfish in the subphylum Vertebrata of the phylum Chordata, which also includes the invertebrate subphyla Tunicata (sea-squirts) and the fish-like Cephalochordata (lancelets or Amphioxus). Recent molecular and morphological phylogenetic studies place lampreys and hagfish in the superclass Agnatha or Agnathostomata (both meaning without jaws). The other vertebrate superclass is Gnathostomata (jawed mouths) and includes the classes Chondrichthyes (sharks), Osteichthyes (bony fishes), Amphibia, Reptilia, Aves, and Mammalia.

Some researchers have classified lampreys as the sole surviving representatives of the Linnean class Cephalaspidomorphi. Cephalaspidomorpha is sometimes given as a subclass of the Cephalaspidomorphi.
Fossil evidence now suggests lampreys and cephalaspids acquired their shared characters by convergent evolution.
As such, many newer works, such as the fourth edition of ''Fishes of the World'', classify lampreys in a separate group called Hyperoartia or Petromyzontida, but whether this is actually a clade is disputed. Namely, it has been proposed that the non-lamprey "Hyperoartia" are in fact closer to the jawed vertebrates.

The debate about their systematics notwithstanding, lampreys constitute a single order Petromyzontiformes. Sometimes still seen is the alternative spelling "Petromyzoniformes", based on the argument that the type genus is ''Petromyzon'' and not "Petromyzonta" or similar. Throughout most of the 20th century, both names were used indiscriminately, even by the same author in subsequent publications. In the mid-1970s, the ICZN was called upon to fix one name or the other, and after much debate had to resolve the issue by voting. Thus, in 1980, the spelling with a "t" won out, and in 1981, it became official that all higher-level taxa based on ''Petromyzon'' have to start with "Petromyzont-".

The following taxonomy is based upon the treatment by FishBase as of April 2012 with phylogeny compiled by Mikko Haaramo. Within the order are 10 living genera in three families. Two of the latter are monotypic at genus level today, and in one of them a single living species is recognized (though it may be a cryptic species complex):

*''Geotria australis'' Gray 1851 (Pouched lamprey)
*''Mordacia lapicida'' (Gray 1851) (Chilean lamprey)
*''Mordacia mordax'' (Richardson 1846) ( Australian lamprey)
*''Mordacia praecox'' Potter 1968 (Non-parasitic/ Australian brook lamprey)
*''Petromyzon marinus'' Linnaeus 1758 (Sea lamprey)
*''Ichthyomyzon bdellium'' (Jordan 1885) ( Ohio lamprey)
*''Ichthyomyzon castaneus'' Girard 1858 (Chestnut lamprey)
*''Ichthyomyzon fossor'' Reighard & Cummins 1916 (Northern brook lamprey)
*''Ichthyomyzon gagei'' Hubbs & Trautman 1937 (Southern brook lamprey)
*''Ichthyomyzon greeleyi'' Hubbs & Trautman 1937 ( Mountain brook lamprey)
*''Ichthyomyzon unicuspis'' Hubbs & Trautman 1937 ( Silver lamprey)
*''Caspiomyzon wagneri'' (Kessler 1870) Berg 1906 ( Caspian lamprey)
*''Caspiomyzon graecus'' (Renaud & Economidis 2010) ( Ionian brook lamprey)
*''Caspiomyzon hellenicus'' (Vladykov et al. 1982) ( Greek lamprey)
*''Tetrapleurodon geminis'' Álvarez 1964 (Mexican brook lamprey)
*''Tetrapleurodon spadiceus'' (Bean 1887) ( Mexican lamprey)
*''Entosphenus folletti'' Vladykov & Kott 1976 ( Northern California brook lamprey)
*''Entosphenus lethophagus'' (Hubbs 1971) ( Pit-Klamath brook lamprey)
*''Entosphenus macrostomus'' (Beamish 1982) (Lake lamprey)
*''Entosphenus minimus'' (Bond & Kan 1973) (Miller Lake lamprey)
*''Entosphenus similis'' Vladykov & Kott 1979 ( Klamath river lamprey)
*''Entosphenus tridentatus'' (Richardson 1836) (Pacific lamprey)
*''Lethenteron alaskense'' Vladykov & Kott 1978 ( Alaskan brook lamprey)
*''Lethenteron appendix'' (DeKay 1842) (American brook lamprey)
*''Lethenteron camtschaticum'' (Tilesius 1811) ( Arctic lamprey)
*''Lethenteron kessleri'' (Anikin 1905) ( Siberian brook lamprey)
*''Lethenteron ninae'' Naseka, Tuniyev & Renaud 2009 ( Western Transcaucasian lamprey)
*''Lethenteron reissneri'' (Dybowski 1869) ( Far Eastern brook lamprey)
*''Lethenteron zanandreai'' (Vladykov 1955) (Lombardy lamprey)
*''Eudontomyzon stankokaramani'' (Karaman 1974) (Drin brook lamprey)
*''Eudontomyzon morii'' (Berg 1931) (Korean lamprey)
*''Eudontomyzon danfordi'' Regan 1911 ( Carpathian brook lamprey)
*''Eudontomyzon mariae'' (Berg 1931) ( Ukrainian brook lamprey)
*''Eudontomyzon vladykovi'' (Oliva & Zanandrea 1959) (Vladykov's lamprey)
*''Lampetra aepyptera'' (Abbott 1860) (Least brook lamprey)
*''Lampetra alavariensis'' Mateus et al. 2013 ( Portuguese lamprey)
*''Lampetra auremensis'' Mateus et al. 2013 ( Qurem lamprey)
*''Lampetra ayresi'' (Günther 1870) (Western river lamprey)
*''Lampetra fluviatilis'' (Linnaeus 1758) (European river lamprey)
*''Lampetra hubbsi'' (Vladykov & Kott 1976) ( Kern brook lamprey)
*''Lampetra lanceolata'' Kux & Steiner 1972 (Turkish brook lamprey)
*''Lampetra lusitanica'' Mateus et al. 2013 ( lusitanic lamprey)
*''Lampetra pacifica'' Vladykov 1973 (Pacific brook lamprey)
*''Lampetra planeri'' (Bloch 1784) (European brook lamprey)
*''Lampetra richardsoni'' Vladykov & Follett 1965 (Western brook lamprey

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