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The
eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
is a long, thin
bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
of the order
Anguilliformes Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stag ...
. The species has a
catadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...
life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring * Life-cycle hypothesis ...
of the eel was a mystery for a very long period of scientific history.


Past studies of eels

The
European eel The European eel (''Anguilla anguilla'') is a species of eel, a snake-like, catadromous fish. They are normally around and rarely reach more than , but can reach a length of up to in exceptional cases. Eels have been important sources of fo ...
(''Anguilla anguilla'') was historically the one most familiar to Western scientists, beginning with
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
, who wrote the earliest known inquiry into the natural history of eels. He speculated that they were born of "earth worms", which he believed were formed of mud, growing from the "guts of wet soil" rather than through sexual reproduction. Many centuries passed before scientists were able to demonstrate that such
spontaneous generation Spontaneous generation is a superseded scientific theory that held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise fr ...
does not occur in nature. In 1777, the Italian Carlo Mondini located an eel's ovaries and demonstrated that eels are a kind of fish. In 1876, as a young student in Austria,
Sigmund Freud Sigmund Freud ( , ; born Sigismund Schlomo Freud; 6 May 1856 – 23 September 1939) was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating psychopathology, pathologies explained as originatin ...
dissected hundreds of eels in search of the male sex organs. He had to concede failure in his first major published research paper, and turned to other issues in frustration. Larval eels — transparent, leaflike two-inch (five-cm) creatures of the open ocean — were not generally recognized as such until 1893; instead, they were thought to be a separate
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, ''Leptocephalus brevirostris'' (from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
''leptocephalus'' meaning "thin- or flat-head"). In 1886, however, the French zoologist
Yves Delage Yves Delage (13 May 1854 – 7 October 1920) was a French zoologist known for his work into invertebrate physiology and anatomy. He also discovered the function of the semicircular canals in the inner ear. He is also famous for noting and prep ...
discovered the truth when he kept leptocephali alive in a laboratory tank in
Roscoff Roscoff (; br, Rosko) is a commune in the Finistère département of Brittany in northwestern France. Roscoff is renowned for its picturesque architecture, labelled (small town of character) since 2009. Roscoff is also a traditional departure ...
until they matured into eels, and in 1896
Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...
zoologist
Giovanni Battista Grassi Giovanni Battista Grassi (27 March 1854 – 4 May 1925) was an Italian physician and zoologist, best known for his pioneering works on parasitology, especially on malariology. He was Professor of Comparative Zoology at the University of Catani ...
confirmed the finding when he observed the transformation of a ''
Leptocephalus Leptocephalus (meaning "slim head") is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 families, ...
'' into a round glass eel in the
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...
. (He also observed that salt water was necessary to support the maturation process.) Although the connection between larval eels and adult eels is now well understood, the name leptocephalus is still used for larval eel.


Search for the spawning grounds


European eel

The
Danish Danish may refer to: * Something of, from, or related to the country of Denmark People * A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark * Culture of Denmark * Danish people or Danes, people with a Danish a ...
professor Johannes Schmidt, beginning in 1904, led a series of expeditions into the Mediterranean Sea and the
North Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe and ...
(the
Dana expeditions The Dana expeditions were four Danish research expeditions undertaken by the ''Dana I'' and ''Dana'' ''II''. They were funded in part by the Carlsberg Foundation and led by Johannes Schmidt. The first three expeditions took place from 1920 to 19 ...
) to investigate eels. The expeditions were largely financed by the
Carlsberg Foundation Carlsberg Foundation ( da, Carlsbergfondet) was founded by J. C. Jacobsen in 1876, by allocating some of his shares in the Carlsberg Brewery to fund and operate the Carlsberg Laboratory and the Museum of National History at Frederiksborg Palace. ...
. He noted that all the leptocephali he found were very similar, and hypothesized that they all must have descended from a common ancestor species. He also observed that the farther out to sea in the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
he went, the smaller the leptocephali he caught were. In a 1922 expedition, he sailed as far as the
Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...
, south of
Bermuda ) , anthem = "God Save the King" , song_type = National song , song = " Hail to Bermuda" , image_map = , map_caption = , image_map2 = , mapsize2 = , map_caption2 = , subdivision_type = Sovereign state , subdivision_name = , e ...
, where he caught the smallest eel-larvae that had ever been seen. Although Schmidt did not directly observe eel
spawning Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquati ...
, or even find ready-to-spawn adult eels, he was able to deduce the following about the life history of the eel, based on the size distribution of the leptocephali he collected: The larvae of European eels travel with the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Current, North Atlantic Drift, is a warm and swift Atlantic Ocean, Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida a ...
across the Atlantic Ocean, and grow to 75–90 mm within one to three years, before they reach the coasts of Europe. Marine eels of the order Anguilliformes also have a leptocephalus stage, and likely pass through a stage similar to the anguillid
glass eel The eel is a long, thin bony fish of the order Anguilliformes. The species has a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything th ...
s, but they are rarely seen in the ocean. Eels in this so-called "recruitment" developmental stage are known as glass eels because of the transparency of their bodies. The term typically refers to a transparent eel of the family
Anguillidae The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Eighteen of the 19 extant species and six subspecies in this family are in the genus ''Anguilla''. They are elongated fish with snake-like bodies, their long dorsa ...
. It is applied to an intermediary stage in the eel's complex life history between the leptocephalus stage and the juvenile (elver) stage. Glass eels are defined as "all developmental stages from completion of leptocephalus metamorphosis until full pigmentation". Once the glass eels arrive at coastal areas, they migrate up rivers and streams, overcoming various natural challenges — sometimes by piling up their bodies by the tens of thousands to climb over obstacles — and they reach even the smallest of creeks. At this stage in their growth they are small enough to benefit from
surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...
in order to climb vertical walls. In fresh water they develop pigmentation, turn into elvers (young eels), and feed on creatures such as small
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s,
worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...
s, and
insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
s. For 10 to 14 years they mature, growing to a length of 60 to 80 cm. The eels can propel themselves over wet grass and dig through wet sand to reach upstream headwaters and ponds, thus colonizing the continent. During this stage they are called yellow eels because of their golden pigmentation. In July, some mature individuals migrate back towards the sea, crossing wet grasslands at night to reach rivers that lead to the sea. Eel migration out of their freshwater growth habitats from various parts of Europe, or through the
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...
in the Danish straits, have been the basis of traditional fisheries with characteristic trapnets. How the adults make the open ocean journey back to their spawning grounds north of the
Antilles The Antilles (; gcf, label=Antillean Creole, Antiy; es, Antillas; french: Antilles; nl, Antillen; ht, Antiy; pap, Antias; Jamaican Patois: ''Antiliiz'') is an archipelago bordered by the Caribbean Sea to the south and west, the Gulf of Mex ...
,
Haiti Haiti (; ht, Ayiti ; French: ), officially the Republic of Haiti (); ) and formerly known as Hayti, is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean Sea, east of Cuba and Jamaica, and ...
, and
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and Unincorporated ...
remains unknown. By the time they leave the continent, their gut dissolves, making feeding impossible, so they have to rely on stored energy alone. The external features undergo other dramatic changes, as well: the eyes start to enlarge, the eye pigments change for optimal vision in dim blue clear ocean light, and the sides of their bodies turn silvery, to create a
countershading Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, and ...
pattern which makes them difficult to see by predators during their long open-ocean migration. These migrating eels are typically called "silver eels" or "big eyes". German fisheries biologist Friedrich Wilhelm Tesch, an eel expert and author, conducted many expeditions with high-tech instrumentation to follow eel migration, first down the Baltic, then along the coasts of
Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
and England, but finally the transmitter signals were lost at the
continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
when the batteries ran out According to Schmidt, a travel speed in the ocean of 15 km per day can be assumed, so a silver eel would need around 140 to 150 days to reach the Sargasso Sea from Scotland and about 165 to 175 days when leaving from the English Channel. Tesch — like Schmidt — kept trying to persuade sponsors to provide more funding for expeditions. His proposal was to release 50 silver eels from Danish waters, with transmitters that would detach from the eels each second day, float up toward the surface, and broadcast their position, depth, and temperature to satellite receivers. He also suggested that countries on the western side of the Atlantic could perform a similar release experiment at the same time. In December 2018 researchers in the
Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...
, (about 1,400 km (870 mi) west of the
Iberia The Iberian Peninsula (), ** * Aragonese and Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, defi ...
n coast—the furthest point on the migration route identified in previous experiments) fitted 26 large female European eels with satellite tags and released them into the Atlantic Ocean. Tracking demonstrated that the fishes' journey to the Sargasso took a further year, or more.


American eel

Another Atlantic eel species is known: the American eel, ''Anguilla rostrata''. First it was believed European and American eels were the same species due to their similar appearance and behavior, but they differ in chromosome count and various molecular genetic markers, and in the number of vertebrae, ''A. anguilla'' counting 110 to 119 and ''A. rostrata'' 103 to 110. The spawning grounds for the two species are in an overlapping area of the southern Sargasso Sea, with ''A. rostrata'' apparently being more westward than ''A. anguilla'', and with some spawning by the American eel possibly even occurring off the Yucatán Peninsula off the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...
, but this has not been confirmed. After spawning in the Sargasso Sea and moving to the west, the
leptocephali Leptocephalus (meaning "slim head") is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 famili ...
of the American eel exit the Gulf Stream earlier than the European eel and begin migrating into the estuaries along the east coast of North America between February and late April at an age around one year and a length around 60 mm.


Japanese eel

The spawning area of the
Japanese eel The Japanese eel (''Anguilla japonica''; Japanese: 日本鰻 ''nihon'unagi'') is a species of anguillid eel found in Japan, Korea, China, and Vietnam, as well as the northern Philippines. There are three main species under the Anguilla genus, and ...
, ''Anguilla japonica'', has also been found. Their breeding site is to the west of the Suruga seamount (14–17°N, 142–143°E), near the
Mariana Islands The Mariana Islands (; also the Marianas; in Chamorro: ''Manislan Mariånas'') are a crescent-shaped archipelago comprising the summits of fifteen longitudinally oriented, mostly dormant volcanic mountains in the northwestern Pacific Ocean, betw ...
. and their leptocephali are then transported to the west to East Asia by the North Equatorial Current. In June and August 2008, Japanese scientists discovered and caught matured adult eels of ''A. japonica'' and '' A. marmorata'' in the West Mariana Ridge.


Southern African eels

Southern Africa's four species of freshwater eels ('' A. mossambica'', '' A. bicolor bicolor'', '' A. bengalensis labiata'', and '' A. marmorata'') have an interesting migratory pattern: It takes them on a long journey from their spawning grounds in the Indian Ocean north of Madagascar to high up in some of the Southern African river systems and then back again to the ocean off Madagascar.


New Zealand longfin eels

New Zealand longfin eel The New Zealand longfin eel (''Anguilla dieffenbachii'') is a species of freshwater eel that is endemic to New Zealand. It is the largest freshwater eel in New Zealand and the only endemic species – the other eels found in New Zealand are the n ...
s breed only once at the end of their lives, making a journey of thousands of kilometres from New Zealand to their spawning grounds near
Tonga Tonga (, ; ), officially the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about , scattered over in ...
. Their eggs (of which each female eel produces between 1 and 20 million) are
fertilized Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
in an unknown manner, but probably in deep tropical water.McDowall, R. M. (1990). ''New Zealand freshwater fishes: a natural history and guide'' (Rev. ed.). Auckland: Heinemann-Reed. The mature eels then die, their eggs floating to the surface to hatch into very flat leaf-like larvae (called
leptocephalus Leptocephalus (meaning "slim head") is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 families, ...
) that then drift along large oceanic currents back to New Zealand. This drifting is thought to take up to 15 months. There have been no recorded captures of either the eggs or larvae of longfin eels.


Decline of the glass eels

No one yet knows the reasons, but beginning in the mid-1980s, glass eel arrival in the spring dropped drastically — in Germany to 10% and in France to 14% of their previous levels — from even conservative estimates. Data from
Maine Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and north ...
and other
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
n coasts showed similar declines, although not as drastic. In 1997,
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
an demand for eels could not be met for the first time ever, and dealers from Asia bought all they could. The traditional European stocking programs could not compete any longer: each week, the price for a kilogram of glass eel went up another
US$ The United States dollar (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official ...
30. Even before the 1997 generation hit the coasts of Europe, dealers from China alone placed advance orders for more than 250,000 kg, some bidding more than $1,100 per kg. Asian elvers have sold in Hong Kong for as much as $5,000 to $6,000 a kilogram at times when $1,000 would buy the same amount of American glass eels at their catching sites. Such a kilogram, consisting of 5000 glass eels, may bring at least $60,000 and as much as $150,000 after they leave an Asian fish farm. In New Jersey, over 2000 licenses for glass eel catch were issued and reports of 38 kg per night and fisherman have been made, although the average catch is closer to 1 kg. Glass eels have been harvested for food from the
River Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...
, England, for centuries, but for about 200 years, from the sixteenth to eighteenth century, the practice was outlawed by act of Parliament. The restriction was removed in 1873 and in 1908 a collection point and holding station for the catch was established at
Epney Epney is a small village on the River Severn. It is South-West of Gloucester, Gloucestershire, England within the parish of Longney and Epney. It is between Longney and Upper Framilode. The village has a pub called The Anchor Inn. The populatio ...
, Gloucestershire. Initially the crop was sold for human consumption but, as infrastructure for live transport improved, the glass eels were exported throughout Europe for
stocking Stockings (also known as hose, especially in a historical context) are close-fitting, variously elastic garments covering the leg from the foot up to the knee or possibly part or all of the thigh. Stockings vary in color, design, and transparen ...
natural waterways and to the Far East for eel
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
. The demand for adult eels has continued to grow, .
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
imported more than $50 million worth of eels in 2002. In Europe, 25 million kg are consumed each year, but in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
alone, more than 100 million kg were consumed in 1996. As the European eels become less available, worldwide interest in American eels has increased dramatically. New high-tech eel aquaculture plants are appearing in Asia, with detrimental effects on the native Japanese eel, ''A. japonica''. Traditional eel aquaculture operations rely on wild-caught elvers, but experimental hormone treatments in Japan have led to artificially spawned eels. Eggs from these treated eels have a diameter of about 1 mm, and each female can produce up to 10 million eggs. However, these treated eels may not solve the eel crisis. Scientists are struggling to get eels to
sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...
without environmental cues. Additionally,
leptocephali Leptocephalus (meaning "slim head") is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 famili ...
(larva) require a diet of
marine snow In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...
which is difficult to recreate in aquaculture.


Threats to eels

Strong concerns exist that the European eel population might be devastated by a new threat: ''
Anguillicola crassus ''Anguillicoloides crassus'' is a parasitic nematode worm that lives in the swimbladders of eels (''Anguilla'' spp.) and appears to spread easily among eel populations after introduction to a body of water. It is considered to be one of the thr ...
'', a foreign parasitic
nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
. This parasite from East Asia (the original host is ''A. japonica'') appeared in European eel populations in the early 1980s. Since 1995, it also appeared in the United States (
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
and
South Carolina )''Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...
), most likely due to uncontrolled aquaculture eel shipments. In Europe, eel populations are already from 30% to 100% infected with the nematode. Recently, this parasite was shown to inhibit the function of the
swimbladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth w ...
as a
hydrostatic Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
organ. As open ocean voyagers, eels need the carrying capacity of the swimbladder (which makes up 3–6% of the eel's body weight) to cross the ocean on stored energy alone. Because the eels are
catadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...
(living in fresh water but spawning in the sea), dams and other river obstructions can block their ability to reach inland feeding grounds. Since the 1970s, an increasing number of
eel ladder A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as move ...
s have been constructed in North America and Europe to help the fish bypass obstructions. In
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
, an ongoing project monitors the glass eel migration with an online ''in situ'' microscope. As soon as more funding becomes available, it will be possible to log into the system via a
Longterm Ecological Observatory The Long-term Ecological Observatory (LEO) is a project off the coast of New Jersey, United States, which monitors the processes in the ocean with online IT systems, spearheaded by the Institute of Marine and Coastal Sciences at Rutgers Univer ...
(LEO) site.


See also

*
Eel ladder A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as move ...
*
Fish migration Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...


References


Sources and further reading

* Banks, R.C., R.W. McDiarmid, A.L. Gardner, & W.C. Starnes (2003). Checklist of Vertebrates of the United States, the U.S. Territories, and Canada. * Bussing, W.A. (1998). Peces de las aguas continentales de Costa Rica reshwater fishes of Costa Rica 2nd ed. San José Costa Rica: Editorial de la Universidad de Costa Rica. * Butsch, R.S. (1939). A list of Barbadian fishes. J. B.M.H.S. 7(1): pp. 17–31. * Böhlke, J.E. & C.C.G. Chaplin (1993). Fishes of the Bahamas and adjacent tropical waters. 2nd edition. University of Texas Press, Austin. * Claro, R. (1994). Characterísticas generales de la ictiofauna. pp. 55–70. nR. Claro d.Ecología de los peces marinos de Cuba. Instituto de Oceanología Academia de Ciencias de Cuba and Centro de Investigaciones de Quintana Roo. * Claro, Rodolfo, & Lynne R. Parenti (2001). Chapter 2: The Marine Ichthyofauna of Cuba. nClaro, Rodolfo, Kenyon C. Lindeman, & L.R. Parenti, ds.Ecology of the Marine Fishes of Cuba. Smithsonian Institution Press. Washington, DC, USA. pp. 21–57. . * Erdman, D.S. (1984). Exotic fishes in Puerto Rico. pp. 162–176. nW.R. Courtney, Jr. & J.R. Stauffer, Jr. ds.Distribution, biology and management of exotic fishes. Johns Hopkins University Press, Baltimore, USA. * Eschmeyer, William N., d.(1998). Catalog of Fishes. Special Publication of the Center for Biodiversity Research and Information, no. 1, vol 1–3. California Academy of Sciences. San Francisco, California, USA. 2905. . * Fish, M.P. & W.H. Mowbray (1970). Sounds of Western North Atlantic fishes. A reference file of biological underwater sounds. The Johns Hopkins Press, Baltimore, MD. * Food and Agriculture Organization (1992). FAO yearbook 1990. Fishery statistics. Catches and landings. FAO Fish. Ser. (38). FAO Stat. Ser. 70:(105) * Food and Agriculture Organization (1997). Aquaculture production statistics 1986–1995. FAO Fish. Circ. 815, Rev. 9. * Greenfield, D.W & J.E Thomerson (1997). Fishes of the continental waters of Belize. University Press of Florida, Florida. * International Game Fish Association (1991). World record game fishes. International Game Fish Association, Florida, USA. * Jessop, B.M. (1987). Migrating American eels in Nova Scotia. Trans. Amer. Fish. Soc. 116: pp. 161–170. * Kenny, J.S. (1995). Views from the Bridge: A memoir on the freshwater fishes of Trinidad. Julian S. Kenny, Maracas, St. Joseph, Trinidad, & Tobago. * Lim, P., Meunier, F.J., Keith, P. & Noël, P.Y. (2002). Atlas des poissons et des crustacés d'eau douce de la Martinique. Patrimoines Naturels, 51: Paris: MNHN. * Murdy, Edward O., Ray S. Birdsong, & John A. Musick 1997. Fishes of Chesapeake Bay. Smithsonian Institution Press. Washington, DC, USA. . * Nelson, Joseph S., Edwin J. Crossman, Héctor Espinosa-Pérez, Lloyd T. Findley, Carter R. Gilbert, Robert N. Lea, & James D. Williams, ds.(2004). Common and scientific names of fishes from the United States, Canada, and Mexico, Sixth Edition. American Fisheries Society Special Publication, no. 29. American Fisheries Society. Bethesda, Maryland, USA. . * Nielsen, J.G. and E. Bertelsen (1992). Fisk i grønlandske farvande. Atuakkiorfik, Nuuk. 65 s. * Nigrelli, R.F. (1959). Longevity of fishes in captivity, with special reference to those kept in the New York Aquarium. pp. 212–230. nG.E.W. Wolstehnolmen & M. O'Connor ds.Ciba Foundation Colloquium on Ageing: the life span of animals. Vol. 5., Churchill, London. * Ogden, J.C., J.A. Yntema, & I. Clavijo (1975). An annotated list of the fishes of St. Croix, U.S. Virgin Islands. Spec. Publ. No. 3. * Page, L.M. & B.M. Burr (1991). A field guide to freshwater fishes of North America north of Mexico. Houghton Mifflin Company, Boston. * Piper, R. (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press. * Robins, C.R. & G.C. Ray (1986). A field guide to Atlantic coast fishes of North America. Houghton Mifflin Company, Boston, MA * Robins, Richard C., Reeve M. Bailey, Carl E. Bond, James R. Brooker, Ernest A. Lachner, ''et al''. (1980). A List of Common and Scientific Names of Fishes from the United States and Canada, Fourth Edition. American Fisheries Society Special Publication, no. 12. American Fisheries Society. Bethesda, MD. * Robins, Richard C., Reeve M. Bailey, Carl E. Bond, James R. Brooker, Ernest A. Lachner, ''et al''. 1980. A List of Common and Scientific Names of Fishes from the United States and Canada, Fourth Edition. American Fisheries Society Special Publication, no. 12. American Fisheries Society. Bethesda, MD. * Smith, C.L. (1997). National Audubon Society field guide to tropical marine fishes of the Caribbean, the Gulf of Mexico, Florida, the Bahamas, and Bermuda. Alfred A. Knopf, Inc., New York, NY. * Tesch, F.-W. (2003) The eel. Blackwell Science, Oxford, UK. * Wallace, Karen (1993) Think of an Eel, Walker Books, UK. 'A picture book for children that describes the life cycle of the eel.''* Wenner, C.A. (1978). Anguillidae. nW. Fischer d.FAO species identification sheets for fishery purposes. West Atlantic (Fishing Area 31). volume 1. FAO, Rome, IT.


External links


The Maine Eel and Elver Fishery, Maine Department of Marine Resources


archived copy
Fishbase entry for ''Anguilla anguilla''

Fishbase entry for ''Anguilla rostrata''

ICES report about eel stock collapse

U.K Glass Eels — a large commercial firm's website, with history and fact pages


{{commercial fish topics Eels Commercial fish Ichthyology de:Europäischer Aal#Lebenszyklus und Fortpflanzung