The European eel (''Anguilla anguilla'') is a species of
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 ...
, a snake-like,
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 ...
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 food both as adults (including
jellied eels
Jellied eels are a traditional English dish that originated in the 18th century, primarily in the East End of London. The dish consists of chopped eels boiled in a spiced stock that is allowed to cool and set, forming a jelly. It is usually s ...
of
East London) and as
glass eels
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 ...
. Glass-eel fishing using basket traps has been of significant economic value in many river estuaries on the western seaboard of Europe.
While the species' lifespan in the wild has not been determined, captive specimens have lived over 80 years. A specimen known as "the
Brantevik Eel" lived for 155 years in the well of a family home in
Brantevik, a fishing village in southern Sweden.
Conservation status
The European eel is a
critically endangered species.
Since the 1970s, the numbers of eels reaching Europe is thought to have declined by around 90% (possibly even 98%). Contributing factors include
overfishing,
parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s such as ''
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 ...
'', barriers to migration such as
hydroelectric
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...
dams, and natural changes in the
North Atlantic oscillation
The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in 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 ...
, and
North Atlantic drift
The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current within the Atlantic Ocean that extends the Gulf Stream northeastward.
The NAC originates from where ...
. Recent work suggests
polychlorinated biphenyl
Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by t ...
(PCB)
pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
may be a factor in the decline.
TRAFFIC
Traffic comprises pedestrians, vehicles, ridden or herded animals, trains, and other conveyances that use public ways (roads) for travel and transportation.
Traffic laws govern and regulate traffic, while rules of the road include traffi ...
is introducing traceability and legality systems throughout trade change to control the decline and encourage a U-turn on the species. The species is listed in Appendix II of the
CITES
CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...
Convention.
Sustainable consumption
In 2010,
Greenpeace International
Greenpeace is an independent global campaigning network, founded in Canada in 1971 by Irving Stowe and Dorothy Stowe, immigrant environmental activists from the United States. Greenpeace states its goal is to "ensure the ability of the Earth t ...
added the European eel to its "seafood red list", and the Sustainable Eel Group launched the Sustainable Eel Standard.
Breeding projects
As the European eel population has been falling for some time, several projects have been started. In 1997,
Innovatie Netwerk in the Netherlands initiated a project where they attempted to get European eels to breed in captivity by simulating the journey from Europe to the
Sargasso Sea with a
swimming machine for the fish.
The first to achieve some success was DTU Aqua, a part of the
Technical University of Denmark
The Technical University of Denmark ( da, Danmarks Tekniske Universitet), often simply referred to as DTU, is a polytechnic university and school of engineering. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmark's fi ...
. Through a combination of fresh and salt water, as well as hormones, they were able to breed it in captivity in 2006 and make the larvae survive for 4.5 days after hatching. By 2007, DTU Aqua scientists were able to set a new record where the larvae survived for 12 days by feeding the mother eel with a special
arginine-enriched diet. At this age the content of the larval
yolk sac
The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is ...
has been used, the mouth and digestive channel have developed, and it requires feeding. Attempts with various substances failed.
Galathea
''Galathea'' is one of the largest genera of squat lobsters, containing 70 currently recognised species (17 in the Atlantic Ocean, 22 in the Indian Ocean and 43 in the Pacific Ocean). Most species of ''Galathea'' live in shallow waters.
Specie ...
3
Åleopdræt.
Retrieved 22 April 2017. Deep water sampling of the presumed habitat of larval European eel in the Sargasso Sea was performed by the
Galathea
''Galathea'' is one of the largest genera of squat lobsters, containing 70 currently recognised species (17 in the Atlantic Ocean, 22 in the Indian Ocean and 43 in the Pacific Ocean). Most species of ''Galathea'' live in shallow waters.
Specie ...
3 expedition in 2006–07, in the hope of revealing the likely feeding preference at the early stage. Their results indicated that they feed on various
planktonic organisms, but especially microscopic
jellyfish
Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
.
A follow-up expedition was performed by DTU's own
research ship to the Sargasso Sea region in 2014.
To further the research, the PRO-EEL project, led by DTU Aqua and involving several research institutes elsewhere in Denmark (
University of Copenhagen
The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in ...
and others), Norway (
Norwegian Institute of Fisheries and Food Research and others), the Netherlands (
Leiden University
Leiden University (abbreviated as ''LEI''; nl, Universiteit Leiden) is a Public university, public research university in Leiden, Netherlands. The university was founded as a Protestant university in 1575 by William the Silent, William, Prince o ...
and others), Belgium (
Ghent University
Ghent University ( nl, Universiteit Gent, abbreviated as UGent) is a public research university located in Ghent, Belgium.
Established before the state of Belgium itself, the university was founded by the Dutch King William I in 1817, when the ...
), France (
French National Center for Scientific Research
The French National Centre for Scientific Research (french: link=no, Centre national de la recherche scientifique, CNRS) is the French state research organisation and is the largest fundamental science agency in Europe.
In 2016, it employed 31,637 ...
and others), Spain (ICTA at
Polytechnic University of Valencia
The Technical University of Valencia ( ca-valencia, Universitat Politècnica de València, UPV; , es, Universidad Politécnica de Valencia) is a Spanish university located in Valencia, with a focus on science, technology, and arts. It was founde ...
) and Tunisia (National Institute of Marine Sciences and Technologies), was started in 2010. By 2014, the eel larvae at their facilities typically survive 20–22 days, but the full
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 ...
has still not been completed in captivity.
Life history
Much of the European eel's
life history was a mystery for centuries, as fishermen never caught anything they could identify as a young eel. Unlike many other migrating fish, eels begin their life cycle in the ocean and spend most of their lives in fresh inland water, or brackish coastal water, returning to the ocean to spawn and then die. In the early 1900s,
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 ...
researcher
Johannes Schmidt identified the
Sargasso Sea as the most likely spawning grounds for European eels. The
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
e (
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 ...
) drift towards Europe in a 300-day migration.
When approaching the European coast, the larvae metamorphose into a transparent larval stage called "glass eel", enter estuaries, and many start migrating upstream. After entering their continental habitat, the glass eels metamorphose into
elvers, miniature versions of the adult eels. As the eel grows, it becomes known as a "yellow eel" due to the brownish-yellow color of their sides and belly. After 5–20 years in fresh or brackish water, the eels become sexually mature, their eyes grow larger, their flanks become silver, and their bellies white in color. In this stage, the eels are known as "silver eels", and they begin their migration back to the Sargasso Sea to spawn. Silvering is important in an eel's development because it allows for increased levels of the steroid hormone cortisol, which is needed for their migration from fresh water back to the sea. Cortisol plays a role in the long migration because it allows for the mobilization of energy during migration. Also playing a key role in silvering is the production of the steroid 11-Ketotestosterone (11-KT), which prepares the eel for structural changes to the skin to endure the migration from fresh water to saltwater.
Magnetoreception
Magnetoreception is a sense which allows an organism to detect the Earth's magnetic field. Animals with this sense include some arthropods, molluscs, and vertebrates (fish, amphibians, reptiles, birds, and mammals, though not humans). The se ...
has also been reported in the European eel by at least one study, and may be used for navigation.
Eels May Use 'Magnetic Maps' As They Slither Across The Ocean
/ref>
Eel-life-circle1.svg, Life cycle of the European eel
Glasseelskils.jpg, Glass eels at the transition from ocean to fresh water
FMIB 35739 Anguilla vulgaris -- Anguilla.jpeg, Mature silver-stage European eels migrate back to the ocean
Ecology
Parasites
Parasite species infecting the European eel include '' Bothriocephalus claviceps'' and a range of other intestinal metazoans.
European eels generally have a low parasite diversity within individuals and ecosystems (component community). The parasite that is most commonly dominant is the acanthocephalan
Acanthocephala (Greek , ', thorn + , ', head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to p ...
'' Acanthocephalus lucii''.
Commercial fisheries
References
External links
*
{{Authority control
Amphibious fish
European eel
Critically endangered animals
European eel
Fish of Europe
Fish of the Baltic Sea
Fish of the Black Sea
Fish of the Mediterranean Sea
Fish of the North Sea
Freshwater fish of Europe
Taxa named by Carl Linnaeus