European eel

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European eel
Anguilla anguilla.jpg
CITES Appendix II (CITES) [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Anguilliformes
Family: Anguillidae
Genus: Anguilla
Species:
A. anguilla
Binomial name
Anguilla anguilla
Eel inEurope.png
Freshwater range of wild European eel
Synonyms

Muraena anguillaLinnaeus, 1758
Anguilla vulgarisShaw, 1803
Anguilla malgumoraKaup, 1856
Leptocephalus brevirostris

Contents

Edouard Manet, 1864 Edouard Manet - Rouget et Anguille.jpg
Édouard Manet, 1864

The European eel (Anguilla anguilla) [3] is a species of eel. [4] Their life history was a mystery for thousands of years, and mating in the wild has not yet been observed. The five stages of their development were originally thought to be different species. They are critically endangered due to hydroelectric dams, overfishing by fisheries on coasts for human consumption, and parasites. [4] [5] [6] [7]

Description

European eels live thru 5 stages of development: larva (leptocephalus), glass eel, elver, yellow eel, and silver eel. Adults in the yellow phase are normally around 45–65 centimetres (18–26 in) and rarely reach more than 1.0 metre (3 ft 3 in), but can reach a length of up to 1.33 metres (4 ft 4 in) in exceptional cases. [8] In addition, they range from having 110 to 120 vertebrae. [9] While European eels tend to live approximately 15–20 years in the wild, some captive specimens have lived for 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. [9] [10] [11]

Ecology

Eels tend to range from 0 to 700 meters underwater and after spawning in the Sargasso Sea, disperse North throughout the Atlantic Ocean, its coasts, and the rivers that empty into it. [12] Feeding occurs mainly at night, via scent and prey consists of worms, fish (including ones too big to eat without biting off chunks), mollusks such as slugs, crustaceans such as crayfish, and plankton on occasion when available in large quantities. [13] [14] European eels are preyed upon by bigger eels, herons, cormorants, and pike. Seagulls also prey on elvers. [14] Eels usually find and compete for shelter by hiding in plants or tube-shaped crevices in rocks. They also hide in muddy fields when inland. [14]

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, parasites such as Anguillicola crassus , barriers to migration such as hydroelectric dams, and natural changes in the North Atlantic oscillation, Gulf Stream, and North Atlantic drift. Recent work suggests polychlorinated biphenyl (PCB) pollution may be a factor in the decline. [15] The TRAFFIC program is introducing traceability and legality systems throughout trade change to control and reverse the decline of the species. [16] The species is listed in Appendix II of the CITES Convention. [17] Hydroelectric dams have been shown to have a significant negative impact on eel populations. Over an 80 year period, waters with large dams have experienced almost twice the reduction of eel numbers as dam-free waters. [7]

Sustainable consumption

Eels have been important sources of food both as adults (including jellied eels of East London) and as glass eels. Glass-eel fishing using basket traps has been of significant economic value in many river estuaries on the western seaboard of Europe. [18] In addition, the United States imports 11 million pounds of eel every year to support its sushi industry, including European eels. [19] In order to make eel consumption sustainable, in 2010, Greenpeace International added the European eel to its "seafood red list", [20] and the Sustainable Eel Group launched the Sustainable Eel Standard. [21]

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 6,500 km (4,000 mi) journey from Europe to the Sargasso Sea with a swimming machine for the fish. [22] [23]

The first to achieve some success was DTU Aqua, a part of the Technical University of Denmark. 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. [24] 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. [25] At this age the content of the larval yolk sac has been used, the mouth and digestive channel have developed, and it requires feeding. Attempts with various substances failed. [26] Deep water sampling of the presumed habitat of larval European eel in the Sargasso Sea was performed by the Galathea 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. [26] A follow-up expedition was performed by DTU's own research ship to the Sargasso Sea region in 2014. [27]

To further the research, the PRO-EEL project, led by DTU Aqua and involving several research institutes elsewhere in Denmark (University of Copenhagen and others), Norway (Norwegian Institute of Fisheries and Food Research and others), the Netherlands (Leiden University and others), Belgium (Ghent University), France (French National Center for Scientific Research and others), Spain (ICTA at Polytechnic University of Valencia) and Tunisia (National Institute of Marine Sciences and Technologies), was started in 2010. [28] [29] By 2014, the eel larvae at their facilities typically survived 20–22 days, [30] and by 2022 they were surviving up to around 140 days, well into the leptocephalus stage (the stage just before glass eel), but the full life cycle has still not been completed in captivity. [31]

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 researcher Johannes Schmidt identified the Sargasso Sea as the most likely spawning grounds for European eels. [32] The larvae (leptocephali) drift towards Europe in a 300-day migration. [33]

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. [34] Cortisol plays a role in the long migration because it allows for the mobilization of energy during migration. [35] 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. [36]

Sometimes the eel will never enter freshwater, and remain in their marine environment their entire life. Others grow up in brackish water, or migrate between saltwater, brackish water and freshwater several times in their lifetime. [37]

Magnetoreception has also been reported in the European eel by at least one study, and may be used for navigation. [38]

Commercial fisheries

Production

The eel farming industry uses recirculating pools to raise glass eels taken from the wild for 8 months to 2 years until they mature enough for sale. [39] Valliculture on coasts through the use of weirs is also utilized instead of recirculating pools for eel farming. [39] New eels are quarantined to prevent disease spread and eels are sorted by size every couple weeks to prevent cannibalism [39] and remove dead animals. [40] A range of 23°C to 28°C is optimal for growth and protein based pellets and pastes are utilized as food sources for the eels after an initial few days of cod roe for the small glass ones. [41] [39] [40] European eels typically have a feed conversion ratio (FCR) in the range of 1.8-2.5, although European fisheries are typically in the 1.6-1.7 range. [40] [42] [43] Filters are essential for eliminating waste and ensuring the eels have clean water to live in. [39] Eels are typically transported via road in tanks with water or via air in styrofoam boxes with a beaker of ice. The beakers keep condensation on the outside and ice on inside to keep the environment moist enough for the 1-3kg of eels to survive and also keep the temperature low enough. [40]

Diseases/parasites in fisheries

Diseases can be spread rapidly in the highly populated environments of fisheries if quarantine measures are not taken immediately upon arrival of new eels. [44] Some common bacterial infections observed in eel fisheries are red fin and red eel pest. When an eel has a red fin infection, its tail and fins start rotting, and a salt solution should be utilized to treat it. [44] Antibiotics can be used to treat red eel pest which is characterized by ulcerated lesions, swelling, and spots of red on the skin of the eel. [44] In addition, Aeromonas sobria and Streptococcus spp. are other more rare bacteria to infect European eels but have been observed in necropsies and are likely the result of other stresses increasing the eel's susceptibility to disease, but can be treated with antimicrobials. [45] Parasites such as from the genus Dactylogyrus have also been observed in necropsies, and some symptoms of parasitic infections in European eels are white spots, mucus increase, fin fraying, rubbing infected spots against the enclosure, respiratory distress, and lethargy. [44] [45] These parasites are best treated with salt solutions or formaldehyde solutions. [44] Viral infections such as red head have also been observed; symptoms include red hemorrhaging spreading from the head to the rest of the eel and can be treated with vaccinations at a young age, salt solutions, or decreased temperature of water within the enclosure. [44] Salt solutions also can treat fungal infections that cause swelling of gills and brown or white skin patches. [44]

Industry

The exportation of European Eels has been restricted since 2010, yet on average 44% of eel sales in the United States consists of these eels. [46] Eel aquaculture is most prominent in Japan, yet China, Scandinavia, Europe, Australia, Morocco, and Taiwan also participate in this practice. [46] Eel breeding programs initiated by humans have been unsuccessful thus far and therefore the entire industry is dependent on the number of eels spawning in the wild, leaving it unsustainable and vulnerable to the factors causing European Eels to be critically endangered. [46] [47] [48] [49]

Global production of European eels in tonnes as reported by the FAO
Wild capture of Anguilla anguilla.png
↑  Wild capture, 1950–2010 [50]
Farmed production of Anguilla anguilla.png
↑  Farmed production, 1950–2010 [50]
Total production of Anguilla anguilla.png
↑  Total production of European eel in thousands of tonnes as reported by the FAO, 1950–2010 [50]
European eel farming.svg
↑  Main European countries producing farmed European eel

Related Research Articles

<span class="mw-page-title-main">Fish farming</span> Raising fish commercially in enclosures

Fish farming or pisciculture involves commercial breeding of fish, most often for food, in fish tanks or artificial enclosures such as fish ponds. It is a particular type of aquaculture, which is the controlled cultivation and harvesting of aquatic animals such as fish, crustaceans, molluscs and so on, in natural or pseudo-natural environments. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Worldwide, the most important fish species produced in fish farming are carp, catfish, salmon and tilapia.

<span class="mw-page-title-main">Fish migration</span> Movement of fishes from one part of a water body to another on a regular basis

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 thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear.

<span class="mw-page-title-main">Leptocephalus</span> Juvenile eel

A leptocephalus 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, and 156 genera. This group is thought to have arisen in the Cretaceous period over 140 million years ago.

<span class="mw-page-title-main">American eel</span> Species of fish

The American eel is a facultative catadromous fish found on the eastern coast of North America. Freshwater eels are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts. The American eel has a slender, supple, snake-like body that is covered with a mucus layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fins can be found near the midline, followed by the head and gill covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are often lighter than those from dark, tannic acid streams.

<span class="mw-page-title-main">Eel life history</span> Eel life cycle

Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous 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 of the eel was long a mystery. Of particular interest has been the search for the spawning grounds for the various species of eels, and identifying the population impacts of different stages of the life cycle.

<span class="mw-page-title-main">Short-finned eel</span> Species of fish

The short-finned eel, also known as the shortfin eel, is one of the 15 species of eel in the family Anguillidae. It is native to the lakes, dams and coastal rivers of south-eastern Australia, New Zealand, and much of the South Pacific, including New Caledonia, Norfolk Island, Lord Howe Island, Tahiti, and Fiji.

<i>Conger</i> Genus of fishes

Conger is a genus of marine congrid eels. It includes some of the largest types of eels, ranging up to 2 m (6 ft) or more in length, in the case of the European conger. Large congers have often been observed by divers during the day in parts of the Mediterranean Sea, and both European and American congers are sometimes caught by fishermen along the European and North American Atlantic coasts.

<span class="mw-page-title-main">Anguillidae</span> Family of fishes

The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Except from the genus Neoanguilla, with the only known species Neoanguilla nepalensis from Nepal, all the extant species and six subspecies in this family are in the genus Anguilla, and are elongated fish of snake-like bodies, with long dorsal, caudal and anal fins forming a continuous fringe. They are catadromous, spending their adult lives in freshwater, but migrating to the ocean to spawn.

<span class="mw-page-title-main">European sprat</span> Species of fish

The European sprat, also known as brisling, brisling sardine, bristling, garvie, garvock, Russian sardine, russlet, skipper or whitebait, is a species of small marine fish in the herring family Clupeidae. Found in European, West Asian and North African waters, it has silver grey scales and white-grey flesh. Specific seas in which the species occurs include the Irish Sea, Black Sea, Baltic Sea and Sea of the Hebrides. The fish is the subject of fisheries, particularly in Scandinavia, and is made into fish meal, as well as being used for human consumption. When used for food it can be canned, salted, breaded, fried, boiled, grilled, baked, deep fried, marinated, broiled, and smoked.

<span class="mw-page-title-main">Flathead grey mullet</span> Species of fish

The flathead grey mullet is an important food fish species in the mullet family Mugilidae. It is found in coastal temperate, tropical and subtropical waters worldwide. Its length is typically 30 to 75 centimetres. It is known with numerous English names, including the flathead mullet, striped mullet, black mullet, bully mullet, common mullet, grey mullet, sea mullet and mullet, among others.

<span class="mw-page-title-main">New Zealand longfin eel</span> Species of fish

The New Zealand longfin eel, also known as ōrea, 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 native shortfin eel, also found in Australia, and the naturally introduced Australian longfin eel. Longfin eels are long-lived, migrating to the Pacific Ocean near Tonga to breed at the end of their lives. They are good climbers as juveniles and so are found in streams and lakes a long way inland. An important traditional food source for Māori, who name them ōrea, longfin eel numbers are declining and they are classified as endangered, but over one hundred tonnes are still commercially fished each year.

<span class="mw-page-title-main">European seabass</span> Species of fish

The European seabass, also known as the branzino, European bass, sea bass, common bass, white bass, capemouth, white salmon, sea perch, white mullet, sea dace or loup de mer, is a primarily ocean-going fish native to the waters off Europe's western and southern and Africa's northern coasts, though it can also be found in shallow coastal waters and river mouths during the summer months and late autumn. It is one of only six species in its family, Moronidae, collectively called the temperate basses.

<i>Anguillicoloides crassus</i> Species of roundworm

Anguillicoloides crassus is a parasitic nematode worm that lives in the swimbladders of eels and appears to spread easily among eel populations after introduction to a body of water. It is considered to be one of the threats to the sustainability of populations of European eel. It was introduced to the European continent in the 1980s, where it was reported independently from Germany and Italy in 1982, having probably been introduced from Taiwan. It is thought to have reached England in 1987 from continental Europe. It is a natural parasite of the Japanese eel in its native range.

<span class="mw-page-title-main">Speckled longfin eel</span> Species of fish

The speckled longfin eel, Australian long-finned eel or marbled eel is one of 15 species of eel in the family Anguillidae. It has a long snake-like cylindrical body with its dorsal, tail and anal fins joined to form one long fin. The dorsal fin also often extends farther than the anal fin. It usually has a brownish green or olive green back and sides with small darker spots or blotches all over its body. Its underside is paler. It has a small gill opening on each side of its wide head, with thick lips. It is Australia's largest freshwater eel, and the female usually grows much larger than the male. It is also known as the spotted eel.

<span class="mw-page-title-main">Japanese eel</span> Species of fish

The Japanese eel is a species of anguillid eel found in Japan, Korea, Taiwan, China, and Vietnam, as well as the northern Philippines. Like all the eels of the genus Anguilla and the family Anguillidae, it is catadromous, meaning it spawns in the sea but lives parts of its life in freshwater. Raised in aquaculture ponds in most countries, the Japanese eel makes up 95% of the commercially sold eel in Japan, the other 5% is shipped over by air to the country from Europe. This food in Japan is called unagi; they are an essential part of the food culture, with many restaurants serving grilled eel called kabayaki. However, presumably due to a combination of overfishing and habitat loss or changing water conditions in the ocean interfering with spawning and the transport of their leptocephali this species is endangered.

<span class="mw-page-title-main">Giant mottled eel</span> Species of fish

The giant mottled eel, also known as the marbled eel, is a species of tropical anguillid eel that is found in the Indo-Pacific and adjacent freshwater habitats.

<span class="mw-page-title-main">Eel</span> Order of fishes

Eels are ray-finned fish belonging to the order Anguilliformes, which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.

<span class="mw-page-title-main">Mahi-mahi fishing</span>

Mahi-mahi are swift and acrobatic game fish with striking colours. These colours darken when the fish dies The current IGFA all tackle record is 39.91 kilograms (88lb), caught in 1998 in Exuma, Bahamas by Chris Johnson of Lake Mary, Florida. Catches average 7 to 13 kilograms, and any mahi-mahi over 18 kilograms (40 lb) is exceptional. Males are often larger than females.

<span class="mw-page-title-main">Juvenile fish</span> Young fish

Fish go through various life stages between fertilization and adulthood. The life of fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.

<span class="mw-page-title-main">Short-tooth sawpalate</span> Species of fish

The short-tooth sawpalate is an eel in the family Serrivomeridae. It was described by Johannes Schmidt in 1916 in its larval form, originally under the genus Leptocephalus, and later as a subspecies of Serrivomer sector by Roule & Bertin in 1929. It is a marine, deep water-dwelling eel which is known from the eastern central and western central Atlantic Ocean, including the Strait of Gibraltar, Cape Verde, the United States, the Bahamas and Bermuda, as well as the Strait of Gibraltar, Cape Verde, Canada and the United States. It dwells at a depth range of 150 to 6,000 metres. Males can reach a maximum total length of 65 centimetres (26 in).

References

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  6. ↑ "A guide to eel farming". The Fish Site. 23 March 2015. Retrieved 10 October 2023.
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  34. ↑ Balm, S. Paul; Durif, Caroline; van Ginneken, Vincent; Antonissen, Erik; Boot, Ron; van Den Thillart, Guido; Verstegen, Martin (2007). "Silvering of European eel (Anguilla anguilla L.): seasonal changes of morphological and metabolic parameters". Animal Biology. 57 (1): 63–77. doi:10.1163/157075607780002014. ISSN   1570-7555.
  35. ↑ Dufour, Sylvie; Ginneken, Vincent van; Durif, Caroline; Doornbos, Jorg; Noorlander, Kees; Thillart, Guido van den; Boot, Ron; Murk, Albertinka; Sbaihi, Miskal (1 January 2007). "Endocrine profiles during silvering of the European eel (Anguilla anguilla L.) living in saltwater". Animal Biology. 57 (4): 453–465. doi:10.1163/157075607782232143. ISSN   1570-7563.
  36. ↑ Lokman, P. Mark; Vermeulen, Gerard J.; Lambert, Jan G.D.; Young, Graham (1 December 1998). "Gonad histology and plasma steroid profiles in wild New Zealand freshwater eels (Anguilla dieffenbachii and A. australis) before and at the onset of the natural spawning migration. I. Females*". Fish Physiology and Biochemistry. 19 (4): 325–338. doi:10.1023/A:1007719414295. ISSN   1573-5168. S2CID   24194486.
  37. ↑ The evolving story of catadromy in the European eel (Anguilla anguilla)
  38. ↑ "Eels May Use 'Magnetic Maps' As They Slither Across The Ocean". NPR . 13 April 2017.
  39. 1 2 3 4 5 "A guide to eel farming". The Fish Site. 23 March 2015. Retrieved 10 October 2023.
  40. 1 2 3 4 Kirkegaard, Eskild (November 2010). "European Eel and Aquaculture" (PDF). DTU Aqua, National Institute of Aquatic Resources.
  41. ↑ Kart, Jeff. "The First Eel Aquaculture Farm In The U.S. Is Raising Elvers For The American Sushi Market". Forbes. Retrieved 10 October 2023.
  42. ↑ Karipoglou, Costas; Nathanailides, Cosmas (11 May 2009). "Growth rate and feed conversion efficiency of intensively cultivated European eel (Anguilla anguilla L.)".
  43. ↑ "Feed conversion efficiency in aquaculture: do we measure it correctly? | TABLE Debates". tabledebates.org. Retrieved 23 October 2023.
  44. 1 2 3 4 5 6 7 "A guide to eel farming". The Fish Site. 23 March 2015. Retrieved 10 October 2023.
  45. 1 2 Pirollo, Teresa; Perolo, Alberto; Mantegari, Simone; Barbieri, Ilaria; Scali, Federico; Loris Alborali, Giovanni; Salogni, Cristian (14 February 2023). "Mortality in farmed European eel (Anguilla anguilla) in Italy due to Streptococcus iniae". Acta Veterinaria Scandinavica. 65 (1): 5. doi: 10.1186/s13028-023-00669-y . PMC   9926715 . PMID   36788544.
  46. 1 2 3 Kart, Jeff. "The First Eel Aquaculture Farm In The U.S. Is Raising Elvers For The American Sushi Market". Forbes. Retrieved 10 October 2023.
  47. ↑ "A guide to eel farming". The Fish Site. 23 March 2015. Retrieved 10 October 2023.
  48. ↑ Kirkegaard, Eskild (November 2010). "European Eel and Aquaculture" (PDF). DTU Aqua, National Institute of Aquatic Resources.
  49. ↑ Pirollo, Teresa; Perolo, Alberto; Mantegari, Simone; Barbieri, Ilaria; Scali, Federico; Loris Alborali, Giovanni; Salogni, Cristian (14 February 2023). "Mortality in farmed European eel (Anguilla anguilla) in Italy due to Streptococcus iniae". Acta Veterinaria Scandinavica. 65 (1): 5. doi: 10.1186/s13028-023-00669-y . PMC   9926715 . PMID   36788544.
  50. 1 2 3 Based on data sourced from the FishStat database Archived 7 November 2012 at the Wayback Machine , FAO.
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