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Overview

Brief Summary

Flounder is the only flatfish that migrates to freshwater without any problem. They have been found in the Rhine by Basel Switzerland. Their preference is to live in brackish waters. Should you find one flounder, you're bound to find more however they are so well camouflaged that they are difficult to discover. The eyes of this flatfish are usually on the right side but they are sometimes on the left.
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Comprehensive Description

Biology

Migratory fish, which is most of the year found in estuaries (Ref. 51442). Occurs on mud and sand bottom in shallow water, at sea and brackish; often entering freshwaters (Ref. 59043). During winter, adults retreat to deeper, warmer waters, where they spawn in spring (Ref. 30193). The growing larvae are moving to the coast (Ref. 51442). The growing larvae are moving to the coast (Ref. 51442). Larvae and early juveniles use selective tidal transport to migrate upstream rivers (Ref. 57575) using a range of triggers such as salinity, prey density and water temperature (Ref. 57573, 57574). Juveniles live in shallow coastal waters and estuaries (Ref. 57574), which are also the summer feeding grounds for the adults (Ref. 30193). Juveniles of less than a year old feed on plankton and larvae of insects, juveniles of more than a year and adults feed on benthic fauna (Ref. 51442), including small fishes and invertebrates (Ref. 30193). Nocturnal and burrowing (Ref. 30193). Marketed fresh and frozen; can be steamed, fried, boiled, microwaved and baked (Ref. 9988). Worms and mollusks are excellent baits for line fishing (Ref. 30578).
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Description

 The flounder has a roughly oval shape, with both eyes on the right side of its head and has a small mouth and pointed snout. The lateral line curves slightly around the pectoral fin. It has a smooth body except for some rough scales along the lateral line and a row of prickly humps along the base of the dorsal and anal fins. The caudal peduncle is long, accounting for about half the length of the tail. The topside colour is variable from dull brown to greyish-green, often with small orange spots, while the underside is white. The flounder grows up to 50 cm in length.Identification of Plactichthys flesus is made more difficult by the existence of 'reversed individuals' in which the eyes are on the left side of the body. Hybrid individuals have been know to occur through interbreeding between flounder and plaice (Pleuronectes platessa) (Dipper, 2001).
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Description

This flatfish is oval in shape and is usually right-eyed. Most adults are between 25-30cm in length however it can be up to 50cm. The upper surface is usually dull brown in colour with reddish-brown blotches and the underside is white. Often the colour is camouflaged with the seabed. There are rows of bony tubercles along the lateral line and the bases of the dorsal and anal fins. The flounder is similar is size and shape to the plaice and dab however bony tubercles along the lateral line and at the bases of the dorsal and anal fins are distinctive of the flounder.
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Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: Native to European waters of the Atlantic Ocean north to the White Sea, and alos known from the Adriatic Sea and Black Sea; common in the Baltic Sea and in the southern and eastern coastal North Sea (Wheeler 1969, Emery and Teleki 1978). Has been captured in commercial nets in Lake Erie on several occasions and at leats once in Lake Superior (Emery and Teleki 1978; D. Sutherland, pers. comm., 1998). May not become established in the Great Lakes because the species evidently cannot reproduce in freshwater (Emery and Teleki 1978).

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Range Description

This natural range of Platichthys flesus extends from the White Sea to the Mediterranean and the Black Sea. Due to accidental introductions in ballast water, it may also be found around North America.
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Baltic Sea, North Sea, Eastern North Atlantic and western Europe; introduced elsewhere.
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Black Sea, Sea of Azov and northeastern Mediterranean Sea; introduced into Caspian Sea.
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Eastern Atlantic: coastal and brackish waters of western Europe and from the White Sea to the Mediterranean and the Black Sea (Ref. 4705, Ref. 51442). Introduced into the USA and Canada accidentally through transport in ballast water (Ref. 1739). Asia: Iran (Ref. 39702).
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Baltic Sea, North Sea, Eastern North Atlantic and western Europe; introduced elsewhere.
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Occurs all around the coasts of Britain and Ireland.
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Physical Description

Morphology

Dorsal spines (total): 0; Dorsal soft rays (total): 53 - 62; Analspines: 0; Analsoft rays: 37 - 46
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Size

Maximum size: 520 mm TL
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Maximum size: 520 mm TL
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Max. size

60.0 cm TL (male/unsexed; (Ref. 35388)); max. published weight: 14.0 kg (Ref. 40637); max. reported age: 15 years (Ref. 3944)
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Diagnostic Description

Flatfish, its disc width less than half its length (Ref. 3137). Small mouth (Ref. 3137, Ref. 51442). Eyes mostly (70%) on right side (Ref. 3137, 51442), 79% of dextrally oriented flounder (n = 1076) in Bos, 2000 (Ref. 57574). Rough skin, especially along the lateral line and the basis of the dorsal and anal fin (Ref. 3137). Lateral line straight, slightly rounded over pectorals (Ref. 3137). Green-olive colored (Ref. 51442), the bottom side white (Ref. 3137). Irregular reddish spots on the eye side (Ref. 35388).
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Ecology

Habitat

Seine River Demersal Habitat

This taxon is one of a number of demersal species in the Seine River system of Western Europe. Demersal river fish are found at the river bottom, feeding on benthos and zooplankton

The Marne and Yonne exhibit the greatest torrential flows, due to the percentage of their courses underlain by impermeable strata, in combination with the river gradients. Although the Loing manifests the highest percentage of impermeable strata of all the tributaries, its low gradient mitigates against torrential velocities. Thus the majority of the Seine and its tributaries exhibit a relaxed generally even flow rate.

Seine water pollutant loads of heavy metals, nutrients, sediment and bacteria are relatively high, especially influnced by wastewater and surface runoff from Paris and its suburbs. Parisian pollutant loadings are noted to be particularly high during periods of high rainfall, not only due to high runoff, but also from the inadequate sewage treatment facilities in periods of high combined wastewater/stormwater flow.

Heavy metal concentrations at Poses weir reveal the following levels: copper, 1.9 milligrams per liter; cadmium, 32 mg/l; and lead, 456 mg/l. Concentrations of zinc are also quite high, making the Seine Estuary one of the most highly contaminated estuaries in the world with respect especially to lead and cadmium. Significant amounts of toxic pollutants are also attached to sediments deposited in the Seine during the last two centuries, including mercury, nickel, chromium, toluene, DDT and a variety of herbicides and pesticides. Downriver from Paris, significant quantites of ammonium are discharged into the Seine from effluent of the Achères wastewater treatment plant.

There are a total of 37 fish species inhabiting the Seine, and another two taxa that are known to have been extirpated in modern times. Two of the largest aquatic fauna known to have lived in the Seine are now locally extinct: the 500 centimeter (cm) long sturgeon (Acipenser sturio) and the 83 cm long allis shad (Alosa alosa).

The largest extant native demersal (species living on or near the river bottom) taxa in the Seine are:

the 133 cm European eel (Anguilla anguilla);

the 150 cm northern pike (Esox lucius);

the 120 cm sea lamprey (Petromyzon marinus); and,

the 152 cm Burbot (Lota lota).

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Habitat Type: Marine

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Habitat and Ecology

Habitat and Ecology
Platichthys flesus is common around the British Isles, where it is typically found resting on the muddy substrate of estuaries. It has been found at a depth range of 1-100 m. It migrates into the open sea to breed from March to June, during which time it can migrate up to 300 km offshore, although it will more often migrate just 30 km. The larvae feed on copepods and diatoms and gradually shift to a diet of mysids, decapods, crustaceans, polychaetes, and bivalves. The young then return to estuarine waters, where they live on the bottom until they are ready to migrate and spawn.

Systems
  • Freshwater
  • Marine
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Depth: 1 - 100m.

Habitat: demersal.
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Environment

demersal; catadromous (Ref. 51243); freshwater; brackish; marine; pH range: 7.5 - 8.2; depth range 1 - 100 m (Ref. 35388)
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Depth range based on 130435 specimens in 1 taxon.
Water temperature and chemistry ranges based on 46390 samples.

Environmental ranges
  Depth range (m): -9 - 234
  Temperature range (°C): 2.641 - 12.274
  Nitrate (umol/L): 1.139 - 16.868
  Salinity (PPS): 5.722 - 35.297
  Oxygen (ml/l): 0.573 - 8.684
  Phosphate (umol/l): 0.114 - 3.328
  Silicate (umol/l): 0.987 - 72.643

Graphical representation

Depth range (m): -9 - 234

Temperature range (°C): 2.641 - 12.274

Nitrate (umol/L): 1.139 - 16.868

Salinity (PPS): 5.722 - 35.297

Oxygen (ml/l): 0.573 - 8.684

Phosphate (umol/l): 0.114 - 3.328

Silicate (umol/l): 0.987 - 72.643
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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 A bottom dwelling fish living in inshore waters to depths of 50 m, Platichthys flesus can often be found in estuaries and sometimes freshwater.
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Depth: 1 - 100m.
From 1 to 100 meters.

Habitat: demersal.
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The flounder usually lives on muddy seabeds from the low shore to at least 50m depth. It feeds on a variety of bottom-living animals e.g. crustaceans, worms and molluscs. Like the plaice, juveniles live in shallow water close to the shore. It is very tolerant of reduced salinities and is frequently found in estuaries.
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Catadromous. Migrating from freshwater to the sea to spawn, e.g., European eels. Subdivision of diadromous. Migrations should be cyclical and predictable and cover more than 100 km.
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Trophic Strategy

Juveniles of less than a year old feed on plankton and larvae of insects, juveniles of more than a year and adults feed on benthic fauna (Ref. 51442). The adults burrow in the sand during daytime and search for food during nighttime (Ref. 173).
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Associations

Animal / pathogen
Icthyophonus hoferi infects muscle of Pleuronectes flesus

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Known predators

  • Hall SJ, Raffaelli D (1991) Food-web patterns: lessons from a species-rich web. J Anim Ecol 60:823–842
  • Huxham M, Beany S, Raffaelli D (1996) Do parasites reduce the chances of triangulation in a real food web? Oikos 76:284–300
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Known prey organisms

  • Hall SJ, Raffaelli D (1991) Food-web patterns: lessons from a species-rich web. J Anim Ecol 60:823–842
  • Huxham M, Beany S, Raffaelli D (1996) Do parasites reduce the chances of triangulation in a real food web? Oikos 76:284–300
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Diseases and Parasites

Vibriosis of salmonids (chronic). Bacterial diseases
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Pomphorhynchus Infestation. Parasitic infestations (protozoa, worms, etc.)
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Lymphocystis Disease. Viral diseases
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Lernaeocera Disease (e.). Parasitic infestations (protozoa, worms, etc.)
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Lepeophtheirus Disease. Parasitic infestations (protozoa, worms, etc.)
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IPN. Viral diseases
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Glugea Infestation. Parasitic infestations (protozoa, worms, etc.)
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Fin-rot Disease (late stage). Bacterial diseases
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Life History and Behavior

Life Cycle

Spawns in the water column (Ref. 7471). Produces 400,000 to 2,000,000 eggs for each female (Ref. 51442).
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Platichthys flesus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 33
Specimens with Barcodes: 52
Species With Barcodes: 1
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Barcode data: Platichthys flesus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 5 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ACCCTCTATCTCGTATTTGGTGCCTGAGCCGGAATAGTGGGGACAGGCCTA---AGTCTGCTCATTCAAGCAGAACTAAGCCAACCTGGGGCTCTCCTGGGAGAC---GACCAAATTTATAACGTAATCGTCACCGCACACGCCTTTGTAATAATTTTCTTTATAGTAATGCCAATTATGATTGGAGGGTTCGGAAACTGACTTATCCCATTAATA---ATTGGGGCCCCCGATATGGCCTTCCCTCAAATAAACAACATGAGTTTCTGACTTCTTCCCCCATCCTTTCTCCTTCTCCTAGCCTCTTCAGGTGTTGAAGCCGGGGCGGGAACAGGTTGAACCGTTTACCCCCCATTAGCTGGGAACCTAGCACATGCCGGGGCATCCGTAGACCTC---ACAATCTTCTCTCTTCACCTTGCCGGAATTTCATCAATTCTGGGGGCAATCAACTTTATTACTACCATCATCAATATGAAACCCACAGCAGTCACTATGTACCAAATCCCACTATTTGTTTGAGCCGTACTATTGACCGCCGTCCTTCTTCTCCTTTCCCTTCCCGTCTTACCCGCT---GGTATCACAATGCTACTACCAGACCGCAACCTAAACCACACCTTCTGTGACCCTGCTGGAGGGGGTGACCCCATCCTCTACCAACACCTA------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------TTC
-- end --

Download FASTA File
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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNA - Not Applicable

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2010

Assessor/s
Munroe, T.A.

Reviewer/s
Collen, B., Richman, N., Beresford, A., Chenery, A. & Ram, M.

Contributor/s
De Silva, R., Milligan, H., Lutz, M., Batchelor, A., Jopling, B., Kemp, K., Lewis, S., Lintott, P., Sears, J., Wilson, P. & Smith, J. and Livingston, F.

Justification
Platichthys flesus has been assessed as Least Concern. This species has a broad geographic range in which it is reported as common. Despite some signficant threats, harvesting and chemical pollution, these are not thought to pose a signficant threat to the global population at this time. However it is recommended that systematic monitoring is undertaken to determine stock status across the entire range.

History
  • 2008
    Least Concern
    (IUCN 2008)
  • 2008
    Least Concern
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Population

Population
Platichthys flesus is common throughout its range.

Population Trend
Decreasing
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Threats

Major Threats
Due to the close association of Platichthys flesus with estuarine waters and the benthic invertebrate fauna within these habitats, it has been impacted by chemical pollution within these sediments. In particular, xenoestrogens, which occur in domestic, industrial and agricultural waste, have been noted to have a negative effect on this species, causing the occurrence of intersex specimens. Intersex individuals are caught in low, but constant amounts (Lye et al. 1998). The effects of xenoestrogen are markedly lower further from the shore (Vethaak et al. 2005).

In addition, this is a commercially important food fish, with some of the most important fisheries existing in Baltic and Danish waters. The total landings for 1999 were 11,879 t, with Denmark and the Netherlands contributing the greatest landings of 3,528 t and 3,159 t respectively.
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Least Concern (LC)
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Management

Conservation Actions

Conservation Actions
There are no known species-specific conservation measures in place for Platichthys flesus. However, it may occur in a number of marine protected areas, affording it some protection from harvesting and high loadings of chemical waste.

It is recommended that systematic monitoring is undertaken to determine stock status across the entire range.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: commercial; gamefish: yes
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Wikipedia

European flounder

The European flounder (Platichthys flesus) is a flatfish of European coastal waters from the White Sea in the north to the Mediterranean and the Black Sea in the south. It has been introduced into the USA and Canada accidentally through transport in ballast water. It is caught and used for human consumption.

The European flounder is oval in shape and is usually right-eyed. It normally grows about 30 cm in length, although lengths of up to 60 cm have been recorded. The upper surface is usually dull brown or olive in colour with reddish spots and brown blotches and this fish can change colour to suit its background, providing an effective camouflage. The underside is pearly-white, giving the fish one of its common names, the white fluke. The lateral line features rows of small tubercles, as do the bases of the dorsal and anal fins.

Description[edit]

The European flounder is a flatfish with an oval-shaped body with a width about half its length. The maximum recorded length is 60 centimetres (24 in) and the maximum recorded weight 14 kilograms (31 lb). However, a more usual mature length is about 50 centimetres (20 in).[3]

The fish is flattened laterally and swims and rests on one side. During development, its eyes usually migrate to the right side of the fish and what appears to be its upper surface is in reality its right side. In about thirty percent of individuals, its eyes move to the left and the left side becomes uppermost. The fish has a small mouth at the end of its bluntly pointed snout. The upper surface is fawn, olive green or pale brown with spots and larger patches of darker brown and some irregular reddish spots. The under surface is opaque pearly-white giving the fish its common name of "white fluke". The lateral line is nearly straight and runs along the middle of the upper surface, curving round the short pectoral fins. The dorsal fin runs from the base of the head to beside the caudal peduncle. It has no dorsal spines but has between 53 and 62 soft rays. The anal fin also runs the length of the body and has no spines and 37 to 46 soft rays. The skin is rough, with prickly tubercles at the base of the dorsal and anal fins, and there are large scales beside the lateral line. The caudal peduncle is about half the length of the tail and the caudal fin has a squared-off end.[4][5]

Distribution and habitat[edit]

The European flounder is native to the north eastern Atlantic Ocean and the Mediterranean Sea. The range extends from the Barents Sea, White Sea and Baltic Sea to Greece, Turkey, the Black Sea and the North African coast. It has been introduced into Iran and has become established off the eastern coast of Canada and the United States, possibly getting there by way of ballast water. It is normally found from the low shore down to depths of about 100 metres (330 ft) on sandy, shingle or muddy bottoms where its dappled colouring camouflage it and make it difficult to detect.[1]

The European flounder can also be found in estuaries where it is tolerant of low salinity levels and, unlike other species of Pleuronectidae, it often spends part of its life cycle in freshwater and regularly makes its way into rivers. In the British Isles has been found as far inland as Montgomeryshire on the River Severn, Dinas Mawddwy on the River Dovey and Garstang on the River Wyre. Unlike the Atlantic salmon, it feeds in the rivers and makes its way out to sea again before spawning.[5]

Biology[edit]

The European flounder lives and feeds on the seabed and in the waters immediately above. It is mainly nocturnal and during the day rests on the sea floor, semi-submerging itself in the substrate. It feeds on bivalve molluscs and other benthic invertebrates such as shrimps, polychaete worms, gastropod molluscs and small fish.[4]

The European flounder leaves freshwater in the autumn and can often be caught in estuaries when the first frosts occur. Then the fish move into deeper water for the winter. In the spring it migrates to the spawning grounds, travelling at three to four miles (five to seven kilometres) per day and not eating en route. Spawning takes place between February and May being later in more northerly latitudes. The female liberates about a million eggs which are lighter than water. The male liberates sperm which also floats and both eggs and sperm rise to the surface. Here the eggs are fertilised and hatch after six to eleven days depending on the water temperature. The developing larvae are planktonic and drift towards the coast with juvenile flounders living in shallow waters and estuaries. Young flounders become mature when still small, the males when they measure 11.5 centimetres (4.5 in) and the females when they measure 18 cm (7 in).[5] The European flounder sometimes hybridises with European plaice (Pleuronectes platessa) and, particularly in the western Baltic Sea, the hybrid is common.[6]

Human interactions[edit]

The European flounder is used for human consumption but is not so highly esteemed as the European plaice or common sole (Solea solea).[5] The most important fisheries are in the Baltic Sea and the waters around the Netherlands and Denmark. In 2010, the total world catch was about nineteen thousand tonnes, mostly caught by bottom trawling. The fish is marketed fresh and frozen and can be fried, boiled, steamed, baked or microwaved.[6]

It has been found that male European flounders living in polluted estuaries may show signs of excess exposure to oestrogens. Substances such as vitellogenins have been identified in their blood at between four and six times the concentration found in the blood of fish from uncontaminated areas; however, the flounder is less sensitive to oestrogens than is the freshwater rainbow trout.[7]

Status[edit]

The European flounder is assessed by the IUCN in their Red List of Threatened Species as being of "Least Concern". This is because it has a large population size and extensive range, and is common in nearly all parts of its range. Numbers of fish may be decreasing somewhat but not to the extent that would warrant listing it under a higher risk category.[1]

References[edit]

  1. ^ a b c Munroe, T. A. (2009-02-04). "Platichthys flesus". IUCN Red List. International Union for Conservation of Nature. Retrieved 2013-08-31. 
  2. ^ a b Bailly, Nicolas (2013). "Platichthys flesus (Linnaeus, 1758)". World Register of Marine Species. Retrieved 2013-08-31. 
  3. ^ Froese, Rainer and Pauly, Daniel, eds. (2013). "Platichthys flesus" in FishBase. October 2013 version.
  4. ^ a b Luna, Susan M. "Platichthys flesus (Linnaeus, 1758)". FishBase. FishBase. Retrieved 2013-08-31. 
  5. ^ a b c d Jenkins, J. Travis (1958). The Fishes of the British Isles. Frederick Warne & Co. pp. 187–190. ASIN B00ABHEN6Y. 
  6. ^ a b Fisheries and Aquaculture Department. "Platichthys flesus (Linnaeus, 1758)". Species fact sheets. Food and Agriculture Organization of the United Nations. Retrieved 2013-09-01. 
  7. ^ Allen, Yvonne; Scott, Alexander P.; Matthiessen, Peter; Haworth, Sarah; Thain, John E.; Feist, Steve (1999). "Survey of estrogenic activity in United Kingdom estuarine and coastal waters and its effects on gonadal development of the flounder Platichthys flesus". Journal of Environmental Toxicology and Chemistry 18 (8): 1791–1800. doi:10.1002/etc.5620180827. 
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