Flatfish

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Flatfish
Temporal range: Paleocene–Recent [1]
Flounder camo md.jpg
A camouflaged flatfish
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Clade: Percomorpha
Order: Pleuronectiformes
Type species
Pleuronectes platessa
Families [2] [3]

Suborder Psettodoidei

Psettodidae (spiny turbots)

Suborder Pleuronectoidei

Superfamily Citharoidea
Citharidae (largescale flounders)
Superfamily Pleuronectoidea
Scophthalmidae (turbots)
Paralichthyidae (large-tooth flounders)
Pleuronectidae (righteye flounders)
Bothidae (lefteye flounders)
Superfamily Soleoidea
Paralichthodidae (measles flounders)
Poecilopsettidae (bigeye flounders)
Rhombosoleidae (rhombosoleids)
Achiropsettidae (southern flounders)
Samaridae (crested flounders)
Achiridae (American soles)
Soleidae (true soles)
Cynoglossidae (tonguefishes)

A flatfish is a member of the ray-finned demersal fish order Pleuronectiformes, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through or around the head during development. Some species face their left sides upward, some face their right sides upward, and others face either side upward.

Many important food fish are in this order, including the flounders, soles, turbot, plaice, and halibut. Some flatfish can camouflage themselves on the ocean floor.

Taxonomy

Over 800 described species are placed into 16 families. [4] Broadly, the flatfishes are divided into two suborders, Psettodoidei and Pleuronectoidei, with > 99% of the species diversity found within the Pleuronectoidei. [5] The largest families are Soleidae, Bothidae and Cynoglossidae with more than 150 species each. There also exist two monotypic families (Paralichthodidae and Oncopteridae). Some families are the results of relatively recent splits. For example, the Achiridae were classified as a subfamily of Soleidae in the past, and the Samaridae were considered a subfamily of the Pleuronectidae. [6] [7] The families Paralichthodidae, Poecilopsettidae, and Rhombosoleidae were also traditionally treated as subfamilies of Pleuronectidae, but are now recognised as families in their own right. [7] [2] [3] The Paralichthyidae has long been indicated to be paraphyletic, with the formal description of Cyclopsettidae in 2019 resulting in the split of this family as well. [4]

The taxonomy of some groups is in need of a review. The last monograph covering the entire order was John Roxborough Norman's Monograph of the Flatfishes published in 1934. In particular, Tephrinectes sinensis may represent a family-level lineage and requires further evaluation e.g. [8] New species are described with some regularity and undescribed species likely remain. [6]

Hybrids

Hybrids are well known in flatfishes. The Pleuronectidae, of marine fishes, have the largest number of reported hybrids. [9] Two of the most famous intergeneric hybrids are between the European plaice (Pleuronectes platessa) and European flounder (Platichthys flesus) in the Baltic Sea, [10] and between the English sole (Parophrys vetulus) and starry flounder (Platichthys stellatus) in Puget Sound. The offspring of the latter species pair is popularly known as the hybrid sole and was initially believed to be a valid species in its own right. [9]

Distribution

Flatfishes are found in oceans worldwide, ranging from the Arctic, through the tropics, to Antarctica. Species diversity is centered in the Indo-West Pacific and declines following both latitudinal and longitudinal gradients away from the Indo-West Pacific. [11] Most species are found in depths between 0 and 500 m (1,600 ft), but a few have been recorded from depths in excess of 1,500 m (4,900 ft). None have been confirmed from the abyssal or hadal zones. An observation of a flatfish from the Bathyscaphe Trieste at the bottom of the Mariana Trench at a depth of almost 11 km (36,000 ft) has been questioned by fish experts, and recent authorities do not recognize it as valid. [12] Among the deepwater species, Symphurus thermophilus lives congregating around "ponds" of sulphur at hydrothermal vents on the seafloor. No other flatfish is known from hydrothermal vents. [13] Many species will enter brackish or fresh water, and a smaller number of soles (families Achiridae and Soleidae) and tonguefish (Cynoglossidae) are entirely restricted to fresh water. [14] [15] [16]

Characteristics

Flatfish are asymmetric, with both eyes lying on the same side of the head Pseudopleuronectes americanus.jpg
Flatfish are asymmetric, with both eyes lying on the same side of the head
European flounder, like other flatfish, experience an eye migration during their lifetime. Platichthys flesus - en.pdf
European flounder, like other flatfish, experience an eye migration during their lifetime.

The most obvious characteristic of the flatfish is its asymmetry, with both eyes lying on the same side of the head in the adult fish. In some families, the eyes are usually on the right side of the body (dextral or right-eyed flatfish), and in others, they are usually on the left (sinistral or left-eyed flatfish). The primitive spiny turbots include equal numbers of right- and left-sided individuals, and are generally less asymmetrical than the other families. [1] Other distinguishing features of the order are the presence of protrusible eyes, another adaptation to living on the seabed (benthos), and the extension of the dorsal fin onto the head.

The surface of the fish facing away from the sea floor is pigmented, often serving to camouflage the fish, but sometimes with striking coloured patterns. Some flatfishes are also able to change their pigmentation to match the background, in a manner similar to some cephalopods. The side of the body without the eyes, facing the seabed, is usually colourless or very pale. [1]

In general, flatfishes rely on their camouflage for avoiding predators, but some have aposematic traits such as conspicuous eyespots (e.g., Microchirus ocellatus ) and several small tropical species (at least Aseraggodes , Pardachirus and Zebrias ) are poisonous. [6] [17] [18] Juveniles of Soleichthys maculosus mimic toxic flatworms of the genus Pseudobiceros in both colours and swimming mode. [19] [20] Conversely, a few octopus species have been reported to mimic flatfishes in colours, shape and swimming mode. [21]

The flounders and spiny turbots eat smaller fish, and have well-developed teeth. They sometimes seek prey in the midwater, away from the bottom, and show fewer extreme adaptations than other families. The soles, by contrast, are almost exclusively bottom-dwellers, and feed on invertebrates. They show a more extreme asymmetry, and may lack teeth on one side of the jaw. [1]

Flatfishes range in size from Tarphops oligolepis , measuring about 4.5 cm (1.8 in) in length, and weighing 2 g (0.071 oz), to the Atlantic halibut, at 2.5 m (8.2 ft) and 316 kg (697 lb). [1]

Species and species groups

Reproduction

Flatfishes lay eggs that hatch into larvae resembling typical, symmetrical, fish. These are initially elongated, but quickly develop into a more rounded form. The larvae typically have protective spines on the head, over the gills, and in the pelvic and pectoral fins. They also possess a swim bladder, and do not dwell on the bottom, instead dispersing from their hatching grounds as plankton. [1]

The length of the planktonic stage varies between different types of flatfishes, but eventually they begin to metamorphose into the adult form. One of the eyes migrates across the top of the head and onto the other side of the body, leaving the fish blind on one side. The larva also loses its swim bladder and spines, and sinks to the bottom, laying its blind side on the underlying surface.

Evolution

Fossil of Amphistium Amphistium.JPG
Fossil of Amphistium

In 2008, a 50-million-year-old fossil, Amphistium , was identified as an early relative of the flatfish and transitional fossil. [22] In a typical modern flatfish, the head is asymmetric, with both eyes on one side of the head. In Amphistium, the transition from the typical symmetric head of a vertebrate is incomplete, with one eye placed near the top of the head. [23] The researchers concluded, "the change happened gradually, in a way consistent with evolution via natural selection—not suddenly, as researchers once had little choice but to believe." [22]

Flatfishes have been cited as dramatic examples of evolutionary adaptation. Richard Dawkins, in The Blind Watchmaker , explains the flatfishes' evolutionary history thus:

...bony fish as a rule have a marked tendency to be flattened in a vertical direction.... It was natural, therefore, that when the ancestors of [flatfish] took to the sea bottom, they should have lain on one side.... But this raised the problem that one eye was always looking down into the sand and was effectively useless. In evolution this problem was solved by the lower eye 'moving' round to the upper side. [24]

As food

Flatfish is considered a Whitefish [25] because of the high concentration of oils within its liver. Its lean flesh makes for a unique flavor that differs from species to species. Methods of cooking include grilling, pan-frying, baking and deep-frying.

Timeline of genera

QuaternaryNeogenePaleogeneHolocenePleist.Plio.MioceneOligoceneEocenePaleoceneSymphurusParophrysIsopsettaEopsettaChibapsettaPegusaLyopsettaLimandaGlyptocephalusClidodermaAtheresthesPleuronichthysParalichthysMonochirusCitharichthysEvesthesMicrostomusMicrochirusAchiurusPlatichthysParaplagusiaDicologoglossaLepidorhombusHippoglossoidesBuglossidiumSoleaMonoleneBothusArnoglossusPsettodesCitharusScophthalmusTurahbuglossusJoleaudichthysImhoffiusEobuglossusEobothusAmphistiumQuaternaryNeogenePaleogeneHolocenePleist.Plio.MioceneOligoceneEocenePaleoceneFlatfish

See also

Related Research Articles

<span class="mw-page-title-main">Flounder</span> Group of flatfish species

Flounders are a group of flatfish species. They are demersal fish, found at the bottom of oceans around the world; some species will also enter estuaries.

Sole may refer to:

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

The true soles are a family, Soleidae, of flatfishes. It includes saltwater and brackish water species in the East Atlantic, Indian Ocean, and West and Central Pacific Ocean. Freshwater species are found in Africa, southern Asia, New Guinea, and Australia.

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

The Scophthalmidae are a family of flatfish found in the North Atlantic Ocean, Baltic Sea, Mediterranean Sea, and Black Sea. Fish of this family are known commonly as turbots, though this name can refer specifically to Scophthalmus maximus, as well. Some common names found in species of this family are turbots, windowpanes, and brills.

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

Pleuronectidae, also known as righteye flounders, are a family of flounders. They are called "righteye flounders" because most species lie on the sea bottom on their left sides, with both eyes on their right sides. The Paralichthyidae are the opposite, with their eyes on the left side. A small number of species in Pleuronectidae can also have their eyes on the left side, notably the members of the genus Platichthys.

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

The European plaice, commonly referred to as simply plaice, is a species of marine flatfish in the genus Pleuronectes of the family Pleuronectidae.

<span class="mw-page-title-main">Demersal fish</span> Fish that live and feed on or near the bottom of seas or lakes

Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes. They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters, they are found on or near the continental shelf, and in deep waters, they are found on or near the continental slope or along the continental rise. They are not generally found in the deepest waters, such as abyssal depths or on the abyssal plain, but they can be found around seamounts and islands. The word demersal comes from the Latin demergere, which means to sink.

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

Large-tooth flounders or sand flounders are a family, Paralichthyidae, of flounders. The family contains 14 genera with a total of about 110 species. They lie on the sea bed on their right side; both eyes are always on the left side of the head, while the Pleuronectidae usually have their eyes on the right side of the head.

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

Tonguefishes are flatfish in the family Cynoglossidae. They are distinguished by the presence of a long hook on the snout overhanging the mouth, and the absence of pectoral fins. Their eyes are both on the left side of their bodies, which also lack a pelvic fin. This family has three genera with a total of more than 140 species. The largest reaches a length of 66 cm (26 in), though most species only reach half that size or less. They are found in tropical and subtropical oceans, mainly in shallow waters and estuaries, though some species are found in deep sea floors, and even a few in rivers.

<span class="mw-page-title-main">Sole (fish)</span> Fish name belonging to several families

Sole is a fish belonging to several families. Generally speaking, they are members of the family Soleidae, but, outside Europe, the name sole is also applied to various other similar flatfish, especially other members of the sole suborder Soleoidei as well as members of the flounder family. In European cookery, there are several species which may be considered true soles, but the common or Dover sole Solea solea, often simply called the sole, is the most esteemed and most widely available.

<span class="mw-page-title-main">Yellowtail flounder</span> Species of fish

The yellowtail flounder, also known as the rusty dab, is a species of flatfish in the family Pleuronectidae. Reaching 56 cm (22 in) in length, it has reddish brown upperparts, pale underparts and yellow fins. Both its eyes are on the right (upper) side of its body. Found in the western North Atlantic, it has been fished commercially by North American fisheries for food. A victim of overfishing, the yellowtail flounder is categorized as "Vulnerable" by the International Union for Conservation of Nature.

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

The European flounder 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 United States and Canada accidentally through transport in ballast water. It is caught and used for human consumption.

<i>Achirus lineatus</i> Species of fish

The lined sole is a ray-finned flatfish found in the Western Atlantic. Its common length is 17 cm. Often considered a trash fish in commercial trawling, it is of little or no economic value.

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

Samaridae is a family of crested flounders, small flatfishes native to the Indo-Pacific. The family contains four genera with a total of 29 species.

<i>Symphurus thermophilus</i> Species of fish

Symphurus thermophilus is a species of tonguefish notable for being the only flatfish known to be an obligate inhabitant of hydrothermal vents. It is known to inhabit several widely dispersed locations in the western Pacific Ocean and occurs in great numbers. These flatfish are distinguished by the prominent dark crossbands on their brown eyed side, black abdominal cavity membrane lining known as the peritoneum, and white blind side. They are tolerant of harsh conditions and are often found in close association with elemental sulfur, including molten sulfur pools that exceed 180 °C in temperature. As they are not significantly different in appearance and feeding habits from other tonguefishes, they are thought to be relatively recent colonizers of vent ecosystems.

<i>Platichthys</i> Genus of fishes

Platichthys is a genus of flatfish native to the North Pacific and North Atlantic oceans. Despite being in the family Pleuronectidae, all three species in the genus Platichthys are often "lefteyed", i.e. they lie on the sea bottom on their right side, with both eyes on the left side.

<span class="mw-page-title-main">Pacific sand sole</span> Species of fish

The Pacific sand sole, also known as simply sand sole, is a flatfish species inhabiting the northeastern Pacific waters where it lives on sandy bottoms. The only species in the genus, Psettichthys, it ranges from the Bering Sea to Northern California.

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

The Poecilopsettidae are a family of flatfish in the order Pleuronectiformes, comprising three genera and 21 species. Species are typically demersal, living on marine bottoms at depths between 60 and 500 m in the Indo-Pacific and northwestern Atlantic; the deepest recorded occurrence is 1,636 m (5,367 ft) in the deepwater dab, Poecilopsetta beanii. Sizes range from 9 to 19 cm in length, though most species are usually under 15 cm (5.9 in) long. Diets consist of zoobenthos.

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

Rhombosoleidae is a family of flatfish in the order Pleuronectiformes, comprising nine genera and 19 species; all members of this family are right eye flounders with asymmetrical pelvic fins. Species are typically demersal, living on bottoms in temperate marine waters on the continental shelf, although some species of Rhombosolea enter fresh water in New Zealand. Most are restricted to waters around Australia and New Zealand, though the Remo flounder, Oncopterus darwinii, occurs in the southwestern Atlantic and the Indonesian ocellated flounder, Psammodiscus ocellatus, occurs in Indonesia.

<span class="mw-page-title-main">Plaice</span> Common name for a group of flatfish

Plaice is a common name for a group of flatfish that comprises four species: the European, American, Alaskan and scale-eye plaice.

References

  1. 1 2 3 4 5 6 Chapleau, Francois; Amaoka, Kunio (1998). Paxton, J.R.; Eschmeyer, W.N. (eds.). Encyclopedia of Fishes. San Diego: Academic Press. xxx. ISBN   0-12-547665-5.
  2. 1 2 Nelson, J. S. (2006). Fishes of the World (4 ed.). Hoboken, NJ: John Wiley & Sons. ISBN   978-0-471-25031-9.
  3. 1 2 J. S. Nelson; T. C. Grande; M. V. H. Wilson (2016). Fishes of the World (5th ed.). Wiley. p. 752. ISBN   978-1-118-34233-6. Archived from the original on 2019-04-08. Retrieved 2018-05-24.
  4. 1 2 Campbell, Matthew A.; Chanet, Bruno; Chen, Jhen-Nien; Lee, Mao-Ying; Chen, Wei-Jen (2019). "Origins and relationships of the Pleuronectoidei: Molecular and morphological analysis of living and fossil taxa" (PDF). Zoologica Scripta. 48 (5): 640–656. doi:10.1111/zsc.12372. ISSN   0300-3256. S2CID   202856805.
  5. ↑ Nelson, Joseph S. VerfasserIn. (2016-03-28). Fishes of the world. John Wiley & Sons. ISBN   9781118342336. OCLC   958002567.{{cite book}}: |last= has generic name (help)
  6. 1 2 3 Randall, J. E. (2007). Reef and Shore Fishes of the Hawaiian Islands. ISBN   1-929054-03-3
  7. 1 2 Cooper, J.A.; and Chapleau, F. (1998). Monophyly and intrarelationships of the family Pleuronectidae (Pleuronectiformes), with a revised classification. Fish. Bull. 96 (4): 686–726.
  8. ↑ Hoshino, Koichi (2001-11-01). "Monophyly of the Citharidae (Pleuronectoidei: Pleuronectiformes: Teleostei) with considerations of pleuronectoid phylogeny". Ichthyological Research. 48 (4): 391–404. Bibcode:2001IchtR..48..391H. doi:10.1007/s10228-001-8163-0. ISSN   1341-8998. S2CID   46318428.
  9. 1 2 Garrett, D.L.; Pietsch, T.W.; Utter, F.M.; and Hauser, L. (2007). The Hybrid Sole Inopsetta ischyra (Teleostei: Pleuronectiformes: Pleuronectidae): Hybrid or Biological Species? American Fisheries Society 136: 460–468
  10. ↑ Food and Agriculture Organization of the United Nations: Platichthys flesus (Linnaeus, 1758). . Retrieved 18 May 2014
  11. ↑ Campbell, Matthew A.; Chanet, Bruno; Chen, Jhen-Nien; Lee, Mao-Ying; Chen, Wei-Jen (2019). "Origins and relationships of the Pleuronectoidei: Molecular and morphological analysis of living and fossil taxa" (PDF). Zoologica Scripta. 48 (5): 640–656. doi:10.1111/zsc.12372. ISSN   1463-6409. S2CID   202856805.
  12. ↑ Jamieson, A.J., and Yancey, P. H. (2012). On the Validity of the Trieste Flatfish: Dispelling the Myth. The Biological Bulletin 222(3): 171-175
  13. ↑ Munroe, T.A.; and Hashimoto, J. (2008). A new Western Pacific Tonguefish (Pleuronectiformes: Cynoglossidae): The first Pleuronectiform discovered at active Hydrothermal Vents. Zootaxa 1839: 43–59.
  14. ↑ Duplain, R.R.; Chapleau, F; and Munroe, T.A. (2012). A New Species of Trinectes (Pleuronectiformes: Achiridae) from the Upper Río San Juan and Río Condoto, Colombia. Copeia 2012 (3): 541-546.
  15. ↑ Kottelat, M. (1998). Fishes of the Nam Theun and Xe Bangfai basins, Laos, with diagnoses of twenty-two new species (Teleostei: Cyprinidae, Balitoridae, Cobitidae, Coiidae and Odontobutidae). Ichthyol. Explor. Freshwat. 9(1):1-128.
  16. ↑ Monks, N. (2007). Freshwater flatfish, order Pleuronectiformes. Archived 2014-08-15 at the Wayback Machine Retrieved 18 May 2014
  17. ↑ Elst, R. van der (1997) A Guide to the Common Sea Fishes of South Africa. ISBN   978-1868253944
  18. ↑ Debelius, H. (1997). Mediterranean and Atlantic Fish Guide. ISBN   978-3925919541
  19. ↑ Practical Fishkeeping (22 May 2012) Video: Tiny sole mimics a flatworm. Archived 2014-05-17 at the Wayback Machine Retrieved 17 May 2014.
  20. ↑ Australian Museum (5 November 2010). This week in Fish: Flatworm mimic and shark teeth. Archived 2013-02-26 at the Wayback Machine Retrieved 17 May 2014.
  21. ↑ Hanlon, R.T.; Warson, A.C.; and Barbosa, A. (2010). A "Mimic Octopus" in the Atlantic: Flatfish Mimicry and Camouflage by Macrotritopus defilippi. The Biological Bulletin 218(1): 15-24
  22. 1 2 "Odd Fish Find Contradicts Intelligent-Design Argument". National Geographic. July 9, 2008. Archived from the original on July 11, 2008. Retrieved 2008-07-17.
  23. ↑ Matt Friedman (2008). "The evolutionary origin of flatfish asymmetry" (PDF). Nature Letters. 454 (7201): 209–212. Bibcode:2008Natur.454..209F. doi:10.1038/nature07108. PMID   18615083. S2CID   4311712. Archived (PDF) from the original on 2013-03-19.
  24. ↑ Dawkins, Richard (1991). The Blind Watchmaker. London: Penguin Books. p. 92. ISBN   0-14-014481-1.
  25. ↑ "Flatfish BBC".

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