Flatfish

Taxobox
name = Flatfish

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image_width = 250px
image_caption = 19th c. engraving depicting several types of flatfish
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Pleuronectiformes
subdivision_ranks = Families
subdivision = Suborder Psettodoidei
Psettodidae
Suborder Pleuronectoidei
Citharidae
Scophthalmidae (turbots)
Bothidae (lefteye flounders)
Pleuronectidae (righteye flounders)
Paralichthyidae (large-tooth flounders)
Achiropsettidae (southern flounders)
Samaridae
Suborder Soleoidei
Soleidae (soles)
Achiridae (American soles)
Cynoglossidae (tonguefishes)

The flatfish are an order (Pleuronectiformes) of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. The name means "side-swimmers" in Greek. In many species both eyes lie on one side of the head, one or the other migrating through and around the head during development. Some species face their "left" side upward, some face their "right" side upward, and others face either side upward. The 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.

Many important food fish are in this order, including the flounders, soles, turbot, plaice, and halibut. There are more than 400 species of this order. Some flatfish can camouflage themselves on the ocean floor.

Origins

Flatfish have been cited as dramatic examples of evolutionary adaptation. For example, Richard Dawkins in "The Blind Watchmaker", explains the flatfish's evolutionary history as:

... 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.

The development of flatfish is thus considered to recapitulate their evolutionary history.Fact|date=July 2008

In 2008, scientists discovered "50-million-year-old fossils have revealed an intermediate species between primitive flatfishes (with eyes on both sides of their heads) and the modern, lopsided versions, which include sole, flounder, and halibut."cite news | url=http://news.nationalgeographic.com/news/2008/07/080709-evolution-fish.html | title=Odd Fish Find Contradicts Intelligent-Design Argument | publisher=National Geographic |date= July 9, 2008 | first= | last= | accessdate =2008-07-17] The research concluded that "the change happened gradually, in a way consistent with evolution via natural selection—not suddenly, as researchers once had little choice but to believe."

The asymmetric geometry of flatfish has been likened to the cubist paintings of Pablo Picasso, and is often perceived as being "imperfect", "grotesque", "strange", etc. It is likely that the asymmetry contributes to their survival by helping to disguise them on the ocean floor.

pecies

Some "species" listed here are groups of species. See individual entries for further lists.
* Brill
* Dab
* Flounder
* Halibut
* Megrim
* Plaice
* Sole
* Tonguefish
* Turbot

ee also

* Angling
* Sport fishing

References

External links

* [http://www.dfo-mpo.gc.ca/zone/underwater_sous-marin/plaice/plaice-plie_e.htm Information on Canadian fisheries of plaice]
* [http://www.nature.com/news/2008/080709/full/news.2008.946.html Nature article about a discovery shedding light on the evolution of flatfish]