Fish are aquaticvertebrates that are cold-blooded, covered with scales, and equipped with two sets of paired fins and several unpaired fins. Fish are abundant in the sea and in fresh water, with species being known from mountain streams (e.g., char and gudgeon) as well as in the deepest depths of the ocean (e.g., gulpers and anglerfish). They are of tremendous importance as food for people around the world, either collected from the wild (see fishing) or farmed in much the same way as cattle or chickens (see aquaculture). Fish are also exploited for recreation, through angling and fishkeeping, and fish are commonly exhibited in public aquaria. Fish have an important role in many cultures through the ages, ranging as widely as deities and religious symbols to subjects of books and popular movies.
A typical fish is cold-blooded; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills or an accessory breathing organ to enable it to breath atmospheric oxygen; has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin; has jaws; has skin that is usually covered with scales; and lays eggs that are fertilized internally or externally.
Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. Their leaf-like appendages enable them to blend in with floating seaweed
To each of these there are exceptions. Tuna, Swordfish, and some species of sharks show some warm-blooded adaptations, and are able to raise their body temperature significantly above that of the ambient water surrounding them.[4] Streamlining and swimming performance varies from highly streamlined and rapid swimmers which are able to reach 10-20 body-lengths per second (such as tuna, salmon, and jacks) through to slow but more maneuverable species such as eels and rays that reach no more than 0.5 body-lengths per second.[5] Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach.[6] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil lungfishes and coelacanths), ganoid (various fossil fishes but also living gars and bichirs, cycloid, and ctenoid (these last two are found on most bony fish.[7] There are even fishes that spend most of their time out of water. Mudskippers feed and interact with one another on mudflats and are only underwater when hiding in their burrows.[8] The catfishPhreatobius cisternarum lives in underground, phreatic habitats, and a relative lives in waterlogged leaf litter.[9][10]
Fish range in size from the 16 m (51 ft) whale shark to the 8 mm (just over ¼ of an inch) long stout infantfish.
Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications.
Fish are classified into the following major groups:
Some palaeontologists consider that Conodonta are chordates, and so regard them as primitive fish. For a fuller treatment of classification, see the vertebrate article.
The various fish groups taken together account for more than half of the known vertebrates. There are almost 28,000 known extant species of fish, of which almost 27,000 are bony fish, with the remainder being about 970 sharks, rays, and chimeras and about 108 hagfishes and lampreys.[11] A third of all of these species are contained within the nine largest families; from largest to smallest, these families are Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae, and Scorpaenidae. On the other hand, about 64 families are monotypic, containing only one species. It is predicted that the eventual number of total extant species will be at least 32,500.[12]
Anatomy
My aquarium contains three different fishes: guppies, platies, and swordtails.
The North Atlantic stock of Gadus morhua is estimated to contain several million fish.
Shoal or school
A random assemblage of fishes merely using some localised resource such as food or nesting sites is known simply as an aggregation. When fish come together in an interactive, social grouping, then they may be forming either a shoal or a school depending on the degree of organisation. A shoal is a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group. Schools of fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages (see article on swarming, the term used to cover such behaviours in animals).[56]
Cichlids congregating at lekking sites form an aggregation.
Many minnows and characins form shoals.
Classic examples of schooling fish are anchovies, herrings, and silversides.
While school and shoal have different meanings within biology, they are often treated as synonyms by non-specialists, with speakers of British English using "shoal" to describe any grouping of fish, while speakers of American English often using "school" just as loosely.
^ Peter Scott: Livebearing Fishes, p. 13. Tetra Press 1997.
^ ab Meisner, A & Burns, J: Viviparity in the Halfbeak Genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae). Journal of Morphology 234, pp 295-317, 1997
^ A.G. Zapata, A. Chiba and A. Vara. Cells and tissues of the immune system of fish. In: The Fish Immune System: Organism, Pathogen and Environment. Fish Immunology Series. (eds. G. Iwama and T.Nakanishi,), New York, Academic Press, 1996, pages 1-55.
^ D.P. Anderson. Fish Immunology. (S.F. Snieszko and H.R. Axelrod, eds), Hong Kong: TFH Publications, Inc. Ltd., 1977.
^ S. Chilmonczyk. The thymus in fish: development and possible function in the immune response. Annual Review of Fish Diseases, Volume 2, 1992, pages 181-200.
^ J.D. Hansen and A.G. Zapata. Lymphocyte development in fish and amphibians. Immunological Reviews, Volume 166, 1998, pages 199-220.
^ Kucher et al.,. Development of the zebrafish lymphatic system requires VegFc signalling. Current Biology, Volume 16, 2006, pages 1244-1248.
^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, pp 95-96, 1997,
^ R. C. Cipriano (2001), Furunculosis And Other Diseases Caused By Aeromonas salmonicida. Fish Disease Leaflet 66. U.S. Department of the Interior.[1]
^ K H Hartman et al (2004), Koi Herpes Virus (KHV) Disease. Fact Sheet VM-149. University of Florida Institute of Food and Agricultural Sciences.[2]
^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 380, 1997,
^ Richard L. Wyman and Jack A. Ward (1972). A Cleaning Symbiosis between the Cichlid Fishes Etroplus maculatus and Etroplus suratensis. I. Description and Possible Evolution. Copeia, Vol. 1972, No. 4, pp. 834-838.
Fish Olympics - Child-oriented edutainment at the Liverpool Museum
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