Fish

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For other uses, see Fish (disambiguation).

Fish Fossil range: Mid Cambrian–Recent PreЄ Є O S D C P T J K Pg N
A giant grouper at the Georgia Aquarium, seen swimming among schools of other fish The ornate red lionfish as seen from a head-on view

 fish is any member of a paraphyletic group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups. Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature.^[1][2] Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish). At 32,000 species, fish exhibit greater species diversity than any other group of vertebrates.^[3]
Fish are an important resource for humans worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries (see fishing) or farm them in ponds or in cages in the ocean (see aquaculture). They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.
Because the term "fish" is defined negatively, and excludes the tetrapods (i.e., the amphibians, reptiles, birds and mammals) which descend from within the same ancestry, it is paraphyletic, and is not considered a proper grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification.
The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods.

Fish

From Wikipedia, the free encyclopedia

Jump to: navigation, search

For other uses, see Fish (disambiguation).

Fish Fossil range: Mid Cambrian–Recent PreЄ Є O S D C P T J K Pg N
A giant grouper at the Georgia Aquarium, seen swimming among schools of other fish The ornate red lionfish as seen from a head-on view
Scientific classification
Kingdom: Animalia Phylum: Chordata (unranked) Craniata
Included groups
Jawless fish †Armoured fish Cartilaginous fish Ray-finned fish Lobe-finned fishes
Excluded groups
Tetrapods

A fish is any member of a paraphyletic group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups. Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature.^[1][2] Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish). At 32,000 species, fish exhibit greater species diversity than any other group of vertebrates.^[3]
Fish are an important resource for humans worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries (see fishing) or farm them in ponds or in cages in the ocean (see aquaculture). They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.
Because the term "fish" is defined negatively, and excludes the tetrapods (i.e., the amphibians, reptiles, birds and mammals) which descend from within the same ancestry, it is paraphyletic, and is not considered a proper grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification.
The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods.

By plane

The majority of visitors arrive in Mongolia through Chinggis Khaan International Airport (IATA: ULN), which is located 18 km to the southwest of Ulaanbaatar. Many locals still call the airport by its old name "Bouyant Uka". The airport was reconstructed in 1990, and the immigration, customs formalities and luggage delivery are relatively efficient.
MIAT [3] (Mongolian Airlines) offers direct international flights to the city from Berlin, Moscow, Irkutsk, Seoul, Beijing,Hong Kong and Tokyo. Domestic flights from ULN to Dalanzadgad, Moron, Khovd, Bulgan Khovd, Altai, and Arvaikheer are also available. Korean Air also flies daily from Seoul to ULN. Air China flies to and from Beijing. The Russian airline Aeroflot flies daily between Moscow and Ulaanbaatar.

By train

Direct (but long) journeys are possible from Mackow Rusia and Beijing, China on the Trans-Mongolian line of the Trans-Siberian Railway. Trains also run to the Chinese border towns of Erlian and Jining 3-4 times a week. There's also a daily train to/from Irkutsk in Russia, which can also be reached from Vladivostok at the eastern end of the Trans-Siberian.
Trains from Beijing run once a week (on Tuesdays) and seats can only be reserved at the International Hotel in Beijing (a ten minute walk north of the main Beijing rail station). The journey takes about 30 hours. Packing a face mask might be a good idea as sandstorms in the Gobi desert may cause difficulty in breathing.