Fish are cold blooded animals i.e. their body temperature is close to ambient temperature and does not exceed it by more than 0.5. 1 deg. So the speed of metabolism they depend on the water temperature. Only tuna as a result of intensive muscular activity in rapid motion the body temperature may exceed the temperature of water at 10 deg.

From vertebrate fish – the largest group of animals. There are over 20 thousand species – more than the amphibians, reptiles, birds and mammals combined. In the superclass of Jawed (Gnathostomata), which include all fish, from 515 to 550 species belongs to the class of Cartilaginous fish (Chondrichthyes) (chimeras, sharks, rays) and from 19135 until 20980 species to the class of Bony fish (Osteichthyes) (all other fishes, including cartilaginous ganoids – sturgeon and others, which in the adult skeleton presents no spine, and the chord, but there are also bones, mainly covering forming the outer skeleton). In addition, there are about 50 species of lampreys and mixin-jawless fish-like animals, which fish are not. They come in the Cyclostomes (Cyclostomata), belonging to another superclass – Jawless (Agnatha), though are together with fish for the same type of Chordates (Chordata) and subtype Vertebrates (Vertebrata), or Skull (Craniata). About 41.2% of fish are typically freshwater, about 0.6% live in both fresh and salt water (brackish). The remaining 52.2 per cent is marine fish, of which 39.9 per cent live in the coastal waters of warm seas and oceans, 5,6% – in cold coastal waters, 6,4% are deep-sea bottom and bottom-dwelling (benthic) species, 5% of deep-sea pelagic and 1.3% live far from the coast in the upper 200 m of the water column of seas and oceans (epipelagic species).

Classes are divided into squads, squads – on family, family – childbirth, childbirth – in types. By G. U. Lindberg (1971), the fish there were 490 (491) families, besides, in 4 the combined family of fishlike vertebrates (Jawless) lamprey and hagfish. In biological nomenclature are also used as intermediate taxa: subclasses, naturade, order, superfamily, subfamily, etc. the Basic unit of biological nomenclature is.

The same view can be named differently not only in different countries or in different parts of the country, but it may even have several different local names. To avoid confusion, use the scientific name of the fish in Latin. The scientific name of the species is indicated by two words: the first indicates the genus, the second species. For example, common gourami (spotted) called Trichogaster trichopterus, and the pearl gourami – Trichogaster leeri. Subspecies, i.e. aggregate forms of one species, the centers of areas which are separated geographically, the three words denote, consistently indicating the genus, species, subspecies. For example, the blue gourami, gourami which is a subspecies of the ordinary, living on the island of Sumatra, called Trichogaster trichopterus sumatranus. After the title fish, put the last name of the researcher who first reported it, and the date of the first publication. If the type first described by any researcher, and later moved to another genus, the name of the original author and date are enclosed in parentheses, then write the name changed the generic name and the date. Quite often, especially in the literature on aquarium, last name and date omitted. However, it’s confusing, because different authors as valid (valid) names for fish sometimes use different synonyms.

To artificially derived fish of the same species, with variations in color or body shape, eyes, fins, etc. (or sometimes nature gets in chromista – individuals with Golden colored), if you want to highlight the feature, use the term varietas (abbreviated var.) – breed, followed by the relevant definition. For example, the full name of goldfish derived from the Chinese silver crucian carp (Carassius auratus auratus), will Carassius auratus auratus var. auratus.

Fish names, especially generic, is usually composed of words of Latin or Greek origin, at least, for this use of local fish names, geographical names, proper names. In practice, fish of one species with differences in body shape, eyes, fins, and in coloration, usually do not stand for the Latin words, and referred to as unofficial names. For example, the same fishes are distinguished breed: telescope , Valuehost , pearl, etc. Within species there are variations (varieties) * different color: black telescope, red telescope, and so on. At the same time in relation to, for example, guppies often it is not about breeds, and breed groups or variations, as in the fish breeding “in itself”, without the use of breeding methods, veiltail, fork, karpovye and other fins will sooner or later adopt the same appearance as wild ancestors, shortened, rounded, and even coloring steadfastly preserved only in some color variations.

In aquariums contain about 10% of all fish species . and bred of these, slightly more than half. Currently the hobby we are addicted to some 20 million people.

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