Fishes are vertebrate animals that adapted to live, swim, and inhale in fresh or salt water. They’re the foremost various and various vertebrate animals on Earth and might be found in each conceivable aquatic surround.

Fishes don’t type a natural cluster. The overall term “fishes” includes four groups of vertebrates that square measure as totally different from each other as mammals, reptiles, and birds. the most important cluster is that the bony fishes, which has acquainted species like cod, salmon, and trout. Sharks, rays, and chimaeras structure the second cluster, the tough fishes.

The remaining 2 little groups are bone marine hagfishes and also the lampreys. Land vertebrates (tetrapods) and bony fishes share a typical ancestry-primitive bony fishes, the lobe-finned coelacanths, and lungfishes square measure sorted along side the tetrapods in fashionable classification systems. Lobe-finned fishes square measure the foremost seemingly ancestors of the primary land vertebrates.



Characteristics
Fishes from of these teams usually breathe mistreatment gills to extract chemical element from the water, swim mistreatment fins, square measure lined with protecting scales or bony plates, and square measure cold blooded

However, there also are lungfishes that breathe air, fishes with no scales, and sharks, like the salmon shark, which will management their temperature. The acquainted vertebrate senses of vision, hearing, touch, taste, and smell square measure employed by all fishes to assemble data regarding their atmosphere.
Most fishes have a system of sensory organs referred to as the receptor running on each side of the body, that detects vibrations created by alternative fishes and animals moving through the water. Fins also are characteristic of most, however not all, fishes.
These sometimes accommodates 2 sets of paired fins (pectoral and pelvic), one, two, or seldom 3 dorsal fins. Associate in Nursing anal fin, and a caudal (tail) fin. The fins square measure used for propulsion, mobility, and stability.
Some fishes, like the scorpaenoid, even use their fins to steer on the ocean floor, and flying fishes use theirs like wings to glide on top of water.

Jawless fishes
Classes Myxini, Petromyzontia
Hagfishes and lampreys square measure long, slimy, eel-like fishes with no biting jaws. Lampreys have a spherical sucker mouth enclosed by attractive, rasping teeth and square measure principally parasitic on alternative fishes. Hagfishes have a slitlike mouth enclosed by four pairs of tentacles and square measure principally scavengers.
They are doing not have a real backbone; instead, an easy versatile rod referred to as a rachis runs the length of the body.



Cartilaginous fishes
Class Chondrichthyes
Cartilaginous fishes comprise sharks, rays, and deep chimaeras. These fishes have an interior skeleton created in the main of versatile gristle. Males have a sex activity organ referred to as a clasper and females offer birth to measure young or lay giant egg capsules. Special sense organs, referred to as ampullae of Lorenzini, permit chondrichthian to trace alternative animals by police work their electrical fields. Sharks have sturdy, standardised teeth and rough skin lined in little, toothed dermal denticles.
Skates and rays square measure flat with winged pectoral fins and an extended, thin tail. The chimaeras square measure unarmored with an outsized head and gnawer tail.

Bony fishes
Class Osteichthyes
All bony fishes have an interior skeleton of onerous, calcified bone, though in some primitive species this might be half gristle. With the exception of the lobe-finned fishes, the skeleton extends into the fins as versatile, movable rays and spines. this method permits the fish to maneuver with way larger exactness than sharks and rays.
Most bony fishes even have a gas-filled air bladder, that is employed to regulate their buoyancy and is roofed in overlapping versatile scales. whereas most tough fishes will be simply recognized intrinsically, bony fishes have evolved many alternative and typically outlandish body shapes and fin functions that alter them to survive in nearly each aquatic surround.

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