Carp are fish species in the minnow family (Cyprinidae), one of the major groups of freshwater fish. The most familiar species are the common carp (Cyprinus carpio) and the closely related goldfish (Carassius aureus). The minnow family is characterized by having no teeth in the jaws, although well-developed teeth occur on the pharyngeal bones (located behind the gill chamber) and are used to grind food against a hard, rough pad in the roof of the pharynx.
The body of the common carp is covered with large scales. A single dorsal fin is present, with 17-22 branched rays and a strong, toothed spine in front. The carp has four barbels, which are fleshy outgrowths of the mouth that play a sensory role in the locating of food. There are two long barbels at the corners of the mouth and shorter ones on the upper lip. Carp mostly eat vegetable matter, but also feed on worms, crustaceans, aquatic insects, and smaller fish. Their food is mostly obtained by probing in the bottom mud of their aquatic habitat. The common carp is colored dull green-brown on the flanks, darkening on the back, and the underside may be golden-yellow. The fins are gray-green or dusky brown, with a reddish tinge.
The common carp is a hardy fish that can live and breed under difficult conditions. Its preferred habitat is lowland lakes and slow-flowing rivers with abundant vegetation for food and shelter. During periods of exceptionally cold weather, carp move into deep water and enter a resting phase in which their metabolism is greatly slowed. Breeding takes place during the spring, generally from May to June, when water temperature reaches about 68°F (20°C). Spawning takes place in shallow water, and the eggs are laid directly onto plants. When the eggs hatch the tiny fry remain in the shallows for several weeks, concealed amongst the vegetation. The growth rate of carp varies considerably according to local conditions. They can attain a large size: individuals weighing more than 66 lb (30 kg) have been recorded. In general, however, mature carp are about 20-25 in (50-60 cm) in length and weigh from 4.4-10 lb (2-4.5 kg). In their natural environment, carp are thought to live for as many as 15 years; in captivity, however, far greater ages have been recorded, with some being credited with a life span of more than 200 years.
Of the fish species that have been reared successfully in captivity from egg to maturity, the carp has probably been one of the most successful on a commercial basis. A number of domesticated varieties of common carp occur, including one that is scaleless. There is a long history of carp aquaculture in the Far East, and these fish are also grown in parts of Europe. Carp have also been released to freshwater habitats in North America, Australia, and New Zealand, both as a sport fish and as a commercial venture. Unfortunately, the release of carp into foreign aquatic ecosystems often causes intense ecological damage. This results from the physical disturbance caused by carp as they feed and spawn, as well as the intense competition and predation they can exert on native species of fish.