Carp are various species of oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes (family Cyprinidae) are traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain common features, such as being found predominantly in fresh water and that they possess Weberian ossicles (an anatomical structure originally made up of small pieces of bone formed from four or five of the first vertebrae); the most anterior bony pair is in contact with the extension of the labyrinth and the posterior with the swimbladder. The function is poorly understood, but this structure is presumed tp take part in the transmission of vibrations from the swimbladder to the labyrinth and in the perception of sound, which explains why the Ostariophysi have such a great capacity for hearing.
Most cypriniformes have scales and teeth on the inferior pharyngeal bones which may be modified in relation to the diet. Tribolodon is the only cyprinid genus which tolerates salt water, although there are several species which move into brackish water, but return to fresh water to spawn. All of the other cypriniformes live in continental waters and have a wide geographical range.
Some consider all cyprinid fishes carp, and the family Cyprinidae itself is often known as the carp family. In colloquial use, however, carp usually refers only to several larger cyprinid species such as Cyprinus carpio (common carp), Carassius carassius (Crucian carp), Ctenopharyngodon idella (grass carp), Hypophthalmichthys molitrix (silver carp), and Hypophthalmichthys nobilis (bighead carp). Carp have long been an important food fish to humans, as well as popular ornamental fishes such as the various goldfish breeds and the domesticated common carp variety known as koi. As a result, carp have been introduced to various locations, though with mixed results. Several species of carp are listed as invasive species by the U.S. Department of Agriculture, and worldwide large sums of money are spent on carp control.