Carp

Carp is a common name for many species of freshwater fish in the family Cyprinidae, a large group of ray-finned fish that are mostly native to Eurasia. In much of the Old World, carp are highly valued as food, ornamental fish, and sport, and are even commercially farmed. However, in many parts of Africa, Australia, and most of the United States, they are seen as trash fish and invasive pests.

The family Cyprinidae belongs to the order Cypriniformes, which is grouped with Characiformes, Siluriformes, and Gymnotiformes into the superorder Ostariophysi. These groups share certain traits, such as living mainly in fresh water and having Weberian ossicles—a structure formed from the first five vertebrae, their ribs, and neural crests. The third pair of ribs connects to the inner ear and the swim bladder. Though not fully understood, this structure likely helps transmit vibrations from the swim bladder to the ear, improving hearing, which explains why Ostariophysi fish have excellent hearing.

Most cypriniformes have scales and teeth on their lower pharyngeal bones, which can be adapted to their diet. The only cyprinid genus that tolerates salt water is *Tribolodon*; a few other species enter brackish water but return to fresh water to spawn. All other cypriniformes live in continental waters and have wide distributions. Some people consider all cyprinids to be carp, and the family is often called the carp family.

In everyday use, "carp" usually refers to larger species like common carp (*Cyprinus carpio*), crucian carp (*Carassius carassius*), grass carp (*Ctenopharyngodon idella*), silver carp (*Hypophthalmichthys molitrix*), and bighead carp (*Hypophthalmichthys nobilis*). Common carp are native to Eastern Europe and Western Asia, so they are sometimes called Eurasian carp.

Carp have long been an important food fish. Several species, including goldfish (*Carassius auratus*) breeds and the domesticated koi (*Cyprinus rubrofuscus* var. "koi"), are popular ornamental fish. As a result, carp have been introduced to many places, with mixed outcomes. Several species are considered invasive in the United States, and large sums are spent worldwide on controlling them.

At least some carp species can survive for months with almost no oxygen—for instance, under ice or in stagnant water—by metabolizing glycogen into lactic acid, which is then converted into ethanol and carbon dioxide. The ethanol diffuses out through the gills.

In 1653, Izaak Walton wrote in *The Compleat Angler* that the carp is "the queen of rivers; a stately, a good, and a very subtle fish." Carp are valued differently by anglers. In Europe, they are highly prized as coarse fish that are difficult to hook, even when not eaten. The UK has a thriving carp angling market, with the British record at 68 lb 1 oz. This market is the fastest-growing in the UK and has spawned specialized magazines and websites. In the United States, carp are classified as rough fish and a damaging exotic species, but they also have sporting qualities. Despite a poor reputation as undesirable for fishing or eating—largely because they are invasive and outcompete native game fish—many state natural resources departments now view them as an angling fish. Groups like Wild Carp Companies, the American Carp Society, and the Carp Anglers Group promote the sport and work with fisheries to host events. Common carp are among the most abundant fish in Midwestern rivers, creeks, lakes, and ponds. They fight hard on the line, making them appealing to recreational anglers. Since their introduction to U.S. waters in the 1880s, they have been seen as game fish, despite being destructive and invasive.

Various carp species have been domesticated and raised as food fish in Europe and Asia for thousands of years. These species appear to have been domesticated independently, as they come from different parts of Eurasia. Aquaculture in China dates back at least 2,400 years; a fifth-century BC tract by Fan Li details pond-raising methods. Common carp originated in Central Europe. Several species known collectively as Asian carp were domesticated in East Asia. Carp from South Asia, such as catla (*Gibelion catla*), rohu (*Labeo rohita*), and mrigal (*Cirrhinus cirrhosus*), are called Indian carp. Their hardiness and adaptability have allowed domesticated species to spread worldwide. Although carp were once an important food fish, their cultural importance in Western Europe has declined as other fish species have become more available.