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The most widely cultured groups of fishes in the world are the carps. While the people of the USA are most familiar with the common or European species, carp culture is dominated by production of a variety of Chinese carps including the common big head, silver and grass carps. In the USA the common carp was introduced from Europe during the 19^th century.

The Chinese have developed carp culture to a fine art. They use a system known as polyculture (two or more non-competing species are reared in the same water system) in which at least four species of carp are grown in the same pond. Ponds in China are often fertilized with organic fertilizers which produce plant and animal food for fish. Agricultural wastes may be also used. Common carp feed on benthos, silver carp on phytoplankton, big carp on zooplankton and grass carp on rooted aquatic vegetation. Thus various supplies are used by various culture species. Stocking rates are related to the food supplies. In recent years, prepared feeds have become more common in China, though pelleted diets may still be used in combination with fertilization.

Indian carps (various species) and common carp are more commonly reared in monoculture (only one species present in the culture system). Depending on expected production the ponds may be fertilized or prepared feeds may be offered. In Europe and Israel common carps are maintained at high densities and are fed pelleted rations that meet their nutritional requirements.

Carps will spawn naturally in ponds, though hatcheries are often maintained. Hormones may be injected into the adults to induce spawning. Eggs and mill may be obtained by manual stripping. The eggs are maintained in a hatchery and the young fish are stocked into nursery ponds. The system is relatively simple. Carps are able to tolerate fairly wide ranges of environmental conditions, so the technology required for their culture is not highly sophisticated.

The second most widely cultured group of fishes in the world today are the tilapias. Tilapias are native to the Middle East and North Africa, but have been introduced throughout the tropical world and in to many subtropical areas. Most species die when water temperature fall below 10ºC. Therefore, culture in a temperate climates depends on production of a crop during the warm months and maintenance of brood stock in warm water (often in indoor heated holding facilities) during winter.

Various species of tilapia are under culture around the world today, primarily in the tropics. All of the popular ones are known for their rapid growth, ease of production and heartiness. Tilapias are extremely tolerant of poor water quality, reproduce readily in almost any environment and reach market size within several months. Most fishes feed on a combination of plants and animals, and they do not require high cost prepared feeds unless they are being reared at high densities where natural food supplies become exhausted.

Tilapias are popular in subsistence culture in much of Africa, the Far East and Latin America. Commercial production is highly developed in Israel, Indonesia, the Philippines, Thailand, Taiwan, Jamaica and various other nations.

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