Long before people began to culture fishes, they were harvesting wild fishes from streams, lakes, and the oceans. As hunters began to domesticate land animals and others learned to plant agricultural crops, ancient fishers captured and raised wild fishes. The Chinese raised fishes as early as the 5th century bc. The ancient Greeks cultured oysters in Rome and Gaul. When Magellan visited the Philippines more than 450 years ago, he found native fishers collecting young milkfish and moving them to brackish water ponds for rearing as food fish.

Farming the Water

Aquaculture is a broad term that includes the culture of fishes, mollusks, crustaceans, algae, and even bullfrogs and alligators (see aquaculture). Fish culture is the process of raising desirable species of fishes in captivity and managing them and their environment to improve growth and reproduction. Fishes are reared in fish farms, or hatcheries, much as farm animals are raised in the barnyard. The fish culturist manages the aquatic environment to protect the fishes from predators, parasites, and disease. The culturist also feeds the fishes and controls water quality to prevent pollution.

In the United States many fishes are raised in hatcheries and released in streams, rivers, and lakes to provide sport fishing. Anadromous species—fishes that live in the sea but return to fresh water to spawn, such as salmon—are released into rivers to swim to the ocean. When these fishes mature they instinctively return to the river from which they were released. Small fishes such as minnows and goldfish are raised and sold for bait. Freshwater and saltwater forms of tropical fishes are raised and sold as aquarium fishes. On a world scale, most fishes are reared by fish culturists to provide food for humans.

Fishes may be cultured in raceways—long, narrow channels with flowing water, tanks, ponds, nets, or pens. Trout and salmon, which live in cold water, are cultured in raceways or in large round tanks and floating cages or pens. The culture of coldwater fishes is limited to hatchery sites with clean cold water. Most coldwater fishes are very sensitive to water pollution and cannot live in contaminated water.

Channel catfish, common carp, and panfish such as bluegills, sunfishes, and bass are some of the warmwater fishes reared for food and sport, mostly in earthen ponds. Hatchery ponds may be of 1/10 acre (0.04 hectare) or less, whereas commercial catfish ponds may be of 20 acres (8 hectares) or more. Some catfish farms are so large that the fish are fed from aircraft. On some of these farms, the fish may eat 20 tons (18 metric tons) of feed in one day.

Fish culture is expanding rapidly in the southern United States and in many tropical regions of the world. In 1960 there were about 400 acres (160 hectares) of commercial catfish ponds in the United States. By the early 1980s that total exceeded 80,000 acres (32,000 hectares).

Fish Feeds

Fishes that feed on algae and other aquatic plants are primary consumers. Among these are those classified in the genus Tilapia and many species of carp reared in ponds to which fertilizers have been added to promote plant growth. Secondary consumers are fishes that eat animals, including other fishes. Examples include trout, salmon, catfish, bluegills, and bass. Because the fish farmer does not want the fishes to eat each other, the secondary consumers are fed a special balanced diet that contains vitamins, minerals, and animal protein, including fish meal. This keeps them well fed and unlikely to prey on each other. Fish feed is manufactured in pellet form. Most fish cultured in the United States are secondary consumers and are fed a pelleted diet.

In many tropical regions of the world, Tilapia and carp species are very important food fishes. These fishes are now reared in the United States for use as food and for biological weed control. When aquatic weeds become too abundant, they interfere with swimming, boating, and fishing. Tilapia and other weed-eating fishes are reared in hatcheries and then released into irrigation canals and lakes to eat the weeds. This form of weed control can be much safer and cheaper than chemical and mowing methods.

World Production

In typical years world production of cultured fishes is estimated to be nearly 10.5 million tons (9.5 million metric tons). The best estimate of United States production is 146,500 tons (132,900 metric tons) of warmwater fishes, 24,000 tons (22,000 metric tons) of coldwater fishes, and 27,000 tons (24,000 metric tons) of marine fishes.

Fish culture is an important industry in Japan, the United States, China, India, and Europe. The catch of wild fishes from the ocean is not expected to increase dramatically. Thus as the demand for fishes increases, more and more of that demand must be met by aquaculturists rearing fishes under controlled conditions. In many underdeveloped countries, fish culture is being expanded to feed hungry people.