Aquaculture is the farming of aquatic organisms in fresh, or salt water. A wide
variety of aquatic organisms are produced through aquaculture, including fish,
crustaceans, mollusks, algae, and aquatic plants. Unlike capture fisheries,
aquaculture requires deliberate human intervention in the organisms\'
productivity and results in yields that exceed those from the natural
environment alone. Stocking water with (juvenile organisms), fertilizing the
water, feeding the organisms, and maintaining water quality are common examples
of such intervention. Most aquacultural crops are destined for human
consumption. However, aquaculture also produces bait fishes, ornamental or
aquarium fishes, aquatic animals used to augment natural populations for capture
and sport fisheries, algae used for chemical extraction, and pearl oysters and
mussels, among others. Aquaculture is considered an agricultural activity,
despite the many differences between aquaculture and terrestrial agriculture.

Aquaculture mainly produces protein crops, while starchy staple crops are the
primary products of terrestrial agriculture. In addition, terrestrial animal
waste can be disposed of off-site, whereas in aquaculture such waste accumulates
in the culture environment. Consequently, aquaculturists must carefully manage
their production units to ensure that water quality does not deteriorate and
become stressful to the culture organisms. History Aquaculture was developed
more than 2000 years ago in countries such as China, Rome, and Egypt. Not long
after, aquacultural practices in Europe, China, and Japan commonly involved
stocking wild-caught seed—for example, carp fingerlings (juvenile fish)
captured from rivers—in ponds or other bodies of water for further growth.

Mollusk culture was advanced in the 1200s by the discovery in France that mussel
spat (newly settled juveniles) would settle on upright posts in the intertidal
zone, and in the 1600s by the discovery in Japan that oyster spat would settle
on upright bamboo stakes driven into the sea floor. The concept of pond
fertilization was developed in Europe about 1500. In this process, manure is
added to the water to encourage the growth of small organisms such as aquatic
invertebrates and plankton, which in turn are eaten by the fish. The United

States system of federal hatcheries for the breeding of anadromous fishes
(fishes that live and mature in salt water but reproduce in fresh water) was
established in the 1870s. Much of the current technology used to reproduce fish
in hatcheries has been developed by these federal hatcheries. In 1959 the first
marine shrimp hatchery and farm was established in Japan, and it was the
forerunner of the commercial shrimp-culture industry. The salmon-culture
industry in Europe and the channel-catfish-culture industry in the United States
both began in the 1960s. Methods Most fish and crustacean aquaculture is
undertaken in earthen ponds. These ponds are usually equipped with water inlets
and outlets that permit independent control of water addition and discharge.

Ponds are stocked with a specific quantity of juvenile aquatic animals.

Management practices range from pond fertilization, which increases the number
of natural food organisms, to provision of a complete, formulated feed that
supplies all nutrients necessary for growth. Animals that have reached market
size are harvested from the ponds. In a complete harvest, the pond is drained
and all animals are removed from the pond for processing. In a partial harvest,
only a portion of the animals are removed from a full pond using a seine net.

Additional juveniles are often stocked into the pond after a partial harvest,
and the production cycle is continued. Channel catfish grown in the United

States, and marine shrimp grown in China, Central America, and South America,
are often cultured in earthen ponds of about 5 to 10 hectares (about 12 to 25
acres). Fish can also be raised in cages and raceways (long, narrow earthen or
concrete ponds that receive a continuous flow of water from a nearby artesian
well, spring, or stream). Often, several raceways are built in series down the
slope of a hill. Cages are used to raise fish in lakes, bays, or the open ocean
and are constructed of flexible netting suspended from a superstructure floating
on the water\'s surface. Many more fingerlings can be stocked into raceways and
cages than into earthen ponds, but nutritionally complete formulated feed must
be provided to fish grown in these systems. Rainbow trout are grown in raceways
in many places, including Chile, Europe, and the United States. Salmon are grown
in cages, and Norway leads the world in the production of farmed salmon. Carp
raising involves at least three different types of ponds for a whole life cycle
in Europe. Special shallow and warm ponds with rich vegetation provides a good
environment for spawning. After spawning, the parent fish are separated from the
eggs and taken to a second pond. The Fry, which hatch