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 after a few days, are
transported to shallow, plankton-rich nursing ponds, where they remain until the
fall of the year or the next spring. An average harvest of 400 to 500 kilograms
per hectare is normal in intensive cultivation of carp. Crustaceans, mainly
shrimps, are also cultivated not just in Europe but in the United States as
well. Shrimps are cultivated by catching adult egg-bearing females. The female
shrimp are then transported to large sea water ponds nearby the sea or indoor
tanks. After hatching, the shrimps are fed in indoor tanks with cultivated
plankton. After ten days they are brought to shallow ponds for even further
cultivation or distribution to farms. Mollusk aquaculture is carried out in
coastal waters either as bottom culture or off-bottom culture. In bottom
culture, juvenile organisms are spread over prepared areas of the ocean floor in
either the intertidal zone or shallow coastal waters. In off-bottom culture,
juveniles attached to a substrate, such as oyster spat attached to oyster shell,
are bound to ropes and suspended from rafts or floats. Advantages of off-bottom
mollusk culture include protection from predators and the ability to use more
vertical space. Seaweed is also grown using off-bottom culture techniques, most
notably in Asia. Production Aquaculture is practiced in many regions of the
United States. Channel catfish are grown primarily in the southern and
southeastern United States, with greatest production in Mississippi, Arkansas,
Alabama, and Louisiana. More than 75 percent of the trout produced domestically
for human consumption are grown in Idaho. Japanese littleneck clams and Pacific
oysters are grown along the Pacific Coast, and hard clams and American bluepoint
oysters are grown along the Atlantic Coast. Most U.S. fish farms that produce
ornamental fishes are located in Florida. The largest bait-fish aquaculture
industry is located in Arkansas. The global aquacultural yield in 1992 was 19.3
million metric tons (42.5 billion pounds), worth approximately $32.5 billion.
This yield, which represented nearly 20 percent of world fishery production, was
composed of 48.8 percent fishes, 5.1 percent crustaceans, 18.1 percent mollusks,
27.9 percent algae and aquatic plants, and 0.1 percent other organisms.
Aquacultural production has grown steadily from an estimated 1 million metric
tons (2.2 billion pounds) in 1966 to the current value. World aquacultural
production is expected to grow 5 percent annually through the year 2000. The
Environmental Impacts of Aquaculture Aquaculture provides for many people a
large production of nutritious, high-quality foods. However, similar to the
conventional agriculture, there are many adverse environmental impacts of
aquaculture. The most important effects are ecological, and these are associated
with the conversion of natural ecosystems into complex and intensively managed
aquaculture ecosystems. For example, the conversion of tropical mangrove systems
into aquacultural facilities used to raise prawns yields a combined loss of
natural ecosystem, In other words, the conversion has significant consequences
for species in the environment, and usually causes damage to offshore
ecosystems. With the world’s steadily growing population limiting supplies of
food, water, minerals and energy, scientists believe we will have to rely on the
vast resources of the sea as key to sustaining human life. Fortunately, the
government is striving for an increase in ocean commercialization (the
development, harvesting and marketing of the ocean’s resources for a profit)
to meet the rapidly growing needs of humanity, and noticing the importance of
preserving and protecting the marine environment. Although, careless ocean
commercialization can have very serious side effects. One of the many effects is
seafood and water contamination by ocean pollution posing health risks for both
marine life and humans. With government support, many businesses such as DuPont,
Lockheed and International Nickel have already begun ocean commercialization.
Most of the current methods of ocean commercialization are aquaculture, the
farming of marine fish and plants; the conversion of saltwater to freshwater;
utilization of tidal and thermal energy; and the incineration of hazardous
wastes.