Aquaculture
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.