FREE ESSAY ON AQUACULTURE

AQUACULTURE

Kieran Roberts
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.