Kieran Roberts AquacultureAquaculture is the farming of aquatic organisms in fresh, orsalt water. A wide variety of aquatic organisms are producedthrough aquaculture, including fish, crustaceans, mollusks,algae, and aquatic plants. Unlike capture fisheries,aquaculture requires deliberate human intervention in theorganisms’ productivity and results in yields that exceed thosefrom the natural environment alone. Stocking water with (juvenile organisms), fertilizing the water, feeding theorganisms, and maintaining water quality are common examples ofsuch intervention.
Most aquacultural crops are destined for humanconsumption. However, aquaculture also produces bait fishes,ornamental or aquarium fishes, aquatic animals used to augmentnatural populations for capture and sport fisheries, algae usedfor chemical extraction, and pearl oysters and mussels, amongothers.Aquaculture is considered an agricultural activity,despite the many differences between aquaculture andterrestrial agriculture. Aquaculture mainly produces proteincrops, while starchy staple crops are the primary products ofterrestrial agriculture. In addition, terrestrial animal wastecan be disposed of off-site, whereas in aquaculture such wasteaccumulates in the culture environment. Consequently,aquaculturists must carefully manage their production units toensure that water quality does not deteriorate and becomestressful to the culture organisms.
History Aquaculture was developed more than 2000 years ago incountries such as China, Rome, and Egypt. Not long after,aquacultural practices in Europe, China, and Japan commonlyinvolved stocking wild-caught seedfor example, carpfingerlings (juvenile fish) captured from riversin ponds orother bodies of water for further growth.Mollusk culture was advanced in the 1200s by the discoveryin France that mussel spat (newly settled juveniles) wouldsettle on upright posts in the intertidal zone, and in the1600s by the discovery in Japan that oyster spat would settleon upright bamboo stakes driven into the sea floor. The conceptof pond fertilization was developed in Europe about 1500. Inthis process, manure is added to the water to encourage thegrowth of small organisms such as aquatic invertebrates andplankton, which in turn are eaten by the fish.
The United States system of federal hatcheries for thebreeding of anadromous fishes (fishes that live and mature insalt water but reproduce in fresh water) was established in the1870s. Much of the current technology used to reproduce fish inhatcheries has been developed by these federal hatcheries. In1959 the first marine shrimp hatchery and farm was establishedin Japan, and it was the forerunner of the commercialshrimp-culture industry. The salmon-culture industry in Europeand the channel-catfish-culture industry in the United Statesboth began in the 1960s.Methods Most fish and crustacean aquaculture is undertaken inearthen ponds. These ponds are usually equipped with waterinlets and outlets that permit independent control of wateraddition and discharge.
Ponds are stocked with a specificquantity of juvenile aquatic animals. Management practicesrange from pond fertilization, which increases the number ofnatural food organisms, to provision of a complete, formulatedfeed that supplies all nutrients necessary for growth. Animalsthat have reached market size are harvested from the ponds.
Ina complete harvest, the pond is drained and all animals areremoved from the pond for processing. In a partial harvest,only a portion of the animals are removed from a full pondusing a seine net. Additional juveniles are often stocked intothe pond after a partial harvest, and the production cycle iscontinued. Channel catfish grown in the United States, andmarine shrimp grown in China, Central America, and SouthAmerica, are often cultured in earthen ponds of about 5 to 10hectares (about 12 to 25 acres).Fish can also be raised in cages and raceways (long,narrow earthen or concrete ponds that receive a continuous flowof water from a nearby artesian well, spring, or stream).Often, several raceways are built in series down the slope of ahill.
Cages are used to raise fish in lakes, bays, or the openocean and are constructed of flexible netting suspended from asuperstructure floating on the water’s surface. Many morefingerlings can be stocked into raceways and cages than intoearthen ponds, but nutritionally complete formulated feed mustbe provided to fish grown in these systems. Rainbow trout aregrown in raceways in many places, including Chile, Europe, andthe United States. Salmon are grown in cages, and Norway leadsthe world in the production of farmed salmon.Carp raising involves at least three different types ofponds for a whole life cycle in Europe. Special shallow andwarm ponds with rich vegetation provides a good environment forspawning.
After spawning, the parent fish are separated fromthe eggs and taken to a second pond. The Fry, which hatch aftera few days, are transported to shallow, plankton-rich nursingponds, where they remain until the fall of the year or the nextspring. An average harvest of 400 to 500 kilograms per hectareis normal in intensive cultivation of carp.
Crustaceans, mainly shrimps, are also cultivated not justin Europe but in the United States as well. Shrimps arecultivated by catching adult egg-bearing females. The femaleshrimp are then transported to large sea water ponds nearby thesea or indoor tanks. After hatching, the shrimps are fed inindoor tanks with cultivated plankton.
After ten days they arebrought to shallow ponds for even further cultivation ordistribution to farms.Mollusk aquaculture is carried out in coastal waterseither as bottom culture or off-bottom culture. In bottomculture, juvenile organisms are spread over prepared areas ofthe ocean floor in either the intertidal zone or shallowcoastal waters.
In off-bottom culture, juveniles attached to asubstrate, such as oyster spat attached to oyster shell, arebound to ropes and suspended from rafts or floats. Advantagesof off-bottom mollusk culture include protection from predatorsand the ability to use more vertical space. Seaweed is alsogrown using off-bottom culture techniques, most notably inAsia.Production Aquaculture is practiced in many regions of the UnitedStates.
Channel catfish are grown primarily in the southern andsoutheastern United States, with greatest production inMississippi, Arkansas, Alabama, and Louisiana. More than 75percent of the trout produced domestically for humanconsumption are grown in Idaho. Japanese littleneck clams andPacific oysters are grown along the Pacific Coast, and hardclams and American bluepoint oysters are grown along theAtlantic Coast. Most U.
S. fish farms that produce ornamentalfishes are located in Florida. The largest bait-fishaquaculture industry is located in Arkansas.
The global aquacultural yield in 1992 was 19.3 millionmetric tons (42.5 billion pounds), worth approximately $32.5billion. This yield, which represented nearly 20 percent ofworld fishery production, was composed of 48.8 percent fishes,5.
1 percent crustaceans, 18.1 percent mollusks, 27.9 percentalgae and aquatic plants, and 0.1 percent other organisms.Aquacultural production has grown steadily from an estimated 1million metric tons (2.
2 billion pounds) in 1966 to the currentvalue. World aquacultural production is expected to grow 5percent annually through the year 2000. The Environmental Impacts of AquacultureAquaculture provides for many people a large production ofnutritious, high-quality foods.
However, similar to theconventional agriculture, there are many adverse environmentalimpacts of aquaculture. The most important effects are ecological, and these areassociated with the conversion of natural ecosystems intocomplex and intensively managed aquaculture ecosystems. Forexample, the conversion of tropical mangrove systems intoaquacultural facilities used to raise prawns yields a combinedloss of natural ecosystem, In other words, the conversion hassignificant consequences for species in the environment, andusually causes damage to offshore ecosystems. With the worlds steadily growing population limitingsupplies of food, water, minerals and energy, scientistsbelieve we will have to rely on the vast resources of the seaas key to sustaining human life. Fortunately, the government isstriving for an increase in ocean commercialization (thedevelopment, harvesting and marketing of the oceans resourcesfor a profit) to meet the rapidly growing needs of humanity,and noticing the importance of preserving and protecting themarine environment.
Although, careless ocean commercializationcan have very serious side effects. One of the many effects isseafood and water contamination by ocean pollution posinghealth risks for both marine life and humans.With government support, many businesses such as DuPont,Lockheed and International Nickel have already begun oceancommercialization. Most of the current methods of oceancommercialization are aquaculture, the farming of marine fish andplants; the conversion of saltwater to freshwater; utilization oftidal and thermal energy; and the incineration of hazardouswastes.