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 seedfor example, carp fingerlings (juvenile fish) captured from riversin 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 ettle 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 uantity 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 he 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 ishes 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 oss 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 worlds 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 oceans resources for a profit) to meet the rapidly growing needs of humanity, and noticing the importance of preserving and protecting the arine 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.
