Aquaculture

I

Introduction

Aquaculture, farming of aquatic organisms in fresh, brackish or salt water. A wide variety of aquatic organisms are produced through aquaculture, including fishes, 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 seed (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 (see Fishing), algae used for chemical extraction, and pearl oysters (see Oyster) 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.

II

History

Aquaculture was developed more than 2,000 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.

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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 propagation 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 (see Catfish) in the United States both began in the 1960s.

III

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 (see 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.

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. France has a long history of mussel culture, and the bouchet culture technique, in which rope containing newly set mussels is wrapped in a spiral up oak poles set in intertidal areas, has changed little in hundreds of years of use. Seaweed is also grown using off-bottom culture techniques, most notably in Asia.

IV

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. Approximately 70 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 (see Clam). 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 at the beginning of the 21st century was 37.5 million metric tons (82.7 billion pounds), worth approximately $56 billion. This yield, which represented about 29 percent of world fishery production, was composed of 51 percent fishes, 23 percent mollusks, 22 percent algae, aquatic plants, and other organisms, and 4 percent crustaceans. Major aquaculture producing countries are China, India, Japan, Philippines, Indonesia, Thailand, South Korea, Bangladesh, and Vietnam. 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 has been growing at an average rate of 9.2 percent since 1970. The U.S. aquaculture production rose more than 400 percent between 1980 and 2000.