Aquaculture is the farming of freshwater and saltwater organisms such as finfish, molluscs, crustaceans and aquatic plants. Also known as aquafarming, aquaculture involves cultivating aquatic populations under controlled conditions, and can be contrasted with commercial fishing, which is the harvesting of wild fish. One half of the world commercial production of fish and shellfish that is directly consumed by humans comes from aquaculture.
Mariculture refers to aquaculture practiced in marine environments. Particular kinds of aquaculture include algaculture (the production of kelp/seaweed and other algae), fish farming, shrimp farming, oyster farming, and the growing of cultured pearls. Particular methods include aquaponics, which integrates fish farming and plant farming.

History

Aquaculture began in China circa 2500 BC. When the waters subsided after river floods, some fishes, mainly carp, were trapped in lakes. Nascent aquaculturists fed their brood using nymphs and silkworm feces, and ate the fish for their protein. A fortunate genetic mutation of carp led to the emergence of goldfish during the Tang Dynasty.
Hawaiians practiced aquaculture by constructing fish ponds (see Hawaiian aquaculture). A remarkable example is a fish pond dating from at least 1,000 years ago, at Alekoko. Legend says that it was constructed by the mythical Menehune. The Japanese cultivated seaweed by providing bamboo poles and, later, nets and oyster shells to serve as anchoring surfaces for spores. The Romans bred fish in ponds.

In central Europe, early Christian monasteries adopted Roman aquacultural practices. Aquaculture spread in Europe during the Middle Ages, since away from the seacoasts and the big rivers, fish were scarce/expensive. Improvements in transportation during the 19th century made fish easily available and inexpensive, even in inland areas, making aquaculture less popular.

In 1859 Stephen Ainsworth of West Bloomfield, New York, began experiments with brook trout. By 1864 Seth Green had established a commercial fish hatching operation at Caledonia Springs, near Rochester, NY. By 1866, with the involvement of Dr. W. W. Fletcher of Concord Mass, artificial fish hatching operations were under way in both Canada and the United States. When the Dildo Island fish hatchery opened in Newfoundland Canada in 1889, it was the largest and most advanced in the world.
California residents harvested wild kelp and attempted to manage supply starting circa 1900, later labeling it a wartime resource.
About 430 (97%) of the aquatic species cultured as of 2007 were domesticated during the 20th century, of which an estimated 106 aquatic species came in the decade to 2007. Given the long-term importance of agriculture, it is interesting to note that to date only 0.08% of known land plant species and 0.0002% of known land animal species have been domesticated, compared with 0.17% of known marine plant species and 0.13% of known marine animal species.
Domesticating an aquatic species typically involves about a decade of scientific research.http://www.sciencemag.org/cgi/content/full/sci;316/5823/382
Aquatic species involve fewer risks than that of land animals, which took a large toll in human lives through diseases such as smallpox and bird and swine flu, that like most infectious diseases, are transferred to humans from animals. No human pathogens of comparable virulence have yet emerged from marine species.

Stagnation in harvests from wild fisheries and overexploitation of popular marine species, combined with a growing demand for this high quality protein encourages aquaculturists to domesticate other marine species.

World production

In 2004, the total world production of fisheries was 140.5 million tonnes of which aquaculture contributed 45.5 million tonnes or about 32% of the total world production.FAO (2006) The growth rate of worldwide aquaculture has been sustained and rapid, averaging about 8 percent per annum for over thirty years, while the take from wild fisheries has been essentially flat for the last decade.

Production by country

Aquaculture is an especially important economic activity in China. Between 1980 and 1997, the Chinese Bureau of Fisheries reports, aquaculture harvests grew at an annual rate of 16.7 percent, jumping from 1.9 million to nearly 23 million tons. In 2005, China accounted for 70% of the world's aquaculture production. It is currently one of the fastest growing areas of agriculture in the U.S.

Approximately 90% of all U.S. shrimp consumption is farmed and imported. In recent years salmon aquaculture has become a major export in southern Chile, especially in Puerto Montt, Chile's fastest-growing city.

Environmental impact

As aquaculture has grown, so have concerns about its environmental impact. In fact, aquaculture can be more environmentally damaging than exploiting wild fisheries. Concerns include waste handling, side-effects of antibiotics, competition between farmed and wild animals, and using other fish to feed consumer-desired carnivorous fish. However, research and commercial feed improvements during the 1990s & 2000s have lessened many of these .

About 20 percent of mangrove forests have vanished since 1980, partly due to aqua-farming. Time special report. September 24, 2009.
Fish waste is organic and composed of nutrients necessary in all components of aquatic food webs. In-ocean aquaculture often produces much higher than normal concentrations of fish waste in the water. The waste collects on the ocean bottom, damaging or eliminating bottom-dwelling life. Waste can also decrease dissolved oxygen levels in the water column, putting further pressure on wild animals.

Cultivators often supply their animals with antibiotics to prevent disease. As with livestock, this can accelerate the evolution of bacterial resistance.

Fish can escape, where they can encounter wild fish and dilute wild genetic stocks through interbreeding. Escaped fish can become invasive and therefore can have a damaging environmental impact.

Farming carnivorous fish such as salmon typically increases the pressure on wild fish, because producing one kilo of farmed salmon requires up to six kilo of fish or other protein. Adequate diets for salmon and other carnivorous fish can be formulated from protein sources such as soy, although are concerns about changes in the balance between omega-6 and omega-3 fatty acids. Espe, M., A. Lemme, A. Petei, and A. El-Mowafi. 2006. Can Atlantic salmon (Salmo salar) grow on diets devoid of fish meal? Aquaculture 255:255-262
Other aquaculture "crops" such as seaweed and filter-feeding bivalve mollusks such as oysters, clams, mussels and scallops are relatively benign or even restorative environmentally. Filter-feeders filter pollutants as well as nutrients from the water, improving water quality. Seaweeds extract nutrients such as inorganic nitrogen and phosphorus directly from the water, and filter-feeding mollusks can extract nutrients as they feed on particulates phytoplankton and detritus.
Despite the environmental concerns, profitable aquaculture can funnel money into promoting sustainable practices. New methods lessen the risk of biological and chemical pollution through minimizing fish stress, fallowing netpens, and applying Integrated Pest Management. Vaccines are being used more and more to reduce antibiotic use for disease control.

Onshore recirculating aquaculture systems, facilities using polyculture techniques, and properly-sited facilities (e.g. offshore areas with strong currents) are examples of ways to manage the negative environmental effects.

Types of aquaculture

Mariculture

Mariculture is a specialized branch of aquaculture involving the cultivation of marine organisms in the open ocean, an enclosed section of the ocean, or in tanks, ponds or raceways which are filled with seawater. An example of the latter is the farming of marine fish, prawns, or oysters in saltwater ponds. Non-food products produced by mariculture include: fish meal, nutrient agar, jewelry (e.g. cultured pearls) and cosmetics.

Integrated multi-trophic aquaculture

Integrated Multi-Trophic Aquaculture (IMTA) is a practice in which the by-products (wastes) from one species are recycled to become inputs (fertilizers, food) for another. Fed aquaculture (e.g. fish, shrimp) is combined with inorganic extractive (e.g. seaweed) and organic extractive (e.g. shellfish) aquaculture to create balanced systems for environmental sustainability (biomitigation), economic stability (product diversification and risk reduction) and social acceptability (better management practices).
"Multi-Trophic" refers to the incorporation of species from different trophic or nutritional levels in the same system. Chopin T. 2006. Integrated multi-trophic aquaculture. What it is, and why you should care... and don’t confuse it with polyculture. Northern Aquaculture, Vol. 12, No. 4, July/August 2006, pg. 4. This is one potential distinction from the age-old practice of aquatic polyculture, which could simply be the co-culture of different fish species from the same trophic level. In this case, these organisms may all share the same biological and chemical processes, with few synergistic benefits, which could potentially lead to significant shifts in the ecosystem. Some traditional polyculture systems may, in fact, incorporate a greater diversity of species, occupying several niches, as extensive cultures (low intensity, low management) within the same pond. The "Integrated" in IMTA refers to the more intensive cultivation of the different species in proximity of each other, connected by nutrient and energy transfer through water.

Ideally, the biological and chemical processes in an IMTA system should balance. This is achieved through the appropriate selection and proportions of different species providing different ecosystem functions. The co-cultured species are typically more than just biofilters; they are harvestable crops of commercial value. A working IMTA system can result in greater total production based on mutual benefits to the co-cultured species and improved ecosystem health, even if the production of individual species is lower than in a monoculture over a short term period. Neori A, Chopin T, Troell M, Buschmann AH, Kraemer GP, Halling C, Shpigel M and Yarish C. 2004. Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture. Aquaculture 231: 361-391.
Sometimes the term "Integrated Aquaculture" is used to describe the integration of monocultures through water transfer. For all intents and purposes however, the terms "IMTA" and "integrated aquaculture" differ only in their degree of descriptiveness.Aquaponics, fractionated aquaculture, IAAS (integrated agriculture-aquaculture systems), IPUAS (integrated peri-urban-aquaculture systems), and IFAS (integrated fisheries-aquaculture systems) are other variations of the IMTA concept.

Species cultivated

Fish

Fish farming is the most common form of aquaculture. It involves raising fish commercially in tanks or enclosures, usually for food. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Fish species raised by fish farms include salmon, catfish, tilapia, cod, carp, tuna and trout.

Shellfish

Abalone farm

Farming of abalone began in the late 1950s and early 1960s in Japan and China. Since the mid-1990s, there have been many increasingly successful endeavours to commercially farm abalone for the purpose of consumption. Over-fishing and poaching have reduced wild populations to such an extent that farmed abalone now supplies most of the abalone meat consumed.

Shrimp

A shrimp farm is an aquaculture business for the cultivation of marine shrimp for human consumption. Commercial shrimp farming began in the 1970s, and production grew steeply thereafter. Global production reached more than 1.6 million tonnes in 2003, representing a value of nearly 9,000 million U.S. dollars. About 75% of farmed shrimp is produced in Asia, in particular in China and Thailand. The other 25% is produced mainly in Latin America, where Brazil is the largest producer. Thailand is the largest exporter.

Shrimp farming has changed from its traditional, small-scale form in Southeast Asia into a global industry. Technological advances have led to ever higher densities per unit area, and broodstock is shipped worldwide. Virtually all farmed shrimp are penaeids (i.e., shrimp of the family Penaeidae), and just two species of shrimp—the Penaeus vannamei (Pacific white shrimp) and the Penaeus monodon (giant tiger prawn) account for roughly 80% of all farmed shrimp. These industrial monocultures are very susceptible to disease, which has decimated shrimp populations across entire regions. Increasing ecological problems, repeated disease outbreaks, and pressure and criticism from both NGOs and consumer countries led to changes in the industry in the late 1990s and generally stronger regulation by governments. In 1999, governments, industry representatives, and environmental organizations initiated a program aimed at developing and promoting more sustainable farming practices.

Freshwater prawns

Freshwater prawn farming shares many characteristics with, and many of the same problems as, marine shrimp farming. Unique problems are introduced by the developmental life cycle of the main species (the giant river prawn, Macrobrachium rosenbergii).New, M. B.: ; FAO Fisheries Technical Paper 428, 2002. ISSN 0429-9345.
The global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tons, of which China produced 180,000 tons, followed by India and Thailand with 35,000 tons each. Additionally, China produced about 370,000 tons of Chinese river crab (Eriocheir sinensis).Data extracted from the for freshwater crustaceans. The most recent data sets are for 2003 and sometimes contain estimates. Retrieved June 28, 2005.

Algae

An open pond Spirulina farm

Algaculture is a form of aquaculture involving the farming of species of algae. Microalgae, also referred to as phytoplankton, microphytes, or planktonic algae constitute the majority of cultivated algae.
Macroalgae, commonly known as seaweed, also have many commercial and industrial uses, but due to their size and specific requirements, they are not easily cultivated on a large scale and are most often taken in the wild.

See also

• Algaculture

• Aquaponics

• Agroecology

• Fish farming

• Fisheries science

• Mariculture

• Industrial agriculture

• Shrimp farm

• Prawn farm