Today, aquaculture comprises much more than the rearing of fish in ponds or rice fields. For statistical purposes, FAO defines aquaculture as the farming of aquatic organisms, including fish, molluscs, crustaceans, and aquatic plants. Farming implies some form of intervention in the rearing process to enhance production as well as ownership of the stock being cultivated.

Aquaculture is far more akin to farming and animal husbandry than to fishing, as it involves the rearing and management of living aquatic resources in a restricted environment. Rather than fishing or hunting, which entail the harvesting of fish or animals from an open or common access resource, aquaculture involves tenure and ownership. Tenure of production facilities, and property rights to the produce, are as important to the success of aquaculture as land tenure is to agriculture.

Aquaculture has been developed to serve a variety of purposes. Today, its more frequent goals are:

producing high nutritional value food for human consumption;
contributing to rural income and employment through farming and related activities;
enhancing capture and sport fisheries;
cultivating ornamental species for aesthetic purposes;
controlling aquatic weeds or pests hazardous to humans or crops;
desalination and other forms of soil recuperation.

SYSTEMS, PRODUCTION, AND TRENDS

A NUMBER OF DIFFERENT AQUACULTURE systems have evolved for the cultivation of the large variety of aquatic organisms in marine, brackish and freshwater environments. Systems may be land or water based:

Land-based systems comprise mainly ponds, rice fields, and other facilities built on dry land. Ponds are the most common of all aquaculture systems, and range from small, rudimentary, gravity-fed facilities to large geometric ones, constructed using machines and with sophisticated water management regimes. Carps and tilapias, both widely cultivated fish species, are commonly grown in freshwater ponds, whereas shrimp and finfish tolerant to more saline waters are cultivated in brackish water ponds.

Water-based systems include enclosures, pens, cages and rafts, and are usually situated in sheltered coastal or inland waters. Enclosures are formed by closing off a natural bay, where the shoreline forms all but one side, and access to open water is closed off by a solid, net or mesh barrier. Pens and cages are enclosed structures, made from poles, mesh and netting. Pens rest on the bottom of a water body, whereas cages are suspended from poles or rafts which float on the water surface.

Similar, for example, to livestock production systems that range from extensive ranching to intensive feedlot systems, aquaculture also is practised at different intensities.

A Vietnamese farmer scoops out duckweed from a shallow pool to feed the fish in the adjacent pond. Duckweed can also be an important component in livestock feeds and a source of income for farmers when sold as a cash crop at nearby markets.
	Cage culture in an Indonesian reservoir where fish are grown from fingerling to marketable size. The cage operators often buy the fingerlings from rice farmers who have raised the fish from fry to fingerling size in their rice fields nearby.

Extensive to semi-intensive aquaculture systems produce the bulk of aquaculture products. Extensive farming usually involves unsophisticated technology, relies on natural food and has a low input to output ratio. Usually only a part of the life cycle is controlled, for example extensively operated fish ponds often rely on the supply of fish juveniles from the wild, and production inputs, in the form of feed and fertilizers, are provided only occasionally, if at all. As production intensity increases, fish are purposely stocked and the natural food supply is enhanced by using organic and inorganic fertilizers and low-cost supplemental feeds such as peanut cake, rice bran, and other agricultural by-products.

Preparation of fish feed for pond aquaculture of local catfish near Phnom Penh, Cambodia.

The system found most frequently is the farming of fish in ponds, but rice-fish farming or the stocking of fish into natural or impounded water bodies are also included.

Intensive systems produce more output from a given production unit. This is achieved through higher levels of technology and a greater degree of management. Fish or other aquatic organisms are often reared from egg to adult stage within the culture facilities, stocked at higher densities, and in smaller, well-designed facilities. With increasing stocking densities, chemical prophylactics are more commonly used to prevent disease.

Intensive farming of tilapias in a partially re-circulated, temperature-controlled environment near Banket, Zimbabwe.

Compound, manufactured feed in the form of pellets is provided on a regular basis. Water quality is carefully controlled with the aid of filters, purifiers, pumps and aerators.

A total of 262 fish, crustacean, and mollusc species representing the most important animals used in aquaculture worldwide are listed in a recent survey. Although not all aquatic organisms are suitable for culture, the variety of cultured species is still increasing. Freshwater finfish, particularly Chinese and Indian carp species, account for the greatest share (52%) of total aquaculture production in 1997. This is followed by molluscs (24%) and aquatic plants (20%), mostly kelp, the majority of which comes from China. Crustaceans account for less than 4% of production volume, but in terms of value the giant tiger prawn is the market leader with a 1997 production value of US$3.5 billion.

Since the 1970s, global aquaculture production has grown rapidly, and is now the fastest growing food production sector in many countries. By 1997, the production of all cultured aquatic organisms had reached 36 million metric tonnes (mt).

WORLD AQUACULTURE PRODUCTION,
BY WEIGHT AND VALUE, IN 1997

DATA SOURCE: FAO 1999. AQUACULTURE PRODUCTION STATISTICS, 1988-1997. FAO FISHERIES CIRCULAR NO. 815, REV. 11, 203 PP.

About 29 million mt of fish and shellfish contributed about one quarter to global fisheries production (and over 30% to the production of food fish). The majority of the latter aquaculture production comes from land-based freshwater culture, and in some countries it exceeds that from freshwater capture fisheries. Currently, over 80% of world aquaculture production originates from developing countries.

WORLD AQUACULTURE PRODUCTION
BY MAJOR ECONOMIC COUNTRY GROUPINGS, 1984-1997

SOURCE: Tacon, A.G.J. and U. Barg (in prep.) Responsible aquaculture development for the next millennium. Proceedings of ADSEA '99 SEAFDEC/AQD Workshop on Responsible Aquaculture Development in Southeast Asia held in Iloilo, The Philippines, 12-14 October 1999.

China is the dominant producer, followed by India, the Philippines and Indonesia. Although Asia is by far the leading region in aquaculture production (89%), Latin America and parts of Africa are also showing steady growth. However, in relation to the potential for the development of aquaculture in these regions, aquaculture production is still marginal.

Freshwater finfish account for the greatest share of world aquaculture production. Here, Chinese carpraised in pond aquaculture are harvested for sale in the markets of Canton, China.

How will aquaculture contribute to aquatic food supplies in the future? Among other factors, the growing world population has placed a heavy demand on capture fisheries, to the extent that many fish stocks are overexploited, or have even collapsed, and are no longer able to satisfy our growing needs. By the year 2010, it is predicted that the world's population will have reached 7.3 billion, over 90% of which will be living in developing countries. At present, an average 20% of people living within developing countries suffer from chronic malnutrition, the majority of whom are children. To those most in need, access to fish and fishery products is decreasing as diminishing supplies elevate market prices above their purchasing power.

Integrating aquaculture into irrigated rice-based farming systems as shown here in Central Java, Indonesia, offers opportunities for improved farm household income and family food supply.

Pond harvest in the Democratic Republic of Congo.

It is expected that aquaculture will play an increasingly important role in an effort to combat these problems. With the aim of improving rural and peri-urban livelihoods in developing countries, development organizations have focused on aquaculture with one, or a combination of the following objectives:

to increase household food supply and improve nutrition;
to increase household resilience through diversification of income and food sources;
to strengthen marginal economies by increasing employment and reducing food prices;
to improve water resource and nutrient management at household or community levels;
to preserve aquatic biodiversity through re-stocking;
to reduce pressure on fishery resources.

To achieve these goals, financial and technical assistance agencies and recipient countries have together channelled substantial amounts of investment into aquaculture development, with varied results. In Asia, development assistance efforts have contributed to the dynamic growth of aquaculture production. Unfortunately, for various reasons the same success story cannot be told for Africa and Latin America where a vast development potential remains to be explored.

Although in the preceding sections it has been attempted to give the reader a wide view of what aquaculture entails, the main focus in the following is on extensive and semi-intensive pond and ricefield aquaculture: in the smallholder farming systems context these production systems are the most relevant.