Raising animals and plants in the water is aquaculture. Aquaculture can take place in water that is still or in running water, fresh or salt. The practice of aquaculture has been growing rapidly. Experts have projected a fivefold increase in harvests during the final quarter of the 20th century. In the 1970s Asia accounted for approximately 85 percent of world production in the field.
Aquaculture is regarded as one possible solution to the world's food supply problems.
The quantity of tillable land is limited and shrinking everywhere. In contrast to agriculture, which is practiced on the land's surface only, aquaculture is three-dimensional. Multiple cropping of this kind, called polyculture, represents an efficient use of labor, materials, and energy. In animal aquaculture much effort has gone into controlling the breeding process. Some fish, such as trout, are easily bred in captivity.