Fish have been raised for centuries in flooded fields and ponds. More recently these technologies have become a major focus of development efforts concerned with food production. Both the raising of fish and of plants in water without soil are unusual agricultural efforts, however. Only the wealthier and more innovative farmers are interested. Consequently, schemes that on paper and in a government-sponsored agricultural station sound quite impressive are not tried.
Aquatic culture goes back at least 4000 years in China, Japan and Egypt, well over 3000 years in Java and India, and at least 2500 years in Europe. Despite this ancient history, fish farming has had very little scientific help. Most of its methods are traditional, developed by trial and error. Aquaculture is characterized by four general types of activity. The first is hatchery, where large numbers of young are raised and then released into coastal waters with the expectation that they will increase the size of the natural population and the commercial catch. This expectation is almost never fulfilled. Exceptions are the cultivation of some species of salmon in the USA and Europe and of sturgeon in the USSR. The second kind of aquaculture involves the capture and impoundment of young. In enclosures, they may be left to fend for themselves, the water may be fertilized to that natural food is increased, or supplemental food may be added. This is the most successful form of aquaculture. Third is production of young from eggs and their retention until they reach marketable size. Japanese shrimp culture is an example of this. The last method involves the full control of the life cycle of the animal; eggs are hatched, the animals are feed until large enough for commercial purposes, they are harvested and brood stock is kept and breed. Trout and catfish are fresh-water examples of this method. The only marine example is oysters on a very small scale.
There is little scientific support of aquaculture. The usable surface area of the oceans is relatively small; the open sea is unsuitable. Coastal areas and shallow seas are highly prized by commercial and sport fishermen, pleasure boaters, swimmers, oil and other mineral explorers, housing developers and those who dump waste. The increasing amounts of pollution: sewage, industrial wastes, fertilizers, pesticides, silt, heated water, trash, oil, and radioactive substances are making some whole seas unsuitable for aquaculture. Unclear ownership rights of seas, even coasts increases the risk of potential sea farmers. Conservation laws sometimes prevent its development by forbidding the capture of young animals or of mature females. The number of marine animals which can be cultivated is small.