The terms intensive, semi-intensive and extensive are commonly used to define culture methods. In practice, the distinction between them is often less than clear. They are, however, generally linked to the level of inputs of feed and/or fertiliser and to the stocking density of the fish that can be supported.
In intensive culture systems there is a decreased dependence on the availability of natural food and greater dependency on the use of commercial feeds. Densities of fish kept within such holding areas are limited by species tolerance, ability to grow at raised stocking densities and maintenance of environmental parameters rather than the production of a natural food supply.
By contrast, fish production in extensive systems is based on the use of organic and inorganic fertilisers. Fertilisation of ponds promotes the growth of simple plants which form the base of the food chain in the pond. Fish stocked in these ponds feed on phytoplankton, zooplankton, bottom-dwelling invertebrates and smaller fish. At its most effective, this type of production can be integrated with other types of crop or livestock production, using animal manure and agricultural by-products as sources to stimulate primary production.
Semi-intensive aquaculture aims to increase the production of fish from pond systems beyone the level supported by food which is naturally available through the use of supplementary feeds. Supplementary feeds range from cereals and agricultural and fishery by-products to formulated feeds. Traditionally they are incomplete and would be inadequate as a sole source of food. Their function is to provide extra nutrients to complment those obtain from natural foods.
Intensive aquaculture: salmon farming in Europe
Extensive aquaculture: subsistence tilapia farming in Africa
Semi-extensive aquaculture: cyprinid farming in China