Polyculture in aquaculture.

Polyculture in aquaculture is the association of fish species of different food habits for the effective use of available fish foods in the pond, where wastes produced by one species may be inputs for other species. In a more comprehensive way polyculture may also refer to aquaculture integrated with other agricultural activities, where wastes produced by one activity may be inputs for another activity. Polyculture is the main fish culture system in Asia, the continent generating over 90% of the world aquaculture production. Today in western countries there are problems of land use and pollution that have led to strict regulations on water disposal, which together with public concern on the use of chemicals and manures is changing the approach to aquaculture, basically in two directions. On the one hand, there is a continuous intensification trend involving sophisticated technologies, high use of energy, recirculation of water and treatment of wastes, which targets 'zero discharge' into the environment. A further step of sophistication following this direction is now developing, marking a return to the polyculture concept: the new industrial scale integrated aquaculture systems consist of several monoculture units linked so that water and residues of one unit are utilized as input by the other. The other direction of aquaculture change is towards less intensive systems that are sustainable and environmentally sound. In this direction there are two main and related approaches, ecological aquaculture and organic aquaculture. With the current world emphasis on environmentally sound polyculture practices, the present review of polyculture in aquaculture examines feeding relations and culture practices in the traditional polyculture pond and in the integrated family/community-scale agriculture-aquaculture system, and the adaptation of the polyculture principles to modern industrial-scale integrated aquaculture and organic aquaculture.