In fact, aquaculture is overwhelmingly concentrated in the developing world, which accounts for more than 85 percent of output by volume and 71 percent by value. More importantly for food security, the production, processing and sale of fish offer the prospects of improved local nutrition by providing a ready source of high-quality protein as well as giving an opportunity to generate income. The fish maintain their own populations and feed on the natural productivitiy of small ponds supplemented by household vegetable wastes and composts. Invariably, the success of subsistence aquatic farming depends on location, which in turn depends on land ownership and available water resources. In spite of this promise, aquaculture projects are vulnerable to disease and environmental problems.
Marine aquaculture is constrained by the rising pollution of coastal waters.
Nutrient and organic over-enrichment, the accumulation of toxic chemicals, microbial contamination, siltation and sedimentation all jeopardize expansion. Where aquaculture results in the degradation of coastal mangroves, the breeding grounds of many wild species, it poses a major threat to biological diversity. Better selection of production sites to safeguard the environment and sound management techniques can overcome most of these difficulties. Few environmental problems are experienced, however, with the low-input systems that make up the bulk of aquaculture.