Many intensive and semi-intensive aquaculture systems use 2±5 times more fish protein, in the form of fish meal, to feed the farmed species than is supplied by the farmed product. In contrast, extensive and traditional systems use little or no fish meal, although nutrient-rich materials are often added to the water to stimulate growth of algae and other organisms on which the fish feed. Dietary requirements vary widely among fish species, depending on the aquaculture system, fish meal source and other dietary components