Integrated systems can also be used for high-valued fish, such as salmon and shrimp, to reduce effluents, diversify products and increase productivity. Several studies show that seaweed and mussels grow well in wastewater from intensive and semi-intensive systems, thereby reducing nutrient and particulate loads to the environment81±85. For example, in Chile salmon can be farmed with Gracilaria chilensis (an agarophytic red alga) that removes large amounts of dissolved nitrogen and phosphorous wastes from salmon cages. The effluent output from salmon farming is used to produce a seaweed crop, and the added revenue from the sale of the seaweed more than pays for the extra infrastructure needed for the integrated system. Policies that require producers to internalize environmental costs of effluent discharge (for example, through
mandatory sewage treatment) can make such systems even more profitable. The marketability of molluscs raised in intensive ®sh farming areas is currently constrained, however, by human health considerations that must be addressed to make these types of
integrated system economically viable.