Efuent discharge. Untreated wastewater laden with uneaten feed and fish faeces may contribute to nutrient pollution near coastal ponds and cages,62. Pollution problems are most severe in shallow or confined water bodies; they also tend to be serious in regions where intensive aquaculture systems are concentrated. In many such areas, sedimentation of food particles and faecal pellets under and around fish pens and cages negatively affects the biogeochemistry of
benthic communities64. Moreover, nitrogen wastes (for example, ammonia and nitrite) that exceed the assimilative capacity of receiving waters lead to deterioration in water quality that is toxic to fish and shrimp65. Problems of ef¯uent discharge from aquaculture have been widely discussed, but management options for
altering nitrogen biogeochemistry are based mostly on controlling
the intensity of ®sh production in monoculture and polyculture
systems65. Aquaculturists have a stake in regulating nutrient pollution,
because poor water quality and high stocking densities often
promote outbreaks of pathogens and subsequent declines in farm
productivity.
D. V. Lightner, personal communication).
endangered populations of wild Atlantic salmon