A theoretical model linking the production of salmon, mussels and seaweed in floating, enclosed units is based on field data, laboratory tests and literature data . First step is the production of 300 metric tons of salmon in 12 production units of 500 m3 each and a total water flow of 60 m3 min . . Using a standard high energy dry feed with a feed conversion factor of 1, a production of 300 metric tons of salmon is calculated to produce 15 metric tons of nitrogen (N) and 2 .4 metric tons of phosphate (P), of which 13 metric tons of N and 0 .7 metric tons of P are dissolved . Outlet water is transferred from the salmon units to 12 closed units (500 m3 each) with blue mussels . A standing stock of 112 .5 metric tons of mussels (WW) is necessary to filtrate 60 m3 min -' . If all particles are filtrated through the mussels, 25% of the nitrogen is accumulated as increased biomass . 25-30% is released as faeces and 45-50% as dissolved matter . Particles are removed by a sedimentation trap . Outlet water from the 12 mussel filter units, containing 13 .9 metric tons of dissolved N (0 .9 metric tons from the mussels), is transferred to closed units (1000 m 3 ) with seaweeds . Concentration of N is calculated to 0 .44 g N m_3 and hydraulic retention time in the seaweed production unit is 4 hours . With a DW of 20% (4% N of DW) and an estimated growth rate of 10% d -' during the production period, a standing stock of 45 metric tons (FW) of seaweed is theoretically needed to bind up all dissolved N from the salmon and mussel production .