A 10-week study was conducted to investigate the effects of feeding rate and frequency on growth performance, digestion and nutrients balances of Atlantic salmon (Salmo salar) in replicated recirculating aquaculture systems (RAS). Replicated groups of juvenile salmon weighing 90 AE 2.5 g (mean AE SD) were fed a commercial feed (21.63 MJ kg À1 gross energy) to designed feeding rate (1.4%, 1.6% and 1.8% body weight day À1 , BW day À1 ) and feeding frequency (2 and 4 meals day À1 ) combinations. Specific growth ratio varied between 1.15 AE 0.02 and 1.37 AE 0.16% day À1 , and feed conversion ratio ranged from 0.96 AE 0.03 to 1.16 AE 0.02. The nitrogen and phosphorus retention rates were from 36.50 AE 1.94 to 47.08 AE 5.23% and from 20.42 AE 1.05 to 38.59 AE 2.80%. Apparent digestibility coefficients (ADC) in dry matter, protein, lipid and energy showed no significant differences for all groups. However, fish fed at 1.6% BW day À1 and 4 meal day À1 groups had relatively better growth and nutrient retention efficiency compared to other groups. In addition, concentrations of nitrogenous and phosphorous compounds were also detected in this study. These results suggested that salmon of 100-200 g in RAS could in practice be fed at 1.6% BW day À1 and 4 meals day À1 , taking environmental impacts into account.

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