Influence of stocking density on growth,body composition and energy budget of Atlantic salmon Salmo salar L. in recirculating aquaculture systems

Atlantic salmon Salmo salar were reared at four stocking densities—high density D ₁ (final density ～39 kg/m³), medium densities D ₂ (～29 kg/m³) and D ₃ (～19 kg/m³), and low density D ₄ (～12 kg/m³)—for 40 days to investigate the effect of stocking density on their growth performance, body composition and energy budgets. Stocking density did not significantly affect specific growth rate in terms of weight (SGR_w) but did affect specific growth rate in terms of energy (SGR_e). Stocking density significantly influenced the ration level (RL_w and RL_e), feed conversion ratio (FCR_w and FCR_e) and apparent digestibility rate (ADR). Ration level and FCR_w tended to increase with increasing density. Fish at the highest density D ₁ and lowest density D ₄ showed lower FCR_e and higher ADR than at medium densities. Stocking density significantly affected protein and energy contents of the body but did not affect its moisture, lipid, or ash contents. The expenditure of energy for metabolism in the low-density and high-density groups was lower than that in the medium-density groups. Stocking density affected energy utilization from the feces but had no effect on excretion rate. The greater energy allocation to growth at high density and low density may be attributed to reduced metabolic rate and increased apparent digestibility rate. These findings provide information that will assist selection of suitable stocking densities in the Atlantic-salmon-farming industry.