Energy, protein and amino acid requirements for maintenance and efficiency of utilization for growth of Atlantic salmon post-smolts determined using increasing ration levels

Abstract Ration levels were used to determine the digestible protein (DP) and amino acids as well as digestible (DE) and metabolizable energy (ME) requirements of Atlantic salmon post-smolts for maintenance and the efficiency of utilization for gain above maintenance. The salmon (96 g) were held in seawater at a temperature of 10 °C and were fasted for 28 days or fed incremental ration levels of a fishmeal-based diet for 51 days. The composition of gain was determined by the comparative slaughter technique. The relationships between intake of digestible or metabolizable nutrients or energy and gain of those nutrients or energy were linear ( R 2  ≥ 0.98) between zero intake and maximum voluntary intake. The DE and ME requirements for maintenance were 31.5 and 30.6 kJ kg − 0.8  d − 1 , respectively, and the efficiency of utilization of DE and ME for gain were 0.80 ± 0.01 and 0.82 ± 0.01, respectively. The efficiency of utilization for gain of DP was 0.64 ± 0.01 and that of the sum of digestible amino acids 0.57 ± 0.02. The efficiency of utilization of the individual amino acids for gain varied from 0.45 for tryptophan to 0.65 for histidine. The maintenance requirement for DP was 117.5 mg kg − 0.7  d − 1 and for digestible sum of amino acids 204.0 mg kg − 0.7  d − 1 . The maintenance requirements for the individual amino acids varied from 4.3 mg kg − 0.7  d − 1 for methionine and tryptophan to 20.9 mg kg − 0.7  d − 1 for leucine. The results suggest more emphasis should be directed towards determining the maintenance requirements and the efficiency of utilization for gain above maintenance for the individual amino acids and the sum of amino acids rather than for crude protein.