Impact of digestible energy levels at three different dietary amino acid levels on growth performance and protein accretion in Atlantic salmon

Nine experimental feeds were prepared, having two different digestible energy levels (DE, 19.5 and 21.5 MJ kg-1) and three different amino acid levels (90%, 100% and 110%), and formulated with two alternative strategies (protein and fat vary freely or only protein varies freely). The design was not balanced and thus the 110% amino acid profile was only studied at 19.5 MJ kg-1 DE. Atlantic salmon (Salmo salar) with a mean body weight of 449 +/- 19 g were distributed in 24 tanks and were fed each of the experimental diets for a period of 90 days. The fish were fed three times daily and uneaten feed was collected. Increasing the dietary DE energy from 19.5 to 21.5 MJ kg-1 and the amino acid level from 90% to 100% of the requirement increased the feed intake and growth performance in Atlantic salmon. Increasing the amino acid level from 90% to 100% had a positive effect on the feed intake, growth and protein accretion. Also, the mRNA levels of insulin-like growth factor I in muscle tissues pointed to this positive effect when the amino acid level increased. High probabilities were associated with a negative effect on the feed intake of reducing the amino acid level regardless of the DE level. It is recommended that the balanced amino acid level should not be adjusted by the same percentage rate as dietary energy, and possibly should not be reduced at all in order to maintain optimum performance and profitability.