The minimum dietary lysine requirement, maintenance requirement and efficiency of lysine utilization for growth of Atlantic salmon smolts

This study was conducted to evaluate and refine the dietary lysine requirement of Atlantic salmon (Salmo salar) smolts using both the dose–response technique to determine the minimum dietary requirement and different ration levels to determine the maintenance lysine requirement and the efficiency of lysine utilization for growth. Diets containing 1.97–3.16% lysine (presented in protein-bound form of lysine) were fed to satiation or at 25–75% ration levels to smolts during the last week in fresh water and the following 9 weeks in seawater. Based on the exponential lysine gain response to increasing dietary lysine concentrations, the minimum lysine requirement was found to be 2.67% of diet (dry matter basis; protein-bound form or 3.05% free form). The smolts fed the unsupplemented diet maximally utilized the digestible lysine intake for growth. The efficiency of digestible lysine utilization for growth was 0.85 in the diet containing 2.88% lysine and the maintenance requirement was 21.7 mg digestible lysine kg−0.7 day−1.