Dietary lysine requirement and efficiency of lysine utilization for growth of Atlantic cod

Abstract This study was conducted to evaluate the minimum dietary lysine requirement, the maintenance lysine requirement and the efficiency of lysine utilization for growth of Atlantic cod. Eight fish meal and wheat gluten-based diets, containing graded levels of crystalline l -lysine–HCl, were fed to quadruplicate groups of cod for 9 weeks. The diets contained 13.7 to 28.3 mg lysine kg −1 (protein-bound form). A fishmeal-based control diet (30.6 mg lysine kg −1 ) was also fed at ration levels of 33, 66 and 100%. Exponential models predicted that the minimum dietary lysine requirement required to reach 95% of maximum nitrogen gain was 23.8 g kg −1 DM (protein-bound form; 27.1 g kg −1 DM free-form lysine) and 95% of maximum lysine gain was 26.2 g kg −1 DM (protein-bound form; 29.9 g kg −1 DM free-form lysine). In cod fed diets containing lysine concentrations up to 89% of the requirement based on lysine gain, a linear relationship was found between digestible lysine intake and lysine gain (R 2  = 0.91); 85% of the digestible lysine intake over maintenance was deposited in the cod. Neither the linear dose–response curve, nor the linear relationship between digestible lysine intake of the control diet and lysine deposition in the cod, had Y-intercepts significantly different from zero and therefore, the maintenance lysine requirement of the cod could not be estimated.