Lysine deposition responds linearly to marginal lysine intake in Atlantic salmon (<i>Salmo salar</i> L.) parr

Abstract

This study investigated lysine utilization at marginal lysine intake (mg day−1) in Atlantic salmon (Salmo salar L) parr fed diets similar to those used in dose–response lysine requirement experiments. Duplicate tanks of salmon were fed Diet PL20.1 (20.1 g lysine kg−1 and 19.8 MJ DE kg−1) containing 54% of the lysine in the crystalline (free) form at four intake levels for 50 days. Feed intake levels were measured at 0.59, 0.85, 1.10 and 1.16 (satiation)%BW day−1. In addition, duplicate tanks of salmon were fed to satiation with Diets FML9.1 (9.1 g lysine kg−1) and FML20.7 (20.7 g lysine kg−1) in which lysine was derived almost entirely from fish meal. Feed intakes of FML9.1 (0.70%BW day−1) and FML20.7 (1.21%BW day−1) were significantly lower and higher (P < 0.001) than the satiation intake of the Diet PL20.1, respectively. Over all dietary treatments, lysine deposition was dependent on lysine intake (LI, mg day−1) as described by the equation: lysine deposition (mg day−1) = 0.708LI − 0.035 (r2 = 0.97, n = 12, P < 0.001). Addition of marginal lysine intakes from Atlantic salmon dose–response lysine requirement literature resulted in an equivalent relationship. The linear relationship suggests that lysine utilization remains constant at marginal lysine intake over different dietary formulations and life-stages. Consequently, the lysine requirement (allowance) of Atlantic salmon would be more appropriately estimated by a factorial approach, assuming constant efficiency of lysine utilization and the addition of obligatory lysine loss (maintenance). Efficiency of lysine utilization and obligatory lysine loss was estimated to be 71% and 0.05 mg day−1 from the current experiment and 78% and 0.10 mg day−1 with the addition of the literature data. Based on the constant lysine utilization observed in this study, it is proposed there is a need to re-evaluate lysine requirements expressed as a dietary concentration.