Physiological responses of Atlantic salmon (Salmo salar L.) fed very low (3%) fishmeal diets supplemented with feeding-modulating crystalline amino acid mixes as identified in krill hydrolysate

Crystalline amino acids and nucleotides, previously identified as potential feed-intake modulators in krill hydrolysate (KH), were mixed into low fish meal diets for Atlantic salmon in five combinations: A1) Arg, A2) Arg + Ala + Pro, A3) Arg + Ala + Pro + Leu + Phe, A4) Arg + Ala + Pro + Leu + Phe + nucleotides (AMP, GMP, CMP, IMP), and A5) Arg + Ala + Pro + Leu + Phe + nucleotides + rest free amino acids as in KH. Each compound mix was added to one of five otherwise identical 3% fishmeal diets. A 15% fishmeal (MFM) diet and a 3% fishmeal diet (LFM) served as positive and negative controls, respectively. The experimental diets were fed to seven triplicate populations of 60 salmon smolts for a period of 83 days. The initial mean body weight of the fish was 130 g while the final weights for the different treatments ranged between 500 and 560 g, with feed efficiency ratio (FCR) values of 0.8 or lower. The compound mixes were efficient in modulating feed intake rates, A1 negatively and A3, A4 and A5 positively, and resulted in a complex matrix of differential physiological responses related to growth, apparent nutrient digestibility, plasma and liver lipids and appetite-regulating neuropeptide relative gene expression, which are analysed in this paper.