Effective replacement of protein-bound amino acids by crystalline amino acids in Senegalese sole (Solea senegalensis) juveniles

Abstract

The objective of this study was to evaluate the potential of free amino acids to replace protein-bound amino acids in diets for Solea senegalensis juveniles. For this purpose, fish with 4.26 g mean initial weight were fed during 55 days with diets containing 500 g kg−1 protein and 100 g kg−1 lipid, based on fish meal and fish oil as main protein and lipid sources (control diet), or diets where 20%, 35% and 50% of fish meal were replaced by crystalline amino acids, using L-lysine HCl as lysine source. To access the efficiency of the crystalline lysine source, another diet was formulated with 35% fish meal replacement but using L-lysine sulphate instead of L-lysine HCl as lysine source. Overall, growth performance, feed utilization, nutrient retention, whole-body and amino acid composition did not show significant differences among groups. In conclusion, up to 50% protein-bound amino acids can be replaced by crystalline amino acids in diets for Senegalese sole juveniles without negative effects in fish performance. Additionally, it was shown that L-lysine sulphate and L-lysine-HCl may be used interchangeably by Senegalese sole juveniles, with the potential economic benefits involved.