Influence of temperature and dietary-protein supplementation either with free or coated lysine on the fractional protein-turnover rates in the white muscle of carp

The effect of protein quality and of supplementation of corn-gluten protein with lysine on the growth, feed conversion and protein turnover rates in white muscle was investigated in carp (Cyprinus carpio) acclimated to either 18 or 25 degrees C. Fish fed the lysine-deficient diet showed a significantly lower food intake, weight gain and feed-conversion efficiency than animals fed the lysine-sufficient diets, regardless of environmental temperature. Coated lysine, compared with free lysine, proved to be a significantly better way of supplementing dietary protein, as shown by feed-conversion indices at 18 and 25 degrees C. White-muscle protein, RNA and DNA contents were not altered by dietary treatment or water temperature. Supplementation with coated lysine, but not with free lysine, significantly increased the protein-synthesis rate (K-s) at 18 or 25 degrees C in comparison to lysine deficiency, although not to control values. The efficiency of protein synthesis (K-RNA and retention (PRE) obtained for fish fed the coated-lysine diet, at 18 degrees C, reached control values. At 25 degrees C PRE and protein accumulation rate (K-G) showed the following significant differences: lysine-deficient diet < free-lysine supplemented diet < coated-lysine supplemented diet < control diet. Significant correlations were observed for Ks in relation with K-D, K-RNA or protein-related growth, at both temperatures.