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 supplementati on 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 °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-conversi on indices at 18 and 25 °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 proteinsynthesis rate (K S ) at 18 or 25 °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 °C, reached control values. At 25 °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.