The effect of protein quality and of supplementation of corn-glutenprotein with lysine on the growth, feed conversion and protein turnoverrates in white muscle was investigated in carp (Cyprinus carpio) acclimatedto either 18 or 25 °C. Fish fed the lysine-deficient diet showed asignificantly lower food intake, weight gain and feed-conversion efficiencythan animals fed the lysine-sufficient diets, regardless of environmentaltemperature. Coated lysine, compared with free lysine, proved to be asignificantly better way of supplementing dietary protein, as shown byfeed-conversion indices at 18 and 25 °C. White-muscle protein, RNA andDNA contents were not altered by dietary treatment or water temperature.Supplementation with coated lysine, but not with free lysine, significantlyincreased the protein-synthesis rate (KS) at 18 or 25 °Cin comparison to lysine deficiency, although not to control values. Theeffiiency of protein synthesis (KRNA) and retention (PRE)obtained for fish fed the coated-lysine diet, at 18 °C, reached controlvalues. At 25 °C PRE and protein accumulation rate (KG)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 withKD, KRNA or protein-related growth, at bothtemperatures.