Effects of varying dietary protein and energy supply on growth, body composition and protein utilization in gilthead seabream (Sparus aurata L.)

Diets formulated with increasing digestible energy (10-22 DE MJ kg(-1)) con tents and decreasing digestible crude protein (DCP)/DE ratios (34-15 g MJ(- 1)) were fed to triplicate groups of Sparus nul atn in three consecutive tr ials. Fish were hand-fed to apparent satiation and voluntary feed intake wa s found to be dependent upon dietary DE content. Daily growth was regulated both by energy and protein intake and reached its maximum at high energy l evels. Growth composition showed narrow limits regarding protein gain (157- 190 g kg(-1)) and a wider range regarding lipid (55-210 g kg(-1)) depositio n reflecting the dietary energy to protein supply. Energy utilization for g rowth was constant at a value of 0.50 regardless of energy intake. Efficien cy of protein utilization for growth varied between 0.33 and 0.60 depending on the DCP/DE ratio in the diet. The optimal protein utilization for prote in deposition was found to be at 0.47. These values allow daily energy and protein requirements for growing S. aurata to be quantified. This demonstra tes that the optimal dietary DCP/DE supply changes with fish size, growth p otential and daily feed intake.