Growth and feed utilization of gilthead sea bream (Sparus aurata, L.) fed to satiation and restrictively at increasing dietary energy levels

Three isoproteic (47% protein) diets were formulated to contain graded levels of crude fat (diet D16:16%, diet D24: 24% and diet D32: 32%). Each diet was fed to satiation in three and to 80% satiation in two replicate groups of gilthead sea bream (Sparus aurata), having an initial body weight of 72-74 g. The trial lasted 81 days. Groups fed to satiation showed higher final body weight (FBW; 238.8-252.3 g vs. 218.0-229.3 g) and daily growth index (DGI; 2.49-2.65%/day vs. 2.27-2.34%/day) than those fed to 80% satiation. Feed intake was significantly different both for feeding level and for diet composition. Fish fed to satiation had higher feed conversion rate (FCR) compared to the 80% satiation groups (1.33-1.44 vs. 1.13-1.17; P a parts per thousand currency sign 0.001). Within satiation groups, FCR was significantly lower in fish fed D16 compared to fish fed D32 (1.33 vs. 1.44, P a parts per thousand currency sign 0.05), whereas no statistical differences were found within the 80% satiation groups. The increase in dietary lipid level did not improve growth performance, feed efficiency and protein utilization but decreased gross lipid efficiency. Conversely, a reduction in ration from satiation to 80% satiation decreased DGI, thus improving FCR. Feed costs were influenced by dietary energy level and feeding ratio, the lowest energy diet at 80% satiation being the most profitable combination among the variables.