Dietary arginine supplementation does not improve nutrient utilisation in gilthead seabream

Abstract

The aim of this study was to evaluate the beneficial effects of dietary arginine supplementation on growth performance, urea biosynthesis, and N excretion of juvenile gilthead sea bream (Sparus aurata) fed fish meal and plant-feedstuffs based diets. For that purpose, five isonitrogenous (45\% crude protein) diets were formulated as follows: two diets were fish meal-based and contained 3.0 and 4.0\% arginine; three diets were plant feedstuff-based and contained 1.6, 3.0, and 4.0\% arginine. Triplicate groups of gilthead seabream juveniles (24 g) were fed each diet for 10 weeks. At the end of the trial, growth performance of fish fed the fish meal-based diets was higher than that of the other groups. Dietary arginine content did not affect growth performance. Ammonia excretion was not affected by diet composition, while urea excretion was directly related with arginine intake. Carbamyl phosphate synthase activity was not detected in the liver, while arginase activity increased and ornithine carbamyl-transferase decreased with dietary arginine content. Overall, an excess of dietary arginine had no beneficial effects on growth performance and feed utilisation of gilthead seabream juveniles fed plant feedstuffs-based diets. A functional urea cycle was not detected in the liver of gilthead sea bream juveniles.