The optimum dietary essential amino acid profile for gilthead seabream ( Sparus aurata) juveniles

Abstract

A study was undertaken to establish the optimum dietary essential amino acid (EAA) profile for gilthead seabream juveniles based on the amino acid (AA) deletion method. For that purpose 11 diets were formulated to be isonitrogenous (6.72% N) and isolipidic (18%). In the control diet half of the nitrogen was provided by protein bound-AAs (fish meal) and the other half by a mixture of crystalline L-AAs. The overall AA profile of this diet was made similar to that of fish meal protein. Ten other diets were formulated identical to the control except for the deletion of 45% of a single EAA in each diet and by adjusting the nitrogen level with a non-essential AA mixture. Each diet was assigned to four groups of 22 fish (initial body weight of 4.6 g) and the trial lasted 43 days at a water temperature of 25 °C. Fish were fed by hand, twice daily, using a pair-feeding scheme. At the end of the trial the relationship between nitrogen gain and AA intake of the test and control diets was determined. Based on these data, and assuming that nitrogen retention responds linearly to dietary EAA content when a given AA is limiting, the quantity of each EAA that can be removed from the control diet without affecting nitrogen retention was computed and the ideal dietary EAA profile for gilthead seabream juveniles was estimated. Expressed relative to lysine (= 100) A/E ratios were estimated to be: arginine, 108.3; threonine, 58.1; histidine, 36.8; isoleucine, 49.7; leucine, 92.7; methionine, 50.8; phenylalanine + tyrosine, 112.3; valine, 62.6; and tryptophan, 14.6. This EAA profile correlates tightly to the whole-body EAA composition of gilthead seabream ( R 2 = 0.99; p > 0.001).