Effect of the dietary essential amino acid pattern on growth, feed utilization and nitrogen metabolism of European sea bass (Dicentrarchus labrax)

The aim of this study was to evaluate the influence of the dietary essential amino acid (EAA) pattern on growth performance, feed utilization and nitrogen metabolism of European sea bass. A diet containing only intact protein (fish meal and wheat meal) was used as a control (diet C). Three semi-purified diets were formulated to be isonitrogenous (8% DM) and isolipidic (15% DM) and to contain crystalline-AAs replacing approximately 60% of fish meal protein-bound nitrogen of the control diet. The AA pattern of these diets was adjusted to resemble the overall AA pattern of the fish meal protein (diet FM); the overall AA pattern of the whole-body protein of sea bass (diet WBC) or to meet the ideal protein AA pattern estimated for sea bass (diet REQ). Each experimental diet was fed to juvenile sea bass (7.3 g) in triplicate for 42 days.Weight gain and specific growth rate were highest in fish fed the control diet, followed by FM, WBC and REQ diets. Voluntary feed intake was highest in fish fed the REQ diet, and did not differ within the other groups. Feed efficiency and protein efficiency ratio were similar between fish fed the control and FM diets, while it was lower in the other groups.At the end of the growth trial, whole-body dry matter and protein content were not significantly affected by dietary treatment, while lipid and energy contents were significantly higher in fish fed the control diet than the other diets. Visceral and hepatosomatic indices were significantly lower in fish fed the REQ diet compared to the other groups.Nitrogen retention (g kg BW− 1 day− 1 and % N intake) of fish fed the control and FM diets was significantly higher than that of fish fed the REQ diet. Total non-fecal N excretion (% N intake) was significantly higher in fish fed the REQ diet than in the other groups, among which no significant differences were observed.Specific activity of glutamate dehydrogenase was significantly lower in fish fed the control diet than the REQ diet. Specific activity of alanine and aspartate aminotransferases and glucose-6-phosphate dehydrogenase were not significantly affected by the dietary treatments. Fatty acid synthetase activity was significantly lower in fish fed the REQ diet than in the other groups, among which no significant differences were observed.Results of this study indicate that the best overall growth and feed utilization of sea bass juveniles were obtained with a dietary AA pattern that resembled the overall AA pattern of fish meal. A diet with an AA profile adjusted to meet the ideal protein AA pattern estimated for sea bass significantly depressed growth.