The influence of dietary protein and fat levels on tissue free amino acid levels of fingerling rainbow trout ( Oncorhynchus mykiss)

Abstract

The influence of six semi-purified diets having different nutrient composition on the tissue free amino acid (FAA) levels of fingerling rainbow trout was examined. Four balanced amino acid diets (casein:gelatin=6:1) with combinations of two protein levels (35% (LP) and 50% (HP)) and two fat levels (10% (LF) and 20% (HF)), and two imbalanced high-protein (50%) diets (IMB-HP, casein:gelatin=1:1) with two fat levels (LF and HF), were each fed to duplicate groups (30 fish/group, 10 g/fish) for 6 weeks at 15°C. FAA in plasma, liver, dorsal white muscle and brain at 12 h after the last feeding were compared. Percentage weight gain of the HPHF diet group was the highest, but was not different ( P>0.05) from the others except for the IMB-HPLF diet group ( P<0.05). Levels of individual amino acids in the whole body protein were not markedly different among the treatments. Most of the free essential amino acid (EAA) levels in the tissues of the HP diet fed fish were higher than in those of the LP diet group. The levels of free phenylalanine and tyrosine of the HF group tended to be higher, and those of taurine lower, than the LF group. Most of the free EAA levels of the IMB diet group were lower even than the LP group. Correlations in EAA patterns between a given diet and tissue were high in plasma, but very low in muscle and brain. These findings suggest that not only dietary protein level and amino acid profile, but also dietary fat level affects the levels of certain FAA of rainbow trout tissues.