An experiment was designed to find out the effect of the replacement of essential amino acids by non-essential amino acids as energy source at sev- en ratios (45%: 55% as a control, 50%: 50%, 40%: 60%, 35%: 65%, 30%: 70%, 25%: 75% and 20%: 80%, essential amino acid: non-essential amino acid,) respectively. The higher significant (P≤0.05) values of average final live body weight, average daily body gain, specific growth rate were observed for Nile tilapia fry fed diets con- taining ratios (50: 50), (45: 55) and (40: 60) (es- sential: non-essential amino acids) than the other treatments. Nile tilapia fry fed the diet containing ratios of (50:50), (45: 55) and (40: 60) (essential: non-essential amino acids) had the better-feed conversion ratio than other treatments. Protein efficiency ratio and nitrogen retention among differ- ent experiments decreased significantly (P≤ 0.05) with increasing dietary ratio of non-essential amiNo acids. This effect was moderate when 60% of dietary protein was substituted by non-essential amino acids, while ratio over than 65%, the val- ues were further reduced. Carcass crude protein was significantly (P ≤0.05) lowest when fish fed diet containing more than 60% non-essential ami- no acid. Carcass lipid content and gross energy content followed the opposite tendency.
Depending on the present data it is of interest to point out that, the dietary crude protein require- ment for tilapia can be reduced to the range of 12.2 15.7% when appropriate energy source that have metabolizable energy values equivalent to protein are used (for example, non-essential ami- no acids) to substitute dietary protein to levels of 30%, with metabolized energy density of 13.71 MJ and had a P/E ratio (CP/ME) of 22.40 g./MJ
The data confirmed that substitution of dietary protein nitrogen by non-essential amino acids