Twelve semi-purified diets were formulated to de- tect the influence of 10 dietary essential amino acid deficiency on Nile tilapia, (Oreochromis niloticus) fry performance. The first diet was formulated for high control (30% CP) and the last diet (12) as low control (20% CP). Diets from 2 to 11 were formulated to add a mixture of synthetic amino acids including all but one of the essential amino acid to the low protein control diet to gave the total crude protein of high control diet.
The deficiency of threonine and methionine + cysteine significantly (P< 0.05) lowered final body weight, average daily gain per fish and specific growth rate. The data showed that threonine was the first limiting amino acid, while, the sec- ond limiting amino acid was methionine + cysTeine. The higher values of feed conversion ratio were observed for fish fed diet deficient in threo- nine or low control, whereas the lower value was noticed for fish fed diet high control (30% CP). The value of protein efficiency ratio of low con- trol diet (20% CP) was significantly (P< 0.05) higher than the other treatments, while the higher significant values of nitrogen retention and energy retention were observed for tilapia fed high con- trol diet and deficient of tryptophan, respectively. Body ether extract content followed the same trend to protein efficiency ratio, while the higher significant (P < 0.05) differences of crude protein and gross energy were observed for tilapia fed high control diet. The lowest nitrogen retention in response to deduction amino acids was threonine followed in increasing order by lysine, phenylala nine + tyrosine and methionine + cystine. Energy retention followed the same trend.