Abstract
The current investigation was done to examine the impact of some amino acids as glutamine with different concentrations on growth performance, biochemical parameters and resistance to bacterial infection as Aeromonas hydrophila in Nile tilapia. Total number used in our study were two-hundred and eighty O.niloticus fish (100 diseased fish for Aeromonas hydrophila isolation and 180 apparently healthy fish for experimental design). 180 fish were divided into four groups, 45 fish / group. The control group was feeding a baseline diet without additives and the treated groups were feeding a diet containing glutamine of 1, 1.5, or 2% for groups 2, 3 and 4 respectively. Fish from the treated and control groups received intraperitoneal (IP) injections of 0.2 ml suspension of A. hydrophila after the feeding trial has concluded. Results of our investigation showed a total of 14 A. hydrophila strains were recovered from 100 samples of diseased fish with a percentage of 14%. Through the use of, cultural, morphological, biochemical characteristics and PCR technique, the isolates were identified. According to the results of the PCR examination all 7 examined isolates were positive for the Aeromonas hydrophila specific gene (16S rRNA) and act gene and 5 isolates were positive for aerolysin gene but the 7 examined strains were negative for ast gene. Also our study showed a significant differences with control and higher growth performance for groups fed on diet containing glutamine 1.5% and 2% concentrations and also showed that diet containing 2% Glutamine augmented Hb%, RBCs, and MCV% and increased serum SOD, CAT, GPx, and bactericidal activities in addition to elevation in the levels of total protein than the other Glutamine inclusion levels (1% or 1.5%). Also the mortality rate and re-isolation rate decreased in groups fed on diet containing glutamine 1.5% and 2% concentrations than the other groups. In conclusion, dietary supplementation with glutamine at a concentration of 2% enhanced the growth performance, improve biochemical parameters and the resistance to Aeromonas hydrophila infection.

Key words: Key words: amino acid(glutamine), growth performance, biochemical parameters, diseases resistance, Nile tilapia.