الفهرس 
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Abstract
The present study was an attempt to study the possible immunomodulatory role of some plant extracts as Echinacea and Ginseng extracts in Nile tilapia (Oreochromis niloticus) and provide a natural alternative to the use of oxytetracycline as growth promoter when added to its feed for 8 weeks . Four hundred Nile tilapia (Oreochromis niloticus) with an, average body weight of 41.S7±OJ g were used by randomly distribution into equal 8 groups, each one contained SO fish (2S fish / replicate),and treated with a basal diet that contained (32.l6%) protein. The I st group was treated with a basal diet without any additives and served as control group (gp.I), the diet of other groups mixed with 19 /kg diet oxytetracycline (gp.2), 0.7Sg /kg diet of Echinacea extract (gp.3) , 0.7Sg /kg diet of Echinacea extract plus 19 /kg diet oxytetracycline (gp.4) , 0.6 g /kg diet of ginseng extract (gp.S), 0.6 gmlkg diet ginseng extract plus Ig/kg diet oxytetracycline to (gp.6), 0.7Sg /kg diet of Echinacea extract and 0.6g /kg diet of ginseng extract
(gp.7) and 0.7Sg /kg diet of Echinacea extract, 0.6g /kg diet of
ginseng extract and 19 /kg diet of oxytetracycline (gp.8). The experiment was carried out in Fish Research Center, Fac. of Vet. Med., Zagazig University, Egypt, and extended for 3 months in the summer season(June-September). At the end of the feeding. experiment, the growth performance and different immunological parameters of experimental fish were assessed. Finally, the fish was challenged with pathogenic A. hyDROPhila to evaluate the effect of the used additives on its ability to withstand the infection. Data were statistically analyzed using the Analysis Of Variance (ANOVA) and considered significantly different at (P <O.OS). The results of growth