الفهرس 
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Abstract
twelve isonitrogenous (30% crude protein), and isocaloric (4.35 kcal / g diet) diets were formulated to contain different oil sources including T1: cod liver oil; T2: poultry by product oil; T3: linseed oil; T4: corn oil; T5: 50%linseed oil + 50%poultry by product oil and T6: 50%corn oil + 50% poultry by product oil and control with out oil which represent experiment (1) , and different levels of prebiotic (power top®) (0.05, 0.1, 0.15 and 0.2%) compared with a control diet containing 0% of it representing experiment (2) ,in both experiments we study the effects of natural feed additives on growth performance, feed utilization, whole body composition, blood parameters and immunity response of Nile tilapia.
Results of experiment one showed that the optimum growth-related parameters were obtained at T5 (50%linseed oil+50%poultry by product oil). Fish fed T3 (linseed oil) diet gave higher feed intake than other additives oil and Fish fed T5 diet showed the best (lowest) for feed conversion ratio (FCR) in comparison to the control diet and other treatments. There were no significant differences with fish protein and lipid contents (P > 0.05) in all diets supplemented with different oil sources. Diets supplemented with different dietary lipid sources showed the best physiological parameters in comparison with the control diet (with out oils) .The blood hemoglobin (HB), red blood cells (RBCs), hematocrite (Ht), and white blood cell were higher in Nile tilapia fed T5, while the lowest RBCs was found when fish fed control diet. Total protein serum, cholesterol and glucose in plasma were increased significantly in the group of fish consumed T5. T5 diet is more economic and reduced the oil cost in fish feed without any effect on growth performance or feed utilization. The reduction in feed cost compared with the control diet to produce one kg fish gain was highest in T2 (poultry by product oil) diet followed by T5 (50%linseed oil+50%poultry by product oil) diet.
In experiment two There were no significant difference in growth performance and feed utilization parameters between fish fed diet containing0.15 and 0.2 % Power top® . The optimum growth performance and feed utilization parameters were obtained on fish fed diet containing 0.15 Power top® .No significant differences were observed in fish body moisture or ash contents at all treatments. While fish body protein content was increased significantly by increasing levels of Power- top®. Blood plasma profile showed an improvement in (HB), (RBCs), (Ht) and total protein, while there were a decrease in creatinine, urea ,aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glucose in fish fed 0.15 and 0.2 % power top® diet. Power top® was found to have antibacterial activity antagonistic to Aeromonas hydrophila infection in fish .Performance and FCR improvement translated into a 12.28 % decrease in feed costs in the 0.15% Power top® diet.