الفهرس 
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Abstract
A factorial design (2×3) was conducted in order to study the effect of fish stocking density (100 and 200 fish/m3) and dietary protein level (25, 30 and 35%) on growth performance, survival rate, feed utilization, blood components, chemical body composition and profit of Nile tilapia fish (Oreochromis niloticus with initial weight 2 g). The experimental period lasted 16 week after start during the period from June to September 2013.
The obtained results could be summarized as follows: 1- Live body weight (LBW), daily weight gain (DWG), and relative growth rate (RGR) (SGR) of fish was significantly (P<0.01) decreased with increasing fish stocking density during the different experimental period. LBW, DWG and RGR of fish significantly (P<0.01) increased with increasing protein level in fish diets at the most of experimental periods. Interaction of fish stocking density and dietary protein level insignificantly affected LBW, DWG and RGR during all of the experimental periods. 2- Daily feed intake (FI) significantly (P<0.01or 0.05) decreased and feed conversion (FC) impaired with increasing in stocking density. Daily FI significantly (P<0.01) increased and FC significantly (P<0.01 or 0.05) improved with increasing dietary protein level at the most of experimental periods. Daily FI and FC insignificantly affected with the interaction between fish stocking density and dietary protein level at the all of the experimental periods. 3- Alanine transferase (ALT) concentration significantly (P<0.01) affected with stocking density, while total protein, albumin, globulin aspartate amino transferase (AST), urea and creatinine insignificantly affected. Serum total protein and albumin significantly (P<0.01 or 0.05,) affected with dietary protein level. On the other hand serum globulin, AST, ALT, urea and creatinine insignificantly affected with dietary protein level. Most of blood parameters studied insignificantly affected with the interaction between fish stocking density and dietary protein level. 4- Dry matter significantly (P<0.01) increased in fish group stocked at the high density than those reared at the low density, while ether extract and ash slightly decreased. Analysis of body composition of Nile tilapia insignificantly affected with dietary protein level. Analysis of body composition of Nile tilapia insignificantly affected with interaction between fish density and dietary protein level. 5- Survival rate significantly (P<0.05) decreased with increasing fish stocking density during the whole experimental period (0-16 weeks). Survival rate insignificantly affected with dietary protein level and the interaction between fish stocking density and dietary protein level. 6- Fish group stocked with high density recorded lower return from body gain and final profit margin by 33.80 and 55.81%, respectively, when compared with the normal density. Fish group which fed on a diet contained 30 and 35% protein recorded lower final profit margin by 4.95 and 24.75%, respectively, when compared with fish group fed on 25% protein. The best final profit margin recorded in fish group stocked at low density and fed on diet with low protein level.