الفهرس 
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Abstract
The present study was designed in the Department of Animal Production, Faculty of Agriculture, Zagazig University, Zagazig, Egypt. The experimental work was carried out at Fish Research Center, Faculty of Veterinary Medicine, Zagazig University, Zagazig, Egypt, during the years 2005-2007. This work involved two experiments. In the first experiment, Nile tilapia (Oreochromis niloticus) fingerlings fed eight experimental diets, the first four diets (T1 W, T2 W, T3 W and T4 W) included 0 (the basal diet), 25, 50 and 100 % barley in place of dietary yellow, the other four diets (T1 E, T2 E, T3 E and T4 E) were the same previous diets with Roxazyme addition (150mg/Kg diet). Results indicated that DM and NFE digestibility of T1 E were higher (P<0.05), while feed and protein utilization of T2 E were better (P<0.05) than those of the other diets. Growth in T1 E and T2 E did not significantly differ. Economically, T2 E recorded the best feed cost per gain. In the second experiment, Nile tilapia fed eight tested diets, the first four diets [D1× Phytase (Ph), D2×Ph, D3×Ph and D4×Ph] included 0% (control), 25% bakery by-product (BBP), 25% mill by-product (MBP) and 25% cassava roots meal (CRM) in place of dietary yellow with Ph addition (500mg/Kg diet), the other four diets [D1×Avizyme TX (Av), D2×Av, D3×Av and D4×Av] were the same previous diets, but with Av addition (500mg/Kg diet). Results showed that digestibilities of CP and NFE, growth, FCR and protein utilization were improved (P<0.05) with D3×Av compared with those of other fish groups. In short, 25% of the dietary yellow corn could substitute by mill by-product with Av addition and resulted in best growth performance, feed utilization, economical feed efficiency and health of Nile tilapia.