This study was designed to determine the maximum replacing levels of Fish Meal protein (FM) by a mixture of oil seeds mealprotein (OSM) in five ration for Nile tilapia and Grey mullet. The OSM consisted of cottonseed, sunflower, canola and linseed meals. FM in the basal diet was replaced by OSM in the ration at replacing levels of (control) 0, 25, 50, 75 and 100%. A total number of 60 fingerlings; 40 of Oreochromis niloticus monosex and 20Mugil cephalus per hapa (3*8*1 m-2.5/m 3 ) were randomly distributed into five treatments, each in two replicates. After 6 months of feeding, replacement of 50% of FM by OSM for Nile tilapia and 25% for grey mullet did not significantly affected Feed Conversion Ratio (FCR) and Protein Efficiency Ratio (PER), Crude Protein (CP) and Ether Extract (EE), while the highest replacing levels (75 or 100%) significantly (P<0.05) reduced these parameters. Growth parameters were relatively parallel to those of FCR and PER whereas, replacement up to 50% exhibited Body Weight (BW), Body Length (BL), Weight Gain (WG) and Specific Growth Rate (SGR) not differing significantly (P<0.05) from the fish fed control diet. Compared to control, increasing OSM in the ration significantly reduced Hemoglobin, Hematocrit and the activity of Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST). The incorporation of OSM in ration did not significantly affect whole-body Dry Matter (DM) and Crude Protein (CP).Based on results obtained in this study and on the economical evaluation, it could be concluded that, replacement of FM by OSM up to 50% in tilapia ration but 25% in mullet ration reduced feed costs/kg diet.

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The field study was done to study the effect of both water and soil quality on cultured Oreochromis niloticus (Nile tilapia) in the farms near Northern Delta Lakes. Six earthen ponds (about one Faddan each) were used in this experiment in three different locations; around Edco, Borollus and Manzala lakes. Three treatment-locations were tested in double replicates (2 ponds/lake); so six ponds were stocked with mono-sex males of tilapia (12000 fingerlings/pond with average initial bodyweight of 37±1 g). Growth performance, assessment of heavy metals residues, clinical, postmortem and laboratory examinations were done. The differences in the final weights (harvest) were significant and the lowest body weight came from farms around Lake Manzala and samples of water and soils suffered more from heavy metals pollution and parasitic diseases than fish from farms around Lake Edco and Lake Borollus. Regarding the clinical, postmortem and laboratory examinations; fish suffered from hepatitis, enlargement of the gallbladder, infested with metacercaria of Digenia and larval nematodes in all farms. From this study, overcoming pollution should be done seriously for producing fish fit for human consumption. The result from the study gave important information on the levels of the heavy metals in water and fish tissue .The concentrations of heavy metals in the water and fish tissue were under the permissible limits in Edko and Borollus lakes while in Lake Manzala the concentrations of heavy metals in the water and fish tissue were above the permissible limits. It is recommended that more attention must give to fish resources by the government to continuously reduce to the minimum level of lakes' pollution.