الفهرس 
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Abstract
The present investigation was carried out for the evaluation of effects of fat source and levels in isocaloric-isonitrogenous diets on growth performance data, physiological response, body composition and healthiness of the internal organs and muscles of the Nile tilapia fingerlings. The experiment was conducted to determine the optimum fat level in Tilapia nilotica diet isocaloric (3000 Kcal DE/Kg), isonitrogenous (32% CP) diets containing 2 sources (fish oil and soybean oil) and three different levels of dietary lipid (4, 8, 10 & 12%). Nile tilapia fingerlings (224 in number and of 14.23+0.91g body weight) were divided into 7 equal groups and reared in 14 glass aquaria ( 2 replicates for each group) were used in this feeding experiment. Daily feed allowance was calculated according to the biweekly body weight as 3% of mean body weight of each group). The experiment was extended for 12 weeks. Fish was weighed once every two weeks. Growth performance (body gain, feed consumption, feed conversion (FCR) & protein utilization (PER) were measured. At end of the experiment, 5 fish were obtained from each group for proximate chemical analysis of whole body. Also, blood samples were collected from 5 fish from each group for serum preparation for determination of total protein, albumin, total lipids, triglycerids total cholesterol. Low density lipoprotein (LDL), very low density lipoprotein (VLDL) and high density lipoproteins (HDL) were also determined. For histopathological examination, 3 fish were taken from each group as random samples for microscopic examination. The results revealed that feeding the diets Supplemented with SBO to contain 8% total lipid did not increase body weight (BWt), body weight gain (BWG) or feed conversion ratio (FCR) compared to the control groups. Increasing the supplemented SBO to raise the total dietary lipid to 10 and 12% significantly (p<0.05) increase BW, BWG, FCR, and protein efficiency ratio (PER). Feeding the Nile tilapia fingerlings diets supplemented with FO to contain 8, 10 and 12% total dietary lipid significantly (p<0.05) increased BW, BWG, FCR, and PER. On comparing the allover effects of SBO or FO supplementation on growth performance, fish groups supplemented with FO had significantly higher BW (44.36 Vs 41.44 g), better FCR (1.46 Vs 1.66) and PER than the fish groups fed the SBO supplemented diets. Feeding the oil supplemented diets increased the level of fat in the whole body of fish. Increasing the dietary lipid levels increased (p<0.05) level of fat in the whole body of fish. Supplementing the fish diets with SBO or FO significantly (p<0.05) increased the serum levels of the total lipids and total cholesterol. Also, serum level of HDL increased as well. In the fish groups fed the oil supplemented diets to contain 12% total lipids, there were some pathological changes in the liver and heart. Therefore, the present results indicated that oil (SBO and FO) supplementation of Nile tilapia fingerlings diet significantly improve body weight gain, feed conversion ratio and protein utilization. However, increasing the dietary lipid level than 10% resulted in pathological changes in liver, and heart and hurt the health condition and flesh quality. Furthermore, fish oil is more profitable than soybean oil in maximizing growth performance.