The present study was conducted at Shakshouk fish research station at Fayoum Governorate, Egypt to evaluate the effects of substitution of some vegetable oils (sunflower seed oil ,SO and cotton seed oil, CO) in juvenile Nile tilapia (Oreochromis niloticus) in growth performance, nutrient utilization and muscle fatty acids contents. Four isontrogenous and isocaloric diets (30.22±0.02% CP and 19.007±0.015 MJ kg-1diet) were formulated to represent four dietary treatments. The first treatment (control) contained 6% of fish oil (FO), the second contained 6% (SO), the third contained 6% (CO) and the fourth diet contained a mixture (MX) 6% FO, SO and CO at a ratio of 1:1:1. Each dietary treatment was performed in three replicates and the experimental lasted 120 days after start. The experimental treatments were performed in 12 fiber glass tanks of (1m3) volume each. Fish were fed diets at a rate 3% of the biomass daily divided into two equal portions. Results obtain are summarizes in the following: 1-the highest (P<0.05) growth performance parameters (finial weight, weight gain, daily gain and specific growth rate were recorded with FO and MX groups compared to other treatment groups; 2-the best nutrient utilization parameters (feed conversion ratio, protein efficiency ratio and net protein utilization) were recorded by FO and MX groups compared to other treatment groups; 3-the applied treatments showed insignificant effects on nutrients digestibility coefficient among dietary groups and ranged from 85.1-85.6, 89.6-90.2, 93.3-93.8,94.1-94.6 and 71.0-71.4% for Dry matter, Energy, CP, Fat and nitrogen free extract, respectively; 4-the applied dietary treatments had no significant effects of dry matter, crude protein and ash contents of whole fish body, however, fat contents in the whole fish body tended to increase in SO and CO and significantly between diets; 5-tilapia juvenile fed on FO diets showed the highest muscle fatty acids contents (P<0.05) of saturated, monounsaturated and polyunsaturated fatty acids compared to MX, SO and CO groups. Based on the obtained results it is to recommended the substitution of 66% fish oil (MX diet) with SO and CO oils in juvenile Nile tilapia diets without any diverse effects on growth performance, nutrients utilization and digestibility coefficient.

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