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he present investigation was carried out at Wady El Raian, Fayoum Governorate, Egypt in order to test the effects of initial weight and stocking density on growth performance and pond productivity of Nile tilapia (Oreochromis niloticus) in semi intensive system. The experiment was carried out in 12 earthen ponds each of a total area of one feddan (4200 m 2 ) to represent six treatment groups in replicates each. The first; second and third two ponds (T1; T2 and T3) were stocked with Nile tilapia fingerlings of an average initial weight of 9.6 g and stocking density 30; 40 and 50 thousands respectively. The second; fourth and sixth tow ponds (T4; T5 and T6) were stocked with Nile tilapia fries of 0.3g and stocking density 30; 40 and 50 thousands respectively. The fish were fed three times daily on a commercial diet containing 27% protein at a rate of 3% of fish biomass. The experiment lasted for 26 weeks from the start. Results obtained are summarized in the following: 1- Water quality (physical and chemical) lied within the permissible levels required for optimum growth and development of Nile tilapia. 2- The highest final weight was obtained by T4; T1; T2; followed in a significant decreasing order by T5; T4 and T6 respectively. 3- Averages of gain in weight; daily gain; specific growth rate and condition factor were influenced significantly with tilapia initial weight and stocking density. 4- Total fish production/feddan was the highest for 50 thousand fingerlings/feddan, stocking density followed by 40 and 30 thousand fingerlings/feddan. 5- The highest net returns were by the 30 thousand fingerlings/feddan stocking density (T1) and 40 thousand fingerlings/feddan stocking density (T2) due to the high contribution of super size and grade 1 fish in the harvest, compared to other densities and initial weights.

Effect of initial weight and stocking density on growth performance of mono sex nile tilapia reared in semi intensive system