The present study was performed in earthen ponds with a total area of 1.25 feddan each and water column of 1.25 meter. The objectives of this study were to evaluate the effect of source of fertilizers (organic and inorganic) on growth performance, feed and nitrogen utilization, whole body composition, water quality, plankton abundance, costs and net returns of Nile tilapia monosex reared in earthen ponds. The first pond (T1) received chicken manure at a rate of 87.5 kg weekly with artificial feeding (25% protein), the second pond (T1) received artificial feed as in T1 plus chemical fertilization (5 kg/pond urea 46.5 N + triple super phosphate 10 kg/pond weekly). The third treatment (T3) received only artificial feed without any fertilization. The artificial feed was offered at a rate of 3% of pond biomass in two portions at 9.00 am and 3.00 pm daily. The experimental ponds were stocked with 15000 monosex Nile tilapia (Oreochromis niloticus) with initial weight ranging between 19.73 and 20.83g and length between 5.5 to 6.0 cm. the experiment lasted 14 weeks after start from August to December 2012. Results obtained are summarized in the following:
1) Water quality parameters tested (water temperature 0C; dissolved oxygen (mg/l); pH value; total ammonia (mg/l); nitrate mg/l; nitrite mg/l and salinity g/l were within the accepTable levels for optimum growth of Nile tilapia.
2) Final weight and length, weight gain, length gain, daily weight gain, specific growth rate and relative growth rate of T1(feed + organic fertilizers) recorded significantly (p˂0.05) the highest values followed in a significant decreasing order by T2 (feed + inorganic fertilizers) and T3 (feed only), respectively.
3) The best FCR was recorded by T1 followed by T3 and T2, respectively.
4) The applied treatments revealed significant (p˂0.05) effects on the whole body chemical composition.
5) Average of nitrogen utilization (nitrogen gained in fish bodies/ total nitrogen input × 100) were 35.72; 31.74 and 39.83% for T1; T2 and T3, respectively.
6) The T1 recorded the highest fish production followed in a decreasing order by T2 and T3, respectively.
7) T1 recorded the highest net returns (15613.24 LE) followed in a decreasing order by T2 (8560.07) and T3 (8094.34 LE).