Abstract

Fingerlings of hybrid tilapia (Oreochromis niloticus x Oreochromis aureus) were cultured in 18 glass aquaria (75 x 40 x 60 cm). Two species of phytoplankton (Chlorella vulgaris & Scenedesmus spp) were used. The experiment included six treatments; each in three replicate aquaria. The 1st treatment (Urea) was fertilization by urea at the rate of 435 mg commercial urea / aquarium. The 2nd treatment (Urea+phy.) was the same rate of urea plus the addition of phytoplankton at a rate of 5X104 cells/ml of water. The 3rd treatment (MSP) was fertilization by mono superphosphate (MSP) at a rate of 830 mg commercial MSP / aquarium. The 4th treatment (MSP+phy.) was the same rate of MSP plus the addition of phytoplankton at a rate of 5X104 cells/ml. The 5th treatment (Urea+MSP) was fertilization with urea and MSP mixture at the rates mentioned above for each fertilizer. The 6th treatment was the Control; without any fertilization or phytoplankton application. Phytoplankton played an important role in removing ammonia and nitrite from the water milieu. The average of individual fish body weight (ABW) at the end of the experiment was (29.37 ± 0.60 g) in the Urea+phy. treatment which was significantly (P