Ecological studies on fish farms of el-fayoum depression (egypt)
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This study was carried out at the fish farms of El-Fayioum province during 2003 farming season. They extend along the eastern bank of Lake Qarun. These farms derive its water and drainage wastes into Diar El-Berka Drain. pH values at the chosen farms ranged between 7.43 and 8.91 and its values are certainly optimum for fish culture. Salinity levels at fish farms adjacent to Lake Qarun (Goda 2, 9.5‰) are generally much higher than the other fishing ponds due to seepage from the lake water. The major nutrient concentrations (N & P) at the main feeder were much higher than the corresponding values at fish farms. Nitrogen concentrations that represented by NO2-N, NO3-N and NH4-N indicated the dominance of NH4-N over NO2-N and NO3-N at the selected fish farms (0.026, 0.091 & 0.59 mg/L respectively). Total organic phosphorus (TOP) concentrations at the chosen farms were much higher than the corresponding values of orthophosphate. The abundance of phytoplankton reached the climax during January and March (8746, 6937 x 104cell/L respectively), but showed a severe drop during September and October (59, 38 x 104cell/L respectively) at all farms under investigation. Oreochromis niloticus prefers diet on Navicula spp. and Cyclotella spp. from diatoms; Prorocentrum apora from dinoflagellates; Euglena spp. and Phacus caudatus from euglenoids and few species of green and blue green algae. So it should decreases supplementary foods at these farms during the abundance of phytoplankton items in spring and summer seasons. Fish production of these farms depends on intensive aquaculture in which the fishes are fed with external food supply. This kind of aquaculture can be changed to extensive production during spring and summer seasons.