T his study was conducted jointly at the Central Laboratory for Aquaculture Research (CLAR) and Faculty of Agriculture, Cairo University. The experiment included six treatments. The first treatment included the application of supplemental diet (17% CP), The second treatment included the application of complete diet (25% CP). Both diets were administrated at a rate of 3% of fish body weight per day. The third treatment included a biweekly application of nitrate and triple super phosphate(ammonium nitrate 33% N and TSP 37% P205) at high dose at a rate of 10.61 and 4.72 kg/pond, respectively. The fourth treatment included a biweekly application at a medium dose at a rate of 53 and 2.36 kg/pond. The fifth treatment included a biweekly application at a low dose at rate of 2.65 and 1.18 kg/pond. The sixth treatment was considered as a control treatment with no addition of nutritional or fertilizer inputs.Water temperature in the experimental ponds was below the thermal requirements offish for optimal growth during winter season and of medium magnitude during fall and spring and close to the optimal thermal range for growth during summer season.Water in experimental ponds was characterized by high alkalinity (263.11 -490.0 mg/1), high hardness (180.79 -339.16 mg/1) and high pH values (8.58-9.8) among treatments during the course of the experiment. 296Mohamed A. El-Nady et al\ Dissolved oxygen under the experiment was within the optimal level for growth of cultivated fishes. The overall average of total ammonia concentration in pond water during the experimental period indicated that high dietary protein treatment had an over abundance of ammonia (1.32 mg/1) followed by the high (0.78 mg/l),medium(0.52 mg/J) and low (0.40 mg/1) fertilizer treatments, respectively. The shallow Secchi disk readings during summer season in the high dietary protein treatment was due to the effect of overabundance of ammonia in water on algae growth enhancement rather than nitrate effect.Nitrate (N03-N) content in water increased from 0.14, 0.26 and 0.24 mg/1 during fall at the start of the experiment to 0.23, 0.13 and 0.37 mg/1 during summer season at the end of the experiment for the control, the low dietary protein and the high dietary protein treatments, respectively. Nitrate contents in water in the low, medium and high fertilizer treatments were 0.65, 0,86 and 1.44 mg/1 in summer at the end of the experiment.Chemically fertilized ponds had higher total phosphorus (P<0,05) compared to treatments fed the experimental rations and the control ponds,The results of the present study indicated a super abundance of algae in all fertilizer treatments over that of the ration and control treatments in all seasons. The control treatment had the lowest algae turbidity compared to that of the ration treatments. In contrast to tilapia and common carp, silver carp grew higher in the higher fertilizer treatment compared to the feed treatments. There was a tendency for silver carp to decrease in harvest size with the decrease in fertilizer dose.

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An experiment was conducted during 7 months to test. the effect of triploidy on growth, sexual maturation, carcass and chemical analysis of O. niloticus. Triploid O. niloticus had heavier and longer bodies than diploids from 3 to 7 months of age, and the differences were not significant only for body length. This trend was also observed for condition factor,. daily gain and specific growth rate. Feed conversion ratios were better for triploids at some studied ages. In triploid of both sexes, the values of Gonado-somatic indices (GSI) were smaller than diploids with significant differences between the two ploidy groups. But Hepato-somatic indices, (HSI) of triploid O. niloticus males were larger than that of diploid with significant differences between the two groups. However HSI of triploid females were smaller than that of diploid females but the differences were insignificant. Carcass traits of O. niloticus had the higher percentages of dressing, viscera, by-products and lower percentages of flesh as compared with that obtained from the diploid.