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Abstract
The present work was conducted to study the effect of weekly application of similar amounts of nitrogen and phosphorus from different sources of fertilizers on the growth performance, body composition of O. niloticus, as well as, phytoplankton abundance, productivity and physico-chemical properties of water.
Five earthen ponds of a size of one fed / each were cultured with O. niloticus at a rate of 2.5 fish m-2, fingerlings obtained from the same hatchery of the farm.
The experiment continued for 98 days, starting from 22 August 2007. During the experimental period, all fish groups were fed on 25.5 % CP diet at a rate of 2 % of fish biomass for all fish groups daily. Group 1 used as a control which received no fertilizers. While, treatment 2 received 100 % organic fertilizers, treatment 3 received 75% organic fertilizers plus 25 % inorganic fertilizers, treatment 4 received 25% organic fertilizers plus 75 % inorganic fertilizers and treatment 5 received 100 % inorganic fertilizers.
The results obtained can be summarized as follow:
1- T3 had the highest average final body weight (114.77 g) followed by those of T2 (106.80 g), T4 (100.64 g), T5 (93.16 g) and finally the control treatment (85.71 g).
2- Tilapia of T3 had the highest average daily gain (0.75 g) followed by those of T2 (0.67 g), T4 (0.61 g), T5 (0.53 g) and finally the control treatment (0.45 g).
3- Fish of T3 had the highest average specific growth rate (1.04 % day-1) followed by those of T2 (0.97% day-1), T4 (0.91 % day-1), T5 (0.83 % day-1) and finally the control treatment (0.75 % day-1).
4- The best average feed conversion ratio (1.98) was recorded with fish of T3 followed by those of T2 (2.14), T4 (2.23), T5 (2.37) and the control treatment (2.66).
5- Fish of T3 recorded the highest average final total fish yield (1072.5 kg fed-1) followed by those of T4 (1009.2 kg fed-1), T2 (919.3 kg fed-1), T5 (818.3 kg fed-1) and those of the control treatment (773.9 kg fed-1).
6- Net fish yield was the highest in pond’s of T3 (6.52 kg fed-1 day-1) followed by those of T2 (5.53 kg fed-1 day-1), T4 (5.28 kg fed-1 day-1), T5 (3.93 kg fed-1 day-1) and those of the control treatment (3.47 kg fed-1 day-1).
7- The protein, lipid, ash and carbohydrates content of O. niloticus fish on fresh basis at the end of the experiment were nearly similar and they were high as compared to initial.
8- Average physico-chemical properties of all fish groups throughout the experimental periods was similar in all fish treatments except for total ammonia – nitrogen of T 5 was higher than other treatments.