الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Feed is one of the most important factors affecting the intensive culture system and represents about 60% of the cost of fish production. Increasing costs and short supply of fish feed has created the need to search for an alternative. One of the best methods to reduce feed cost is through the use of feed additives. Biochar is gaining attention as a locally sourced feed additive with capacity to improve growth performance, intestinal function and water quality as well as fish health status and productivity. Therefore, the present study was performed to estimate the role of rice husk biochar (RHB) at various stocking densities on growth performance, body composition of Nile tilapia. (Oreochromis niloticus) fingerlings as well as water quality in rearing units. Rice husk (RH) feedstock was converted into biochar through slower pyrolysis at 450oC for 30 min in absence of oxygen environment in a muffle furnace, and some physicochemical parameters were determined in rice husk and rice husk biochar as follow: total yield, total surface area, total pore volume, total pore volume, moisture content, ash content, crude protein content , crude lipid content ,total elements . Also, scanning electron microscopy (SEM) was applied to examining the surface morphology of biochar and changes in surface functional groups of the biochar was examined using Fourier transform infrared (FT-IR) spectrometer. Biochar was incorporated into the feed of tilapia, Oreochromis niloticus in the ratio of 0.0,1,2 and 3% and fed to the fish grown in aquaria for 12 weeks. Three hundred and sixty of Nile tilapia fry were applied to attain the impact of dietary supplementation of rice husk biochar (RHB) at different Stocking densities on the performance of Nile tilapia (Oreochromis niloticus). Three levels of rice husk biochar (10, 20 and 30 g/kg diet)were added to the control diet (without RHB) and fed to fry of Nile tilapia which reared at three stocking densities(fish/aquarium): stocking density (10 fish), intermediate stocking density (15 fish ), and higher stocking density (20fish). The experimental fish (with an average weight 0.63g) were randomly divided into 12 experimental groups in duplicates Therefore, the experimental treatments were designed as follow: Treatment 1((0.0 RHB - lower stocking density (B1 S1)), Treatment 2((1% RHB - lower stocking density (B2 S1)), Treatment 3((2% RHB - lower stocking density (B3 S1)), Treatment 4((3% RHB - lower stocking density (B4 S1)), Treatment 5((0.0 RHB), intermediate stocking density (B1 S2)), Treatment 6((1% RHB - intermediate stocking density (B2 S2)), Treatment 7((2% RHB - intermediate stocking density (B3 S2)), Treatment 8((3% RHB - intermediate stocking density (B4 S2)), Treatment9 ((0.0 RHB – higher stocking density (B1 S3)), Treatment10 ((1% RHB – higher stocking density (B2 S3)), Treatment11 ((2% RHB – higher stocking density (B3 S3))and Treatment12 ((3% RHB – higher stocking density (B4 S3)). At the termination of the experiment. The interactive effect of the rice husk biochar (RHB) and stocking density (S) were noticed in terms total weight, body weight gain, specific growth rate, feed conversion ratio, total yield, Protein efficiency ratio and protein productive values and the improvement were recorded in fish fed on various levels of rice husk biochar and the differences were significant (P>0.05) when comparing with the control fish groups at all stocking density (S1, S2, and S3 respectively. 60 Variation in final body weights and lengths of different treatment groups were calculated and the differences were significant. The minimum average body size and total length were observed in the Treatment 9 (B1S3) which fish fed on control diet ( 0.0% RHB) and fish stocked at higher stocking density (20 fish/aquarium), and with an average total body (7.57g) and total length (6.15 cm). However, the highest value of final body weight was noticed in Treatment 4(B4S1) which fish fed on 2% RHB and stocked at lower stocking density (10 fish/aquarium). The improvement was recorded in final weight , gain and average daily gain in fish fed experimental diets in all dietary biochar inclusion treatments when compared with treatments not received dietary rice husk biochar at all stocking densities and the lowest value was recorded for Treatment 9 (B1 S3)which no dietary biochar inclusion and reared at higher stocking density .No significant differences were recorded in feed intake in experimental fish ((P>0.05). On the other hand, for a food conversion ratio, the worst value was recorded for fish in treatment 9 (B1 S3) which no dietary biochar inclusion and reared at higher stocking density. But the best value was recorded for fish in treatment 4(B4 S1) which reared at lower stocking density and fed on a diet containing 3% RHB and the differences were significant (P>0.05) Significant differences were noticed in protein efficiency ratio (P>0.05),lowest value of PER was noticed in tretment9(B1S3)which reared at highest stocking density and fed on diet not containing RHB(control 0.0%RHB) but the highest values were recorded by fish at lower stocking densities (B2S1,B3S1 and B4S1 ).