الفهرس 
Cover Page Title in EnglishOnly 14 pages are availabe for public view
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Abstract
Biofloc technology offers beneficial effects on the production and environmental performances of the intensive aquaculture system. Compared to other aquaculture systems, the biofloc system provides a more economical alternative in land and water usage, relatively straightforward, simple and robust technology, and additional microbial protein source. The potential of this system in increasing land, water, and nutrient utilization efficiency has drawn more attention for research and application during the past decade. The general objective of this study was to explore the contribution of biofloc technology application to aquaculture productivity enhancement while maintaining sustainable practices. Meanwhile, the precise objective of this study was to investigate the application of Biofloc technology (BFT) using different carbon sources and its suitability for Nile tilapia O. niloticus maintained under different stocking density. Generally, the application of BFT (zero-exchange water) for tilapia intensive culture appears to be a suitable alternative to the conventional intensive culture system as deduced from the growth measurements, water quality and the health status of the investigated fish groups. The glycerol-based BFT significantly increased the final BW, TBWG, TADG and TSGR of juveniles tilapia maintained in LSD followed by those grown in the molasses-based BFT in both LSD and HSD (Fig. 6, 7, 8 and 9). On the other hand, and irrespective of the BFT treatment, the NFY, and the GFY were significantly higher in the HSD maintained fish at than that of the LSD group. Meanwhile, the highest (P<0.05) NFY and GFY were recorded for the HSD-molasses based BFT (8.76 and 10.23 kg m-3). Proximal analysis of biofloc generally showed high nutritive value with respect to CP percentage, and lipid % with the highest values observed in the LSD glycerol-based BFT treatment (CP % 36.6, Lipid % 12.35). This nutritive value together with the stability of both the floc volume along this study are supportive to the growth performance and feed utilization measures recorded in this experiment. Additionally, the use of BFT efficiently stabilized the water quality despite the zero-exchange water pattern. Regardless of stocking density, the addition of different carbon sources in the rearing system efficiently reduced the un-ionized ammonia and nitrite level than control groups. The water of the control tanks (conventional intensive system) presented the highest overall means ammonia and nitrite (LSD tanks; 0.23and HSD tanks; 0.25mg l-1) and (LSD tanks; 4.92 and HSD tanks 5.74 mg l-1). Moreover, DO levels were significantly lower in control fish groups than biofloc treatments all over the experiment. DO level was significantly higher in glycerol-based biofloc reared at LSD (7.41 mg l-1) than other fish group. Overall, this study demonstrated that the application of biofloc technology may contribute to the robustness of cultured tilapia by immunostimulation and that this effect is independent of the type of carbon source used to grow the flocs. The application of biofloc technology had certainly improved the non-specific immune response of Nile tilapia O.niloticus. The BFT application improved the hematological parameters in terms of RBCs count, HB %, PCV % and monocyte % with the highest PCV value (46.4 %) recorded for the LSD Glycerol-based BFT. Whereas significantly higher serum total protein (5.73 g dl-1), albumin (1.79 g dl-1) and globulin (3.94 g dl-1) were detected in the HSD starch-based BFT treatment. Meanwhile, the lowest glucose and cortisol levels were presented in the biofloc based group regardless of the stocking density indicating the stress-relieving effect of the BFT even at high culture density. On the other hand, control fish group maintained at high stocking density showed a significantly higher lysosomal activity (773.2 unit ml-1). Additionally, the BFT application had reduced the oxidative stress; the serum antioxidant enzymes levels were significantly improved in the LSD glycerol-based biofloc group [Superoxide dismutase (62.4 UL-1), Glutathione reductase (43.4 UL-1) and Catalase (44.6 UL-1)]. On the basis of these results, it would be concluded that: BFT offers aquaculture a sustainable tool to simultaneously address its environmental, social and economic issues concurrent with its growth. Microbial flocs developing in bio-flocs technology (BFT) are a potential food source for tilapia. Indeed, the BFT can be considered as a self-sustaining biotechnology machine as it maintains water quality in situ and manufactured food concurrently thereby becoming the neglected asset in the aquaculture industry. As the cost of fish feed continues to rise, BFT could be the solution. It is because of the stress-free environment created by the bioflocs that enhance the quick growth rate of disease-free fish in BFT aided aquaculture systems. Nevertheless, further investigations should be focused on some aspects of the BFT such as management of the biofloc production and the health effects of bioflocs on cultured animals. The biofloc technology is not yet fully predictable and can, therefore, be risky to implement at farm level in developing countries. It is not easy to convince farmers to implement the technique since the concept of biofloc technology goes in against common wisdom that water in the pond has to be clear. The release of polluted effluents from bioflocs also pause challenges as environmentalists are keen to prevent such happenings. Some microbial community in the bioflocs may turn to cause diseases to the cultured fish. The most challenging issue is the experience and technical knowledge regarding management of biofloc technology and the economic benefits that go with it. In this respect, BFT is certainly the bright idea for farmers in developing countries because less water is used. However, the government, GAFRD, and researchers should join hands to improve livelihood in such countries through BFT initiatives.