الفهرس 
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Abstract
Due to the increasing demand for environment friendly aquaculture, the use of probiotics in aquaculture is now widely accepted. The commercial probiotics used in our study is EM.1® which contains a mixture of about 80 species of beneficial naturally occurring microorganisms which can improve the water quality and establishing an optimal condition for the culture of Nile tilapia (O. niloticus) fingerlings as affected by stocking density.
The present study included two experiments; one was carried out to evaluate the effect of probiotic on improving water quality, survival rate, growth performance and body composition of Nile tilapia (Oreochromis niloticus) reared in experimental condition within seven treatments (control, 50 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm and 500 ppm). The water analysis indicated that adding EM.1® with 200 ppm in rearing water was significantly increased DO and NO3. Whilst, decreased BOD; NH4+; NH3 and NO2. The water parameters were improved non significantly with the increase of EM.1® concentration till 500 ppm. The maximum SR; WG%; ADG; SGR. Moreover, the best FCR; PER were for 200 ppm of EM.1®. The best protein and lipid content and the less ash content were also for 200 ppm of EM.1®. The present study recommends the use of EM.1® in rearing water with 200 ppm to improve water quality reducing the water exchange in fish farms and enhancing productivity.
The second experiment designed to establishing an optimal method under a certain condition for the culture of Nile tilapia by comparing the growth pattern of O. niloticus fingerlings as affected by stocking density and investigated water quality, survival rate, body composition, some histopathological aspects and hematological parameters under different concentrations of probiotic EM within twenty four treatments. The water parameters, the survival rate, body composition, hematological parameters and the histopathology of both liver and gills were improved with the increase of EM.1® concentration in spite of increasing stocking density from SD of 20 fish/m3 to 60 fish/m3 and started to decrease as the stocking density increase from SD of 70 to SD of 90 fish/m3 at all EM.1® concentrations. from the results obtained the best SD with the best concentration was 60 fish/m3 at 300 ppm.
The present study indicated the importance of using probiotics EM.1® in the fish culture due to its positive effect on improving the water quality and growth performance. The study recommends widely use in fish farming.