الفهرس 
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Abstract
The objectives of the present study were to evaluate effects of graded levels of a new commercial probiotic Hydroyeast Aquaculture® on both sexes of adult Nile tilapia Oreochromis niloticus, of 0, 5, 10 and 15 g/Kg diet, referred to treatments No. T1, T2, T3 and T4, respectively, for males and T5, T6, T7 and T8 treatments for females, concerning their growth performance, feed utilization, carcass composition, blood hematological measurements and serum biochemical parameters, serum sex hormones, morphological, anatomical and histological characteristics of the gonads for 8 weeks.The obtained results showed that tested probiotic Hydroyeast Aquaculture® at level 15 g /kg diet (T4) and 10 g /kg diet (T7) for adult males and females Nile tilapia O. niloticus respectively, enhancing fish growth, feed and nutrients utilization, physiological responses, fish reproduction performance, besides histological development of fish gonads (ovaries and testes).So, it could be concluded that this probiotic under study is useful for tested probiotic Hydroyeast Aquaculture® is useful at levels 15 g /kg diet (T4) and 10 g /kg diet (T7) for adult males and females Nile tilapia Oreochromis niloticus respectively, so may be using of this experimental probiotic is useful also from the economic point of view especially, for fish hatcheries.
Yet, it is to recommend also more research works on this new Hydroyeast Aquaculture® probiotic are needed on Nile tilapia Oreochromis niloticus brood stock and other brood stock species to improve their reproductive performance on the commercial and applied scales. Also, more studies could be carrying out on this probiotic under various conditions, e.g. initial weight, stocking rates, feeding rates, dietary protein levels and sources, etc.