Three months feeding experiments were carried out in concrete ponds, filled with fresh water, in order to evaluate the probiotic (Biogen) potential, and assess its effect on growth and net returns of both O. niloticus in average initial
body weight 13.8±1.02 g. and body length 13.5±0.9 cm and Cyprinus carpio at mean initial body weight 15.3±0.05g and body length 13.5±0.05 cm Fish were fed basal diet that containd 30% crude protein, and Biogen® at four levels ( 0, 2,3 and 4g./kg. diet). O. niloticus and C. carprio were divided into (4) treatment groups . T1 was the control fed on basal diet without adding Biogen® , T2 , T3 and T4 fed on basal diet and Biogen® at levels 2, 3 and 4 g. /kg diet.
The results show that: (FBW), (WG), (ADG) (S.G.R) and nutrient utilization (P.P.V), protein efficiency rate (PER) values were significantly (p<0.0l), higher in the treatments receiving probiotic than those offered the
control diet in both O. niloticus and C. carprio. Concerning the influence of different dietary Biogen® levels on the chemical proximate analysis of whole carcass ash was significantly (p<0.0l) higher for fish offered the control diet,
while protein has a significant difference (p<0.0l) for fish offered basal diet contained Biogen® , than those offered the control diet, but results showed no clear trend. Differences were observed in carcass lipid and gross-energy content
with significantly (p<0.01) higher values recorded in fish offered the control diets compared to fish fed a diet containing 3. g /kg. diet Biogen®.The production and subsequent cost - benefit analysis clearly indicated that the diets containing 3.g / kg. diet recorded the highest return. In comparison between O. niloticus and C. carpio, the results showed that the former recorded the highest significant values than C. carpio in all growth parameters and the net
return. At the end of this research, results indicated that fish offered diets containing Biogen® exhibited greater growth than control. The observed improvement in fish growth, survival and net return by using probiotic bacteria
can open a new scope for intensive use in aquaculture.