A series of three experiments were conducted in plastic troughs and lined ponds using GIFT Tilapia juveniles. Azolla meal (0, 15, 30 & 45%) and S. platensis (0, 1, 3 & 5%) inclusion level diets were prepared to replace fish meal. GIFT Tilapia juveniles (3.3 ± 0.32g) were stocked at a density of 10 fish per plastic troughs (70L) in triplicates for 60 days.In all experiments the fish were fed isonitrogenous (32%) and isocaloric (17 KJ Kg-1 DM) diets at 5% body weight throughout the experimental trials. In each experiment, all fishes in the experimental units were weighed after every fifteen days to ascertain the increase in biomass. The results in first experiment indicated that, growth performance, apparent digestibility coefficient, digestive enzymes activity and the final body proximate composition of GIFT Tilapia were higher in 15% inclusion diet. Antioxidant enzymes activity (catalase, SDO and GPx) and metabolic enzymes activity (AST and ALT) did not significantly differ between the dietary treatments. Blood serum biochemistry (serum protein, albumin and globulin), immunological indices (RBT, lysozymes and MPO) and muscle quality index were significantly higher in 15% inclusion diet. The histological changes in liver sections were not affected by dietary treatments, however the intestinal tissues showed a higher intestinal villi length and muscular layer thickness in 15% inclusion diet than the other groups. At this inclusion level, stress parameters (RBT, MPO) and survival rate were significantly higher than the control diet, while glucose content was significant low xii when GIFT tilapia were challenged with A. hydrophila. Thus, the use of Azolla as a fish feed ingredient has been attempted for the first time in GIFT tilapia strain and the study results recommends 15% inclusion level in diets. In the second experiment, the results revealed that, growth performance, digestibility and final body proximate composition, were significantly improved in 3% Spirulina inclusion diet compared to the rest. At this level of inclusion, fish digestive enzymes (amylase, protease and lipase), antioxidant enzymes activity, blood serum biochemistry and immunological indices, as well as muscles quality index were significantly higher, however metabolic enzyme activities were not influenced by dietary treatments. The liver histology was not affected by dietary treatments, however the intestinal tissues showed a higher intestinal villi length and muscular layer thickness than the other groups. Following the A. hydrophila challenge test, fish stress parameters such as RBT and MPO were significantly higher in 3% Spirulina inclusion diet compared to other treatments, however glucose content was significantly low. It can be concluded that, S. platensis meal can be supplemented up to 3% without compromising the overall performance of GIFT tilapia. Based on the results of these two experiments which showed better performance of fish at 15% Azolla and 3% S. platensis inclusion levels respectively, the third experimental trial was conducted by testing a dietary mixture of these two ingredients with commercial diet. A total of 1500 fingerlings (Initial body weight 5.5 ± 0.04g) were randomly stocked in 100 m2 lined ponds in duplicates and reared for 90 days. The fish were fed with isonitrogenous (32%) and isocaloric (17 KJ Kg-1 DM) diets at 5% body weight throughout the experimental trial. The results showed that, water quality parameters (temperature, DO, ammonia and nitrite) were not affected by dietary treatments, however pH, alkalinity, hardness and nitrate were significantly higher in test diet used culture system. The growth performance, final body proximate composition and fish digestive enzymes (amylase, protease and lipase) were higher in test diet compared to the control. In this diet, antioxidant enzymes activity, blood serum biochemistry and immunological indices, as well as muscles quality index were significantly higher than the control, however metabolic enzyme activity (AST and ALT) were not influenced by either supplemented diets or control. The liver histology didn’t show any changes, however the intestinal villi length and muscular layer thickness were significantly higher in test diet. The Yield, Gross returns, Net returns, Cost Benefit Ratio and Return on Investment (ROI) were higher in test diet compared to the control. Therefore, this study concluded that, partial replacement of fish meal with a mixture of Azolla (15%) and S. platensis (3%) meal in feeds meant for semi-intensive system of GIFT tilapia culture is more profitable.