A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MANAGEMENT OF NATURAL RESOURCES FOR SUSTAINABLE AGRICULTURE (MNRSA) OF SOKOINE UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA. 2016A study was conducted to evaluate housefly maggots (HFM) and earthworms (EW) as protein sources in Nile tilapia, Oreochromis niloticus diets. HFM and EWM were raised in three different culturing substrates. Cow manure, fermented maize bran and chicken manure were used to culture HFM while cow manure, rabbit manure and chicken manure were used for culturing EW. Yields of HFM and EW from chicken and cow manure respectively were significantly higher (P<0.05). Protein content of HFM and EW from cow manure was significantly higher (P<0.05) than others. HFM and EWM from cow manure substrates (with high protein contents) were then used to formulate nine isonitrogenous diets (30% crude protein) with fixed five percent of fishmeal. These diets were named as HFM0/EWM0 (0%EWM, 0%HFM), HFM25 (25%HFM), HFM30 (30%HFM), HFM35 (35%HFM), HFM40 (40%HFM), EWM25 (25%EWM), EWM30 (30%EWM), EWM35 (35%EWM) and EWM40 (40%EWM). Feeding trial was done for a period of eight weeks. Every treatment was assigned in triplicates in which 14 fingerlings with a mean weight of 2.52 ± 0.12 grams were allocated using complete randomized design. The fish were fed up to 5% of their body weights twice daily throughout the experimental period. Effect of inclusion levels of either HFM or EWM on growth, feed utilization and cost of production of the fish were determined. There was significant difference (P<0.05) in growth and feed utilization of fish. Fish fed diets at35% inclusion level of HFM and EWM had highest performance. Profits were higher in diets with inclusion level of 25 to 40% of HFM and EW. It is included that, inclusion of 35% of either HFM or EWM is the most optimum to achieve high performance of O. niloticus.