Ethiopia lost 10,000 tons of fish per annum among 28,000 tons of production. This research aims to identify the major factors that affect the overall fish losses at Finchawa and Amerti reservoirs during harvest. The research was conducted by adopting Informal Fish Loss Assessment Method (IFLAM), Load Tracking (LT) and the Questionnaire Loss Assessment Method (QLAM). The study was conducted between August 2011 and July 2012. The result indicated that from the total annual 98, 784 kg tilapia catch the post-harvest loss constitutes 6,816 kg (6.9 %) of which 2,076 kg of tilapia due to size discrimination, 1,323 kg due to operational loss, 648 kg due to market access and 2,497 kg due to spoilage was discarded. The total carp species catch were 31,317 kg. Among the total carp species catch, the post-harvest loss constitutes 3,539 kg(11.3%), of which 560 kg of carp species due to size discrimination, 2,143 kg due to species preference and 447 kg due to spoilage was discarded. The determinant factors for fish post-harvest losses include less market access, size and species preference, inadequate infrastructure for fish handling, processing, storage and transportation and distance from the central market. In tropic climates fish will become unfit for human consumption within 12 hr of capture unless it is subjected to some forms of cold preservation or further processing; Unfortunately, it was not applicable for it is expensive and no electric at fishing area, thus, from this paper it is possible to conclude that fish post-harvest technology such as, drying, retaining cage, smoking, fish meal and fertilizer, processing table, solar ice making are very important in reducing loss. Therefore, it is very important to further adopt, verify, popularize and disseminate these technologies for end users to secure food and nutrition.