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The existing reservoirs on the River Tana (Kenya) were mainly constructed for hydropower generation, with inadequate consideration of the long-term impacts on downstream livelihoods. We investigated the impacts of the reservoirs on people's livelihoods downstream. The results showed a few positive impacts in the vicinity of the reservoirs and numerous negative impacts downstream (i.e. reduced flood-recess agriculture and floodplain pastoralism, and escalating resource-use conflicts). Inadequate stakeholders' consultation during reservoir development was also observed. We recommend a detailed basin-wide socioeconomic assessment for future reservoir developments and controlled flood release to simulate the natural flow regime, thereby restoring indigenous flood-based livelihoods while retaining sufficient reserves for power generation.

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Insects have been proposed as potential alternative animal protein sources to replace fishmeal (FM), which is expensive and has limited availability for fish feed formulation.However, studies on the effects of replacing FM with black soldier fly (Hermetia illucens) larvae (BSF-L) on growth performance of Nile tilapia (Oreochromis niloticus) fry, water quality and economic benefits are currently limited. This study determined the effects of replacing 100% FM, 75% FM, 50% FM, 25% FM and 0% FM with cheap BSF-L meal, hereafter referred to as BSF-L0, BSF-L25, BSF-L50, BSF-L75 and BSF-L100 diets, respectively for rearing all-male Nile tilapia fry produced by YY technology. The study further determined the optimum percentage of BSF-L meal for maximum growth of Nile tilapia fry. A total of 2400 visually healthy Nile tilapia fry weighing 0.001 g were randomly stocked into 20 plastic tanks (120 fry per tank, four replicates per treatment) and fed the BSF-L diets for 12 weeks. The BSF-L75 diet increased significantly specific growth rate, total weight gain, Zihler's index of fry and nitrate in the culture water but reduced feed conversion ratio of diet and total suspended solids in the culture water (p < 0.05). Feeding the Nile tilapia fry with BSF-L50 diet increased significantly hepatosomatic index (p < 0.05). The diets with BSF-L75 and BSF-L100 reduced significantly the incidence cost by 31.97% and 28.77% (p < 0.05), and increased profit index by 3.97 and 3.44%, respectively. The optimum percentage of BSF-L inclusion required for maximum growth performance of Nile tilapia fry was estimated as 81% to 84% based on polynomial analysis. Taken together, feeding Nile tilapia fry with diets containing 81% to 84% BSF-L meal improved growth performance. The BSF-L75 diet enhanced feed efficiency and had no deleterious effect on the liver and intestines. Meanwhile, it improved nitrate concentration for increased natural productivity. Incorporating 75% BSF-L meal in diets for Nile tilapia fry reduced 30% of feed cost leading to 4% higher economic returns.