Assessing the Economic Returns and Environmental Sustainability of Cage Fish Culture in Kainji Reservoir

This study assessed the economic returns and environmental sustainability of cage fish culture operations in the Kainji Reservoir, Niger State, Nigeria, as the technology has been promoted by government and development agencies as a productive use of reservoir water surface area. Cage culture in inland reservoirs offers the potential for high-density fish production without land acquisition, but concerns about water quality impacts, disease risk, and economic viability under Nigerian conditions have not been rigorously evaluated. Twelve commercial cage units operated by six farmers were monitored over two complete production cycles of tilapia (Oreochromis niloticus) and catfish (Clarias gariepinus). Economic data including capital investment, operational costs, production output, and market revenue were analysed using partial budget analysis. Environmental indicators including dissolved oxygen, ammonia, phosphorus, and chlorophyll-a were measured monthly in cage zones and at control stations. Results showed positive financial returns for all operators, with average return on capital investment of 28 percent per cycle for tilapia and 34 percent for catfish. Ammonia and phosphorus concentrations were significantly elevated in cage zones relative to control stations, with nutrient loading correlated with cage density and feeding intensity. Dissolved oxygen declined to suboptimal levels within cage zones during early morning hours at three sites, occasionally causing fish stress. Recommendations include the introduction of cage stocking density guidelines, nutrient loading carrying capacity estimates for Kainji Reservoir, mandatory environmental monitoring for licensed cage operators, and the formalisation of a cage aquaculture regulatory framework by the federal dam authority. Keywords: cage culture, Kainji Reservoir, economic returns, environmental sustainability, inland aquaculture