Mass fish mortalities have become increasingly prevalent on Lake Victoria, especially in the past five years, even affecting well-sited fish cages and resulting in significant losses (Fig 2). This phenomenon, often attributed to periodic water quality deterioration caused by natural seasonal mixing events, is not new and has been observed by indigenous fishermen on some lakes for generations. In Uganda, it is known as "Kaliro," meaning "small fire," likely due to the half-burnt appearance of the dead fish, which are rancid, with milky eyes and dull whitish skin. This case report examines the intrinsic and extrinsic factors contributing to mass fish mortalities and the water quality dynamics of shallow tropical freshwater lakes (Fig. 1).
Given the recurrent nature of this natural calamity and its impact on aquaculture in Lake Victoria, we propose strategic measures to mitigate its effects. These include strategic fish cage siting involving proper zoning and spatial planning, enforcement of appropriate cage culture management practices (fallowing, daily site-based water quality measurement), development of stakeholder and citizen scientist networks, IoT and AI early warning systems, effective legislation, and advocating for sustainable aquaculture practices such as Integrated Multi-trophic Aquaculture (IMTA). Addressing these challenges requires a comprehensive, transboundary approach to ensure the sustainable development of aquaculture in Lake Victoria.