Economic Impact of Disease Outbreaks on Cage Fish Farming in Tanzania's Lake Victoria Basin

ABSTRACT Cage aquaculture in Lake Victoria has expanded rapidly, yet disease outbreaks remain a major constraint to productivity and farmer livelihoods. This study assesses the economic impact of bacterial disease outbreaks on cage fish farms in Tanzania's Lake Victoria Basin, focusing on Mwanza, Simiyu and Mara regions. Using a multi‐stage cluster sampling method, 84 cage fish farmers were surveyed across six districts. Our findings reveal that bacterial diseases, particularly fin and tail rot, were most prevalent, with medium‐level outbreaks (affecting 11%–30% of fish) reported in over half of the farms. The average mortality rate was 15.92%, resulting in significant economic losses ranging from $1800 to $19,093 per production cycle. Poor biosecurity, handling practices and water quality were key contributors to disease spread. Profitability indicators such as gross margin, net income and profit ratio declined sharply with increasing mortality. Farms with lower mortality rates achieved better financial outcomes, while those with higher mortality faced reduced output and rising costs. The study highlights the urgent need for improved disease management, biosecurity training and support services to enhance the sustainability and profitability of cage fish farming in the region.