Lake Victoria, the world’s largest tropical lake, is a vital ecological and economic resource shared by Kenya, Uganda, and Tanzania. The lake supports millions through fishing, agriculture, and increasingly, aquaculture. In response to declining capture fisheries and rising protein demand, cage aquaculture has expanded rapidly. While economically beneficial, this practice raises ecological concerns, particularly regarding its impact on benthic biodiversity.
This study assessed the effects of cage farming on benthic macroinvertebrate communities across five sites—Dunga, Naya, Ndere Island, Sena, and Rasira—representing both aquaculture and non-aquaculture zones. Using Ekman grab samplers, sediment samples were collected and analyzed for species composition, abundance, and diversity. Water quality parameters, including temperature, dissolved oxygen, pH, turbidity, and nutrient concentrations (nitrogen and phosphorus), were measured in situ and in the laboratory. Data analysis employed the Shannon-Weaver Diversity Index and the Hilsenhoff Biotic Index (HBI) to evaluate biodiversity and organic pollution levels.
Findings revealed that areas near cage farms exhibited reduced benthic diversity and increased abundance of pollution-tolerant species, such as Chironomus tentans and Tubifex tubifex. Elevated nutrient levels from fish waste and uneaten feed led to eutrophication, algal blooms, and hypoxic conditions, adversely affecting sensitive benthic taxa. Notably, Naya and Ndere Island, with fewer cage installations, recorded higher taxonomic richness compared to heavily farmed sites like Sena and Rasira.
The study underscores the need for sustainable aquaculture practices that mitigate environmental impacts. Recommendations include strategic site selection away from ecologically sensitive areas, regular monitoring of water quality and benthic communities, and implementation of best management practices to reduce nutrient loading. Such measures are crucial to balance the economic benefits of cage farming with the preservation of Lake Victoria’s ecological integrity.