Effects of fish cage farming on water quality and diversity of Macrobenthos on L. Victoria - Tende Bay

Abstract

This study assessed the environmental impacts of fish cage farming on water quality and the diversity of benthic macro-invertebrates in Lake Victoria Tende Bay, Garuga. A comparative and experimental study design was employed where samples were collected from both cage (study site) and non-cage (control) sites. Water quality parameters measured included temperature, dissolved oxygen, pH, conductivity, and total dissolved solids (TDS). Nutrient concentrations specifically total nitrogen, ammonia-nitrogen, total phosphorus, and orthophosphates, were determined using standard spectrophotometric methods. Benthic macroinvertebrates were sampled and analyzed for species composition, abundance, and diversity using the Shannon-Wiener and Hilsenhoff Biotic Indices. The results indicated that most water quality parameters remained within acceptable limits and did not show significant variations between cage and non-cage sites. However, total nitrogen levels were markedly elevated at cage sites, surpassing recommended thresholds by NEMA/WHO, suggesting localized nutrient pollution likely due to fish cage farming at the cage site. The composition and abundance of benthic macroinvertebrates revealed notable differences; pollution-tolerant species such as Chironomus sp. and Melanoides tuberculata were more dominant near cages, while sensitive taxa were either absent or significantly reduced. Cage site 2 (study site) exhibited the lowest biodiversity and the highest Hilsenhoff Biotic Index values, indicating high levels of organic pollution. These findings demonstrate that while cage fish farming in Tende Bay may not severely impact basic water quality parameters, it significantly alters the benthic ecosystem and contributes to nutrient loading, posing potential risks of eutrophication and ecological imbalance. The study underscores the importance of continuous environmental monitoring and the development of sustainable aquaculture practices to protect Lake Victoria's aquatic biodiversity.