Aquaculture in East Africa is expanding rapidly, providing a vital source of nutrition and economic livelihood. However, environmental contamination, particularly heavy metal pollution, poses a significant threat to fish health, aquaculture productivity, and consumer safety. Mercury (Hg), arsenic (As), chromium (Cr), and lead (Pb) are of particular concern due to their persistence in aquatic ecosystems and potential to bio accumulate in farmed and wild fish ultimately entering the human food chain. This study investigates heavy metal concentrations in Enteromius paludinosus (straightfin barb) from River Malewa, a key tributary of Lake Naivasha; an important hub for both capture fisheries and aquaculture. Unlike previous research, this study also examines the role of the parasitic cestode Ligula intestinalis in metal bioaccumulation, assessing its potential as a bio-indicator for aquatic pollution. A total of 1,307 fish were sampled at the river mouth, and water, sediment, and fish tissue including L. intestinalis were analyzed for heavy metal concentrations using thermal-electron atomic absorption spectrophotometry. While sediment concentrations remained below critical thresholds, fish exhibited elevated levels of As, Cr, Pb, and Hg, with mean concentrations of 5.07, 22.09, 45.21, and 1.55 mg/kg, respectively. Bioconcentration factors confirmed significant metal accumulation in fish tissue, raising concerns over food safety risks for human consumers. Additionally, L. intestinalis demonstrated a notable capacity for heavy metal accumulation, with bio-concentration factors of 2.41, 2.19, 5.86, and 5.14 for As, Cr, Pb, and Hg, respectively. These findings highlight its potential use as a cost-effective bio-indicator for monitoring pollution in freshwater systems. This study emphasizes the critical need for enhanced environmental monitoring and robust regulatory frameworks to mitigate heavy metal contamination in aquaculture. Establishing routine heavy metal assessments, adopting best management practices, and enforcing stricter pollution controls are vital for promoting sustainable aquaculture, preserving aquatic ecosystems, and ensuring consumer safety.
Keywords: Heavy metal contamination; Aquaculture sustainability; Bioaccumulation; Environmental monitoring; Food safety