Impact of heavy metals on health and quality of Oreochromis niloticus cultured in biofloc and earthen pond systems

Heavy metal contamination in aquaculture threatens fish health and consumer safety, with bioaccumulation differing between farming systems. The study compares heavy metal (Cd, Cr, Pb and Cu) contamination in fish feed, water and organs (muscle, gills and liver) of Nile tilapia (Oreochromis niloticus) from biofloc and pond farming systems. Samples were collected from ten biofloc tanks and ten earthen ponds, with heavy metals quantified using atomic absorption spectrophotometry. Heavy metal levels in fish feed were below permissible limits, while pond water showed significantly higher (P < 0.05) contamination than biofloc water. Pond-reared tilapia exhibited higher heavy metal accumulation in muscles, gills and liver compared to biofloc-reared fish. The liver showed the highest bioaccumulation, followed by gills, in both systems. Cd levels exceeded standard limits in the liver and gills of pond-reared fish. Principal component analysis (PCA) and cluster analysis revealed strong correlations between heavy metals in gills, water and liver, while muscles and feed formed a separate cluster. Pb, Cd and Cu were closely associated, suggesting a common contamination source. The health index (HI) for muscle was <1 in both systems, indicating safety for consumption. Overall, biofloc-reared tilapia was found safer for human consumption compared to pond-reared fish.