Assessment of Proximate Composition and Heavy Metal Bioaccumulation in Labeo rohita from Aquaculture Ponds in Taluka Mehrabpur, Sindh, Pakistan

Abstract

This study evaluated the proximate biochemical composition and heavy metal bioaccumulation in Labeo rohita harvested from five commercial aquaculture ponds (Theba, Memon, Sheikh 1, Sheikh 2, and Malik) in Taluka Mehrabpur, Sindh, Pakistan. A size-stratified sampling protocol was deployed across N=50 specimens (n=10 per fish pond), categorized into 0.5 kg and 1.0–1.6 kg weight tiers to control for growth differentials. Target tissues were muscle, liver, gills, and scales and were analysed for moisture, protein, crude fat, ash, and heavy metals using ICP-OES following thermal acid digestion. Moisture distribution ranged from 51% to 83%, peaking in muscle (83%) and reaching a minimum in scales (51%). Proximate analysis revealed organ specialization: scale tissue contained the highest ash content (21.0%) and lowest crude fat (0.11%), respiratory gills exhibited maximum crude fat (0.36%), and hepatic tissue recorded the lowest protein (1.2 mg/kg) and ash (10.3%) concentrations. Heavy metal bioaccumulation demonstrated pronounced organ-specific partitioning, where the liver served as the primary accumulation centre for Iron (13.8 mg/kg) and Lead (0.073 mg/kg), gills concentrated Zinc (3.05 mg/kg), and scales sequestered Chromium (0.10 mg/kg). Edible muscle tissue maintained the lowest affinity for metal storage across all evaluated elements (1.13mg/kg), (0.67mg/kg) and (0.0013mg/kg). All observed muscle concentrations were well below the maximum permissible safety limits set by the FAO/WHO. Human health risk modelling yielded Target Hazard Quotient values far below unity (1.0), confirming that chronic dietary consumption of Labeo rohita from these aquaculture systems poses zero non-carcinogenic health hazards to human consumers.