Bacterial Contamination and some Heavy Metal Accumulation in Fresh and Smoked Clarias Gariepinus and Heterotis Niloticus in Hadejah Fish Market, Jigawa State, Nigeria

Abstract

Fish is a vital source of protein in Nigeria, but contamination with bacteria and heavy metals poses public health risks. This study evaluated bacterial load and selected heavy-metal concentrations (Pb, Cd, Cr, and Ni) in fresh and smoked Clarias gariepinus and Heterotis niloticus from Hadejia Fish Market, Jigawa State. Thirty-six fish samples (500 g–1.5 kg) were collected, preserved with nitric acid, and analyzed in the laboratory. Bacterial load was determined using serial dilution, plating on selective media (Nutrient, MacConkey, Mannitol Salt, and Salmonella Shigella Agar), Gram staining, and biochemical tests. Heavy metals in gills, liver, and smoked tissues were quantified using Atomic Absorption Spectrophotometry after acid digestion. Results showed diverse bacterial contamination, mainly Staphylococcus spp., Salmonella spp., Escherichia coli, Pseudomonas spp., and Bacillus spp. Total bacterial counts in fresh fish ranged from 3.2 × 10⁵ to 7.8 × 10⁵ cfu/g, exceeding safe limits, while smoked fish had lower counts (1.1 × 10⁴–2.5 × 10⁴ cfu/g). Heavy-metal concentrations were Pb: 0.12–0.48 mg/kg, Cd: 0.03–0.15 mg/kg, Cr: 0.10–0.32 mg/kg, and Ni: 0.08–0.26 mg/kg. Smoked fish generally had higher metal levels due to moisture loss and deposition from smoke. Cd exceeded WHO/FAO limits in several samples. The study concludes that H. niloticus and C. gariepinus sold in Hadejia are contaminated with bacteria and heavy metals. Traditional smoking reduces microbial load but may concentrate metals. Recommendations include improved hygiene, adoption of modern smoking technologies, regular monitoring by food-safety authorities, proper waste management, and consumer education on safe fish handling and cooking.