Biochemical Assessment of Oxidative Stress in African Catfish (Clarias Heterobronchus) from Oil-Polluted Rivers in The Niger Delta, Nigeria

Abstract

This study ascertained the biochemical state of the African catfish, Clarias heterobronchus, from the Oloibiri and Warri rivers in Nigeria's Niger Delta, both of which have been exposed to crude oil spills for 50 years. Fish samples (n=10 each) were obtained from the two rivers and also from a fish pond in Ibadan, Oyo State, Nigeria which served as checkpoint (reference location). The physicochemical properties of the two rivers were examined as well as the concentration of heavy metals in the fish samples. The catfish's muscle, liver, gut, and gills were also examined for the activities of catalase, superoxide dismutase, glutathione S-transferase, glutathione, and malondialdehyde production. Both rivers' pH values (6.35 for Oloibiri and 6.03 for Warri river) were below the threshold that various regulatory agencies have determined is acceptable (6.5-8.5 USEPA). The control water had a high dissolved oxygen (DO) concentration (6.69±1.15 mg/l), while the Oloibiri (4.50±0.50 mg/dl) and Warri (4.01±0.25 mg/l) rivers had lower DO concentrations. The two rivers had significantly greater amounts (p<0.05) of all the heavy metals evaluated than the control. Total hydrocarbon content (THC) concentrations in the control, Oloibiri, and Warri rivers were 9.52, 35.32, and 48.56 mg/l respectively. In every tissue analyzed, the MDA levels of Clarias heterobronchus were significantly (P <0.05) higher in the fish from the Oloibiri and Warri rivers than in the control group. When compared to the control, lipid peroxidation in the gills of fish from the Warri River increased by 222%, while those from the Oloibiri River increased by 184%. The organs of fish from the Oloibiri and Warri rivers had significantly higher (p<0.05) levels of expression of antioxidant enzymes. Overall, oxidative stress in key organs and tissues (muscle, liver, gut, and gills) indicated that Clarias heterobronchus from the Olobiri and Warrı rivers are physiologically stressed.