Oxidative stress responses to heavy metal burden in African catfish (<i>Clarias gariepinus</i>) from Warri River, Niger-Delta, Southern Nigeria

Abstract

Despite the degradation and threat of ubiquitous contaminants, such as heavy metals, in Warri River, Southern Nigeria, little is known about the ecological effects of such pollution using pro-oxidant variables. This study investigated oxidative stress responses to heavy metals (lead (Pb), cadmium (Cd), manganese (Mn), nickel (Ni) and copper (Cu)) burden in the heart, kidney, liver and gills of African catfish inhabiting Warri River. Fish (N=30) were collected during August-September, 2018 from two contaminated sites along the course of Warri River and a fish farm which was considered a reference site. The concentrations of Pb, Cd and Ni in the two contaminated sites were above the WHO permissible limits and significantly higher (p<0.05) as compared to the fish collected from the reference site. The trend of accumulation of the metals followed the order: Reference site (site 1)-Mn>Ni>Cu>Pb>Cd; site 2-Pb>Cu>Cd>Mn>Ni and site 3-Ni>Mn>Cu>Cd and Pb respectively. The activities of catalase (CAT) and superoxide dismutase (SOD) were significantly higher (p<0.05) in the organs of fish caught at the two contaminated sites. Malondialdehyde (MDA) was significantly elevated (p<0.05), in the liver and heart of fish obtained from site 3, relative to sites 2 and 1. Fish obtained from the two contaminated sites had significantly decreased (p<0.05) levels of reduced glutathione (GSH) in their organs, however, the reduction was more in site 2. The results of this study confirm that environmental stressors, such as heavy metals, can alter antioxidant enzymes and glutathione systems, as well as induce lipid peroxidation, leading to oxidative stress in aquatic organisms.