Investigation of Selected Heavy Metals, Histopathological and Oxidative Stress Responses of Nile Tilapia, <i>Oreochromis niloticus</i> in Water from the Hadejia-Nguru Wetlands Nigeria

Abstract

Hadejia-Nguru wetland has been known to be a productive area of Agricultural engagements and fisheries activities allowing for intensive farming and fishing activities, effluents from agricultural activities, sewage, and chemical seepages enter this water body. This study investigated the levels of several heavy metals Mercury (Hg), Lead (Pb), Cadmium (Cd),Chromium (Cr), and Aluminum (Al) in O. niloticus tissues (gills, liver, muscle) collected from five sampling sites in the study area. Tissue histology and the presence of antioxidant enzymes revealed the degree of tissue damage and stress in fish. The results for heavy metals showed concentrations in the order Hg>Cr>Pb>Al>Cd, which are higher than the maximum residue limits recommended by FAO and WHO. Superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and reduced glutathione (GSH) activities were observed at high concentrations in gills, liver, and muscle. Liver of the fish showed a high level of SOD concentration of 18.3μg/ml, followed by a concentration of 16.93 μg/ml in the gills, and CAT with a concentration of 1.48 U/ml was observed in the liver, MDA was highest in the liver with a concentration level of 1.08n/mol and there was no significant difference between MDA concentrations in liver and other organs (P < 0.05). Reduced glutathione levels of 18.36 μg/ml was seen in the liver of the fish. Histopathology of the select organs i.e. gills, liver and muscle cells showed that the organs of the fish were affected by the level of toxicity in the Hadejia-Nguru environment. The presence of metal toxicity, antioxidant enzymes, and tissue damage in fish is an indication of contamination and serves as a means for monitoring the safety of freshwater organisms.