Evaluation of Gonadotoxicity of Waste Burnt Tyres Residues on Clarias gariepinus Juveniles

Waste tyres are intentionally burned for various purposes, releasing toxic substances that ultimately find their way into aquatic environments. This study examined the sublethal effects of water-soluble fractions (WSFs) of waste burnt tyre residue (WBTR) on the gonads of Clarias gariepinus juveniles. Juveniles of C. gariepinus were exposed to sublethal concentrations (0.00, 0.23, 0.46, 0.94, 1.87, and 3.74 g/L) of WSF derived from the 11.2 g/L median lethal concentration over two months. Antioxidant activities, as well as the histological and histomorphometric features of testes and ovaries, were analyzed using standard protocols. The average antioxidant activity of superoxide dismutase (SOD), malondialdehyde (MDA), and catalase (CAT) were found to be higher in the testes and ovaries of catfish exposed to the highest WSF concentration (3.74 g/L) compared to the control. Glutathione peroxidase (GPx) showed a similar trend, while the highest levels of reduced glutathione (GSH) and GPx were observed in the ovaries of control fish. Significant differences (P < 0.05) in CAT and SOD activity were noted in the ovaries and testes of exposed fish compared to controls. The histo-architecture of the testes and ovaries in control fish displayed normal structures, while exposure to WSF led to dose-dependent depletion of seminiferous luminal contents in the testes and mild nuclear atrophy in the ovaries, with the highest severity observed in fish exposed to the highest concentrations. Histomorphometric analysis of the ovaries showed significant differences (P < 0.05) in mean values for Maturing Follicular Diameter (MGD) and Matured Follicular Diameter (MFD) in fish exposed to varying WSF concentrations compared to controls. In the testes, there was no significant difference (P > 0.05) in seminiferous luminal diameter (SLD), but a significant difference (P < 0.05) was found in seminiferous tubular diameter (STD) in fish exposed to WSF compared to controls. In conclusion, the study confirmed that the WSF of WBTR affects antioxidant levels, histology, and histomorphometry of the reproductive organs of C. gariepinus juveniles.

Keywords: Waste Burnt Tyres, Sublethal-Toxicity, Testes and Ovaries, Antioxidants, Histology, Histomorphometry, African Catfish.