Abstract: Copper sulphate is a naturally-occurring inorganic salt used as herbicide and algaecide in irrigation and treatment of municipal water, also, as a molluscicide in destroying snails and slugs. Its toxicity to fish varies with the species and the physical and chemical characteristics of the water. When used at recommended doses, it may be poisonous to trout and other fish, especially in soft or acid waters. The effect of copper sulphate on spawning success in Clarias gariepinus was determined using a pair of adult Catfish (Male and female broodstock) and exposed to copper sulphate at the recommended treatment dose of 0.26 mg L-1 of copper sulphate for 10 days. The control pair was exposed to copper-free water for the same period after which both sets were subjected to artificial spawning. Water quality test was monitored pre and post treatment. Blood sample was collected for haematological assessment while organs and tissues were collected for histological assessment. Copper sulphate had no significant effect on both haematology and water quality parameters. However, significant histological changes observed in copper-exposed broodstock were multifocal severe degenerative necrosis of the testes resulting in the production of watery and brownish milt, necrosis of the ovaries producing shrunken, discoloured and cloudy eggs and severe matting of the gills lamina. Caution should be applied in the use of copper as a therapy for external parasites in catfish broodstock due to its effect on reproductive performance as observed in the present study.