Copper (Cu) is one of the most commonly reported metal pollutants in African water bodies, but there are few studies on African freshwater fish species of copper accumulation and copper toxicity. Adult O. mossambicus were exposed to 0mg l−1 (control) and 0.75mg l−1 Cu for 96h and 0 (control), 0.11, 0.29 and 0.47mg l−1 copper for 64 days. Samples of liver and gills were collected after 96h, and after 1, 32 and 64 days, respectively. There were significant differences in the mean Cu accumulation values in the liver and gills between the control and the Cu-exposed fish after the 96-h exposure. In fish exposed to 0.11 and 0.29mg l−1 Cu for 64 days there was an increase in copper level in the tissues. In fish exposed to 0.47mg l−1 Cu the concentration in the gill and liver tissue did not increase between Day 1 and Day 32. At this time, Cu accumulation in the liver was higher than for fish exposed to 0.11 and 0.29mg l−1 Cu for 64 days. Exposure to approximately 0.47mg l−1 Cu for more than 32 days induced mortality.