Bioaccumulation of copper and zinc in Oreochromis mossambicus and Clarias gariepinus, from the Olifants River, Mpumalanga, South Africa

The upper and lower catchments of the Olifants River are characterised by m any anthropogenic activities that adversely impact on the water quality of the fiver. The present study indicated that both Cu and Zn are present in e levated levels as reflected in the bioaccumulation of these metals in the f ish. Bioaccumulation differences in the different age and gender groups wer e generally not significant (P>0.05). This was due to the sampling of mostl y adult fish and the exclusion of reproductive organs (gonads). Copper cont ent in the organs and tissues indicated the following pattern: liver>gills> skin>muscle, but no specific pattern for Zn content was observed. The exten t of accumulation differed in many cases between the two species, possibly due to differences in behaviour and feeding. Temporal variation in bioaccum ulation occurred and generally indicated increased levels of bioaccumulatio n during periods of high flows. This phenomenon was ascribed to the influen ce of sediment-bound metals, being brought into contact with the fish at a higher intensity during these periods. Both Loskop Dam and Mamba Weir, the latter to a greater extent, are at present being exposed to levels of Cu an d Zn which cause bioaccumulation. A more holistic biomonitoring approach is proposed for these impacted areas in an attempt to guide managers in a dir ection of improvement.