Sublethal effects of manganese on the haematology and osmoregulation ofOreochromis mossambicusafter acute exposure

Oreochromis mossambicus were exposed for 96 hours to sublethal manganese concentrations in a continuous flow-through system. The sublethal concentrations were determined from the LC50 value of manganese (1.723mg/l), which included a 10% (172.3mg/l), 15% (259.8mg/l) and 20% (345.6mg/l) concentration of the LC50 value. Haematological and osmoregulation variables were investigated after acute sublethal manganese exposure and the differences in the values of haematological and osmoregulation values of exposed fish were compared statistically against control values to determine significant differences. After the exposures it was evident that sublethal manganese concentrations had a disruptive influence on the different variables measured. Most of the haematological variables (white blood cells, red blood cells, haemoglobin content and haematocrit percentages) except the mean corpuscle volume decreased significantly after the 20% sublethal exposure. The osmoregulation variables also fluctuated but started to do so at lower sublethal concentration exposures (10% and 15%). Information concerning the sublethal effects of pollutants, such as metals, forms an integral part of ecosystem health assessment programmes and of procedures followed to develop water quality guidelines for environmetal protection. The data from this study were incorporated into a water quality index (RAUWaterz) compiled for the Olifants River, Mpumalanga. This can aid water quality managers, engineers and consultants in assessing the impact of pollutants on the aquatic environment.