Sublethal effects of manganese on the carbohydrate metabolism of Oreochromis mossambicus after acute and chronic exposure

Abstract

Carbohydrate metabolism variables of Oreochromis mossambicus were investigated after acute and chronic sublethal manganese exposure. The sublethal concentrations were determined from the LC₅₀ value of manganese. After the exposures, the fish were carefully netted and blood was drawn from the caudal aorta. The differences in the values of carbohydrate metabolism variables of exposed fish were measured against control values and statistically analysed to prove statistically significant differences in variable values, caused by the metal pollutant (P < 0.05). The results obtained showed changes in the carbohydrate metabolism variables (glucose, lactate, glucose-6-phosphate dehydrogenase and pyruvate kinase concentrations). These alterations are produced as a result of increased levels of Cortisol and catecholamines, as well as hypoxic conditions. The latter induce hyperglycemia and increased lactate levels. Hypoxia may be a result of the damaging effect of manganese on the gills after exposure. The enzymes involved in the carbohydrate metabolism are sensitive to metal exposure and therefore enzyme concentrations fluctuated after the exposure to manganese. Enzyme function plays an important role in the catalysing of chemical reactions in an organism and the disturbance thereof could lead to death. Fish enzyme levels are therefore important biomarkers in the event of metal pollution in a water source.