Bioaccumulation of metals in selected fish species and the effect of ph on aluminium toxicity in a cichlid oreochromis mossambicus

M.Sc.The upper catchment of the Olifants River, from its origin near Bethal, to its confluence with the Wilge River, north of Witbank, as well as it tributaries, are being subjected to increasing afforestation, mining, power generation, irrigation, domestic and industrial activities. These activities have a profound effect on the water quality and the major point sources of pollution in this area include mines, industries and very importantly, combined sewage purification works, located alongside the river, which, in addition to oxidizable material contains detergents, nutrients, and metals. It was therefore necessary to determine the extent to which these activities affect the water quality of the system. The impact of these activities was therefore addressed by a Water Research Commision Project namely "Lethal and sublethal effects of metals on the physiology of fish" of which the present study investigated effects at two localities, namely in the Olifants River (locality OR1) before its confluence with the Klein Olifants River and a locality in the Klein Olifants River (locality KOR1). Apart from the field study, toxicity tests were also performed in a laboratory, in order to determine the effects of low pH and elevated aluminium concentrations on the haematology, osmoregulation and carbohydrate metabolism of the Mozambique Tilapia, Oreochromis mossambicus as the acidification of soil systems may cause the transfer of aluminium into aqueous solutions, where it may be present in different forms. During the field study, the chemical and physical characteristics of the river water were evaluated, with special attention to the concentrations of certain metals (manganese, copper, chromium, lead, nickel, zinc, iron and aluminium) in the water and sediment, as well as in fish, which are known to accumulate the elements supra and are therefore valuable as indicators of these pollutants. The two fish species used for the investigations were the African sharptooth catfish, Clarias gariepinus and the moggel, Labeo umbratus. Four tissue types were dissected, namely the muscle, liver, skin and gill tissues. The metal concentrations in these organs/tissues, as well as in the water and sediment, were determined in a laboratory with an atomic absorption spectrophotometer. Statistical analyses were performed on the results obtained from this study and the order and extent of bioaccumulation of these metals in the water and sediment were determined, as well as in the fish organs/tissues. Its dependence on the size, sex and species of the fish and the localities and seasons were investigated