Aquatic systems are very sensitive to heavy metal pollutants and the gradual increase in the levels of such metals in aquatic environment, mainly due to anthropogenic sources, became a problem of primary concern. This is due to their persistence as they are not usually eliminated either by biodegradation or by chemical means, in contrast to most organic pollutants.  Moreover, the decay of organic materials in aquatic systems together with detritus formed by natural weathering processes, provides a rich source of nutrients in both the bottom sediments and overlying water body. Microorganisms, microflora and algae are capable of incorporating and accumulating metal species into their living cells from various supply sources. Consequently, small fish become enriched with the accumulated substances. Eventually man, consuming the fish, inevitably suffers from the results of an enrichment taken place at each trophic level, where less is extracted than ingested (Forstner and Wittmann, 1983). In the present study, effect of Aluminium toxicity on carbohydrate, protein and lipid of Oreochromis mossambicus was seen. Our experiments demonstrate that increasing concentrations of aluminium decreases the carbohydrate, protein and lipid content of muscles and liver in the tilapia fish.