Heavy metals are common pollutants of estuarine ecosystems where they induce adverse effects on the aquatic biota. Copper is one of the most toxic heavy metal to fish and consumption of fish after copper treatment in water may pose a serious risk to human health. Fishes are generally used as pollution indicators in water quality management. Chronic effects include reduced growth, shorter lifespan, reproductive problems, reduced fertility and behavioral changes. Estuarine fish, Mugil cephalus is an important fin fish species of Uppanar estury in Cuddalore region having good nutritional values. Fishes living in close association with the sediment may accumulate copper sulphate. In the present observation, the toxic effects of the copper sulphate LC50 35 µg/L (CuSO4) on (10% and 30%) two sublethal concentrations of total protein in gill, liver and muscles tissues of the estuarine fish, Mugil cephalus were estimated during the periods of 5, 10 and 15 days exposure. There is decreased in all tissues on comparison with control. The results indicated the toxic nature of the heavy metal copper sulphate.
