Abstract: The sublethal effects of water soluble fractions of petrol (WSF) to the plasma glucose and liver glycogen of Clarias gariepinus with mean weight of 4.76�0.4 g were investigated under laboratory conditions for 10 weeks. At sublethal concentrations of 1.36, 0.68, 0.34, 0.17 and 0.09 gL 1 of WSF of petrol, hyperglycaemia, a situation of increased plasma glucose level above the control was observed. Exposed group of fish to the toxicant were significantly lower (p<0.05) in liver glycogen content than the control group of fish.