Fresh water fishes C.carpio and synthetic pyrithrode cypermethrin were used in the present study. After the determination of LC50 96 hr value of the pesticide (2.0 ppm) to the fishes, a group of fishes were exposed to the sublethal concentration of the pesticide (0.2 ppm). The impact of the pesticide on various electrolytes namely K+, Na+, Cl- and Hco3- ions in the serum and tissues like gills, liver, kidney and muscle was determined during various exposure periods (days 4, 7,14,21 and 28). Cypermethrin was found to bring an overall reduction of Na+, Cl- and HCo3- ions where as the K+ ions were increased. The obtained results were discussed.