Variations in some electrolytes namely Sodium (Na+), Potassium (K+), Chloride (Cl- ) and Calcium (Ca2+) in the plasma of Sarotherodon melanotheron exposed to paraquat dichloride (PARAQ), 2,2-dichlorovinyl phosphate (DDVP) and dimethoate (DMC) at the concentrations of 0.00 control, 0.50, 1.00, 1.50, 2.00 and 2.50 mg/L were carried out to determine the extent of osmotic injury in fish exposed to these chemicals. A total of seventy five adult sizes of Sarotherodon melanotheron were used for the study. Results from the study indicated that the values of Na+ and K+ ions significantly increased (P<0.05) in the exposed fish when compared to the control values, while significant reduction (P<0.05) of Ca2+ was equally observed in the treated fish and no significant difference (P >0.05) in the values of Cl- between the control and exposed fish. Comparatively, these variations were more prominent in the fish exposed to paraquat dichloride.