Variations in selected electrolytes such as Sodium (Na+), Potassium (K+), Chloride (Cl-) and Calcium (Ca2+) in the plasma of juveniles and adult sizes of Tilapia guineensis exposed to dimethoate (DMC) at the concentrations of 0.00 (control), 1.00, 1.50, 2.00, 2,50 and 3.00 mg/L were conducted to assess the variations in electrolytes alterations in fish exposed to Dimethoate (DMC) under laboratory conditions. A total of seventy- five juvenile sizes and seventy-five adult sizes of T.guineensis were utilized for this trial. Results from the examination demonstrated that significant alterations comparable to the control values were observed in all the electrolytes under consideration. These alterations were pronounced in juvenile fish than the adult sizes.