In this study, Dimethoate (DM) (a pesticide)'s histopathological and electrophoretic effects were investigated on Capoeta capoeta (Guldenstaedt 1773) that were captured from Kars creek, and the protective effect of ascorbic acid (AA) (vitamin C) was tested. After allowing time for their adaptations to their new environment, the fish caught from Kars creek were divided into 4 groups (each including 10 fish), and placed in 300-liter tanks in the laboratory. The fish were kept in water containing different solutions: group I in normal water medium, group II in 100 mg/L AA, group III in 2 mg/L DM, and group IV in 100 mg/L AA and 2 mg/L DM. They were kept in these water mediums for 10 days. After this period, blood and tissue samples were taken from the fish for electrophoretic and histopathological studies. Tissue samples were detected in 10% formaldehyde solution and paraffin blocks were prepared by routine histological methods. The samples were cut into sections 3-5 thick, all stained according to hematoxylin and eosin staining methods, and they were examined under a microscope. Obtained serum samples were carried out in Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE). When we compared the serum samples with the control group of fish, protein bands in the application of 100 mg/L AA and 2 mg/L DM, thickening in 36 kD band, thinning in 100 kD, 97 kD, 76 kD, 56 kD and 30 kD bands were observed, and the bands of 93 kD, 46 kD, 44 kD and 26 kD were detected as newly-synthesized in SDS-PAGE electropherogram. In the histopathological examinations, depending on DM in intestine, liver, and kidney tissues obtained from the group formed by application of DM and AA, degeneration, necrosis, pyknotic nuclei and cell infiltrates were detected. As a result, whereas DM application was found to create toxic effects on Capoeta capoeta, AA was found to have a healing effect.