Treatments with copper sulphate (CuSO4), paraquat (PQ) and methidathion (MD) caused tissue damage and stress effects in carp, indicated by the increased lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT), and glutamate dehydrogenase (GIDH) enzyme activities and elevated blood-sugar levels. Copper sulphate, administered together with PQ and MD, were synergistic in terms of tissue damage and stress effects. The isoenzyme patterns showed organ-specific tissue damage. The administered chemical and isoenzymes indicating liver damage were detectable in the blood. The combination of CuSO4 and MD caused focal cell necrosis, which was observable in the liver tissue by light microscopy. Electron microscopic studies revealed the presence of damaged parenchymal cells with electron transparent cytoplasms, myelin figures, and altered mitochondria ER and Golgi.