In this study where the effects of naturel (clove oil) and synthetic (2-phenoxyethanol) anes-thetic substances were investigated, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta fario) were used as fish material. In the blood samples taken from the fishes ex-posed to the doses of both compounds for 28 days, enzyme activity values were inspected. When enzyme activity values are considered, although the effect of anesthetic substance appli-cation on glucose 6-phosphate dehydrogenase and 6-phospho gluconate dehydrogenase en-zymes have been found to be important (p0.05). The effect of type on the glutathione reductase enzyme activity values is found to be important (p0.05), whereas catalase enzyme is not effected by application, type and interaction. Clove oil showed inibition effects on glutathione reductase but 2-phenoxy-ethanol did not. 2-phenoxyethanol did not exhibit inhibition on catalase enzyme from brown trout.