Abstract: “In this study, effects of oxytetracycline on glutathione s-transferase enzyme activity and gene expression levels in rainbow trout (Oncorhynchus mykiss) liver were investigated. For this purpose, liver tissues from rainbow trout exposed to oxytetracycline application were collected at third, sixth and 12th hours. The group not exposed to oxytetracycline was assigned as control. While the lowest enzyme activity of GST was at 12th, the highest enzyme activity was observed in control. While compared with the control group, enzyme activity at 12th hour was highly significant (p 0.001), the third and sixth hours groups were significant (p 0.05). The lowest gene expression level was found in 12th group and the highest level was the third. While compared with the control group, difference at the third hour of gene expression level was highly significant (p 0.001), at the sixth and 12th hours groups was not significant. As a result, there was understand that no correlation between gene express”

Keywords: Oncorhynchus mykiss, Liver, Glutation STransferase, Oxytetracycline, Enzyme Activity.