In this study, we investigated the oxidative stress-related biomarkers (catalase and malondialdehyde) on selected tissues (liver, gills, and muscle) of Chelon labrosus in İzmir Bay to evaluate spatial differences between Inner and Outer Bay.C.labrosus specimens were collected by fishing at both Inner Bay (İnciralti) and Outer Bay (Foça) in December 2019. Liver, gills, and muscle tissues were separated and rapidly placed in the liquid nitrogen tank (-198°C). Catalase (CAT) and malondialdehyde (MDA) levels were determined spectrophotometrically by using a microplate reader.Mean CAT levels (U/mL) were found in muscles as 0.181 in gills as 0.779 and in livers as 0.622 at the Inner Bay. On the other hand, CAT levels were detected in muscles as 0.265, in gills as 1.093, and in livers as 0.666 at the Outer Bay. Also, mean MDA contents (pmol MDA/mg tissues) were determined in muscle tissues as 0.0191, in gills as 0.0768, in livers as 0.0372 at the Inner Bay. MDA contents were found in muscle tissues as 0.0385, in gills as 0.1045, in livers as 0.0588 at the Outer Bay. Therefore, biomarker levels in Outer Bay results are generally higher than Inner Bay.According to the ANOVA and Tukey post-hoc tests, significant differences between tissues and locations were observed for MDA. Also, statistical differences were found between only tissues for CAT, however, no significant differences were detected between locations.It’s known that these biomarkers (CAT and MDA) are indicators of pollution status in the marine environment. Inner Bay of İzmir has affected negatively harbor activities and urbanization. Also, biomarker results showed that Outer Bay is under threat of pollution by the Gediz River and other anthropogenic activities. Therefore, biomonitoring researches should be maintained in İzmir Bay for ecological risks and human health.Keywords: Biomarkers, catalase, malondialdehyde, Chelon labrosus, İzmir BayT22ABSTRACT</p
