Gill histopathological and oxidative stress evaluation in native fish captured in Portuguese northwestern rivers

► Gill biomarkers were tested in fish catch in Portugal NW. ► The histological evaluation was indicative of some degree of stress. ► The quantitative evaluation of each gill injury revealed differences among species. ► There was an increase in antioxidant defenses in more contaminated sites. ► FEP, necrosis and GST activity contributed to discriminate the ecological status of the sampling sites.