Gill Filament-Based EROD Assay for Monitoring Waterborne Dioxin-like Pollutants in Fish

Abstract

A sensitive, accurate, and straightforward way to determine basal and induced ethoxyresorufin O-deethylase (EROD) activities in gill filaments, using rainbow trout as model species, is described. Tip pieces of primary gill filaments were incubated in tissue culture plate wells containing HEPES-Cortland buffer supplemented with 7-ethoxyresorufin. Each well was sampled on two occasions, and resorufin concentrations were determined by measuring the fluorescence with a plate reader. EROD activity was calculated from the difference in resorufin concentration and the interval between the two samplings. EROD activity was found to be significantly induced by 6 h of exposure to waterborne beta-naphthoflavone (1 microM). EROD in gills was also induced by caging rainbow trout in a polluted river or by laboratory exposure of fish to water extracted from that river. There was no loss of EROD activity when gill tissue was kept in ice-cold buffer for up to 1 d, which promotes the use of the method for studying fish exposed in the wild. We propose this novel method as a way to monitor dioxin-like compounds in aquatic environments.