Nondestructive indicator of ethoxyresorufin-O-deethylase activity in embryonic fish

Many environmental contaminants of concern produce aryl hydrocarbon (Ah) receptor‐mediated effects often assessed as ethoxyresorufin‐O‐deethylase (EROD) activity. We modified a standardized embryonic and larval fish bioassay using an estuarine fish species (Fundulus heteroclitus) to include measurement of fluorescence in the urinary bladders of living embryos as a nondestructive indicator of EROD activity. This fluorescence was observed only in embryos exposed to the EROD substrate and Ah receptor agonists and was consistent in fluorescence characteristics with the EROD product, resorufin. Aryl hydrocarbon receptor‐agonist exposures at sublethal concentrations in the parts per billion range, produced significant increases in EROD fluorescence in embryos as young as 3 d postfertilization. These findings are consistent with the conclusion that this fluorescence method is a specific and sensitive nondestructive indicator of Ah receptor‐mediated effects in an embryonic fish. As such, this simple method may be useful for assessing effects of environmental contaminants on the early development of fishes and to link molecular indicators with organism‐level responses.