Evaluation of Whole-Body Vitellogenin as An Estrogenic Biomarker in Rio Grande Silvery Minnow Juveniles

Recent investigations have detected the presence of estrogen active compounds (EAC) in effluents from several wastewater treatment plants that discharge into critical habitat for the endangered Rio Grande silvery minnow (Hybognathus amarus).  Little is known about the impacts of these compounds on silvery minnows and laboratory studies are needed to measure their responses to known EAC and to assess the suitability of vitellogenin (Vtg) induction as an estrogenic biomarker for use in field studies.  We exposed Rio Grande silvery minnow juveniles (22-weeks old) to three concentrations of 17α-ethynylestradiol (EE2; at 1, 5, and 25 ng/L), a solvent control (100% ethyl alcohol), and a dilution water control for 21 days in reconstituted water that simulated the Middle Rio Grande.  The fish were sexed by histological examination of the gonads and the bodies (minus the caudal region) were analyzed for Vtg.  Mean measured EE2 concentrations in water were about 66-92% of nominal concentrations.  After 21 days of exposure, there were no differences in survival or weight of fish among treatments, but the condition factors of fish at 5 and 25 ng/L were higher then those in both control treatments.  Whole-body Vtg concentrations (ng/mg protein) in EE2 exposed fish were significantly greater than those in the controls and increased in a concentration-dependent manner.  There were no differences in whole-body Vtg concentrations between sexes at a given treatment, but Vtg concentrations were numerically higher in females at all EE2 treatments.  These findings indicate that whole-body Vtg is a suitable biomarker of exposure to estrogenic substances for juvenile silvery minnows.