Reproductive responses of common carp (Cyprinus carpio) exposed in cages to influent of the Las Vegas Wash in Lake Mead, Nevada, from late winter to early spring

The Las Vegas Wash (LW) delivers tertiary-treated municipal wastewater effluent, nonpotable shallow groundwater seepage, and runoff from the urbanized Las Vegas Valley to Las Vegas Bay (LX) of Lake Mead. To investigate the potential for contaminants in LW influent to produce effects indicative of endocrine disruption in vivo, adult male and female common carp (Cyprinus carpio) were exposed in cages for 42-48 d at four sites in Lake Mead: LW, LX, and two reference locations in the lake. End points examined included gonadosomatic index; gonad histology; concentrations of plasma vitellogenin (VTG) and plasma sex steroids (17β-estradiol (E2), testosterone (T), 11-ketotestosterone (11-KT)); plasma estrogen:androgen ratios (E2:T, E2:11-KT), in vitro production of T by gonad tissue, and hepatopancreas ethoxyresorufin O-deethylase activity. Few differences among fish caged at different sites were potentially attributable to exposure to contaminants in LW influent. Male carp caged at LW had slightly greater concentrations of plasma VTG than those at other sites, and a modest elevation in plasma E2 was observed in male carp at LX and LW, but causes other than contaminant exposure cannot be ruled out. Water temperature differences among sites complicated interpretation of the results. Variation in some end points among carp at two different reference sites supports the use of multiple reference sites in field studies of the effects of endocrine-disrupting chemicals.