US Geological Survey


Date of this Version



Poster (November 22, 2004)


The Large River Monitoring Network (LRMN) of the Biomonitoring of Environmental Status and Trends (BEST) Program measured tissue concentrations of selected contaminants and evaluated biomarker responses in black bass (Micropterus sp.), common carp (Cyprinus carpio), and channel catfish (Ictalurus punctatus) at 14 locations within Colorado River Basin (CDRB) in 2003. Major tributaries including the Yampa, Green, Gunnison, San Juan, and Gila Rivers were also sampled. Organic and inorganic contaminants were measured in whole-body composite fish samples, and the H4IIE bioassay determined dioxin-like activity in these samples. Fish health indicators (condition factor, somatic indices), immune system indicators (macrophage aggregate parameters), various molecular biomarkers (EROD, vitellogenin), and reproductive indicators (steroid hormones, gonadal histology) were measured in individual fish. Mean microsomal EROD activity was greatest in carp (>9 pmol/min/mg) from Phoenix, AZ, in channel catfish (>10 pmol/min/mg) from Vernal, UT and Grand Junction, CO, and in Bass (>60 pmol/min/mg) from Vernal, UT. Fish health indicators including macrophage aggregates and oocyte atresia indicated poor health of carp in the Lake Mead area. High health assessment index (HAI) values in bass, channel catfish, and carp collected throughout the CDRB were attributed to abnormalities of the liver, kidney, and spleen. Histological examination of the gonads revealed several intersex fish. Previous contaminant studies in this basin have a wide range of focus from high concentrations of selenium in irrigation return flows to emerging contaminants downstream of Las Vegas. Other concerns include dropping water levels in the lower Colorado River and the reestablishment of endangered species within the CDRB. The goal of this BEST LRMN project is to help characterize fish health and contaminant concerns in the CDRB.