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U.S. GEOLOGICAL SURVEY
Data Series 286

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Abstract

The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, National Park Service, Bureau of Reclamation, and Nevada Department of Wildlife, collected and assessed data to determine the general health and reproductive status of common carp (Cyprinus carpio) at two study areas in Lake Mead, Nevada, during May 1999–May 2000. These data will form the basis of interpretations and provide a comparison for continuing studies on the health of the ecosystem in Lake Mead. One study area, Las Vegas Bay, is in the western part of Lake Mead. Las Vegas Bay receives inflows from Las Vegas Wash, which is predominantly tertiary-treated wastewater effluent, and to a lesser extent stormwater runoff from Las Vegas, Henderson, and other nearby communities, and from ground water underlying Las Vegas Valley. The other study area, Overton Arm, is in the northern extent of Lake Mead. Overton Arm receives inflow from the Virgin and Muddy Rivers, which historically are not influenced by wastewater effluent. Both sexes of common carp were collected bimonthly for 12 months using boat-mounted electrofishing gear (a direct electric current is used to temporarily immobilize fish for capture) to determine their health and reproductive status and any relation between these factors and environmental contaminants.

This report presents fish tissue chemistry, organic chemical compound concentrations, and biomarker data for 83 male common carp collected from Las Vegas Bay, similar organic chemistry results for 15 male common carp, and similar biomarker measures for 80 male common carp collected from Overton Arm. Tissue chemistry results also are presented for 16 female common carp and biomarker measures for 79 female common carp collected from Las Vegas Bay, and tissue chemistry results for 15 female common carp and biomarker measures for 81 female common carp collected from Overton Arm.

Thirty-three organic chemical compounds plus total concentrations for four groups of compounds (chlordanes, polychlorinated biphenyls [PCBs], brominated diphenyl ethers [BDEs], and triclosans) were analyzed from extracts of whole-body tissue using gas chromatography/mass spectrometry in male common carp from Las Vegas Bay during May 1999 through May 2000. All 33 compounds were detected in at least one sample of whole-body tissue from male common carp collected in Las Vegas Bay. In Overton Arm, 37 organic compounds plus total concentrations of three groups of compounds (PCBs, BDEs, and triclosans) were analyzed in male common carp where 20 (54 percent) of the compounds were detected. Sixteen of the 33 compounds detected in male common carp from Las Vegas Bay and 10 compounds detected in males from Overton Arm have the potential to disrupt the endocrine system in fish in Lake Mead. During May and June 1999, the mean concentration of all organic compounds detected in male common carp was 670 micrograms per kilogram from Las Vegas Bay and 109 micrograms per kilogram from Overton Arm.

Twenty-seven organic compounds plus total PCBs were analyzed from extracts of whole-body tissue in female common carp collected in Las Vegas Bay and Overton Arm during May 1999. Twenty-four (86 percent) of these compounds were detected in at least one sample of whole-body tissue from female common carp collected from Las Vegas Bay while 10 (36 percent) chemical compounds were detected in female common carp from Overton Arm during that same period. Median concentrations of all chemical compounds were higher in female common carp from Las Vegas Bay compared to those collected from Overton Arm except Dacthal (DCPA), which was similar between sites.

Biomarker measures obtained for male and female common carp include gonadosomatic index (percentage of gonad weight to total body weight), plasma vitellogenin (a phospholipid protein normally produced by female common carp and other oviparous fish), and condition factor [body weight/(fork length)³]. Biomarker measures for male common carp include five indicators of sperm quality: viability, motility, mitochondrial function, distribution of germ cell stages, and concentration of sperm. Biomarker measures for female common carp include total fecundity (estimate of total number of follicles per fish available for spawning), normalized fecundity (number of follicles per kilogram of body weight) during January and March 2000 only, and follicle size-frequency distribution.

Monthly medians for reproductive biomarkers were variable between sites and among months. Median concentrations of vitellogenin in blood plasma from male common carp collected from Las Vegas Bay ranged from not detected (detection limit 0.005 milligram per milliliter) to 0.631 milligram per milliliter, whereas monthly median concentrations in male common carp from Overton Arm ranged from not detected to a high of 0.100 milligram per milliliter. Vitellogenin concentrations in individual male common carp collected from Las Vegas Bay were as high as 68.1 milligrams per milliliter. Monthly median sperm counts also varied between sites and among months; values ranged from 1.20 × 10¹⁰ per milligram of testis to a high of 6.42 × 10¹⁰ per milligram of testis in male common carp from Las Vegas Bay and from 1.52 × 10¹⁰ per milligram to 7.41 × 10¹⁰ per milligram of testis in male common carp from Overton Arm. Monthly medians for another sperm quality biomarker, viability, ranged from 79.5 percent to a high of 98.2 percent in male common carp from Las Vegas Bay, and from 90.0 percent to 97.3 percent in male common carp from Overton Arm.

Monthly median concentrations of vitellogenin in blood plasma ranged from 0.863 to 9.368 milligrams per milliliter in female common carp collected from Las Vegas Bay and from 0.785 to 11.126 milligrams per milliliter in female common carp collected from Overton Arm. Vitellogenin concentrations generally increased in late autumn through winter and reached a maximum just before spawning in March. Normalized fecundity was more variable during the pre-spawning months of January and March 2000 in female common carp from Las Vegas Bay (medians of 190,883 and 231,232, follicles per kilogram respectively) but was fairly consistent in female common carp from Overton Arm (medians of 164,054 and 162,409 follicles per kilogram, respectively).

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