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326 ence (LSD;- iX:='0.05);'Differeneesbetweenmean pairs ex- ceeded the LSD of 0.57 only when one pair member included the anterior -inuscle,plug mean (6.07). AIl other mean pair combinations Were'. insignificant, indicating that muscle plugs from dorsal and posterior areas of a razorback sucker and other fish species may provide an accurate assessment of selenium concentrations that exist in adjacent muscle tissue. The effect of harvesting a single muscle plug on infection and survival oflive flShis not known, but field observations of adult razorbacks frOm. which. single plugs have been taken indicate little or no effect. Other studies currently underway to confirm selenium cause and effect include: in situ survival of razorback sucker fry in the Green River; to day survival tests of razorback sucker fry exposed to various concentrations of selenium. in natural waters; 1lurvival of razorback sucker fry to varying concentrations. of selenium in the diet; and hatching and 30 day survival tests on razorback sucker eggs. Conclusions Concentrations of selenium found in the muscle tissue and eggs of razorback suckers inhabiting the Colorado River basin are significantly elevated and may be a cause of reproductive prob- lems responsible for the decline of this species. The collection of small muscIeplugs from the external surface of live razor- back suckers and other fish species provided an accurate assess- ment of selenium concentrations present in fish muscle tissue. This collection technique is particularly valuable when lethal fish collection methods are prohibited, as is often the case with endangered species. Although the plugs are very small, they can be accurately and precisely analyzed for selenium by the method of instrumental neutron activation. Ackrwwledgmellls. The authors thank Shawn Stephenson, Ecological Services, and personnel of the Colorado River Fishery Project for the B.~WaddeU'3rid T. S. May collection of samples, and Jesse Anus of the .MidweStScience Center for excellent technical assistance. Thanks also to Dr. Steve Morris and - the team at the University of Missouri Research Reactor for the neutron activation analyses. References Clinton DE (1977) Detennination of selenium in blOod lilid 'plant mate- rial by hydride generation and atomic absorPtion spectroscopy. Analyst 102:187-192 Hamilton SJ, Waddell B (1994) Selenium in eggs and miltofrazoroack sucker (XyrilUChen texanus) in the Middle'GreeriRiver. Arch " Environ ContamToxicoI27:195-201 Lemly DA, Smith GJ (1987) Aquatic cycling of selenium: Implications for fish and wildlife. U.S. Dept of Interior, Fish and Wildlife Service, Fish andWildlife Leaflet 12, Washington DC McKown DM,'Morris JS (1978) Rapid measurement of selenium in biological samples using instrumental neutron activation analysis. J Radioanal Chem 43:411-420 Minckley WL (1983) Status of the razorback sucker (Xyrauchen lem- nus Abbott) in the lower Colorado River basin. Southwestern Naturalist 28:165-187 Peltz LA, Waddell B (1991) Physical, chemical, and biological data for detailed studyof irrigation drainage in the middle Green River basin, Utah, 1980-89, with selected data for 1982-r987. U.S. Geological Survey, Open File Report 91-530, Salt Lake City, UT Snedecor GW, Cochran WG (1972) Statistical Methods, Sixth Edition. Iowa State University Press, Ames, IA. Sixth Edition. pp 272-275 Tyus HM (1987) Distribution, reproduction, and habitat use of the razorback sucker in the Green River, Utah, 1979-1986. Trans Amer Fisheries Society 116: 111-116 Tyus HM, Karp CA (1990) Spawning and movements of razorback sucker (Xyrauchen texanus) in the Green River basin of Colorado and Utah. Southwestern Naturalist 35:427-433 Williamson, JH (1992) Colorado Squawfish Genetic Survey - Tissue sampling protocol 1992. U.S. Fish and Wildlife Service, Fisheries and Federal Aid, Denver Federal Center, Denver, CO, 12 pp