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~JaJdt Il~ I'\CL Y Arch. Environ;Contam. Tox.icol. 18, 321-326 (1995) ~,.~ .r. I, 0'79:5/ A A CH I veQ3'dF Environmental Contamination a n'dToxicola9Y C 1995 Spring<r-Vedag NewYClltt1nc. t Selenium Concentrations in the ~r~~Sucker (Xyrauchentexanus): Substitution of Non-Lethal Muscle Plugs for MuScI.eTissue in Contaminant Assessment ') B. Waddell I , T. May2 I Fish and Wildlife Service, Ecological Services, Lincoln Plaza Suite 404, 145 East 1300 South, Salt Lake City, UJah, 84115, USA 2 National Biological Survey, Midwest Science Center, 4200 New Haven Road, Columbia. Missouri, 65201. USA Received: 7 March 1994lRevised: 19 September 1994 Abstract. A single muscle plug was collected from each of 25 live razorback suckers inhabiting the Colorado River basin and analyzed for selenium by instrumental neutron activation~Eight fish from Ashley Creek and three from Razorback Bar exhib- ited selenium concentrations exceeding 8J1.g1g, a level associ- ated with reproductive failure in fish. Concentrations of sele- nium in eggs and milt were significantly correlated with selenium concentrations in muscle plugs and togetherindicate a possible explanation for the decline of this species in the Colo- rado River basin. Muscle plugs (<50 mg) and muscle tissue (20 g) were collected from dorsal, anterior, and;,pos!eriorareas of common carp, tlannelmouth sucker, and an afchivedrazorback sucker and analyzed for selenium. Concentrations of selenium in muscle plugs were significantly correlated~ith"selenium concentrations in muscle tissue from the same location and fish (r = 0.97). Coefficients of variation for seleniurii'&nceritra- tions in each fish were ,<6.5% for muscle tissue,but,ranged' from 1.5 to 32.4% for.muscle plugs. Increased variation in muscle plugs was attributed to lower selenium concentrations found in the anterior muscle plugs of tlannelmouth suckers. Mean selenium concentrations in muscle plugs and tissue from dorsal and posterior areas and muscle tissue from the anterior area were not significantly different. The non-lethal collection of a muscle plug from dorsal and posterior areas of the razor- back sucker and other fish species may provide an accurate assessment of selenium concentrations tIrtlt exist in adjacent muscle tissue. The razorback sucker, Xyrauc~ntexanus, is an endangered species that inhabits the Colorado River;basin/These.f1sh are extremely rare, considerably more so than the Colorado squaw- fish, but a significant population exists in the' GreenIDver, a tributary to the Upper Colorado River. Thisi>6pulatiorfmay be Correspondence to: B. Waddell the largest surviving population still in its native riverine envi- ronment (Tyus and Karp 1990). Smaller populations of razor- back suckers also exist in the lower Colorado River, but these have been described as relict subpopulations of very old indi- viduals -(Mincldey 1983). The fish is so rare that basic life history infonnationis difficult to obtain, and much about its distribution, abundance, ~nd habitat requirements remains un- known. A rigorous sampling of razorback populations in the Green and upper Colorado rivers from 1979 to 1986 indicated that successful spawning was occurring but yielded no collec- tions-of juvenile fish (Tyus and Karp 1990). This lack of re- cruitment indicates that the existing Green River stock will continue to decline as old individuals die without replacement. The causes of this population decline are unknown. The Green River receives significant concentrations of sele- nium from Stewart Lake and Ashley Creek (Figure I). Stewart Lake water averages 10 J1.g1L selenium, and selenium concen- trations in Ashley Creek waters are 4-5 times higher (Peltz and Waddell 1991). The source of selenium is presumably from drainwater resulting from irrigation practices and possibly leachate from the natural geological strata of the area. Concen- trations of selenium in the Green River average < 10 J1.g1L. Field and laboratory data indicate that selenium concentrations >2.0-5.0 fLgIL in water can cause toxicity and reproductive failure in sensitive warmwater fish (Lemly and Smith 1987). Preliminary results from razorback sucker gamete collections have~hown seleniumcpncentrations ranging from. 3.7 to 28 fLglg ~ weight in eggs, and from < 1.0 to 6.8 J1.g1g ~ weight in milt (Hamilton and Waddell 1994). The Green River,popula- Lion of razorback suckers may be at risk becauses.pawning adults could accumulate selenium to the extent that larval hatchability or post-hatch vitality may be affected. Few residue data exist for Xyrauchen texanus, andinforma- tion about selenium residues in major organs or other tissues is virtuallyD()nexistent. .J(nowledge of the selenium.btmien of razorback suckers inhabiting the Colorado River basin may aid in assessing the role this contaminant plays.in population de- cline. Oneobjectiveof.this study was to provide. b~line data for concentrations of selenium in muscle tissue of.razorback suckers intheGreenRiver..Becai.Jse sacrificing this endangered