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Razorback sucker <br />Razorback sucker larvae were obtained from the Grand Valley Propagation Facility (U.S. <br />Fish and Wildlife Service, Colorado River Fishery Project, Grand Junction, Colorado) when they <br />were approximately 2-days old (after hatching) and transported to laboratory culture facilities at <br />Colorado State University (Fort Collins, Colorado). Culture-facility water temperature was 19°C. <br />Razorback sucker larvae were reared in mass cultures until selected for testing. Fish in mass <br />cultures were offered _< 24-h-old brine shrimp nauplii twice daily. Exposures were planned to <br />begin when 75% or more of fish were observed feeding on live brine shrimp nauplii or rotifers <br />(10-12 days after hatching). However, exposures were delayed until razorback sucker larvae <br />were 41-days old because flannelmouth sucker larvae were not available until that time. <br />Consequently, razorback sucker larvae were 41-days old (after hatching; mesolarva) at the start <br />of the ELS test, and 16-days old (protolarva) at the start of the acute test. <br />Flannelmouth sucker <br />Fertilized flannelmouth sucker eggs were obtained from the Grand Valley Propagation <br />Facility (U.S. Fish and Wildlife Service, Colorado River Fishery Project, Grand Junction, <br />Colorado) and transported to laboratory culture facilities at Colorado State University (Fort <br />Collins, Colorado). Mean selenium concentration in fertilized eggs was 4.06 µg/g dry weight. <br />Flannelmouth sucker were hatched in a Heath incubator at 19°C, then reared in mass cultures <br />until selected for testing. Fish in mass cultures were offered s 24-h-old brine shrimp nauplii <br />twice daily. Larvae were 11-days old (protolarva) at the start of the acute and ELS tests. <br />5 <br />