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J J I' J ) l J 1 J .~ ] ] ] ] J ] ] -- ] C.J C.-) /-~ c.o <".0 W Investigations conducted by U.S. Department of the Interior agencies have documented elevated concentrations of selenium in water, sediment, and biota at various locations in the San EXECUTIVE SUMMARY Juan River basin. The San Juan River provides critical habitat for two endangered fishes, Colorado pikeminnow (Ptychocheilus lucius, formally named Colorado squawfish) and razorback sucker (Xyrauchen texanus) and concern has been raised about the effects of selenium on these native fishes. At present, little is known about the sensitivity of Colorado pikeminnow to long-term selenium exposures. The objective of this study was to determine the effects of dietary and waterborne selenium on survival, growth, and reproduction of adult Colorado pikeminnow under controlled laboratory conditions. Adult Colorado pikeminnow (16 years old) were obtained from Dexter National Fish Hatchery, Dexter, NM, and exposed to one of six combined dietary and waterborne selenium treatments for 155 days and then held tmder control conditions for 90 days to allow for selenium depuration. The treatments consisted of three dietaryconcentrations (2.2 [control], 7.3, 11.8 ~g/g dry weight, as seleno-DL-methionine) and two waterborne concentrations (control and 5 ~g/L, as a 6: I ratio of selenate: selenite ). Growth was measured on all fish and muscle plugs taken from females at test initiation and every 30 days thereafter. The fish were tested in reconstituted water designed to simulate the water quality of the San Juan River, near Shiprock, NM. The test water was routinely monitored for selenium concentrations and general water quality characteristics. The fish were artificially spawned after 154 days of exposure and the number of eggs expressed, egg diameter and weight, and selenium residues in eggs were determined. The eggs produced were monitored for survival, hatchability, hatch time, and deformities in a separate test IX