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ADULT STUDY This section of the report will describe the methods, results, and discussion of the adult razorback sucker portion of the reproduction study. Also included is information derived from informal observations of adult razorback sucker held at North Pond. Methods One hundred eight razorback sucker were acquired on July 6, 1995, as 3-year-old adults from Wahweap Fish Facility, Big Water, UT, operated by the Utah Division of Wildlife Resources. The adults were transported to Grand Junction, CO, by personnel of the CRFP and the u.s. Bureau of Reclamation. Parents of these fish were from the San Juan River arm of Lake Powell, UT. All the fish used were progeny of a single spawn of two adult razorback sucker (female: PIT 7F7FI9036C, and male: PIT 7F7D055802). Fish were treated with oxytetracyline via intraperitoneal injection administered by personnel of the CRFP before release at the three study sites to treat potential infections incurred during transport or after release at the study sites. An additional 36 were transferred from Wahweap to Horsethief on July 27, 1995, and an additional 26 transferred on September 8, 1995. Site descriptions The partiallife-cyc1e chronic toxicity study was conducted by exposing adult fish for about 9 months to water and natural foods at three sites adjacent to the Colorado River in the , Gral1d Valley near Grand Junction, CO: Horsethief Canyon State Wildlife Area (reference site; hereafter referred to as Horsethief), Adobe Creek, and North Pond at Walter Walker State Wildlife Area (WWSW A) (Figures 2-6). The Horsethief facility is operated by the CRFP, Grand Junction, CO. The Horsethief site was located about 19 km (12 miles) west of the Grand Junction city limits, the Adobe Creek site was located about 5 km (3 miles) west of the Grand Junction city limits, and the North Pond site was located about a half km to the southwest of the Grand Junction city limits. Sampling stations were established at each site a few months before fish were stocked for the study as follows: Horsethief (HTi [inlet] and HTo [outlet]), Adobe Creek (ACl through AC7), and WWSW A (WWl through WWlO). At Horsethief, fish were held in earthen ponds, either pond 1 or 6, along with other endangered fish stock (Figure 3). The water in the ponds was maintained by water pumped directly from the Colorado River near Fruita, CO, and was believed to have little or no selenium contamination. The Adobe Creek site was a tertiary river channel about 200 m long and 3 to 5 m wide and was isolated from river flow by dikes at both ends. Both dikes have large gate valves and the downstream dike also had an overflow water control structure (Figure 4). Fish were held in the section of the channel with sample stations AC3, AC4, and AC5. The water level at Adobe Creek was maintained with water pumped from the secondary channel (location AC2). Overflow water from an irrigation ditch (AC7) also entered the diked area. Water at the site was maintained at about 1.5 m deep, and was believed to have relatively low levels of selenium contamination. The North Pond site was an isolated pond about 1 ha (2.5 acre) in size with a maximum depth of 1.5 m located on a terrace about 2 m above the floodplain (Figure 5). Water in North Pond was supplied primarily by ground water 7 I I I I I I I I I ,I I I I I I I I I I