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temperature for this group of fish was 22.2°C (Utah DWR, 1965). Similarily, YOY bonytail chub tested by Bulkley et al (Appendix) had individual mode temperature preferences that ranged from 15°C to 31°C and a final preferendum of 24.2°C. Survival and development of bonytail eggs and larvae are greatly affected by water temperature (Appendix). Of 1,300 eggs incubated at from 12°C to 13°C, only 4 percent hatched and only 13 feeding larvae survived. About 55y of the eggs incubated at from 16°C to 17°C hatched with no more than a 4~ additional loss to feeding. At temperatures from 20°C to 21°C hatching success was from 88-912 and larval survival was from 98-999. In addition, Bulkley et al (Appendix) reported from 70-90X hatching success of bonytail eggs at 26°C and from 50-70y at 14°C. None survived at 10 or 31°C. Embryological development and hatching were delayed by cooler water temperatures. At 20-21°C, 16-17°C and 12-13°C, hatching occurred at 4-7 days, 7-11 days and 14-21 days respectively (Appendix). Bonytail chub reared at Willow Beach NFH grew at a rate of 0.61 mm per day at a mean temperature of 21.2°C from a mean total length of 6.8 to 49.5 mm in 70 days. The stocking density was approximately 1,900 fish per unit. This compares closely with the rate of growth (0.536 mm/day) and temperature (20.1°C) reported above for the humpback chub. Juvenile bonytail chub's swimming performance improved significantly with temperature (Appendix). They were able to swim for about 60 minutes at velocities of 0.45, 0.57 and 0.63 m/sec at 14, 20 and 26°C respectively. Overall, their swimming performance was slightly better than that of the Colorado squawfish juveniles (Figure ). While the performances of the Colorado squawfish and razorhack sucker were best at 20°C, the bonytail chub performed best at 26°C as did the humpback chub. Total Dissolved Solids - The TDS at Lake Mohave in Arizona, where some adults are still found, is about 750 mg/1. Willow Beach NFH, located on the lake, has successfully spawned the adults and reared the young using the lake water. Some YOY were transferred to Utah State University for testing their TDS tolerance and preference in the labor- atory. Bulkley et al (Appendix) found YOY bonytail chub preferred TDS levels from 4,091 to 4,679 mg/1 and avoided Levels above 6,600 mg/1. Actual concentrations of TDS found in the main rivers seldom exceed 2,000 mg/1. However, the Dolores River often exceeds 6,000 mg/1 TDS, which could force bonytail chub to leave this system. Food - No bonytail chub stomachs were analysed. However, their food preferences are likely to be similar to the humpback and roundtail chub. Vanacek and Kramer (19$1) found they fed on insects. None were found to be feeding on fish as does the roundtail.