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handling stress. Although larger ponds can be used to maintain larger marked fish, all lots would have to be handled when the fish are separated for spawning that stresses all fish in such ponds. Raceways require much more water than ponds that would have cooler water temperatures because they are operated as flow-through systems. Also, experience in culturing razorback suckers, bonytail, and Colorado squawfish has demonstrated that fish cultured in ponds have about twice the growth rate of fish cultured in raceways. However, raceways or other propagation facilities may be needed to physically condition captive-reared endangered fish so that they are able to cope with the riverine environment and escape predators. Using the average number and weight of each family lot from one paired mating and applying the estimated production capacity of ponds in the Upper Colorado River Basin, the surface area of ponds needed to develop and maintain broodstocks and water use (evaporation and water exchange) were calculated. Pond carrying capacity of fish by weight is less when the fish are smaller because their metabolism is higher (i.e., application of the ecological law of inverse size - metabolic rate relating energy flow to standing crop). Experience with the four endangered large river fishes suggests that 500 pounds of fish can be reared per surface acre during the first growing season, 1,000 pounds of fish during the second growing season, and about 1,500 pounds during and after the third growing season. Under these loading capacities, dissolved oxygen should be adequate and unionized ammonia toxicity should not become a problem. Evaporation at altitudes in Intermountain West valleys is approximately 4 acre-feet per surface acre of water annually. Water exchanges in ponds can be kept to 2 1/2 times the volume (about 10 acre-feet per surface acre of water) during the growing season to allow heating of the water by solar radiation. Identified Need for Propagation Facilities to Rear Endangered Fish in the Upper Colorado River Basin 1 1 D 1 Existing hatchery facilities are not sufficient to develop and maintain endangered fish in refuges for broodstock development. The available pond space in propagation facilities that are dedicated for endangered fish in 1994 is 6 acres. The space will be expanded to about 7.2 acres by 1995. The space requirement to meet anticipated Program immediate and short-term needs for captive-reared endangered fish is 27.3 acres. Therefore, a deficit exists of 20.1 acres in primary and backup refuges. This deficit does not include the need for captive-reared fish for proposed augmentation and restoration stocking. The estimated space needed to rear fish for this tentatively proposed stocking effort is about 43.25 acres of ponds and 606 acre-feet of water. The Ouray Endangered Fish Facility UT will be expanded using funds in the U.S. Fish and Wildlife Service budget for Fiscal Year 1994. These funds will be used to construct a water conditioning reservoir, install water supply and drain lines, correct problems with the effluent pond, install an electric security fence, and construct about 6 additional 0.2-acre ponds. t