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Horsethief State Wildlife Area CO o Continue to use Horsethief ponds to meet Recovery Program propagation needs. o A Bureau of Reclamation warehouse in Grand Junction, Colorado will be converted into a propagation facility that will be able to rear razorback suckers of Upper Colorado River stock in family lots to be used in broodstock development as well as for stocking in the Upper Colorado River system. Valley City National Fish Hatche~ ND o Pfopagation activities of endangered Colorado River fishes will be discontinued at the Valley City NFH because facilities inlnear Grand Junction and at the Wahweap State Fish Hatchery will be available for the Upper Colorado River Recovery Program. Research Fish Hatchery, Bellvue CO o The Colorado Division of Wildlife will no longer rear endangered Colorado River fishes because they have other obligations for the space at the Research Fish Hatchery in Bellvue. 31 CHEMORECEPTION STUDIES Investigations were initiated in 1991 to determine if razorback sucker and Colorado squawfish utilize chemosensory cues to relocate spawning sites during reproductive migrations; and, if so, to determine if these species can be artificially imprinted to synthetic chemicals. If these fish do natally imprint, then it will be a useful tool I) to segregate fish of wild and hatchery origin during the spawning season, so that mixing of wild and hatchery fish gnomes can be minimized, and 2) to attract reproductive fish to spawning areas where there are fewer predators or where nursery habitat has been established (e.g. flooded bottomlands). Our experiments have shown that both the razorback sucker and Colorado squawfish are very chemosensitive and pl'O'duce spikes of thyroxine hormone just prior to hatching, a necessary condition for imprinting to occur. ,The eggs and larvae of two year-classes of each species have been exposed to two synthetic chemicals - morpho line and phenethyl alcohol - known to result in imprinting of Pacific salmon. These fish are being held at the Ouray hatchery. Although the 1991 year-class of razorback sucker was not sexually mature, preliminary behavioral tests were conducted in 1994 and 1995 to determine if the fish exposed to synthetic chemicals were attracted to their exposure odor and to refine study protocol. Definitive results will not occur until the fish are sexually mature and in migratory state. We estimate the first razorback suckers will reach sexual maturity in 1996 but the majority will be sexually mature in 1997. The Colorado squawflsh should begin reaching sex:ual maturity in 1997. The study is scheduled to conclude in FY 2000. A-25