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~. ~~.' .:- ~~~~ ~ t ~ ~~~ i Z~f~, ~~ U I} Narth American Journal of Fisheries Management 22:66-76, 2002 © Copyright by the American Fisheries Society 2002 Biochemical Genetics of Colorado Pikeminnow DONALD C. MORIZOT University of Texas, M. D. Anderson Cancer Center, Science Park, Research Division, Post Office Box 389, Smithville, Texas 78957, USA h ,4 _ . I~ i~ j~ ~- - ~' ~~.. J. HOLT WILLIAMSON U.S. Fish and Wildlife Service, Dexter National Fish Hatchery and Technology Center, Post Office Box 219, Dexter, New Mexico 88230, USA GARY J. CARMICHAEL* U. S. Fish and Wildlife Service, Mora National Fish Hatchery and Technology Center, Post Office Box 689, Mora,. New Mexico 87732, USA Abstract.-We evaluated the genetic relationships among two captive populations of Colorado pikeminnow Ptychocheilus Lucius from the Dexter National Fish Hatchery and Technology Center, New Mexico, and 15 samples of wild adult, juvenile, and age-0 fish from the Green, Yampa, Colorado, and San Juan rivers. The products of 89 or more loci were resolved by starch gel electrophoresis and histochemical staining; 8 loci were polymorphic in at least one sample. Min- imally invasive sampling of fin and skeletal muscle tissue resulted in data from wild adults and juveniles (N = 207) and hatchery-produced adults (N = 60) with no mortality. Additionally, 426 . wild and 34 hatchery-reared age-0 fish were sampled by necropsy. Allele frequencies did no[ differ significantly among geographically separated breeding populations, suggesting essential panmixia. Mean FsT values ranged from 0.003 among wild age-0 Green and Colorado River fish to 0.108 among all wild adult fish and captive broodfish. Significant deviations from Hardy-Weinberg equilibrium were observed at four loci in the Colorado and Green River samples of adult, juvenile, and age-0 fish. No hatchery samples showed such deviations. The most striking geographic var- iability observed was the presence of the rare private alleles GR*b and TPI-2*c in Green River basin samples and GP/-2*c, PEPB*a, and PEPS*b in Colorado River basin samples. The lowest genetic variability was observed in the San Juan River tributary of the Colorado River, possibly as a result of prior population bottlenecks. Our gene frequency and genetic divergence results do not support the proposition that there is significant genetic differentiation among populations of Colorado pikeminnow. Rather, the significant heterozygote deficiencies at several loci suggest that although geographic differentiation may have existed in the pas[, current barriers to fish movement and widespread stocking of hatchery fish now mask it. The Colorado pikeminnow Ptychocheilus Lucius (formerly the Colorado squawfish; Nelson et al. ~~ 1998) is endemic to the Colorado River basin of k i f; ' c the southwestern United States (Holden and W - ~~ ~ 1982). It is a large river cyprinid that was listed ~ ~ - as endangered by the U.S. Fish and Wildlife Ser- ~~ ~ vice in 1967. Declines in the abundance and range of the species have been associated with habitat ~''a~` i, ' fragmentation and blocked passage, water diver- , -"` sions, lost spawning and nursery habitat, dewa- tering, contaminants, and introductions of non- native fishes (Hinckley and Deacon 1991). A large literature documents the history of threats to the existence of the Colorado pikeminnow (see Os- mundson et al. [1997, 1998] and Osmundson and Burnham [1998] for references). Endangered Species Act recovery goals for the Colorado pikeminnow call for the protection, maintenance, and establishment of self-sustaining populations throughout the species' historical range in the Colorado River basin (U.S. Fish and Wildlife Service 1990). However, population iden- tification is difficult because very little is known about the demographic characteristics of this spe- cies, particularly fish movement and behavior as- sociated with reproduction (Tyus 1986; Osmund- son and Burnham 1998). Even less is known about its genetic structure. Biochemical genetic analyses of two wild populations provided basic genetic information on Colorado pikeminnow (Ammer- man and Morizot 1989) but did not examine sus- pected spawning populations. Hardy-Weinberg (H-W) disequilibrium at two loci in these wild * Corresponding author: gary_carmichael@fws.gov Received April 19, 1999; accepted May 7, 2001 66 qy~`F TA brooc wiila prods Year 1973 1974 1978 1979 1981 1987 1991 1991 popul indic~ rather merm 0 fish two c Fish 1 ico. 7 were sampl for w ulatio Pro tive bt (Table in trit stocki Colon TABI Kenne} .z;