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13 <br />' River-derived population. Though panmixia of all Colorado pikeminnow reproductive adults still appears <br />to be likely among river systems, distribution of rare alleles suggests that if any population genetic <br />differentiation exists, it is between the Colorado River and the Green River-Yampa River systems. <br />ImPlicationsfor genetic management.- In sum, without resorting to DNA-based technologies, the <br />information gleaned from allozyme variation is more than sufficient to identify population structure in the <br />' Colorado pikeminnow in rivers in the upper Colorado River basin. Management units comprising the <br />Colorado River and the Green River systems were identified by variable presence of uncommon alleles and <br />were selected for inclusion into captive breeding programs. Very large sample sizes will be required for <br />discrimination among allele frequency estimates to describe subpopulation genetic structure. Future <br />increases in sample size in the middle and upper Colorado River and middle Green will render more <br />information. <br />"Additional genetic studies are needed to determine statistical significance of differences in allele <br />frequency estimates among populations in an overall sample of Colorado pikeminnow. Future studies with <br />larger and more comprehensive dissection of allele frequencies into subpopulations may revise our results, <br />' but for the present, geographic variability in allele frequencies suggests populations with minimal or no <br />rare allele sharing, in agreement with the results of Ammerman and Morizot (1989). <br />We conclude that the null hypothesis (Ho:) tested, Colorado pikeminnow are genetically <br />homogeneous or panmictic, is suggested herein: 1) We identified genetic components and characterized the <br />species as presented in Tables 1-7 and the Appendices; 2) We defined genetic profiles for the proposed <br />management units of the Colorado River and the Green River (including the Yampa River); 3) We <br />' determined the genetic status of management units is that they are genetically similar, with no useful <br />genetic markers present. Only rare alleles potentially differentiate the management units; 4) We failed to <br />identify genetic markers for management purposes. No such markers exist within our nuclear DNA or <br />' biochemical genetics data sets; 5) We generated genetic data required to develop breeding strategies and <br />broodfish populations. Caution on the side of conservative management is recommended because the <br />habitat of the Colorado pikeminnow has been drastically altered. Panmixia might be of recent origin due to <br />restriction of spawning sites. Rare alleles might be relicts of previously well differentiated subpopulations. <br />In this study, it was likely that the populations were neither "completely panmictic" nor have "no admixture <br />or migration". The results suggest minimal differentiation, perhaps only of short temporal duration, but in <br />the off-chance that it's important to recovery of an endangered species, conservative management strategies <br />are called for. <br />Recommendations <br />Future examination would be well directed to combine the use of arbitrarily primed polymerise <br />' chain reaction (AP-PCR) or random amplification of polymorphic DNA (RAPD) and isozyme mapping <br />(Kazianis et al. 1996). Such mapping in Xiohophorus species with the use DNA sequencing-style <br />acrylamide gels and carefully controlled conditions of amplification and silver staining allowed exceptional <br />resolution and reproducibility of up to 87 AP-PCR/RAPD markers (e.g. Naim et al 1996a; Naim et al. <br />1996b). <br />Three hatchery stocks should be developed in order to use as many existing hatchery-reared fish as <br />possible. We presume that the Yampa River DX=F2(91) year class derives from Yampa River fish <br />established as a 1974 broodstock; this conclusion should be verified by biopsies of Yampa River DX- <br />F,(74) and Yampa River DX-F2(91) populations to assess allele frequencies at all polymorphic loci, <br />including those expressed in-liver, muscle, fin, and other tissues. Additional wild fish collected from the <br />' Yampa River should periodically be incorporated into the current broodfish population. Two additional <br />populations should be established based upon determination of genotypes of wild fish for stock <br />establishment at all polymorphic loci: first, 20-50 fish from the Colorado River system should be <br />characterized to assure inclusion of rare GPI-2 *c and PEPS*B alleles into breeding stock; and second, 20- <br />50 fish from the Green River system should be genotyped from biopsied tissues to assure inclusion of rare