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68 MORIZOT ET AL. Colorado pikeminnow tend to migrate to their na- tal spawning areas, and such behavior may be char- acteristic of the species (Tyus 1985, 1986; Horton and Sholz 1993; Osmundson and Burnham 1998), suggesting the possibility of genetic divergence among spawning populations (Tyus 1991). The goal of this investigation was to provide the ge- netic information required for more effective man- agement and recovery of the Colorado pikemin- now. The specific objectives were to (1) identify the genetic variability within and among indige- nous and captive Colorado pikeminnow popula- tions; (2) estimate allozyme allele frequencies in adult and age-0 populations associated with known spawning areas; (3) further evaluate and maximize the use of nonlethally sampled tissues to obtain genetic information; and (4) consider the manage- ment implications of the findings. Methods Samples from throughout the currently recog- nized range of the Colorado pikeminnow were ob- tained from the upper main-stem Colorado, Yam- pa, Green, and San Juan rivers (Figure 1; for more detailed collection site, river kilometer, and fish data, contact J.H.W.). Hatchery broodfish popu- lations were sampled from the Dexter fish tech- nology center. One captive broodfish population was derived from Yampa River fish (Yampa DX- Fl [74]) and one from Colorado-Green River fish (Colorado-Green DX-F1 [81]). For histories of these hatchery fish, see Ammerman and Morizot (1989) and Table 1. We reexamined data from fish populations sampled by Ammerman and Morizot (1989), namely, Colorado-Green DX-Ft (81) adults and Yampa DX-FZ (87) age-0 fish. Another population maintained at Dexter (Yampa DX-FZ [91] age-0 fish) was also sampled, as was a recent addition to the populations at Dexter consisting of 10 wild adults from the Colorado River (Colorado DX-Fo [91]). Biologists for the Upper Colorado River Recovery Implementation Program selected populations and- sampling locations where adult and age-0 Colorado pikeminnow could be col- lected during or following spawning (Table 3). Adult and juvenile fish were collected using tram- mel nets and electroshocking from 1990 through 1993, and tissue samples were obtained nonle- thally. Juveniles (not necessarily associated with their natal areas) were, defined by field biologists on the basis of size and the absence of secondary sexual characteristics. Age-0 fish were captured mainly during the autumn in 1990 and 1991 using electroshock and small-mesh brail seines. We ex- amined 745 Colorado pikeminnow, including 168 wild adults, 39 juveniles, 478 age-0 individuals (including 52 reported by Ammerman and Morizot [1989]), and 60 hatchery-reared individuals, by starch gel electrophoresis and histochemical stain- ing of protein-coding locus products. Age-0 fish collected in the field were euthana- tized with an overdose of MS-222 (tricaine meth- anesulfonate). Fish were frozen on dry ice. After they were transferred to the laboratory and stored at-80°C, samples of skeletal muscle and fins were obtained and stored at-80°C. Adult and juvenile Colorado pikeminnow collected in the field were anesthetized with MS-222 and samples of skeletal muscle and fin taken. To prevent contamination, samples were taken from fish using separate, dis- posable muscle punches and minced with scissors that had been sterilized, rinsed, and dried. Biolo- gists wore new disposable latex gloves for each fish. Samples of skeletal muscle and fins were fro- zen on dry ice until transfer to the laboratory and storage at-80°C. To determine the expression of biochemical ge- netic loci in various tissues, 34 age-0 individuals produced at the Dexter fish technology center from Yampa DX-Fl (74) were euthanatized with an overdose of MS-222, and samples were stored at -80°C. These individuals were sampled in 1991 and are designated Yampa DX-FZ (91). Samples of the skeletal muscle, liver, brain, eye, caudal fin, pectoral fin, erythrocytes, blood plasma, and go- nads were prepared and subjected to vertical starch gel electrophoresis and histochemical visualiza- tion using the methods of Morizot and Schmidt (1990). For tissue specificity of loci, see William- son et al. (1998).. The products of 89 or more loci were resolved and assessed for electrophoretic polymorphism (see Ammerman and Morizot [1989] for particu- lars; other methods are available from D.C.M. on request). The gene and protein nomenclature used follows that proposed by Shaklee et al. (1990). Isozymes (numerically) and allozymes (alphabet- ically in lowercase letters) were designated in or- der of increasing anodal mobility. Data were an- alyzed using the BIOSYS-1 program of Swofford and Selander (1981, 1989), with the data entered as individual genotypes at each locus. Sequential Bonferroni analyses were performed on statistical tests provided by BIOSYS-1 comparisons to adjust for type I error rates (Rice 1989); Z-tests of the normal approximation to the binomial distribution were used to test for significant differences in al- lele frequencies between populations at loci con- Fact are riv Colora River distant tainin tests ~ at lot scribe was at age-0 Ana pikemi