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.. 436 AMMERMAN AND MORIZOT r - -40.N latitude f N I 110. W longitude FIGURE I.-Sampling localities for Colorado squaw- fish from the Green and Colorado rivers. The numbers identify river kilometers, measured from the confluence of the Green and Colorado rivers, where samples were collected. river individuals (N = 7) and fish of the 1987 year class derived from Yampa River individuals (N = 31). Twenty-six individuals from each of two wild populations were collected and immediately placed on dry ice. Fish were collected from three localities in the Colorado River and from five lo- calities in the Green River (Figure I). We dissected liver, brain, eye, muscle, fin (com- bination of dorsal, caudal, and pelvic fins), gill, kidney, and heart tissues from each frozen speci- men and stored them at -80.e. Muscle, brain, liver, and eye samples (0.1 g of tissue) from the 1981 year class were diluted with 0.2 mL buffer (0.01 M tris HCl at pH 7.5, 0.001 M 2-mercap- toethanol, and 0.00 I M EDT A) and homogenized on ice. Lens and retinal tissues were prepared sep- arately for samples from the 1981 year class. Be- cause of their small size, individuals of the 1987 year class and the two wild populations were pre- pared as follows: 0.03 mL buffer with livers, 0.05 mL buffer with brain and eye (containing retina and lens), and 0.2 ml buffer with 0.1 g muscle. Tissue homogenates were refrozen at -80.C for at least 5 min. Samples were thawed and centri- fuged for 15 min at 4.C before electrophoresis. Some liver samples from hatchery stocks required extraction of lipids with toluene and filtration for optimum resolution. An equal volume of toluene was added to the sample and stirred in a vortex mixer for 5 sec. After a 10-min centrifugation, we removed the upper toluene layer. Some samples were centrifuged through 0.45-JoLm-pore cellulose acetate filters for additional purity. Liver super- natant was removed from the pellet for storage. Fin samples did not require grinding, but they were minced and allowed to freeze in sample buff- er before centrifugation. We performed vertical starch gel electrophore- sis on muscle, liver, fin, and brain plus eye ac- cording to the methods of Siciliano and Shaw (1976). Enzyme numbers (IVBNC 1984), loci, and buffer systems for all enzymes examined are given in Table l. Gels (12% weight/volume) were run routinely at about 200 V for 18 h. Stain recipes were from Shaw and Prasad (1970), Siciliano and Shaw (1976), Harris and Hopkinson (1977), and Morizot et al. (1983). We used StarchArt starch (Smithville, Texas). Loci are indicated in italics followed by an as- terisk; alleles also are in italics, and are preceded by an asterisk. Both isozymes and allozymes are in roman characters. Loci are designated numer- ically in order of decreasing anodal mobility. Al- leles and allozymes are designated according to relative electrophoretic mobility, calculated as a percentage of the mobility of the most common allele, which was arbitrarily assigned the value of 100. Data analyses were performed with the BIO- SYS-l program of Swofford and Selander (1981). The values used for data entry were individual genotype scores at each locus. We calculated mean heterozygosity values by the direct-count method (Swofford and Selander 1981). For chi-square tests of Hardy-Weinberg proportions, we employed the Levene (1949) correction for small sample size and used exact probabilities. The unweighted pair- group method with arithmetic averaging was used with Nei's (1978) unbiased genetic identity.