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<br />. <br /> <br />further anatomical resolution might be achieved by simultaneous <br />consideration of morphometric and meristic data. <br /> <br />Protein electrophoresis was done was done on 24 loci for 159 <br /> <br /> <br />Gila. One-hundred and thirty-one fishes from the Upper Basin <br /> <br /> <br />were examined: (a) q. cypha, several sites on the Green River, <br /> <br /> <br />Westwater Canyon on the mainstem Colorado River, and the Little <br /> <br /> <br />Colorado River; (b) ~. robusta robusta, Black Rocks and Westwater <br /> <br /> <br />Canyon on the mainstem Colorado River as well as Cottonwood <br /> <br /> <br />Creek, a tributary of the San Rafael River; and (c) @. robusta <br /> <br /> <br />seminuda, the Virgin River. Gila elegans may be nearing total <br /> <br /> <br />extinction and has become virtually absent from the Upper Basin, <br /> <br /> <br />so hatchery stock derived from the only known population, at Lake <br /> <br />Mojave in the Lower Basin, was examined. Three G. robusta <br /> <br /> <br />robusta X Little Colorado River [. cypha or F2 backcrosses were <br /> <br /> <br />obtained from the Dexter National Fish Hatchery. Some alleles <br /> <br /> <br />pehaps unique to taxa were indicated. However, their specifici- <br /> <br /> <br />ties were obscured by results for sympatric situations in which <br /> <br /> <br />G. cypha and G. robusta were electrophoretically very similar. <br /> <br /> <br />Hybridization is proposed as a likely explanation. Conspecifi- <br /> <br /> <br />ci ty for [. cypha and G. elegans was not contraindicated by <br /> <br /> <br />electrophoresis. <br /> <br />Cytogenetic studies indicated that taxa have indeed undergone at <br /> <br /> <br />least some hybridization. G. robusta has nucleolar organizing <br /> <br /> <br />regions located on a different chromosome than either G. cypha or <br /> <br />3 <br />