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<br />Tn <br /> <br />~ <br /> <br />Robert T. Muth <br />Larval Fish Laboratory <br />Colorado State University <br />Fort Collins, Colorado 80523 <br /> <br />~..J <br />X 0 J <br />" ~o.} ~lj <br />"""" Cyc-~~,/ <br />',\ ~) ~\ <br />~ ~..). ~j' <br />~ ~1,. "t.' <br />~~ ~.V~. <br />~. ~...P) <br /> <br />TAXONOMIC IDENTIFICATION OF LARVAL AND EARLY-JUVENILE <br />Gila NATIVE TO THE UPPER COLORADO RIVER BASIN <br /> <br />Charles M. Haynes <br />Colorado Division of Wildlife <br />Fort Collins, Colorado 80526 <br /> <br />Clarence A. Carlson <br />Department of Fishery and Wildlife Biology <br />Colorado State University <br />Fort Collins, Colorado 80523 <br /> <br />ABSTRACT <br /> <br />The cyprinid genus Gila includes 3 historically sympatric, closely related <br />species endemic to the Colorado River Drainage, Le., G. robusta robusta <br />(roundtail chub), G. cypha (humpback chub), and G. elegans (bony tail) . <br />Efforts to monitor and manage these species have been complicated by the <br />lack of reliable taxonomic criteria for specific identification of their <br />larval and early-juvenile stages. Over the past 4 years, comparative <br />taxonomic research has been conducted on the early life-history stages of <br />these species by the Larval Fish Laboratory, Colorado State University, <br />Fort Collins and the Colorado Division of Wildlife. About 1000 cultured <br />and field-collected Gila larvae and early juveniles were examined and data <br />recorded en approximately 50' morphometric and 25 meristic characters, <br />melanophore pigmentation, developmental osteology, and developmental state <br />relative to size and age. Linear regression and multivariate statistical <br />techniques were used to enhance resolution of the morphometric and <br />meristic data. Bony tail can be distinguished from roundtail and humpback <br />chub using one of several meristic characters, e.g., myomeres typically 21 <br />or more post-vent for bony tail and 16-17 post-vent for roundtail and <br />humpback chub. Meristic characters seem to have limited value for <br />separating roundtail and humpback chub; however, morphometric data, <br />although not always definitive, do provide useful discriminating <br />criteria. Results of these analyses were used to develop a provisional <br />taxonomic key for these 3 species. <br /> <br />fYb<-. \N" M.$X- <br />r~ b . ^~"..~-iQj <br />b~ ( (q&,~) <br /> <br />165 <br />