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.. . 0311," ... 07Z-5~ ~--- ~ORPHOMETRY IN CHUBS OF THE GENUS GILA FROM THE GREEN A~D COLORADO RIVERS, COLORADO AND UTAH: Principal Component Analysis :--1 ark J. R 0 s e n f e 1 d . -;:i17 Utah ~useum of Natural History University of Utah Salt Lake City, Utah 8411;:> ABSTRACT Principal component analysis (PCA) of box-truss and traditional morphometry was used to study morphologic~l variation among UDper Colorado River chubs: "roundtail" and "humpback" chubs as well as suppospd intermediate morphs. Measurements were made from 3 X 5 inch black-and-white photographs with a digitizer. Relation- ships of fishes within and between collecting localities were suggested by PCA, these verifiable using biochemical methods: (a) "roundtail" chubs comprise a distinct lineage; (b) "hump- back" chubs and those previously considered intermediate or unidentified morphs are members of the same species, "humpback" chub; (c) hybridization between the two lineages may be rare or non-existant; (d) most Green River collecting sites are inh2bited by "humpback" chubs; although (e) 'rJhirlpool Canyon appears occupi(~d solely by "roundtail" chubs. Discriminating measure- ments were discovered through PCA, those contrasting mid-body and head proportions having diagnostic value. Measurements of the nuchal hump and caudal peduncle do not appear to be necessary for identifications; however, the ability to differentiate seems to depend on specimen size, with smaller congeners resembling each other. [I qfq fr ]