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<br />noted by Winn and Miller (1954), the subject of <br />the latter photograph is actually an adult <br />speckled dace (Rhinichthys osculus). In the <br />process of documenting hybridization among <br />several catostomids, Hubbs et al. (1943) published <br />descriptive information for young-of-the-year <br />juveniles (and some larvae) of flannelmouth, <br />white, bluehead, and mountain suckers. Hubbs <br />and Hubbs (1947) did the same for flannelmouth <br />and bluehead suckers. <br />In contrast, larvae and early juveniles of the <br />non-native white and longnose suckers (both <br />widely distributed elsewhere in the United <br />States (U.S.) and Canada) have been well de- <br />scribed by other authors and included in other <br />guides. Early life stages of white sucker have <br />been described by Crawford (1923), Stewart <br />(1926), Fish (1929, 1932), Long and Ballard <br />(1976), Buynak and Mohr (1978), Fuiman <br />(1978,1979), Loos et al. (1979), and McElman <br />and Balon (1980), and included identification <br />manuals by Mansueti and Hardy (1967), Lipp- <br />son and Moran (1974), Jones et al. (1978), <br />Wang and Kernehan (1979), Auer (1982, sec- <br />tion on Catostomidae by Fuiman), Holland- <br />Bartels et al. (1990), and Kay et al. (1994). The <br />pattern of three large lateral spots often obser- <br />ved on early juveniles was recognized at least as <br />early as Ellis (1914). Longnose sucker larvae <br />and early juveniles have been described by Fui- <br />man and Witman (1979) and Sturm (1988) and <br />included in guides by Auer (1982) and Kay et al. <br />(1994). Although Metcalf (1966) suggested that <br />there is little rationale for subspecies designa- <br />tions of white sucker (e.g., C. commersoni <br />suckeyi for western white sucker), descriptive <br />information and illustrations herein for white <br />sucker (except four larval illustrations) and <br />longnose sucker are based mostly on specimens <br />from Colorado populations rather than previous <br /> <br />descriptions from eastern ornorthern U.S. popu- <br />lations. This was necessary in part because <br />prior descriptions, despite being very good and <br />detailed, lacked much of the specific informa- <br />tion needed to directly compare them with our <br />descriptions of other species in the UCRB. <br />Larvae and early juveniles of the third non- <br />native species, Utah sucker, had not been pre- <br />viously described except by us. <br />All UCRB species except Utah sucker are <br />covered to some degree in larval and early <br />juvenile descriptions and a preliminary key to <br />metalarvae by Snyder (1981) and an unpub- <br />lished provisional key to proto larvae and meso- <br />larvae prepared by Snyder in 1984 for the <br />Colorado Division of Wildlife and Ecosystems <br />Research Institute of Logan, Utah (definitions of <br />developmental intervals in later section). How- <br />ever, except for flannelmouth sucker, descriptive <br />species accounts in the 1981 publication are <br />incomplete, and the tentative keys in both docu- <br />ments are based on limited descriptive informa- <br />tion. Mountain sucker was further described in <br />a comparison with Tahoe sucker (Catostomus <br />tahoensis) and cui-ui (Chasmistes cujus) by <br />Snyder (1983a) and completely described (to the <br />extent herein), along with Utah sucker, in a com- <br />parison with June sucker (Chasmistes liorus) by <br />Snyder and Muth (1988). Snyder and Muth <br />(1990) then completed descriptive accounts for <br />all UCRB catostomids except for longnose <br />sucker (and a couple three-view illustrations of <br />white sucker) and included those species in a <br />comparative summary and 60-page key. As an <br />expanded, updated, and retitled edition of that <br />1990 publication, this guide completes and up- <br />dates coverage for all species and replaces the <br />printed keys with a more flexible, easier-to-use, <br />computer-interactive key, the first application of <br />such to fish larvae. <br /> <br />Status and Distribution of the Fish <br /> <br />Identification of larval and early juvenile <br />fishes, or any organism, is largely a process of <br />elimination, and often the list of possible species <br />can be immediately reduced by knowledge of <br />what species are present in the waters sampled. <br />Since 1980, the general distribution of catos- <br />tomid and other fishes in the UCRB has been <br />reviewed by Snyder (1981), Behnke et al. <br />(1982), Carlson and Carlson (1982), Miller et al. <br /> <br />(1982b), Tyus et al. (1982), Woodling (1985), <br />Carlson and Muth (1989), Platania (1990), <br />Sublette et al. (1990), Baxter and Stone (1995), <br />Sigler and Sigler (1996), and Wheeler (1997). <br />Razorback sucker is an endangered species <br />(federal and state of Colorado), and in the <br />UCRB, its recovery is one objective of inten- <br />sive, multiple-agency, multiple-species efforts <br />by the Upper Colorado River Endangered Fish <br /> <br />4 <br /> <br />, <br />