<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
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