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<br />INTRODUCTION
<br />
<br />Despite the information explosion and
<br />technological advances of the past few
<br />decades, knowledge of the biology of many
<br />North American fishes remains inadequate
<br />for either evaluation of potential environ-
<br />mental impacts on aquatic ecosystems or
<br />optimal management of fisheries. Knowledge
<br />of early-life stages (eggs, larvae, and early
<br />juveniles) is especially weak. For most spe-
<br />cies, the larvae and early juveniles represent
<br />several life-intervals that are ecologically
<br />distinct from each other and from their later
<br />juvenile and adult counterparts. Knowledge
<br />of habitat requirements and limitations, popu-
<br />lation dynamics, and behavior of these early-
<br />life intervals will improve our understanding
<br />of aquatic ecosystems and communities and
<br />facilitate more effective monitoring and
<br />management of fish populations and habitats.
<br />Such knowledge is particularly valuable in
<br />evaluation of environmental impacts and
<br />recovery of endangered species such as the
<br />razorback sucker (Xyrauchen texanus).
<br />
<br />Early-life stages of fishes are or should
<br />be a principal focus of many ecological stud-
<br />ies (Snyder 1976a). Their distributions and
<br />densities are indicative of spawning and nur-
<br />sery areas, spawning seasons, larval behavior,
<br />and year-class strength. Even in baseline
<br />surveys designed to determine presence and
<br />relative abundance of fishes, larval collections
<br />can often provide information on certain spe-
<br />cies that because of gear selectivity, behavior,
<br />or habitat are difficult to collect or observe as
<br />adults. Studies of fish larvae also can provide
<br />informat~on on morphological development,
<br />systematIcs, growth rates, survival rates, food
<br />habits, predation, and various other ecological
<br />relationships.
<br />
<br />Research on ecology of early-life stages
<br />and subsequent management efforts depend
<br />on accurate identification of collected speci-
<br />mens. Inland fishery managers and research-
<br />ers often exclude potentially critical larval-
<br />fish investigations specifically because they
<br />"haven't done it before" or they don't have
<br />the taxonomic tools needed for the job.
<br />Unfortunately, acquisition of this vital taxo-
<br />nomic information is very time-consuming
<br />and expensive. While such information is
<br />slowly building, the many individual efforts
<br />are piecemeal, uncoordinated, and often "a
<br />
<br />labor of love" on the part of the researchers
<br />involved.
<br />
<br />Of approximately. 775 species of fresh-
<br />water and anadromous fishes in North Amer-
<br />ica (Lee et al. 1980), less than 20% are ade-
<br />quately described as larvae for identification
<br />purposes (extrapolated from 15% reported by
<br />Snyder 1976a). In a relatively comprehensive
<br />listing of regional guides, keys, and compar-
<br />ative descriptions of larval fishes by Simon
<br />(1986), only about 80 of 230 citations (35%)
<br />pertain to freshwater species. Snyder (1983b)
<br />listed 11 regionally oriented larval fish identi-
<br />fication manuals for or including freshwater
<br />species (some of these are for the same
<br />regions and all are incomplete in coverage).
<br />Since 1983 five local or regional guides for
<br />freshwater larvae have been published
<br />(Conrow and Zale 1985, McGowan 1984 and
<br />1988, Sturm 1988, and Wang 1986).
<br />
<br />The purpose of this publication is to
<br />facilitate identification of larval and early-
<br />juvenile razorback, flannelmouth, bluehead,
<br />mountain, white, and Utah suckers (Xyrau-
<br />chen texanus, Catostomus latipinnis, C. disco-
<br />bolus, C. platyrhynchus, C. commersoni, and
<br />C. ardens respectively). All but Utah sucker
<br />are covered to some degree in the metalarva
<br />key and descriptions by Snyder (1981), a
<br />mountain sucker description by Snyder
<br />(1983a) and in an unpublished provisional key
<br />to protolarvae and mesolarvae Sp.yder pre-
<br />pared in 1984 for the Colorado Division of
<br />Wildlife and Ecosystems Research Institute
<br />of Logan, Utah. However, except for flannel-
<br />mouth sucker, species accounts in the 1981
<br />publication are incomplete and previously
<br />prepared keys are tentative and based on
<br />limited descriptive information. By compar-
<br />ison, species accounts and keys in this manual
<br />are much more comprehensive for the char-
<br />acters studied and the accounts include full
<br />sets of three-view illustrations for all but
<br />white sucker. Species accounts for mountain
<br />and Utah suckers are modifications of those
<br />in Snyder and Muth (1988).
<br />
<br />The early-life stages of white sucker have
<br />been described or included in identification
<br />manuals by many other authors: Crawford
<br />(1923), Stewart (1926), Fish (1929,1932),
<br />Mansueti and Hardy (1967), Lippson and
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<br />J
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