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<br />Introduction <br /> <br />Collections of the early life stages of fish are essential to research on and monitoring of <br />fish spawning sites and seasons, larval production, transport, distribution, nursery habitat, and <br />survival, as well as other aspects of early life history. Such research cannot proceed effectively <br />without accurate identification of at least the target species. However, morphological <br />identification requires knowledge of the appearance of not only the target species, but all similar <br />species in the waters sampled and the diagnostic criteria for segregating them. <br />For the early life stages of many species, including the suckers and minnows of the <br />Colorado River Basin (Fig. 97), morphological criteria for identification change dramatically as <br />the fish grow and develop, making diagnosis especially difficult and complicated. This is <br />exemplified by the 60-page set of keys in the Colorado Division of Wildlife (CDOW) guide by <br />Snyder and Muth (1990) which covers the larvae and early juveniles of just six of seven <br />catostomids (suckers) in the Upper Colorado River Basin (VCRB). Descriptive information and <br />diagnostic criteria must be well founded, sufficiently detailed, and documented in such a way <br />that they are retrievable, usable, and verifiable by any interested researcher. <br />Covering the larvae and early juveniles of native-endangered razorback sucker <br />Xyrauchen texanus, native bluehead sucker Catostomus discobolus, mountain sucker C. <br />platyrhynchus, and flannelmouth sucker C. latipinnis, and non-native (introduced) Utah sucker <br />C. ardens and white sucker C. commersoni, the 1990 guide (Snyder and Muth 1990) has served <br />CDOW, the Upper Colorado River Endangered Fish Recovery Program (Recovery Program), <br />and other regional researchers well. But species coverage of the document is incomplete, some <br />descriptive data needs to be updated, and users have found its very long and intricate set of <br />polychotomous keys formidable, inflexible, and occasionally in error. <br />Longnose sucker C. catostomus was not included in the 1990 guide (Snyder and Muth <br />1990) because of budgetary limitations and the improbability of encountering its larvae or early <br />juveniles in Recovery Program collections. However, with collection of a significant number of <br />juvenile longnose sucker and many larvae suspected to be longnose sucker or hybrids in the <br />lower Gunnison River in 1993, confidence in identification of those and other suckers, was <br />compromised, and the need to comparably describe and incorporate the last of the UCRB suckers <br />in the keys became evident. Existing descriptions of longnose sucker larvae by Fuiman and <br />Witman (1979; partially reproduced in Auer 1982 and Kay et al. 1994) and Sturm (1988) lack <br />much of the descriptive data and detail needed to directly compare them with potentially <br />sympatric species described by Snyder and Muth (1990). <br />Intricate printed keys, such as the one in Snyder and Muth (1990), are very difficult to <br />prepare, correct, update, or expand, in part because each change cascades through most <br />subsequent portions of the key. As a modem alternative, computer-interactive keys are much <br />easier to prepare and modify, and users find them much more flexible and user-friendly <br />(Dallwitz et al. 2000 onwards). Among other features, users can limit consideration to only <br />likely candidate species, elect to have available characters listed in most diagnostic order, and <br />select from that list in any desired sequence, bypassing characters that are unfamiliar, difficult to <br />assess, or based on structures that are damaged or missing. <br />The goal of this project was to facilitate more accurate identification of the larvae and <br />early juveniles of endangered razorback sucker and other suckers collected in the UCRB, <br />including longnose sucker in the lower Gunnison River or wherever else it might occur in the <br />basin. The primary objective was to update and complete the 1990 guide to suckers (Snyder and <br />Muth 1990) as Part 1 of a comprehensive guide to the larvae and early juveniles of cyprinifonn <br /> <br />10 <br />