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CHARACTERISTICS USEFUL IN IDENTIFICATION OF CYPRINIFORM FISH LARVAE The following discussion of taxonomically useful characters is reprinted with minor modification from Snyder (1981) and Snyder and Muth (1988). Fishes of the families Cyprinidae (minnows and carps) and Catosto- midae (suckers) are closely related and mor- phologically similar. Together the two fami- lies account for nearly half of over SO species in the Upper Colorado River System. Gener- alizations with respect to the order Cyprin- iformes refer specifically to North American species of these families. Figures 2 and 3 identify the more obvious morphological features and structures of catostomid (and cyprinid) eggs and larvae. Identification of fish larvae is in part a process of elimination. Even before examin- EARLY CLEAVAGE ation of a single specimen, the number of candidate species can be substantially reduced by a list of known or likely species based on adult captures in the study area or connected waters. However, there are cases in which the presence of certain species was first docu- mented by collection and identification of lar- vae. Incidental transport of eggs or larvae from far upstream or distant tributaries also must be considered. Knowledge of spawning seasons, temperatures, habitats, and behavior coupled with information on egg deposition, larval nursery grounds, and larval behavior are also useful in limiting possibilities. Berry and Richards (1973) noted that "although species of a genus may vary from one geographical area to another, generally Axi a 1 Strand (best seen from above) Ya 1 k under thin yalk-sac wi th cavi ty between Germ Ri ng MORULA Yolk protruding GASTRULA through Genn Ri ng Mesodenna 1 Areala Yolk Plug with pratruding Periblast Material EARLY EMBRYOS Fig. 2. Selected anatomical features of cypriniform fish eggs and embryos (from Snyder 1981; based on drawings from Long and Ballard 1976). 7