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46 adequate description of the young, a series of 15 detailed drawings was made using a "camera lucida". These drawings document the development of young Colorado squawfish from egg, various larval stages, and juveniles. Morphometrics and meristics were tabulated for each stage. Age and growth were similar for fish captured in the Yampa- Green Rivers and Colorado River at Grand Junction, Colorado, during 1974-76. Moreover, there was no significant difference between these fish and those from the upper Green River in 1964-66. Colorado squawfish became mature when individuals reached a size of 428-503 mm in total length and an age of 6-8 years. Spawning requirements were speculated from observations in the field and hatchery, and comparison from related species. Food habits are similarly deduced from observations and the literature. Movement of the Colorado squawfish has been difficult to validate, but seasonal patterns were noted. Two squawfish were tracked briefly with the use of sonic tags. The most common parasite of the Colorado squawfish is the copepod, Lernea sp. Other parasites and diseases include the fungus, Ichthyophthirius sp., the tapeworm Proteocephalus ambloplites, and the protozoa Myxosoma sp. and Myxobolus sp. The decline of the species appears to have resulted from the loss of habitat due to environmental changes in stream flow and biological composition. Dewatering, dams and reservoirs, alteration of stream flow and stream morphology, changes in water quality, and the introduction of exotic species are discussed as being the principal causal factors. While additional studies would be useful to management, the urgency of the situation indicates the need for expeditious efforts at preservation. Artificial propagation is a very important means of buying time and should be vigorously undertaken for all endangered native species. Public education, in the long run, is probably the most important consideration. Further water development projects, especially in the upper Green River and its tributaries, should be considered incompatible with the recovery effort.