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DISCUSSION One-year old bonytail show strong preferences for high velocity habitats near the substrate. This is consistent with morphological findings suggesting that the bonytail's specialized features such as the narrow, elongate caudal peduncle, falcate fins, raised nuchal hump and imbedded scales indicate it may have an advantage in swift water environments. The small eyes and terminal mouth may have been adapted as a result of the high sediment load of the Colorado River system (Minckley 1973). Approximately 90% of their time was spent in these habitats when they were alone. When red shiners were present, bonytail spent virtually all of their time near the substrate. However, because red shiners were often found in the higher velocity areas, bonytail showed weak switches to using low-velocity habitats in the presence of red shiners. Behaviorally, bonytail show very similar patterns to those observed for trout (citations ). The presence of red shiners did not significantly affect bonytail behavioral patterns in these experiments and suggest that red shiners will have few effects on bonytail (greater than 100 mm) in terms of substrate or velocity selection. One-year old bonytail overwhelmingly prefered cobble substrate, regardless of whether it was day or night. Based on observations, it seems that juvenile bonytail prefer any substrate that is large enough for them to get under and hide. If this is so, their preferred substrate size should be relative to the size of the fish. Therefore, this suggests that larger fish will select for larger substrate or that larger fish may not be in shallow shorelines or backwaters 24 cm deep. One-year old bonytail also preferred to be at deep depths in substrate replicates that included cobble treatments, and in fact they were found exclusively at deep depths, regardless of whether it was day or night. However, in substrate experiments without cobble treatments bonytail were observed at all depths in different frequencies. This suggests that bonytail were selecting for cobble substrate over depth and the reason that they were found at deep depths is directly related to the location of the cobble 24