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Figure 67. Bonytaillcharalito eleganti, 52 cm in total length, from Lake Mohave, Arizona-Nevada. This is considered by many workers to be the most endangered freshwater fish in western North America. An attempt is underway to move all individuals encountered in nature into captivity to serve as a broodstock for future reintroductions. been thought to be adapted to turbulent habitats, similar to those inhabited by humpback chubs. It seems more likely, however, that their body shape makes them most at home in relatively swift but laminar flow, as is still found over smooth sand bottoms in the Colorado River channel. A few adults examined for food habits had eaten a high percentage of terrestrial invertebrates, drifting insects that had been blown by wind or otherwise fallen into the river. Occurrence of adult aquatic insects in stomachs also implies feeding at or near the water surface. The only reproductive activities recorded for bony tail are of aggregations of adults over gravelly "reefs" in artificial impoundments; habitats and activities of young are unknown in nature. The largest recorded bony tail was about 65 cm in length. Two other species of the mainstream Colorado River attain relatively large sizes. Flannelmouth suckers can grow to nearly a meter in length and roundtail chub to more than 40 cm; both are discussed elsewhere. The next two species are relatively small. Woundfin (Fig. 68) rarely exceed 10 cm long, and desert pupfish rarely exceed 40 mm, even as an extremely large adult. The first three of these were rare in early collections from the lower Colorado River basin, and the last was almost certainly common in more ephemeral habitat too severe for other species, such as on the delta itself. Desert pupfish persist on the delta at present, typically in highly saline pools associated with inflowing springs and seeps. The woundfin was the only small, short-lived species known from the channel of the lower Colorado River. This species is one of a unique group of North American minnows in having the leading rays of its dorsal fin modified into a stout spine. Other members of this minnow group also have such rays, but not so spectacularly developed. The species is adapted for life in highly turbid water over shifting sand bottoms. Its fins are large and sickle-shaped, and dorsal streamlining is extreme while the lower body is flattened to fit closely to the Figure 68. Woundfin, ca. 90 mm in total length, from the Virgin River, Arizona. This endangered species, once known from both the lower Colorado and Gila rivers, is now completely restricted to the Virgin River mainstream. Nevada-Arizona-Utah. 34