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hybrid, and some deny that they are separate species at all. <br />Bonytail Biology <br />The following description is extracted from the Bonytail Recovery Plan published by the <br />U.S. Fish and Wildlife Service (1990). The adult bonytail has an elongated body with a <br />long, thin caudal peduncle, a white belly, silvery sides, and an olivaceous belly. The <br />base of the fins exhibit a slight orange coloration, in both sexes, throughout much of the <br />year (Vanicek 1967). Adults commonly reach lengths of 300-350 mm, but larger <br />specimens of up to 600 mm have been taken from Lakes Mojave and Havasu in the <br />Lower Basin (Minckley 1973, Minckley pers. commun.). In the Lower Basin, very old <br />bonytail have been taken, with ages up to 49 years old. The bonytail taken from the <br />Upper Basin were seven years old (Vanicek and Kramer 1969). The head is small and <br />has a somewhat oblique mouth. The skull is concave dorsally and, in adults, the head <br />arches smoothly into a predorsal hump. Scales are often lacking or embedded on the <br />top of the hump, belly, or caudal peduncle (Minckley 1973). The fins are large, with 9- <br />11 (typically 10) dorsal fin rays and anal fin rays (Holden and Stalnaker 1970). The <br />dorsal fin origin is nearer to the tip of the snout than it is to the base of the caudal fin. <br />Pharyngeal teeth are typical for large-river chubs at 2, 5-4, 2 (USFWS 1990). <br />Adult bonytail appear to prefer eddies and pools adjacent to deep, swift, semi-rocky <br />areas in the main channel (Vanicek 1967). They also seem to prefer turbid water with <br />total dissolved solids of 4100-4700 mg/I (Pimental and Bulkley 1983). In the lab, <br />bonytail preferred temperatures of 24.2°C. Juveniles inhabit backwaters and other <br />sheltered shoreline habitats (Vanicek and Kramer 1969). Adult bonytail appear <br />relatively quiescent during the day and their activity level increases during the twilight <br />hours (Tyus and Karp 1991). <br />When bonytail reach 5-7 years of age they are mature enough to spawn (Behnke and <br />Benson 1980). The only recorded spawning data in the wild comes from Lake Havasu <br />(Jonez and Sumner 1954), in which bonytail spawned over gravel bars. During <br />5