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General Description <br /> <br />Adult razorback suckers may grow to a total length of about 1 m -and a weight of 5-6 kg. <br />However, most specimens of the fish are smaller. The largest fish presently occur in <br />the warmer climate of the lower Colorado River. Females are larger than males of the <br />same age, and sizes of 470-740 mm are reported in Lake Mohave, Arizona (Minckley <br />1983). <br />The razorback sucker shares many characters with other catostomids, but is <br />distinguished from all other catostomids by a pronounced bony keel that grows from the <br />dorsal surtace of its back (i.e., behind the occiput; Frontispiece). Formed mostly from <br />enlarged neural and intemeural bones, this relatively thin, sharp-edged keel is the <br />basis for its common name. It is also distinguished by well-developed, elongated <br />filaments on its gill rakers, an adaptation for feeding on zooplankton. Characteristics <br />shared with other member; of its family include an intermediate number of moderately <br />compressed pharyngeal teeth arranged in comb-like fashion, which is presumably an <br />adaption to benthic feeding (Eastman 1977; Sublette et al. 1990). Its bony dorsal keel, <br />heavily ossified caudal skeleton, and thickened and foreshortened caudal rays are <br />thought to be adaptations to the strong river currents in which the fish lives (Eastman <br />1980; Moyle- and Cech 1988). <br />4 <br /> <br />1 <br /> <br /> <br />1 <br /> <br /> <br /> <br />t <br />1 <br />1 <br />I <br /> <br />LI <br /> <br /> <br />