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Razorback Sucker Xyrauchen texanus Status The razorback sucker is listed as endangered on the Colorado list and has been proposed for threa- tened status on the federal list. Distinguishing Features The abrupt, sharp-edged hump on the back imme- diately posterior to the head identifies the razor- back sucker from all other suckers and from all other fishes. The hump of the humpback chub is rounded and lacks the sharp leading edge. The size and development of the hump is related to size and age. Young razorback suckers less than 6 to 8 inches long have only a slight hump, and might therefore be confused with the flannelmouth sucker. Hybrids between razorback and flannelmouth suckers are common in some areas. The razorback sucker typically has 14 or 15 dorsal fin rays vs. the typical 12 or 13 in the flannelmouth sucker. The razorback sucker has the larger number of gillrakers (small protuberances on the upper surface of the gill arches): typically the first gill arch has 45 or more gillrakers in razorback suckers and about 35 in flannelmouth suckers. Hybrid specimens are inter- mediate in the size of the hump and in other charac- ters. Life History The peculiar body shape of the razorback sucker, which suggests a design for stability on the bottom in turbulent flow, may be a useful adaptation for migration during high river flows; however, virtually all captures of razorback suckers have been from essentially still water, particularly off channel ponds created from gravel excavation or for irriga- tion storage. As is typical of species in the sucker family, the razorback sucker has fleshy lips that enable it to suck up small invertebrate animals and organic debris from the bottom. Also, numerous gillrakers make the razorback sucker well adapted for straining small animals (zooplankton) from the water passed over the gills for respiration. The food is sifted by the gillrakers and funneled into the throat, where it is finely ground by rows of pharyngeal teeth. The razorback sucker attains an old age (probably more than 20 years) and can reach a large size (more than 10 pounds). When formerly abundant, the razorback sucker and the squawfish were the most common and desirable food fish of the Colorado River basin, and supported local commercial fisheries. Although the razorback sucker is well adapted to thrive in reservoirs, reproduction has not been sufficiently successful to maintain its numbers. When impoundments were created in the lower basin, razorback suckers soon established large populations; however, the populations declined as the fish became fewer and older each succeeding year. Razorback suckers have been observed spawning along the shores 23