Desert Sucker (Catostomus clarkii) is a medium-sized (up to 33 cm) fish that occurs in the lower Colorado River basin below the Grand Canyon, the Virgin River Basin, and in New Mexico, Arizona, and Sonora, Mexico is found in the Gila River drainage. As adults they use shady pools during the day and riffles during the night in small to medium rivers; they do not occur in reservoirs, lakes, or water with low levels of dissolved oxygen. They feed primarily by scraping algae from rocks and other substrates.