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Figure 36. Mexican stonerollerlrodapiedras mexicano, 93 mm in total length, from Rucker Canyon, Arizona. This species is rare in the United States, but remains locally common in Mexico. It is listed as a species of special concern. Mexican stonerollers (Fig. 36) have cartilaginous sheaths on their jaws for scraping encrusting algae from stones and other solid substrates. Large adults, which may attain lengths of 15 cm or more, live in pools except in breeding season; young frequent riffles and runs. Breeding males not only display bright colors on the body and fins, but also develop an enlarged head and humped back and strong, sharp tubercles on the snout and head. These tubercles are used in combat between males, stimulating and guiding females, and for digging. The term "stoneroller" comes from the movement of gravel by a male during nest excavation. Stones are pushed about with the head and carried in the mouth, which results in an elongate depression on riffles that is actively defended against other males. Females enter the depression and spawn, then the male protects the eggs until hatching. Male ornate minnows (Fig. 37) are almost as spectacular as Mexican stonerollers in that their heads become swollen and covered by coarse tubercles. The species is, however, much smaller in size, rarely achieving more than 75 mm long, and develops dark bluish black coloration on the body when in breeding condition. The fins also are darkened, overlying a milky white, opaque pigmentation that lies deep in tissues of the fin membranes. The eggs are deposited on the underside of stones in shallow water and vigorously defended by the male. Longer lived Suckers and Minnows.-Desert mountain-sucker and Sonoran sucker/mata/ote sonorense (Figs. 38-39) together comprise the most common larger fishes remaining in the lower Colorado basin. Both occupy hard-bottomed habitats from 300 to 2000 m elevation. Adults of both live in pools, with the former commonly moving to swift riffles and runs to feed at night. Young mountain-suckers Figure 37. Ornate minnow/sardinita ornata, male (above) and female (below) (56 and 55 mm in total length, respectively), from Rio Papigochic, Chihuahua. Ornate minnows are widespread in a number of river basins in Mexico, and may represent a complex of species. abundantly inhabit riffles throughout the day, feedir on encrusting algae scraped from stones with well- developed cartilaginous sheaths on the jaws (Fig. 40 Young Sonoran suckers also may be on riffles, but more typically live in runs and quieter eddies. They feed on aquatic insect larvae and other invertebrate~ and only rarely on plants. Both species spawn in spring on riffles, where adults congregate in large numbers. Spawning is typically of one larger female and two or more smaller males. A depression in th( bottom is formed by lateral movements of the female's body, and adhesive eggs are buried in loose gravels. They develop to hatch in a few days. The Little Colorado sucker (Fig. 41) and tributary populations of bluehead mountain-suckers have similar ecologies in streams of the Little Colorado River basin. In the Rio Yaqui basin, Yaqui suckers/mata/ote Yaqui (Fig. 42) are widespread from the lowest elevations (on and near the river's delta) to higher than 2000 m in mountain streams. They resemble Sonoran suckers both ecologically and morpholog- ically, and may represent only a subspecies of that Gila River form. Three other species of suckers in the Rio Yaqui basin all tend to be at higher elevation: Leopold sucker and Rio Grande 19