About Gila robusta Baird & Girard, 1853
The roundtail chub (Gila robusta Baird & Girard, 1853) has a body that is significantly larger in the section forward of the dorsal fin, and tapers toward the tail in the posterior section. Its forehead is concave. It has a moderately large mouth that does not extend as far back as the eye's pupil, and the mouth is overhung by the snout. The tail is deeply forked. Its dorsal coloration is grayish brown, and its ventral side is a lighter shade. During the breeding season, mature males sometimes develop red-orange coloring on their lower cheeks and paired fins. Roundtail chub can reach nearly 49 cm (19.5 in) in total length, but most individuals only grow to around 25–30 cm (10–12 in). More recently, recorded maximum lengths for the species have reached up to 43 cm (17 in). This species is often described as "trout-like" because it has a large mouth with a black-outlined lower lip, but it lacks the adipose fin that characterizes trout species. The roundtail chub's range covers the entire Colorado River drainage basin, from the headwaters down to the river mouth, across Utah, Colorado, Arizona, Nevada, California, and northwestern Mexico. It also occurs in other rivers in northwestern Mexico. This species is quite morphologically variable, and was previously split into multiple separate species before intermediate forms were documented. Currently recognized subspecies are Gila robusta grahami, Gila robusta jordani (found in small streams along Nevada's White River), Gila robusta robusta (found in small rivers), and Gila robusta seminuda. The species has been completely extirpated from the Zuni and San Francisco Rivers of New Mexico. In Arizona, specifically within Gila, Mohave, and Yavapai Counties, the roundtail chub inhabits multiple tributaries including Fossil Creek, Oak Creek, Burro Creek, Francis Creek, Big Sandy River, Santa Maria River, Boulder Creek, Trout Creek, Sycamore Creek, and Beaverhead Springs, as well as the entire length of the Verde River. It is also found in the Gila River and the Rio Yaqui.
