Description: This large chub is also a member of the minnow family. It’s similar to the humpback chub, but it has only a slight hump behind the head and a long, narrow tail. Adults are dark on top and light below. They are very dark in clear waters and pale in turbid waters. Bonytails can reach 24 inches in length. They have green-gray backs with lighter sides and white bellies. During breeding, males turn red-orange on the belly and paired fins. Their fins are large, slightly falcate. Dorsal fins typically have 10 rays, tail fins have 10 to 11 rays.
Range: Historically, bonytails were present in the Colorado River system, which includes the Yampa, Green, Colorado and Gunnison rivers. Today, there are no known populations in Colorado. They can be found in the Green River drainage in Utah and Mohave Reservoir on the Arizona-Nevada border.
Habitat: This fish typically lives in large, fast-flowing waterways of the Colorado River system. But their distribution and habitat status are largely unknown due to its rapid decline prior to research into its natural history.
Diet: Adult bonytail feed on terrestrial insects, zooplankton, algae and plant debris. Young feed mainly on aquatic insects.
Breeding: Although bonytail spawning in the wild is now rare, the species does spawn in the spring and summer over gravel substrate. Many bonytail are now produced in fish hatcheries, with the offspring released into the wild when they are large enough to survive in the altered Colorado River system environment. Females produce between 1,000 and 17,000 eggs. Hatching occurs about nine hours after fertilization and swim-up begins generally 48 to 120 hours later. Survival rate of young fish is about 17 to 38 percent.
Endangered status: The bonytail is listed as endangered federally and in Colorado. Reasons for its decline are probably similar to the other endangered Colorado River fishes. The large-scale damming of the river has diminished available habitat. Damming and channeling not only change the speed, location and volume of water flow, the practices change the temperature and clarity of the water and block migration routes. Other threats to the bonytail have been the introduction of non-native fish that compete for food and habitat, and may prey on it or hybridize with it. The bonytail is extremely rare in Colorado and no self-sustaining population exist throughout the Colorado River basin. Only one has been captured in the state since 1980. Restoration stocking of bonytail in the wild to develop adult populations is the priority recovery action in Colorado and the Upper Basin Recovery Program. Stocking of bonytail has occurred in the Green River in Utah and the Green and Yampa rivers in Dinosaur National Monument in Colorado. While these releases continue over the next several years, efforts will be made to monitor their survival and learn as much as possible about their habitat needs and limiting factors.
For more information, see the Natural Diversity Information Source species profile.