The Bluehead sucker (Catostomus discobolus) is endemic to the intermountain Western US. There are a total of 23 members of the genus Catostomus, all of which can be found in North America. C. discobolus and C. yarrowi are two sister species that have very similar Arizona habitats.
The Bluehead Sucker is the largest of all Arizona endemic suckers, reaching lengths of over 11.8 inches. Their colors are very similar to the Desert Sucker, with dark green or dark silvery top portions and light yellow bottoms. The Bluehead has the largest lips of any sucker and has tiny papillae on the lower lip. This is also the only species with the absence of an inguinal process, just behind the pectoral fins, distinguishing it from the other eight suckers. The lower lip is slightly notched at the midline, with lateral line scales in large numbers that range from 70 to 100. They have 7 to 9 dorsal fin rays and a smaller amount of caudal fin rays. During breeding, the males obtain a blue patch on the top of their large heads, and the lower fins become yellow/orange with red/rosy lateral lines. These drastic coloration changes are probably due to sexual selection and female mate choice. An easy way to distinguish the Bluehead from the other Arizona suckers is to notice the distinct cartilaginous lower jaw.
Distribution in Arizona
Primary records are concentrated at the Colorado River main stem and the Grand Canyon tributaries, as well as the Colorado River drainages at Lake Mead. Blueheads are also found at Snake River above Shoshone Falls and Bear/Weber River drainages. There are scattered reports around the Bonneville Basin. Arizona Bluehead sucker distributions are more specifically the Clear, Bright Angel, Shinumo, Kanab, and Havasu Creeks rarely below Diamond Head. Some can be found near the Navajo Reservation and the San Juan drainage. Their biotic communities are restricted to aquatic wetland and riparian zones within Arizona, with a more restricted elevation distribution of 609 to 2060 meters.
Bluehead suckers prefer larger streams and rivers due to their larger size, however they can be found in a variety of habitats (Sublette et. Al. 1990). This species has a wide temperature preference as well, ranging from cold mountain brooks at 12 degrees Celsius, to warmer desert rivers at 27 degrees Celsius. If times are good and water is clear, the suckers will stay in shallow steams and eddies during the day, finding their way to hard-bottomed streams to forage at night. Primary spawning areas include a high concentration of juvenile minnows in the Grand Canyon Tributaries and Colorado River drainages. Populations will remain stable unless humans destroy habitats.
The Bluehead sucker has unique spawning techniques, which make it different from most of the other Arizona native fish. Arizona fish usually mate and breed during the winter months, due to specific physiological parameters and water temperature preferences. The Bluehead sucker is the opposite, preferring the spring/summer months and much warmer water temperatures, exceeding 15.72 degrees Celsius. Males will join females in gravel/sandy-bottomed streams and copulation begins, taking only a few seconds. In the Grand Canyon Tributaries, mating can extend even later into the year through April, May, and July. This species will not mate unless the water depth is strictly fewer than 1 meter, probably because the shallow water is easily heated to their desired temperature by the sun. Juveniles grow exponentially fast, reaching lengths of 60 mm and sexual maturity within the first year.
Suckers use their cartilaginous jaws to scrap the algae and detritus off the stones at the bottom, and despite any shortages of these foods, suckers show little seasonal movement. Diatoms, detritus, algae, and other organic debris have been found in the gut. Bluehead suckers are unique in that they are the only members of the genus to hybridize with other members of the same genus, increasing gene flow among species. They can also live to be more than twenty years old.
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- Arizona Game and Fish Department. 1988. Threatened Native Wildlife in Arizona. Arizona Game and Fish Department Publication. Phoenix, Arizona. p. 8.
- Arizona Game and Fish Department. In prep. Wildlife of special concern in Arizona. Arizona Game and Fish Department Publication. Phoenix, Arizona. 32 pp.
- Arizona Game and Fish Department Native Fish Diversity Review. 1995. Tempe, Arizona.
- Beyers, D.W. et al. 2001. Habitat Use and Movements of Bluehead Sucker, Flannelmouth Sucker, and Roundtail Chub in the Colorado River. Larval Fish Laboratory, Colorado State University, Fort Collins, CO.
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