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Flannelmouth sucker are native throughout the Colorado River in medium to large, lower elevation rivers. It also occurs in smaller tributaries and occasionally in lakes and reservoirs. While flannelmouth suckers are currently present in streams and rivers of the Upper Colorado River drainage not heavily impacted by impoundments or other habitat degradation, they are thought to be in decline in many places. Flannelmouth suckers typically inhabit the mainstem of warm, moderate to large rivers but can be found in small streams. Pools and deep runs are preferred, but are also found in the mouths of tributaries, riffles, and backwaters. Adults gravitate to cover and shade during the daytime. They are rare in the cooler waters of headwater streams, preferring temperatures in the seventies.
Flannelmouths are a large long lived fish, reaching ages of 30 years and measuring over 24 inches in length. These suckers are elongated with an oval profile. They exhibit distinct, enlarged fleshy lips located under the snout. Their thickened lower lip is elongated compared to other suckers and completely divided by a center groove. The back is a dark brownish-green turning yellow to orange along the sides and whitish underside. Colorations are more prominent during spawn, when tubercles becoming highly evident on male fish.
They spawn from April to June, after reaching sexual maturity by year four. Spawning occurs when water temperatures reach the mid to upper fifties, usually once runoff begins to abate. Fins of both sexes often become orange during reproduction. This species spawns over a gravel or cobble bottom. Several fish congregate together releasing eggs and milt at the same time. The fertilized eggs are adhesive and sink to the bottom falling between the rocks or adhering to them. Parents give no care, leaving the area after spawn. Eggs typically hatch within a week.
This species is omnivorous, feeding on a wide variety of items, including algae, detritus, inorganic materials, insect larvae, aquatic invertebrates, known to eat inorganic material, and crustaceans. Their feeding pattern is highly dependent on ages and availability of food sources, being very opportunistic feeders.
Flannelmouth Sucker in Colorado
Courtesy of NDIS, Colorado Parks and Wildlife
Habitat: The flannelmouth sucker inhabits larger streams and rivers in all habitat types including riffles, runs, eddies, and backwaters. The species does not appear to maintain viable populations in impoundments (Minckley 1973).
Description: An elongated sucker, oval in cross section; snout blunt and broad, overhanging ventral mouth; no notch or indentation at the lateral connection of lower and upper lips, thick upper lip with 5-8 rows of papillae, median indentation of lower lip complete, at most one row of papillae separating indentation and edge of lower jaw; dorsal fin is falcate (sickle-shaped) with 11-13 rays; scales are small, crowded near head; more than 90 scales along lateral line. Adults in clear water are greenish-blue- grey on the back, fading to yellow on the sides and to white on the belly. In turbid water, with a sand or mud bottom, flannelmouths are light tan on the back, white and silver on the sides and belly. Young are lighter colored. Anal and pelvic fins yellowish. Dorsal and tail fin dusky. A large species, one specimen attained a weight of 3.5 pounds and was 22 inches long (McDonald and Dotson 1960).
Range in Colorado: The flannelmouth is restricted to larger streams and rivers in the middle and upper Colorado River Drainage, including parts of Wyoming, Colorado, New Mexico, Utah, Arizona and Nevada. In Colorado, the flannelmouth is found only in large rivers on the western slope. This species and the bluehead sucker have disappeared from some waters, such as the Gunnison River above Blue Mesa Reservoir, since the 1960's. The white and longnose suckers, introduced from East Slope waters, have replaced the flannelmouth and bluehead in the upper Gunnison River. Competition with the introduced species and/or cold water temperatures from reservoir releases probably led to the disappearance of the flannelmouth from the upper Gunnison.