The Rio Grande sucker is a small bottom-feeding fish that lives in slow-moving waters in the Rio Grande river drainage in Colorado and New Mexico, as well as several river basins in Mexico. This mottled algivore, meaning an organism that consumes algae, is the only native sucker to the Rio Grande Basin. It co-evolved with the Rio Grande cutthroat trout (Oncorhynchus clarki virginalis) and the Rio Grande chub (Gila pandora), forming a balanced fish community that was the dominant fish assemblage in the Rio Grande drainage. Historically, the Rio Grande sucker was common throughout low elevation, low gradient streams and tributaries of the Rio Grande Basin, but range-wide water diversions, dams, as well as competition and predation from non-native species, have reduced their populations. The Rio Grande sucker is a state endangered species in Colorado and was petitioned for federal listing under the Endangered Species Act in 2013, but currently no listing decision has been made.
Populations have been impacted from reduced flows due to increased temperatures and dewatering, as well as habitat degradation from channelization of streams and trans-basin water diversions. Non-native species like northern pike (Esox lucius), brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis) prey on Rio Grande suckers, while white suckers (Catostomus commersonii) compete for limited resources like food and spawning habitat and can hybridize with their Rio Grande cousins.
Undersized or improperly designed culverts at road crossings can create barriers to Rio Grande sucker’s movement, especially at low flows typical of the streams they inhabit. Low head dams and small capacity irrigation reservoirs reduce streamflow and alter the natural hydrograph, as well as creating additional barriers. Rio Grande suckers require the ability to move upstream and downstream for genetic exchange and to support necessary life history events such as reproduction. Also important is their access to suitable habitat like streams throughout their range that seasonally flood and then dry up in late summer and fall. Improving upstreamby replacing and retrofitting culverts is an important part of conservation for this species.
Recovery efforts for the Rio Grande sucker involves a variety of state, federal, tribal and private organizations. Examples of these recovery efforts include habitat restoration, improving fish passage, removing non-native species and reintroductions. Population monitoring throughout their range helps identify changes and patterns. Research on genetics, movement and life history helps us further understand this species and implement more effective conservation efforts across its range.
Like all fish in the Catostomidae or sucker family, Rio Grande suckers have soft fin rays and an extendable downturned fleshy sucker mouth. They also have a well-developed, cartilaginous ridge that is specifically adapted for scraping algae off rocks. They lack pelvic fins and protective spines. Adults are usually less than 6.7 in (170 mm) in length, averaging 4 to 6 in (100 to 150 mm) in the wild. Hatchery fish can grow up to 8 to 10 in (200 to 250 mm) and females are typically larger than males.
The back and sides of the fish are brownish green to dusky brown overlain with dark blotches and their underside is pale. Dorsal and tail fins are pigmented, while pectoral and anal fins are pale. Females are typically larger than males. During spawning season, males will develop a large black band on their sides, with a crimson red lateral line sometimes with a yellow golden band above. Males will also develop tubercles, or bumps, on their anal and tail fins. Females develop faint red coloration on their sides and tubercles on the peduncle, the narrow part of the body just above the tail.
Like most species of freshwater fish, Rio Grande suckers begin life as an egg. An embryo develops inside the egg which eventually hatches into a larval fish that can acquire its own food. They grow into juvenile fish, sometimes called fry. At this stage they look like small adults, and although their coloration may be different, they have all their normal fins and internal organs. Fish are considered adults when they are reproductively mature. For Rio Grande suckers this occurs after three or four years. If they can avoid predation, they continue to produce annually throughout their lives.
Male Rio Grande suckers sexually mature at 2 to 3 inches (60 to 80 millimeters), while females mature at 2.75 to 3.5 inches (70 to 90 millimeters). For most Rio Grande suckers this is around age 3 or 4, but can be as early as age 2. Growth rates and maturity depend on food resources and temperatures of a given stream. When Rio Grande suckers are ready to reproduce, or spawn, they move upstream much like salmon in the Pacific Northwest. Spawning time is influenced by temperatures and spring runoff patterns and can occur as early as February, in the southernmost range, but typically occurs between March and July throughout most of the range. Males and females will brush up against each other, using the tubericles, or bumps, that develop on their bodies during spawning time to stimulate reproduction. Each year females can produce an average of 2000 ova, or reproductive cells, that develop into eggs when they are fertilized in the water then sink to the gravely stream bottom. After spawning, the fish migrate back downstream, leaving their offspring to hatch and survive on their own.
Rio Grande suckers can live up to seven years in the wild based on individuals captured in New Mexico. In captivity, such as in a hatchery, they typically live 12 to 13 years.
The white sucker (Catostomus commersonii), a non-native species in the Rio Grande watershed, can hybridize with Rio Grande suckers. White suckers are members of the Catostomidae or sucker family, so they possess the same downturned fleshy sucker mouth, but they are typically larger, with dark gray uniform scales and no mottling. Genetically pure individuals of both species are distinct, but hybrids may be harder to differentiate. Other sucker species may look similar but they are not found in the same areas as Rio Grande suckers.
Rio Grande suckers are omnivores. Their diet mostly consists of periphyton, or algae, detritus and aquatic invertebrates on the bottom of the stream that are scraped from rocks, gravel or boulders with a specifically adapted scraping ridge on their jaw.
Rio Grande suckers have likely always been confined to a small portion of Colorado and New Mexico in the Rio Grande Basin and their distribution is further controlled by temperature, gradient and elevation. They are rarely found about 9,000 feet in elevation and populations are concentrated in low gradient streams. Rio Grande suckers occupy clear pools and clean gravel riffles in streams with abundant woody cover and aquatic vegetation. They move between pool and riffle habitats for feeding, as well as development and breeding. Streams with natural flow cycles, including seasonal runoff, help maintain suitable habitat and rearing conditions. This species is adapted to extreme drought conditions that exist naturally in the Rio Grande drainage, but water development projects - even at a small scale - can significantly impact their persistence.
A natural body of running water.
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