Rio Grande Chub, Gila pandora

Rio Grande Chub, Gila pandora. Fish caught from the Jemez River. Jemez Pueblo, New Mexico, October 2023. Length: 9.4 cm (3.7 inches). Catch, photograph and identification courtesy of Chris Moore, Peoria, Arizona.

Rio Grande Chub, Gila pandora, Breeding Male. Fish caught from the San Antonio Creek within the Jemez National Recreational Area, New Mexico, May 2024. Length: 12 cm (4.7 inches). Catch, photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

Rio Grande Chub, Gila pandora. Fish caught from the Jemez River. Jemez Pueblo, New Mexico, October 2023. Length: 19 cm (7.5 inches). Catch, photograph and identification courtesy of Chris Moore, Peoria, Arizona.

The Rio Grande Chub, Gila pandora, is a member of the Carp and Minnow or Cyprinidae Family, and is known in Mexico as chirality del Rio Bravo. Due to the complexities in assigning the Gila genera to this species it was named for Pandora’s Box. Globally, there are twenty-one species in the Gila Genus, of which eleven are found in Mexico’s freshwater systems.

The Rio Grande Chub is a mid-sized-finned minnow with an elongated compressed body with a deep caudal peduncle. They are an olive-gray dorsally, with two dusky stripes on their sides, the upper one extends into the caudal fin and the lower one into the anal fin, and they have a black caudal spot. The breeding males have red-orange anal, dorsal, and pelvic fin bases and lower head and lower sides colorations. The males also have pronounced tubercles on the caudal peduncle, anal fins, and caudal fins. Their anal and dorsal fins are triangular, their caudal fin is deeply forked with broadly pointed lobes, and their pectoral fins are rounded. Their dorsal fin is inserted behind the pelvic fins. They have 7 to 9 anal rays, 8 or 9 dorsal rays, 12 to 20 pectoral rays, and 8 to 10 pelvic rays. Their mouth is slightly subterminal and extends to the front of the large eyes with a rounded fairly blunt snout. They have 6 to 10 gill rakers on the first arch. They reach a maximum length of 25 cm (9.8 inches). The females are larger and more robust than the males. Their lateral line is straight or broadly arched.

The Rio Grande Chub resides in flowing pools of headwaters, creeks, and small rivers, often near inflow of riffles and in association with cover such as undercut banks, aquatic vegetation, and plant debris at elevations between 600 m (1,970 feet) and 1,700 m (5,600 feet). They have been documented to thrive at elevations up to 3,470 m (11,370 feet) in New Mexico. They also occurs in impoundments. Adults are found in deeper waters than juveniles. They are normally found mixed in with Desert Suckers, Gila Topminnows, Longfin and Speckled Dace, and Sonora Suckers. They are omnivores that consume algae, zooplankton, small fishes, aquatic insects, terrestrial insects, and limited amounts of detritus. They rely on their cryptic coloration for camouflage to avoid predation. Reproduction is polygynandrous (promiscuous) and oviparous in annual cycles commencing in the spring. Reproduction occurs within the riffles of streams with each female producing between 1,300 and 6,300 eggs with external fertilization. The females deposit eggs in the larger pools and bury their eggs to protect them from predation. No additional parental care is provided. They experience a high level of mortality in their first year of life and after the first year of spawning. The Gila Chub, in general, is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Rio Grande Chub is easily confused with the Chihuahua Chub, Gila nigrescens (which can only be separated visually by range).

The Rio Grande Chub is native to the Upper Rio Grande and Pecos River systems in Colorado, New Mexico and Texas. They are believed to have been extirpated from the mainstream of the Rio Grande and can now only be found in the tributaries. In many areas where they have been introduced viable populations have become quickly established. In Mexico the Rio Grande Chub has a very limited distribution being found in the tributaries of the Rio Grande River in the State of Chihuahua.

From a conservation perspective the Rio Grande Chub is currently considered to be of Least Concern. However, their overall populations both in numbers and range are in decline which is attributed to human development that includes the habitat modification, water diversion, enhanced sedimentation, and the introduction of non-native highly predatory fishes. They have now found themselves in competition for several introduced species including the Common Carp, the Northern Pike, the White Sucker and over twenty-five other species; they are also subject to predation by the introduced Brook Trout and Brown Trout. They are known to hybridize with non-native introduced Longnose Dace, Rhinichthys cataractae. They are also prone to disease and parasitism from introduced organisms. They are relatively small in stature and of limited interest and caught on occasion by recreational anglers fishing for trout. In the Pre-Columbian area, when the Rio Grande Chub were abundant and larger in size, they were a valued human food.