Sonora Chub, Gila ditaenia

Note:  This Species is currently considered to be VULNERABLE and if encountered should be handled accordingly.

Sonora Chub, Gila ditaenia. Fish collected from Sycamore Canyon, Santa Cruz County, Arizona, September 2020. Length: 8.9 cm (3.5 inches). Fish was immediately photographed and quickly returned unharmed to its native environment.

Sonora Chub, Gila ditaenia. Fish above placed in an in-field aquarium type setting for a photo shoot and then immediately returned unharmed to its native environment.

The Sonora Chub, Gila ditaenia, is a member of the Carp and Minnow or Cyprinidae Family, and is known in Mexico as carpa sonorense. Globally, there are twenty-one species in the Gila Genus, of which eleven are found in Mexico’s freshwater systems.

The Sonora Chub is small in stature with a fusiform cylindrical very stout body. They are very dark in color dorsally with two noticeable black stripes that run above and below the lateral line, that transition to very light ventrally. During breeding season they have red markings on their anal, pectoral and pelvic fins with orange areas on their bellies and a round spot at the base of the caudal fin. Their head has a pointed snout with a small terminal mouth equipped with pharyngeal teeth. Their anal fin has 7 or 8 rays; their dorsal fin has 8 or 9 rays, and, their pelvic fins have 7 or 8 rays. They have 63 to 75 exceedingly small scales on their lateral line, a key to identification.

The Sonora Chub are found in rocky and sandy pools near cliffs, boulders and other cover in small streams, headwaters and seeps. During periods of drought they are forced  out of the deeper streams into shallower pools. They have a strong tenacity, capable of maintaining populations in small habitats under severe environmental conditions. They reach a maximum of 25 cm (9.8 inches) in length.

The Sonora Chub is an omnivore, consuming algae, small fishes, aquatic insects, and terrestrial insects. They rely on their cryptic coloration for camouflage to avoid predation but are known to be heavily preyed upon by the non-native highly invasive Green Sunfish, Lepomis cyanellus. Reproduction is polygynandrous (promiscuous) and oviparous with external fertilization that involves annual breeding cycles commencing in the spring. The females deposit eggs in the larger pools and bury their eggs to protect them from predation. The Sonora Chub 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 Sonora Chub is a resident of the freshwater systems of northern Mexico but limited to the Rio de la Concepcion drainages in Sonora at elevations between 300 m (1,000 feet) and 1,220 m (4,000 feet). In the United States their populations are limited to Southern Arizona and they are considered to be endangered with extensive on-going efforts to recover their populations.

The Sonora Chub is similar in stature and can be confused with the Rio Grande Chub, Gila pandora (larger lateral scales).

From a conservation perspective the Sonora Chub is currently considered to be VULVERNABLE due to their very limited range and the ongoing destruction of their native habitats especially in arid years. Their long term viability is threatened by water pollution, stream flow depletion, siltation from human activities, and predation by introduced fishes. In Southern Arizona their long term survival is of interest to many and numerous efforts are on-going for preservation and reestablishment of native populations. They are scientifically interesting due to their survival skills.