Rio Grande Darter, Etheostoma grahami

Rio Grande Darter, Etheostoma grahami, Male. Fish caught from Río San Juan, Coahuila, August 2014. Length: 6.0 cm (2.4 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).

Rio Grande Darter, Etheostoma grahami. Fish caught from Independence Creek, Sheffield, Texas, February 2022. Length: 6.1 cm (2.4 inches). Catch courtesy of Brayden Moore, Peoria, Arizona. Photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

Rio Grande Darter, Etheostoma grahami. Fish caught from San Felipe Creek, Del Rio, Texas, March 2022. Length: 6.4 cm (2.5 inches). Catch, photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

The Rio Grande Darter, Etheostoma grahami, is a member of the Darter and Perches or Percidae Family and is known in Mexico as perca del Bravo. Globally, there are one hundred fifty species in the genus Etheostoma, of which four are found in Mexico’s freshwater systems.

The Rio Grande Darter has a deep body with an oval cross section. Their body is olive brown dorsally with 10 to 12 bars, that are prominent under the dorsal fins and on the sides transitioning to yellow or white ventrally. They are sexually dimorphic with males having red throats, red anal, dorsal and pelvic fins and yellow caudal and pectoral fins. The males have numerous red small spots on the sides and females have similar sized black spots. Their head profile is rounded with a short snout, a large mouth that opens at the front and extends to the middle of the large eyes. Their anal fin has 2 spines; their caudal peduncle is wide; their caudal fin is rounded; their first dorsal fin has 9 to 11 spines; their second dorsal fin has 9 to 12 rays; and, their pectoral fins are shorter than the head and do not reach the anus. They are covered with large scales with less than 50 scales on the lateral line. Their lateral line is straight.

The Rio Grande Darter is a freshwater benthopelagic that is found in clear rocky riffles and pools of creeks and small rivers with gravel substrate and vegetated pools at depths up to 1.5 m (5 feet). They reach a maximum of 6.0 cm (2.4 inches) in length. They are herbivores that consume algae and other plant materials. The females frequently produce small batches of eggs that are laid on vegetation and on rocks. The Rio Grande Darter 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 Darter is native to the freshwater systems of northern mainland Mexico being limited to the Atlantic slope of the San Juan and Salado of the Río Grande drainage in the States of Coahuila, Nuevo León, and Tamaulipas.

The Rio Grande Darter is most likely confused with the Greenthroat Darter, Eteostoma lepidum (naked gill cover; more than 50 lateral line scales, males with blue or green throat) and the Orangethroat Darter, Eteostoma spectabile (8 or 9 body bars; orange throat).

From a conservation perspective the Rio Grande Darter is currently considered to be Vulnerable which is attributed to its limited range distribution. Their populations are believed to be in decline due to the decline of their native habitats by human development changing water quality and quantity. They are small in stature, rare, and of limited interest to most.