Roundnose Minnow, Dionda episcopa

Roundnose Minnow, Dionda episcopa. Fish caught from Sandy Creek, Henry, Illinois, August 2014. Length: 7.4 cm (2.9 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).

Roundnose Minnow, Dionda episcopa. Fish caught from the Pecos River, Sheffield, Texas. June 2021. Length: 7.4 cm (2.9 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

Roundnose Minnow, Dionda episcopa. Fish caught from the Pecos River, Sheffield, Texas. June 2021. Length: 8.2 cm (3.2 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

Roundnose Minnow, Dionda episcopa. Fish caught from Independence Creek, Sheffield, Texas, February 2022. Length: 8.0 cm (3.1 inches). Catch, photograph, and identification courtesy of Chris Moore, Peoria, Arizona.

Roundnose Minnow, Dionda episcopa. Fish caught from El Rito Creek, Santa Rosa, New Mexico, July 2017. Length: 8.0 cm (3.1 inches). Catch, photograph, and identification courtesy of Ben Cantrell, San Diego, California.

Roundnose Minnow, Dionda episcopa.  Fish caught from Independence Creek, Sheffield, Texas, September 2018. Length: 8.2 cm (3.2 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

The Roundnose Minnow, Dionda episcopa, is a member of the Carp and Minnow or Cyprinidae Family, that is also known as the El Rito Roundnose Minnow and in Mexico as carpita obispa. Globally, there are six species in the genus Dionda, of which five are widespread throughout Mexico’s freshwater systems.

The Roundnose Minnow has a slender compressed fusiform body that are deepest anterior of the dorsal fin origin with a slightly arched back. They are dusky olive dorsally transitioning to silvery on their sides and to yellow ventrally with a small black spot at the base of the caudal peduncle. They have a faint dark bar, composed of small broken lines that run from the front margin of the eye to the caudal fin. Some fish have a black band that runs through the eye to the snout. Their head is large and rounded and compressed with large-sized eyes and a slightly sub-terminal mouth. Their anal fin has 8 rays; their caudal peduncle is wide; their caudal fin is concave with wide lobes; their dorsal fin has less than 10 rays; and, their pelvic fins and inserted behind the dorsal fin. They are covered with large scales. They have an indistinct lateral line along the flank.

The Roundnose Minnow is a non-migrant mid-water schooling freshwater species found in clear streams, small rivers, spring-fed tributaries with uniform temperatures in the presence of filamentous algae. They reach a maximum of 7.6 cm (3.0 inches) in length. They are herbivores that consume algae and other plant materials. The Roundnose Minnow 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 Roundnose Minnow is native to the freshwater systems of northern mainland Mexico being limited to the Atlantic slope of the Río San Carlo of the Río Grande drainage in the State of Coahuila.

The Roundnose Minnow is a straight forward identification that might be confused with the Devils River Minnow, Dionda diaboli (thinner body, double dashes along the lateral line; larger eyes; wedge-shaped spot on the caudal peduncle) and the Manantial Roundnose Minnow, Dionda argentosa (longer and stouter bodies; lack cross-hatch scales and double dashes along the lateral line).

From a conservation perspective the Roundnose Minnow is currently considered to be of Least Concern with stable widely distributed populations. They are considered to be an important forage fish. Their long-term survival is threatened by changes in water quantity and quality with pollution caused by human development and the introduction of foreign taxa.