River redhorse (Moxostoma carinatum)

Synonyms: Placopharynx carinatus
GenusMoxostoma (1)
SizeLength: up to 77 cm (2)
Weightup to 3.96 kg (2)

The river redhorse is classified as Least Concern (LC) on the IUCN Red List (1).

One of the largest redhorse (Moxostoma) species (3), the river redhorse (Moxostoma carinatum) is a large, stout freshwater fish with a brownish, olive or bronze back, golden or brassy sides and a bright orange-red tail. The scales of the upperparts have dark bases, and the underside of the body is whitish (3) (4) (5) (6) (7). The dorsal fin and anal fin of the river redhorse are usually reddish, and the pelvic fins and pectoral fins are orange (3) (5) (6).

The river redhorse has a relatively large head and mouth, and the large, protruding lips are covered in folds (3) (4) (5) (6). The dorsal fin of this species is fairly short, and the tail is large and forked (3) (5). Breeding male river redhorses develop tubercles on the snout and cheek, as well as on the anal fin, tail fin, and sometimes on other parts of the body (3). The breeding male is also reported to have a dark stripe along the side of the body (5).

Like other cyprinid fish (species in the order Cypriniformes), the river redhorse does not have teeth in its jaws. Instead, it processes food using enlarged bones in the throat, known as ‘pharyngeal teeth’ (8), which in the river redhorse are large and molar-like (3) (5) (6). The shape of these teeth helps distinguish the river redhorse from similar redhorse species, such as the golden redhorse, black redhorse and greater redhorse (Moxostoma erythrurum, Moxostoma duquesnii and Moxostoma valenciennesi), which have more comb- or blade-like pharyngeal teeth (3) (5). In addition to tooth shape, this species is also distinguished from the shorthead redhorse (Moxostoma macrolepidotum) by its longer head, V-shaped rather than straight rear edge to the lower lip, and straighter edge to the dorsal fin (3) (5).

The river redhorse occurs in the St Lawrence and Ottawa River basins, the Great Lakes basin and the Mississippi River basin, from southern Quebec in Canada to central Minnesota and western Iowa in the United States, and south to Alabama and Oklahoma. It also occurs in Gulf Slope drainages in the United States, from the Escambia River in Florida, to Pearl River in Louisiana and Mississippi (2) (3) (4) (5) (6) (9).

As its common name suggests, the river redhorse most commonly inhabits large rivers (2) (3) (4) (9). It is typically found in rocky pools or areas with a moderate to swift current and a gravel, rubble or bedrock bottom (2) (3) (5) (9) (10), although it has also been recorded in impoundments such as reservoirs (2) (3) (5) (9). This species prefers clear water, without much silt or pollution (3) (6).

Adult river redhorses may move upriver into smaller streams and rivers during the spawning season (3) (9). Younger individuals are often found in shallower pools and backwaters (9).

The diet of the river redhorse includes small bivalve molluscs, snails, crustaceans and the non-native Asian clam (Crobicula fluminea) (2) (3) (4) (6) (7) (9). The shells of its prey are crushed using the strong, molar-like pharyngeal teeth (modified bones in the throat) (6) (8). The river redhorse also eats aquatic insects and their larvae (3) (4) (6) (7), and mainly takes its prey from the river bottom (7) (9).

The river redhorse usually spawns between April and June (3) (4) (6) (7) (9), when the adults move upstream and the males maintain territories (3) (6). The river redhorse spawns over gravel substrates, and may make a small depression into which the eggs are deposited (3) (4) (6) (7) (9). In this species, two males often pair with one female (3).

A female river redhorse of about 45 to 65 centimetres in length can produce around 6,000 to 23,000 eggs (3) (7). The eggs of this species are quite large, at about three to four millimetres in diameter, and hatch in three to six days (3) (7) (9). The river redhorse probably reaches maturity at about five years old, and has been known to live for up to 29 years (3).

The river redhorse is locally common, but its populations are declining in some areas, particularly in the northern and western parts of its range (2) (3) (4) (5) (9). The main threat to this species is likely to be habitat degradation in the form of siltation and pollution, to which the river redhorse is particularly susceptible, as is its mollusc prey (3) (4) (7) (9).  It may also be affected by the alteration of its river habitat due, for example, to channelization and the building of impoundments (9).

This species is considered a tasty food fish (3) (6), but is not protected by fishing regulations such as catch limits or size restrictions (7). In some areas, fishing may contribute to local declines in the river redhorse population (7) (9).

In Canada, the river redhorse is not specifically protected, but it does receive some general protection under the fish habitat sections of the Fisheries Act (7). There are not known to be any specific conservation measures targeting this large river fish, but further population surveys have been recommended to better determine its status throughout its range (9).

The river redhorse would also benefit from more research into its life history, and from the protection of its habitat from activities that cause siltation and pollution (9).

Find out more about the river redhorse and its conservation:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (August, 2013)
  2. FishBase - River redhorse, Moxostoma carinatum (June, 2011)
  3. Ross, S.T. (2001) Inland Fishes of Mississippi. University Press of Mississippi, Jackson.
  4. Werner, R.G. (2004) Freshwater Fishes of the Northeastern United States. Syracuse University Press, New York.
  5. Page, L.M. and Burr, B.M. (1991) A Field Guide To Freshwater Fishes of North American North of Mexico. Houghton Mifflin Company, New York.
  6. Miller, R.J. and Robison, H.W. (2004) Fishes of Oklahoma. University of Oklahoma Press, Norman.
  7. Parker, B. and McKee, P. (1984) Status of the river redhorse, Moxostoma carinatum, in Canada. The Canadian Field-Naturalist, 98(1): 110-114.
  8. Campbell, A. and Dawes, J. (2004) Encyclopedia of Underwater Life. Oxford University Press, Oxford.
  9. NatureServe Explorer - Moxostoma carinatum (June, 2011)
  10. Yoder, C.O. and Beaumier, R.A. (1986) The occurrence and distribution of river redhorse, Moxostoma carinatum and greater redhorse, Moxostoma valenciennesi in the Sandusky River, Ohio. The Ohio Journal of Science, 86(1): 18-21.