Sturgeon chub

The sturgeon chub (Macrhybopsis gelida) iis a species of freshwater ray-finned fish belonging to the family Leuciscidae, the shiners, daces and minnows.^[2] It is found only in the United States. It is a species of concern in the Charles M. Russell National Wildlife Refuge in Montana.^[3]

Sturgeon chub
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cypriniformes
Family:	Leuciscidae
Subfamily:	Pogonichthyinae
Genus:	Macrhybopsis
Species:	M. gelida
Binomial name
Macrhybopsis gelida (Girard, 1856)
Synonyms[2]
Gobio gelidus Girard, 1856 Hybopsis gelida (Girard, 1856)

Names and documentation

The type species was collected in the Milk River in Montana, and described by Charles Frédéric Girard in 1856.^[4] Girard named it Gobio gelidus, but it was reclassified as Hybopsis gelidus in 1900 and Macrhybopsis gelidus in 1935.^[4] A new classification of Hybopsis gelida was suggested in 1965.^[4]

Description and habitat

The sturgeon chub is slender, streamlined fish with a long, flat snout.^[5][6] The snout resembles that of a sturgeon, which gives the fish its name. Adults grow to be about 3 inches (7.6 cm) in length.^[7] There is a small barbel near the corner of the mouth, and small pustules on the throat.^[4] The scales on the sturgeon chub's back and sides have a small ridge-like projection known as a "keel". The purpose of the keel is not established, but may help the fish stabilize and orient itself in fast currents^[5] or as a means of detecting currents.^[7] The eyes are small and it does not see well.^[8] The fish's color ranges from silvery-white on the belly to silvery sides, with a light-brown back.^[6] The tail is deeply forked, with the lower lobe darker than the upper lobe.^[6] The body fins are triangular,^[9] slightly rounded,^[4] and straight-edged (unlike the sicklefin chub).^[10] The last dorsal fin ray extends beyond the first ray of the depressed fin.^[10]

Little is known about its feeding habits,^[9] although it does have teeth in its throat.^[6] The body is covered with taste buds which help it locate food.^[11] It lives in waters which are little populated by other small fish, but can be found associating with the flathead chub, sicklefin chub, and speckled chub.^[6]

Sturgeon chub exhibits little sexual dimorphism, and neither sex exhibits color changes during breeding. However, the male does develop small tubercles behind the gills during breeding.^[9] It lays eggs on gravel or clean sand to reproduce.^[5] Breeding probably occurs in June.^[12]

The habitat of the sturgeon chub is murky river bottoms in fast-flowing streams with gravel bottoms.^[5] Its habitat extends over the Missouri River and its primary tributaries, the lower Mississippi River in the states of Mississippi and Louisiana, and some streams in northeastern Wyoming.^[5] Increased silt and the construction of dams (which cause silt to settle and slow river currents) have destroyed extensive portions of its habitat.^[5] It remains common in the middle Missouri River, but rare elsewhere.^[10] The United States Fish and Wildlife Service (FWS) estimated in 2001 that it only inhabited about 59 percent of its former range.^[13]