Sturgeon chub

The type species was collected in the Milk River in Montana, and described by Charles Frédéric Girard in 1856.[3] Girard named it Gobio gelidus, but it was reclassified as Hybopsis gelidus in 1900 and Macrhybopsis gelidus in 1935.[3] A new classification of Hybopsis gelida was suggested in 1965.[3]

The sturgeon chub is slender, streamlined fish with a long, flat snout.[4][5] 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.[6] There is a small barbel near the corner of the mouth, and small pustules on the throat.[3] 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[4] or as a means of detecting currents.[6] The eyes are small and it does not see well.[7] The fish's color ranges from silvery-white on the belly to silvery sides, with a light-brown back.[5] The tail is deeply forked, with the lower lobe darker than the upper lobe.[5] The body fins are triangular,[8] slightly rounded,[3] and straight-edged (unlike the sicklefin chub).[9] The last dorsal fin ray extends beyond the first ray of the depressed fin.[9]

Little is known about its feeding habits,[8] although it does have teeth in its throat.[5] The body is covered with taste buds which help it locate food.[10] 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.[5]

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.[8] It lays eggs on gravel or clean sand to reproduce.[4] Breeding probably occurs in June.[11]

The habitat of the sturgeon chub is murky river bottoms in fast-flowing streams with gravel bottoms.[4] 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.[4] Increased silt and the construction of dams (which cause silt to settle and slow river currents) have destroyed extensive portions of its habitat.[4] It remains common in the middle Missouri River, but rare elsewhere.[9] The United States Fish and Wildlife Service (FWS) estimated in 2001 that it only inhabited about 59 percent of its former range.[12]