About Rhinichthys obtusus Agassiz, 1854
Rhinichthys obtusus, commonly known as the western blacknose dace, is a common ray-finned fish species in the genus Rhinichthys, part of the Leuciscidae family that includes shiners, daces, and minnows. Western blacknose dace have tan to dark brown backs, lighter sides, and cream-colored undersides. Dark blotches are scattered sporadically across their sides and backs. They have a distinctive dark mid-lateral stripe that runs from the tip of the snout to the caudal peduncle. Their snout is relatively long, and they have a slightly sub-terminal mouth. The stripe is dark brown in females, and turns rusty pink in males during spawning season. In juveniles, the lateral stripe is more pronounced, and a caudal spot is present. Like other dace species, western blacknose dace appear to have no scales, but their scales are actually just very small and hard to see. They are typically 2 to 3 inches long, and can reach a maximum length of 4 inches. They have a forked tail, a single dorsal fin with 8 rays and no spines, an abdominal pelvic fin, no adipose fin, and an anal fin with 7 rays and no spines. The western blacknose dace lives in the upper Mississippi, Ohio, and Great Lakes drainages, ranging north to south-central Canada, south to northern Alabama and Georgia, and east to eastern Lake Erie. Young dace prefer shallow, quiet pools with silty bottoms. Mature dace prefer streams with consistent high turbulence and abundant hiding spots, as they are a prey species. They most often occupy water between 100 and 200 mm deep, over gravel or cobble bottoms. They can also be found in riffles, hiding under large rocks or boulders. Spawning starts in spring and continues to mid-summer, depending on water temperature. Unlike many other dace species, western blacknose dace spawn in gravel-bottomed areas rather than in the spawning beds of other cyprinids; the two Rhinichthys species found in Ohio also do not spawn in the nests of larger minnow species. This species is short-lived, with a maximum lifespan of four years, so individuals begin reproducing after two years of age. Western blacknose dace are mostly carnivorous, and their diet changes as they age. Young dace feed mostly on Dipteran larvae. When Dipteran larvae are available, mature dace will still feed on them, but amphipods also make up a large portion of their diet. This dietary shift is thought to be linked to the habitat shift that occurs as dace mature.
