The Bayou darter (Etheostoma rubrum) is a rare species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is endemic to western Mississippi in the United States, where it is found only in Bayou Pierre and its tributaries. Its typical habitat is fast-flowing creeks and streams, in riffles and in areas between riffles with firm gravel bottoms. It feeds on small insects and their larvae. Breeding probably takes place twice a year, in spring and late summer. The population of this fish is declining due to loss of suitable habitat. This is caused by siltation and pollution, particularly erosion caused by changes in land use. The International Union for Conservation of Nature has assessed its conservation status as being "endangered".