The relict darter (Etheostoma chienense) is a rare species of fish in the perch family, and is endemic to Kentucky, where it occurs only in the drainage of the Bayou du Chien. It is a federally listed endangered species of the United States. . It shelters in areas where the riverbank is undercut and water flows beneath a mat of roots. The substrate is sand and gravel covered in leaf litter. This type of habitat is not continuous on the river, leaving wide spaces between patches of appropriate habitat.