Relict Darter

The relict darter (Etheostoma chienense) 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 Kentucky, where it occurs only in the drainage of the Bayou de Chien. It is a federally listed threatened species of the United States.

The relict darter is part of the Etheostoma squamiceps species complex and was formally described in 1992. It grows up to about 7.2 centimetres (2.8 in) in length and is characterized by "lollipop-like" white knobs on the second dorsal fin of the male that develops during the breeding season. The species is only found in a 35-kilometre (22 mi) stretch of the Bayou de Chien, a tributary of the Mississippi River in Kentucky. 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.