The bluemask darter (Etheostoma akatulo) is a 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 the eastern United States. It is a federally listed endangered species of the United States. This fish was not formally described until 2009, but it was added to the US Endangered Species List in 1993. During breeding, the male has bright blue patches on its head and other areas. This fish is found only in the Caney Fork River system, a tributary of the Cumberland River in Tennessee. The species name akatulo comes from the Cherokee for "mask", referring to the solid blue coloration on the lower face of the fish. Anatomy and appearance The species differs from other species of the subgenus Doration by having fully scaled cheeks, complete lateral line, breeding males with bright blue pigment completely covering the lower face, and breeding males with soft dorsal and anal fins lacking orange and blue pigment. Geographic distribution Etheostoma akatulo is known from five small rivers and large creeks of the upper Caney Fork River system, Tennessee, including Collins River, Rocky River, Calfkiller River, Cane Creek, and upper Caney Fork River. Etheostoma akatulo is most abundant and widely distributed in Collins River, where it occurs in a 37-km reach between Shellsford, Warren Co., and Tennessee Highway 56, 1.2 km east of Mt. Olive, Grundy Co. In Rocky River, the species inhabits only a 4.3-km reach from Tennessee Highway 30 upstream to Laurelburg Road ford, Van Buren Co., including a 1.7-km reach that alternates between backwater and free-flowing conditions as Great Falls Reservoir fluctuates between maximum (244 m) and minimum (240 m) pool elevations. In Cane Creek, recent collections are from the lower 200 m of free-flowing waters in Van Buren Co. In upper Caney Fork River, the species has been collected in an intermittent reach located only 1.8 river km upstream of reservoir maximum pool in White Co. Etheostoma akatulo is restricted in distribution to the Caney Fork River system in free-flowing streams upstream of Great Falls. All four extant populations apparently are isolated from one another by the impounded waters of Great Falls Reservoir. Ecology Not much is known about the ecology of Etheostoma akatulo. All darters, as their name implies, dart about on the bottoms of streams and eat small crustaceans and