Slackwater darter  (Etheostoma boschungi)

Classified as Endangered (EN) on the IUCN Red List (1).

The North American darters are a diverse group of around 145 freshwater species in the Percidae, or perch family. Adapted to a bottom-dwelling lifestyle, these fish dart between the sanctuary of large stones, a behaviour that has earned the darters their common name. The body is deep and slender, with two separate dorsal fins and a sharp flap of skin covering the gills, but unlike other teleosts, the darters lack a swim bladder, a gas-filled sac typically used to regulate buoyancy (3). The somewhat drab-coloured slackwater darter is distinguished by a conspicuous vertical bar below the eye, and three saddle-shaped dark brown or blue-black patches that contrast with the brownish body. The male is similar to the female, but may have slightly more intense yellow and orange spotting around the base of the tail (4).

The slackwater darter is endemic to the States of Alabama and Tennessee in the south-east of the United States. It is found around the middle Tennessee River drainage, occupying upper Shoal Creek, Swan Creek, Cypress Creek and the Flint and Buffalo Rivers (2) (5).

Inhabiting creeks and small rivers, the slackwater darter is typically found in slow-moving areas with gravel bottoms, no more than twelve metres wide and two metres deep. As a bottom-dwelling species it prefers areas with an accumulation of leaves and detritus, often with dense growths of filamentous algae, and is more tolerant of low levels of oxygen than other, related species (2) (5). During the breeding season the slackwater darter will migrate to shallow spawning pools of four to ten centimetres depth, often traversing rapids and swifter streams along the way (5).

The slackwater darter feeds on a variety of invertebrates, including larval insects, limpets and isopods (2) (5). Arriving at the breeding grounds in February, reproduction in the slackwater darter is highly dependant on heavy rainfall flooding breeding pools, as well as water temperature, which must be at least 14 degrees Celsius before spawning takes place (4) (5). Fertilised eggs are laid on clumps of plants and aggressively defended by the male parent (5) (6). Once hatched, the juvenile fish grow rapidly, doubling in size between April and June and leaving the breeding areas around May. A short-lived species, the slackwater darter reaches maturity at two years of age, with a life expectancy of only three years (4).

With an extremely restricted range and a dependency upon areas with adjacent breeding and non-breeding sites, the slackwater darter is extremely vulnerable to any detrimental changes to its habitat. Unfortunately, urbanisation and agricultural activities are increasingly encroaching upon the species’ habitat and, consequently, the species’ habitat has dwindled, and the population has declined (4). The principle agent behind this decline is the extraction of ground water for agriculture and human consumption causing breeding areas to dry up. Streams have also been dammed to form fish-farm ponds, while pollutants seeping into the water table from septic tanks and sewer pipelines continue to degrade this rare species’ habitat (4) (5). These threats are compounded by the species’ short life span as two consecutive poor breeding seasons could wipe out a substantial portion of the remaining population (4) (6).

The future of the slackwater darter is very much dependant on the careful management of its habitat (4). The conservation objectives for this Endangered species are set out in a detailed recovery plan, with the protection of both breeding and non-breeding habitat a key priority (6). Monitoring of water quality and surveys of population trends will also be required if the slackwater darter is to be saved (4).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the slackwater darter, see:

• U.S. Fish and Wildlife Service Species Account:
  http://www.fws.gov/cookeville/docs/endspec/slkdrtsa.html