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The reedfish, ropefish (more commonly used in the United States), or snakefish, Erpetoichthys calabaricus, is a species of fish in the family Polypteridae alongside the bichirs. It is the only member of the genus Erpetoichthys. It is native to fresh and brackish waters in West and Central Africa. The reedfish possesses a pair of lungs in addition to gills, allowing it to survive in very oxygen-poor water. It is threatened by habitat loss through palm oil plantations, other agriculture, deforestation, and urban development.
The largest confirmed reedfish museum specimen was 37 cm (15 in) long, and three studies where more than 2,000 wild reedfish were caught (using basket traps, meaning that only individuals longer than 15–20 cm [6–8 in] were retained) found none that exceeded 41.4 cm (16.3 in). Although sometimes claimed to reach up to 90 cm (3 ft) long, this is incorrect.
Body elongation in fishes, such as eels, usually happens through the addition of caudal (tail) vertebrae, but in bichirs it has happened through the addition of precaudal vertebrae. Reedfish have evolved a more snakelike body by having twice as many precaudal vertebrae as the members of its sister genus Polypterus, despite having the same number of tail vertebrae. Pelvic fins are absent, and the long dorsal fin consist of a series of well-separated spines, each supporting one or several articulated rays and a membrane. The reedfish possesses a pair of lungs, enabling it to breathe atmospheric air. This allows the species to survive in water with low dissolved oxygen content and to survive for an intermediate amount of time out of water. The sexes are very similar in both median and maximum length, but females average heavier than males of a similar length, and they can be reliably separated by the shape of their anal fin. Reedfish are dark above and on the sides, with lighter orangish or yellowish underparts. Males are generally more olive-green in colour, whereas females generally are more yellowish-brown. Larvae have conspicuous external gills, making them resemble salamander larvae.
The genus name derives from the Greek words erpeton (creeping thing) and ichthys (fish).