Dermogenys is a genus of halfbeaks in the family Zenarchopteridae, small, slender, surface-dwelling fish named for the elongated lower jaw that projects well past a short upper jaw, an adaptation for snapping insects and other food from the water's surface film. The atlas's 12 species are native across Southeast Asia, including Indonesia, Malaysia, the Philippines, Thailand, Cambodia, Myanmar, Bangladesh, and Brunei, typically in still or slow-flowing lowland streams, ponds, and waters near rice paddies. Like the true livebearing poeciliids they share tank space with in the hobby, female Dermogenys give birth to free-swimming young rather than laying eggs, even though the two groups are not close relatives.
The genus is kept for its unusual jaw shape and for the sparring bouts males engage in over territory and females, a behavior historically formalized into betting matches in parts of Southeast Asia in a manner comparable to betta fighting. The pygmy halfbeak and the wrestling halfbeak, a name applied to more than one species in the genus, are the ones most likely to turn up in the trade. Conservation is mostly reassuring, with 5 Least Concern and 4 Data Deficient species out of 12, though 2 Vulnerable and 1 Near Threatened species show real concern for a modest slice of the genus.