Wrestling halfbeak

The wrestling halfbeak (Dermogenys pusilla) also known as Malayan halfbeak is a species of viviparous halfbeak native to the fresh and brackish waters of rivers and coastal regions in South-East Asia, in Singapore, Indonesia, Thailand, Malaysia, Borneo and Sumatra. It is a small, slender, livebearing fish, with the elongated lower jaw characteristic of its family. The colour of this species varies, depending on where the specimen is found. It is the type species of the genus Dermogenys.

Wrestling halfbeaks are surface-feeding fish and feed on a variety of small invertebrates including crustaceans and insect larvae, but especially mosquito larvae and flying insects that have fallen onto the surface of the water. As with all halfbeaks, the upper jaw lifts upwards when the fish is opening its mouth. Wrestling halfbeaks are livebearing fish, the females giving birth to around twenty offspring after a gestation period of about a month.

Wrestling halfbeaks are sexually dimorphic. The females are larger than the males and grow up to 7 cm (3 in) long; males only reach about 5.5 cm (2.2 in) and typically has red or yellow patches on the dorsal fin and the beak. The males of wrestling halfbeaks will fight among themselves by locking jaws, hence their name, for up to thirty minutes.

This species was described as Dermogenys pusillus by Heinrich Kuhl and Johan Coenraad van Hasselt in 1823 with the type locality given as Bogor, Java, the name was subsequently amended to the feminine form.