Paedocypris is a genus of tiny cyprinid fish found in swamps and streams on the Southeast Asian islands of Borneo, Sumatra and Bintan.[1]
Paedocypris progenetica has been claimed to be the one of smallest known species of fish in the world. The smallest mature female measured 7.9 mm (0.31 in) and the largest known individual was 10.3 mm (0.41 in).[1]
Two species were discovered and identified by ichthyologists Maurice Kottelat from Switzerland and Tan Heok Hui from the Raffles Museum of Biodiversity Research and the National University of Singapore in 1996.[1] Their osteology was studied by Ralf Britz at London's Natural History Museum. In 1994, the same ichthyologists had already discovered in Sarawak (Malaysian part of Borneo) another miniature species of the same genus Paedocypris. Like P. progenetica, P. micromegethes was found in the slow-flowing blackwater streams and peat swamps.
The genus, Paedocypris, and two species, Paedocypris progenetica and Paedocypris micromegethes, were first described in 2006. Paideios is Greek for children and cypris is Greek for Venus and is a common suffix for cyprinid genera; the gender is feminine. Progenetica (from the word progenetic) is used as an adjective. Micromegethes is Greek for small in size, and is used as a noun in apposition.[1]
Paedocypris is considered a danionin genus by Tyson Roberts.[4] Sundadanio and Paedocypris were found to share a sister group relationship, supporting its close relationship to danionin genera; however, this study included danionins among the subfamily Rasborinae.[5]
Their miniature transparent bodies lack the typical features characteristic of adult fish, for instance a bony skull structure around its brain, and it retains the postanal larval fin-fold along the ventral edge of the caudal peduncle, characteristic of fish larvae.[6] They have a unique sexual dimorphism: The males have highly modified pelvic fins, with the first ray terminating with a hook-like projection of keratinized skin, supported by hypertrophied pelvic musculature. Males also have a pad of keratinized skin in front of the pelvic fins. These modified fins are thought to be used to grasp the female during mating, or to keep position over a spawning surface.