paedocypris progcnetica is the smallest fish

Paedocypris is an Indonesian genus of fish in the family Cyprinidae (which also includes carps and minnows). Previously the two species, Paedocypris progenetica and Paedocypris micromegethes were known. In 2006 however, an undescribed third species was discovered in Bukit Bauk, Terengganu in Malaysia.
Paedocypris progenetica has been claimed to be the smallest known species of fish and vertebrate in the world. The smallest mature female measured 7.9 mm and the largest known individual 10.3 mm.

Taxonomy

Both 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. 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, Paedocyrpis, and both 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.
Paedocypris is considered a danionin genus by Tyson Roberts.It was found that Sundadanio and Paedocypris share a sister group relationship, supporting its close relationship to danionin genera; however, this study included danionins among the subfamily Rasborinae.

Appearance

Their miniature transparent body lacks typical features characteristic of adult fish, for instance a bony skull structure around its brain, and it retains the post-anal larval-fin-fold along the ventral edge of the caudal peduncle, characteristic of fish larvae. 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. It is hypothesized that these modified fins are used to grasp the female during mating, or to keep position over a spawning surface.

Smallest vertebrate

Paedocypris progenetica has been claimed to be the smallest known species of fish and vertebrate in the world. The smallest mature female is only 7.9 millimetres (.31 in) standard length, smaller than the female of any other vertebrate species. The largest known individual is 10.3 mm (.41 in).
Male individuals of the species anglerfish Photocorynus spiniceps have been documented to be 6.2-7.3 mm at maturity, and thus claimed to be a smaller species. However, these survive only by sexual parasitism,and the female individuals reach the significantly larger size of 50.5 mm.

 Habitat and conservation

Paedocypris progenetica lives in the dark colored peat swamps of the Indonesian island of Sumatram
Paedocypris micromegethes lives in the peat swamps of Sarawak (Borneo). Their small size helps them to survive through extreme droughts, as they can live in small remaining puddles of acid water (pH as low as 2.9, at least 100 times more acidic than rainwater). Their habitat is threatened by forest fires, logging and plantations.