Scientists from Europe and Singapore say they have discovered the world's tiniest fish - a species that lives in peat wetlands in Southeast Asia and, when fully grown, is the size of a large mosquito.The record-busting newcomer to the biodiversity book, Paedocypris progenetica, is a distant cousin of the carp, say the discoverers, who publish their findings on Wednesday in Proceedings of the Royal Society B, a British journal.
Skinny and transparent, the elusive fish lives in highly acid peat swamps on the Indonesian island of Sumatra and in the Malaysian part of Borneo that are threatened by forestry and agriculture.
These so-called "blackwater" swamps are a unique landscape of flooded trees growing in water-logged, soft peaty soil that is often several meters (10 feet) thick.
The water is stained reddish-black, like very dark tea, appearing black at the surface. It is extraordinarily acidic, having a pH3 value of only three, the same as a sour apple.
The scientists needed a special stereoscopic microscope to accurately measure the fish.
The smallest adult specimen they netted was a mature Paedocypris progenetica female, found in Sumatra, that came to just 7.9mm (0.31 of an inch) from nose to tail, making it not only the world's smallest fish but the smallest vertebrate too.
She nudged out the previous record holder, a marine fish of the Western Pacific called the dwarf goby (Trimmatom nanus), which comes in at 8mm (0.32 of an inch) at sexual maturity.
"The discovery of such a tiny and bizarre fish highlights how little we know about the diversity of Southeast Asia," said Kottelat.
"This is all the more serious because the habitat of this fish is disappearing very fast, and the fate of the species is now in doubt."