World's smallest creatures with backbone

The world's smallest freshwater fish has been found -- in the peat swamp forest of Sumatra. It is a fish about the size of a large mosquito.


The fish (Paedocypris progenetica) was discovered by Dr Tan Heok Hui, and Dr Maurice Kottelat of the Raffles Museum of Biodiversity Research at the National University of Singapore, while working with their colleagues from Indonesia and Mr Kai-Erik Witte from the Max Planck Institute in Germany. The detailed anatomy of the fish was investigated by Dr Ralf Britz of the Natural History Museum of London. Their findings were published in Proceedings of the Royal Society: Biological Sciences

Looking like a larva, the fish is transparent and has a very rudimentary skull which leaves the brain exposed. The fish can only be measured accurately with a stereoscopic microscope. Surprisingly, it is a distant cousin of the carp which can grow to quite a large size.


"The discovery of such a tiny and bizarre fish only now, highlights how little we know about the diversity of the region. This is all the more serious because its habitat is disappearing very fast and fate of the species is now in doubt," said Dr Kottelat who is now based in Switzerland. He is an Honorary Research Associate with the Raffles Museum of Biodiversity Research and has been exploring the rivers of Asia. He has discovered numerous new fishes for the past 25 years.

Said Dr Tan, a researcher at the Raffles Museum and a specialist of the biology and systematics of the fishes of Southeast Asia: "This fish lives in highly acidic peat swamps on the Indonesian island of Sumatra and in the Malaysian part of Borneo that are threatened by logging and agricultural practices. Many of these swamp forests were destroyed in the prolonged 1997 forest fires of Sumatra and Borneo."

These swamps are a unique community of flooded trees growing in water-logged, soft peaty soil that is often several metres thick. The reddish black water is extremely acidic, having a pH value as low as three. These tiny fish feed mainly on plankton. Such swamps, contrary to common belief that they are species-poor ecosystems, with low faunal diversity, do harbour a signifcant number of miniature endemic fish species.

"In peat swamps, miniature fishes survive droughts in shallow pools, burrows of other animals, or in the soil, and small size is a considerable advantage when the water level falls. Even in very dry periods, the peat acts as a buffer and retains isolated pools of clean and cold water," the researchers wrote in their paper. The team's star find, a female Paedocypris progenetica, was just 7.9mm from nose to tail. The previous record holder, a marine fish of the Western Pacific, the dwarf goby (Trimmatom nanus) measured 8mm at sexual maturity.