The world's smallest backboned animal, a species of fish called Paedocypris progenetica, has been discovered in highly acidic peat swamps on the Indonesian island of Sumatra.
The new species belongs to the carp family and females mature at 7.9 mm. The male fish have enlarged pelvic fins with exceptionally large muscles, which may be used to grasp females during sex.
'This is one of the strangest fish that I've seen in my whole career', said Ralf Britz, zoologist at the Natural History Museum. 'It's tiny, it lives in acid and it has these bizarre grasping fins. I hope we'll have time to find out more about them before their habitat disappears completely.'
The new fish was discovered by fish experts Maurice Kottelat (from Switzerland) and Tan Heok Hui from the Raffles Museum of Biodiversity Research in Singapore, while working with their colleagues from Indonesia and with Kai-Erik Witte from the Max Planck Institute in Germany. Ralf Britz, at the Natural History Museum, helped analyse its skeleton and the complex structure of the pelvic fin.
The tiny, see-through Paedocypris fish have the appearance of a larvae and a reduced head skeleton, which leaves the brain unprotected by bone. They live in dark tea-coloured waters with an acidity of pH3, which is at least 100 times more acidic than rainwater. These swamps were once thought to harbour very few animals, but recent research has revealed that they are highly diverse and home to many species that occur nowhere else. The peat swamps were damaged by large forest fires in 1997 and are threatened by logging, urbanisation and agriculture. Several populations of Paedocypris have already been lost.
The previous record for size was held by an 8mm-species of Indo Pacific goby. The UK's smallest fish is the marine Guillet's goby, Lebetus guilleti , reaching 24 mm in length.
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