Researchers have found the smallest known fish on record in the peat swamps of the Indonesian island of Sumatra.
Individuals of the Paedocypris genus can be just 7.9mm long at maturity, scientists write in a journal published by the UK's Royal Society.
But they warn long-term prospects for the fish are poor, because of rapid destruction of Indonesian peat swamps.
The fish have to survive in extreme habitats - pools of acid water in a tropical forest swamp.
Food is scarce but the Paedocypris - smaller than other fish by a few tenths of a millimetre - can sustain their small bodies grazing on plankton near the bottom of the water.
Human threat
To keep their size down, the fish have abandoned many of the attributes of adulthood - a characteristic hinted at in their name.
Their brain, for example, lacks bony protection and the females have room to carry just a few eggs.
The males have a little clasp underneath that might help them fertilize eggs individually.
Being so small, the fish can live through even extreme drought, by seeking refuge in the last puddles of the swamp; but they are now threatened by humans.
Widespread forest destruction, drainage of the peat swamps for palm oil plantations and persistent fires are destroying their habitat.
Science may have discovered Paedocypris just in time - but many of their miniature relatives may already have been wiped out.
