The Worlds Smallest Fish - Paedocypris progenetica

The world's smallest known fish is Paedocypris progenetica, having only been discovered in the last decade. Scientists found this fish species living in the forest swamps on the Indonesian island of Sumatra, with a mature female Paedocypris only measuring tiny 7.9 mm in length! In fact, only until recently, Paedocypris was the world's smallest known vertebrate or backboned animal, which has now been superseded by a minute frog (Paedophryne amauensis) from the New Guinean rain forests.

The fish, a member of the carp family, has a partially see-through body and a reduced head skeleton, which leaves the brain completely unprotected by bone. This tiny, translucent fish has the appearance of larvae, possesses some bizarre grasping pelvic fins and lives in dark tea-coloured waters with an acidity of pH3, which is at least 100 times more acidic than rainwater!

The Sumatran swamps were once thought to harbour very few animals, but research has revealed that they are highly diverse and home to many unique species that occur nowhere else. However, as with many such areas, this habitat is in much danger as the peat swamps have been damaged by large forest fires and they are still being threatened by industries such as logging and agriculture. As a result several populations of Paedocypris have already been lost.

The previous record for smallest fish was held by an 8 mm species of Indo Pacific goby. The UK's smallest fish is the marine Guillet's goby (Lebetus guilleti) reaching, in comparison, a whopping 24 mm in length!