Smallest freshwater fish

In 2006, scientists announced the discovery of a bizarre, transparent relative of the carp, since named Paedocypris progenetica, in highly acid peat swamps of Sumatra, Indonesia, and Sarawak in Malaysian Borneo. The smallest adult specimen so far recorded of this new species is a mature female, which measured just 7.9 millimetres (0.31 inches) in total length; the smallest mature male was 8.2 millimetres (0.32 inches).

The research was a collaboration between the National University of Singapore (Singapore), the Natural History Museum (UK) and the Max Planck Institute for Developmental Biology (Germany), led by Dr Maurice Kottelat (Switzerland) and Dr Tan Heok Hui (Singapore). The findings were published in the journal Proceedings of The Royal Society B on 24 January 2006.

Prior to the discovery of Paedocypris progenetica, the smallest-known freshwater fish was the dwarf pygmy goby (Pandaka pygmaea), a colourless and nearly transparent species found in streams, rivers and lakes of Luzon in the Philippines, as well as in mangrove areas of Singapore and several Indonesian islands. Mature males are typically only 9–11 millimetres (0.28–0.38 inches) long and weigh 4–5 milligrams (0.00014–0.00018 ounces), making them the lightest-known freshwater fish based on current available data; female dwarf pygmy gobies are slightly longer at 15 millimetres (0.5 inches).