Which Is the Smallest Fish in the World?

Paedocypris progenetica was formally described in 2006 from the acidic blackwater peat swamps of Sumatra and Borneo. Mature females have been recorded at only 7.9 millimetres, making it one of the smallest vertebrates on Earth. Its skeleton is so reduced that parts of the skull never fully develop, leaving the brain unprotected by bone. Rivals for the title include the stout infantfish of Australia and males of the anglerfish Photocorynus spiniceps, which live fused to much larger females. Many of these swamps are being drained for palm oil plantations, threatening the species' survival.