The title of world's smallest fish is a matter of controversy. In 2006, the prestigious scientific journal of the UK's Royal Society published an article touting the discovery of a lilliputian fish from the genus Paedocypris, which dwells in Sumatran swamps and is only 7.8 milimeters in length, or about a third of an inch. Soon after that, other scientists came forward to cite an even smaller fish that already had been described in the scientific literature: an Australian specimen of the stout infantfish (Schlindleria brevipinguis), which is 7.0 millimeters long.
But the tiniest of fish turns out to be a male anglerfish (Photocorynus spiniceps), discovered in the Philippines, that measures just 6.2 centimeters (about a quarter of an inch) from snout to tail. The male spiniceps is a parasite that spends its life fused to a much larger female. She takes care of all the work, like swimming and eating, while he just hangs on.