The Tiniest Fish is Male

After much debate, the male anglerfish is named the world's smallest fish.

Courtesy of Theodore W. Pietsch, University of Washington

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.