What is the rarest fish in the world?

One of the rarest fish in the world is the Devils Hole pupfish. In April 2013, it was estimated that only 35 of these fish were left in the wild. Though that number has since increased slightly, the natural population of the Devils Hole pupfish has rarely been measured at over 500, even in the autumn when the population peaks.

The Devils Hole pupfish was one of the first fish species to be federally protected by the Endangered Species Act. The approximately 2-centimeter long fish are found in one location: Devils Hole, a naturally occurring desert pond near Death Valley in Nevada. The fish live in the pond over a limestone shelf and are confined to a space approximately 2 meters wide and 4 meters long.