Devilishly Rare

Rare species of fish are always fascinating because of their scarcity, but one species has taken things to such extremes that it’s earned itself the unenviable title of “rarest fish in the world.”

The Devil’s Hole Pupfish (Cyprinodon diabolis) can only be found in “Devil’s Hole” - a single geothermal pool in a limestone cave in the middle of Death Valley in Nevada’s Mojave Desert. With a habitat that incredulous scientists have dubbed “ridiculous”, the little fish survive in temperatures of 32-33 degrees Celsius with low levels of oxygen and dramatic changes in water level – all of which would be enough to kill other species in a few hours.

Each fish is less than one inch long and perhaps fewer than 50 individuals now survive, but even more remarkably, every member of the species has existed in the wild within an area no larger than the average living room. Although the cavern opens to the air, the pool inside is not connected to any other water source, and at one end of this pool is a small limestone shelf, measuring just 3 by 6 metres, which is the fish’s only known feeding and spawning ground.

As a result, the pupfish has the smallest geographic range of any vertebrate species and is quite possibly the most isolated animal species in the world. So while some affluent aquarists can boast of their Platinum Arowanas or Masked Angelfish, it’s worth remembering that there’s rare, and then there’s rare...