The Rarest Fish on Earth Has an Unlikely Home—Nevada

Amid the vast Mojave Desert sits an oasis, one brimming with rare flora and fauna that exists nowhere else on earth

What is the Devils Hole Pupfish?

American ichthyologist Joseph H. Wales first declared Devils Hole pupfish a stand-alone species in 1930. Although pupfish in general are famous for living in extreme and isolated places, Wales determined that the Devils Hole pupfish was especially unique. About the size of a goldfish, the species is smaller in size than its counterparts—many of which reside in Ash Meadows’ various pools—and sports a bright, silvery-blue body (females are more olive colored) and a large flat head. These resilient little creatures also lack pelvic fins, a distinct characteristic that sets them apart from other pupfish.

Devils Hole pupfish share no homology, or common ancestry, with any other species given their isolated and singular cavern environment. Still, the same “orphaned evolution” that’s helped make the Devils Hole pupfish so distinct has also led to its genetic instability due to extremely high levels of inbreeding. In fact, when American ichthyologist Robert Rush Miller first visited Devils Hole in 1937, he worried for the future of this precarious fish. His research eventually earned the Devils Hole pupfish a place on the U.S. Department of Interior’s first endangered species list in 1967.

The Rarest Fish on Earth Has an Unlikely Home—Nevada — Devils Hole, Ash Meadows National Wildlife Refuge. Brett Seymour, National Park Service

The protected status was welcome as these tiny survivors were facing serious peril—not just because of their isolation, but also from environmental disruption caused by agricultural development. When local ranchers started pumping the region’s groundwater during the 1960s and ‘70s, Devils Hole’s water level dropped. Since its resident pupfish use the cavern’s upper shelf for reproducing and feeding, their numbers drastically decreased. A series of court battles finally resulted in a 1976 Supreme Court decision that limited pumping and banned the installation of new wells—providing a much-needed win for the fish.

How Did Ash Meadows Form?

As part of the larger Amargosa Desert ecosystem—long sacred grounds for Death Valley’s indigenous Timbisha People—Ash Meadows is a land of extremes. It likely formed at the end of the Pleistocene Ice Age, about 12,000 years ago, when melting glaciers and a warming climate led to a series of fragmented wetlands. Today Ash Meadows’ more than 50 natural springs form the Mojave Desert’s largest remaining oasis.

Most of the refuge’s endemic species reside in or next to these pockets of streams, including other species of pupfish that have also evolved in relative isolation. This includes the Warm Springs pupfish—nearly half of which live in School Spring—and the Ash Meadows Amargosa pupfish, which call multiple pools home, including Jack Rabbit Spring and Crystal Pool.

Why is the Devils Hole Pupfish so Rare?

Twice annually for the past 50 years, scientists have conducted population surveys on the Devils Hole pupfish. Counts ranged from a high of 550 to a low of just 35 total. In 2022 and 2023’s spring count, the population reached a 22-year high at just 175 pupfish. But what makes these incredible fish so rare?

Devils Hole pupfish have one of the smallest, most distinctive habitats on the planet—their entire species exists in a singular 72 foot long by 11.5 foot wide underground cavern that connects to a nearly 500 foot deep subterranean lake. Water temperatures remain at a constant 92 degrees Fahrenheit year-round—a temperature hot enough to kill most fish. To add to the habitat’s mystique, the cavern’s bottom has never been mapped, though not for lack of trying. Legendary adventurer Jim Houtz completed more than 300 dives in Devils Hole, going as deep as 315 feet. He described the first 160 feet as straight down, before opening into one room and then another. He once told the Associated Press, “It’s like infinity.” While scientists have tried raising populations of Devils Hole pupfish in other locations—even perfectly recreating the cavern’s upper 22 feet—the species lack of genetic diversity makes successful reproduction difficult.

Today, various groups work to protect the pupfish including the Desert Fishes Council, a nonprofit that was founded in 1969 in response to groundwater pumping.

How to See the Devils Hole Pupfish

A 10-foot tall fence surrounds Devils Hole, making the cave off-limits to the general public. However, visitors may spot one or two of its iconic pupfish from a viewing platform built above the cave’s entrance. Simply bring along a pair of binoculars and start looking. The Meadows’ other springs provide a closer view of other desert pupfish species.

Ash Meadows is free to visit and includes a visitor center that is home to a variety of exhibits, including a film highlighting the refuge’s history. There are designated boardwalks for hiking, and swimming is allowed at the refuge’s Crystal Reservoir.