Tiny Devils Hole pupfish doubles in population size in a year–USFWS

One of the world’s rarest species could be making a tentative comeback.

The Devils Hole pupfish is a colorful yet tiny fish that grows to only about 30 millimeters in length. This species occurs in only one place on Earth: Devils Hole, a water-filled cavern within the Ash Meadows National Wildlife Refuge, which is a detached portion of Death Valley National Park in southern Nevada, near the California border. The species’ closest cousin is the Death Valley pupfish.

Its habitat is small, and by consequence so is the species’ population size. But now the population is a little larger, according to the US National Park Service.

Last fall, NPS counted 69 pupfish living in Devils Hole. As of October 2026, that figure had risen to 137 individuals, a near doubling in the population size within a year.

Death Valley National Park Superintendent Mike Reynolds credits tireless conservation efforts and federal protections for the populations’ dramatic growth.

“These results reflect the dedication of our scientists and conservation partners working to protect this extraordinary species,” Reynolds said. “While challenges remain, we’re encouraged by this progress and committed to its long-term survival.”

Devils Hole is deep, extending approximately 150 meters down, but the pupfish survives in just the first 24 meters. Its only breeding ground is a submerged limestone shelf. The fish eat pretty much anything that happens to enter the water. Algae growing on the shelf also provide sustenance for the pupfish.

The water in Devils Hole, the column the fish inhabit, is at a constant water temperature of 33 degrees Celsius or 91 degrees Fahrenheit. It is a very short-lived species, with adults lasting only about a year; thus, the population is represented by almost an entirely new generation in any given year.

With the species almost always on the verge of extinction, conservation work is carried out continuously. NPS said some 72 pupfish raised in captivity were introduced to Devils Hole between March 2025 and February 2026 in a bid to save the species.

Aside from threats to its tiny habitat, NPS says the Devils Hole pupfish is vulnerable to earthquakes, even quakes occurring thousands of kilometers away.

“Two earthquakes in 2025 disrupted the habitat and contributed to population declines,” NPS reports. “Following an Oct. 9, 2026, earthquake in Panama, nearly 3,000 miles away, biologists initially observed signs of stress in the fish but found them in healthier condition during a subsequent visit.”

The Devils Hole pupfish is classified as “critically endangered” under the Red List of threatened and endangered species maintained by the International Union for Conservation of Nature (IUCN).

“It’s exciting to see Devils Hole pupfish numbers increase so significantly over the past year,” Reynolds said.