Devil’s Hole pupfish

The Devil’s Hole pupfish, Cyprinodon diabolis, is an endangered species of fish native to Devil’s Hole, a geothermal (92°F), aquifer-fed pool within a limestone cavern in the Amargosa Desert of Nevada east of Death Valley. It is the smallest desert pupfish species, averaging .75 in (19 mm) in length.

Physical Description

Devil’s Hole pupfish are less than .98 in (2.5 cm) long and resemble other pupfish in shape. They lack pelvic fins and have large heads and long anal fins. Breeding males are solid deep blue and have a black band on the caudal fin.


The natural population at Devil’s Hole fluctuates depending on the season. Low algae growth and other winter conditions cause spring populations to range only from 150 to 250; they swell to 400 to 500 individuals in the fall.

Several other populations of Devil’s Hole pupfish have been established in artificial refuges that mimic the environment of Devil’s Hole. These populations also fluctuate by season and are monitored regularly.


Devil’s Hole pupfish have been the subject of considerable attention and litigation, due to their ancient origins, unusual habitat, and precarious existence. A 22,000 year old species, these pupfish depend on a shallowly submerged limestone shelf of only 6.56×13.12 ft (2×4 meters) in area for spawning as well as for much of their diet (primarily diatoms). Natural threats from flash floods to earthquakes have been known to disrupt this fragile ecosystem, but the major threat has been groundwater depletion due to agricultural irrigation.

C. diabolis was first noticed in 1890 but only identified as a unique and highly divergent species by Joseph Wales in 1930. Formal protection of the species began in 1952 when Devil’s Hole was made part of Death Valley National Monument (now Death Valley National Park). Endangered species designation occurred in 1967, followed by the formation in 1969 of the Desert Fishes Council to fight agricultural interests for the protection of the fish. Water rights litigation went all the way to the US Supreme Court who in the 1976 Cappaert v. United States decision ruled against neighboring land developers.

A number of artificial refugia (concrete tanks approximating conditions in Devil’s Hole) have been established to ensure species survival should the natural population at Devil’s Hole die out: one at Hoover Dam established in 1972 (reported 2004 population, 79), and two near Devil’s Hole itself within the Ash Meadows National Wildlife Refuge established in 1980 and 1991 that comprise the Amargosa Pupfish Station (with populations fluctuating between 90 and 120 depending on season).

In May of 2005, nine pupfish were moved from the hole and a Federal Hatchery to both a Las Vegas Strip casino aquarium and another Federal Hatchery in hopes of augmenting the population. In November 2005, divers counted just 84 individuals in the Devil’s Hole population, the same as the spring population, despite observations of egg-laying and baby fish during the summer. As much as half of the population was estimated to have been destroyed during the summer of 2004 when a flash flood pushed a quantity of scientific equipment into the hole; later about 60 cubic feet of debris, washed into the cave by floods, was removed. Reasons for the continued decline remain unknown, although one possibility is to add some artificial lighting to encourage growth of the algae that the pupfish eat.

Two males from the hole and two females from a hatchery at Hoover Dam were moved to the Shark Reef aquarium and exhibit at the Mandalay Bay hotel-casino. Another five younger pupfish were moved to the Willow Beach National Fish Hatchery in Arizona in order to establish the pupfish in aquaria. 36 adults are believed to still reside in the hole after the moves.