Why You Should Care About the Devil’s Hole Pupfish

In California’s Death Valley National Park, there is a water-filled cavern known as the Devil’s Hole. These waters maintain temperatures of 91°F with oxygen levels as low as 2–3 ppm, and they are home to the critically endangered Devil’s Hole pupfish, hereafter referred to as D.H. pupfish.

Devil’s Hole pupfish, Feuerbacher. (2011). Creative Commons License.

The D.H. pupfish has the most limited range of any known vertebrate, found only in the upper 100 feet of a small cavern. Trapped in an area smaller than some aquarium tanks and in water that would kill most other fish, the D.H. pupfish is an evolutionary wonder that fascinates me. 

The D.H. pupfish alive today represent generations of fish that have survived to reproduce in their hostile environment. They are extremophiles, evolved to withstand environmental pressures far beyond their ancestral environment in a highly restricted range. A normal environmental range for fish maxes at around 60-80°F and oxygen levels of 6-8ppm.

As a Biology major with an interest in evolution and genetics, my own interest in the D.H. pupfish seems self-explanatory. Landlocked fish offer unique insights into speciation and population dynamics in restricted ranges, none so restricted as the D.H. pupfish. Extremophiles have evolved into niches that are outliers in the normal environmental ranges of life on Earth and represent unique evolutionary paths and environmental adaptations. But while extremophile, environmentally locked fish are rare, the D.H. pupfish is far from alone in this category.

Fish such as the Mexican Tetra, which have subterranean populations that inhabit cave systems, have evolved a lack of external eyes, reduced melanin pigmentation, and increased nutrient efficiency. The Kildin cod is a population of Atlantic cod that was trapped in Lake Mogilnoye in Russia 1,800 years ago. They have evolved distinct morphology, faster growth rate, earlier age of maturation, shorter lifespans, and cannibalistic tendencies in response to the lake’s unique environment.

Thus, while the D.H. pupfish’s status as an extremophile landlocked fish is rare, it does not make it unique. In addition to its restricted environment and range, the population of the D.H. pupfish is highly restricted.

The spawning area of the D.H. pupfish is a shallow shelf of only 215 square feet. This means the total population is restricted by both the nutrient availability of the Devil’s Hole and the breeding space availability of this shelf. Additionally, the Devil’s Hole has been found to reach at least 430 ft deep, but the bottom has never been reached. The water has been observed to transmit the energy of earthquakes from as far away as Russia, Japan, and Indonesia. 

In 2025, two earthquakes off the coast of California caused large waves in the Devil’s Hole. These waves knocked algae, fish eggs, and other material off the shelf. Following these events, the population of D.H. pupfish dropped drastically, from 191 to 38.

Since scientists began monitoring in 1972, the population has fluctuated between 35 and 577. There have been three severe bottleneck events: a count of 38 fish in 2007, 35 in 2013, and the most recent count of 38 in 2025. Bottleneck events are severe population declines that leave a small and random subset of the original genetic diversity of a population. While population numbers can recover, the genetic diversity lost cannot be regained, and the buildup of new genetic diversity through mutations is a very slow process. 

Recent genetic studies have shown that the D.H. pupfish are facing an increasingly large genetic load. Genetic load is the loss of fitness due to a buildup of deleterious alleles in a population. This means that its small population size, bottleneck events, and random chance have finally caught up to it, leaving many potentially harmful genes circulating in the population.

Following the spring 2025 population count, the Devil’s Hole Pupfish Strategic Plan was consulted, and biologists decided to release captive-bred D.H. pupfish into the wild population. This makes an important point in the management of the population and its future outlook.

The D.H. pupfish isn’t the only species with a lot of specific conservation efforts focused on its care and longevity. But what strikes me about the D.H. pupfish are the unique causes of its conservation status. None of the complex reasons for its reduced population are human-caused. 

While this could be seen as a reason not to care, people care anyway. People are continuing to study, care for, and conserve the D.H. pupfish not out of any responsibility, but out of genuine care for all of Earth’s creatures. And isn’t that the whole point?

Devil’s Hole pupfish, Feuerbacher. (2010). Creative Commons License.

I could tell you to care about the Devil’s Hole pupfish for its unique evolution and adaptations, for its status as a critically endangered species, or just for it being cute. Instead, if you feel any sort of kinship towards this fish, I offer you the chance to care about it as well as all and any of the wide diversity of life forms on Earth. For no reason besides the astonishingness that is life on Earth.

Opinion by Beatrice Tauer

Sources:

David Tian, Austin H. Patton, Bruce J. Turner, Christopher H. Martin. Severe inbreeding, increased mutation load and gene loss-of-function in the critically endangered Devils Hole pupfish. Proc Biol Sci, 1 November 2022; 289 (1986): 20221561. https://doi.org/10.1098/rspb.2022.1561 

Katherine Rivard. The Extraordinary Lives of Death Valley's Endangered Devils Hole Pupfish. National Park Foundation. https://www.nationalparks.org/connect/blog/extraordinary-lives-death-valleys-endangered-devils-hole-pupfish 

Recent earthquakes threaten Devils Hole pupfish, but conservation efforts offer hope. National Park Service, 15 April 2025. https://www.nps.gov/deva/learn/news/deva_2025-04-15.htm 

Devils Hole. National Park Service. https://www.nps.gov/places/devils-hole.htm