The entire population of the Devils Hole pupfish lives in one cave in Death Valley, Nevada, USA. The cave (Devils Hole) is about 22m long and 3.5m wide. While it is deep – at nearly 150m – the fish tend to live within 15m of the surface.
This means the Devils Hole pupfish probably has the smallest habitat range of any vertebrate.
They are also the rarest fish. While 191 fish were counted in 2024, only 38 fish were found in 2025. Two earthquakes are thought to be the cause of the sudden population decline. The quakes disturbed algae (the fish’s main food) and the fish’s eggs.
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Thankfully, biologists had an action plan in place for just such an event. They have supplemented the wild population with captive-bred individuals and will provide food until the algae regrow.
Some studies suggest the Devils Hole pupfish has been isolated since the cavern’s formation 60,000 years ago, while others suggest they have only been isolated for a few thousand years.
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Nobody knows exactly how they first appeared – theories range from the fish arriving via underground water systems to birds accidentally transporting them to the cavern.
But it’s safe to say there’s a lot we still don’t know about this enigmatic species.
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Top image © a U.S. Fish and Wildlife Service
