• The rare Sonoyta pupfish were introduced into a desert river habitat inside the huge Biosphere 2 structure near Tucson.
• The dish are native to Quitobaquito Springs near the Arizona-Mexico border, but their numbers have dwindled with water levels in the habitat.
• Biosphere 2 was built as a sealed habitat for humans, but the first two “missions” failed and it has evolved into a laboratory owned by the University of Arizona.

ORACLE, AZ — Four dozen Sonoyta pupfish are now swimming beneath the towering glass pyramids of the University of Arizona’s Biosphere 2 after a multi-year effort to conserve the critically endangered species.

The rare desert fish were introduced into a newly constructed desert stream habitat at the research facility on Oct. 24, welcomed by a cheering crowd of university students, biologists and self-proclaimed fish lovers. 

“Biosphere 2 is a theater of all possibilities,” said Joaquin Ruiz, director of the facility. “In addition to what we do to try to understand how ecosystems operate, we’re also going to be the safe harbor of a species that is endangered.”

The release is a collaboration between the University of Arizona, U.S. Fish and Wildlife, and the Arizona Game and Fish Department. 

Measuring about two inches long, the small blue-green and brown-striped fish are also called Quitobaquito pupfish because they can only be found in the wild at Quitobaquito Springs, a small, spring-fed oasis in Organ Pipe Cactus National Monument near the U.S.-Mexico border.

“Whenever I talk about pupfish in my class, I know they’re really easy to identify. They’re very cute. They’re called pupfish because they look like little puppy dogs,” said University of Arizona associate professor Peter Reinthal, who originated the idea for the pupfish introduction.

A new use for a storied structure

After teaching a hands-on portion of his class on ichthyology (the study of fish) inside Biosphere 2, Reinthal wrote a grant through the U.S. Fish and Wildlife’s Desert Fish Habitat Partnership to fund the construction of the stream inside a giant habitat once intended for humans.

Biosphere 2 — named after the planet Earth, the original biosphere — was built in the late 1980s by Space Biospheres Ventures, a private company with a goal of creating an entirely self-sustaining Earth ecosystem beneath the glass walls. In the 1990s, the facility gained national attention when researchers were locked inside Biosphere 2 for two years to simulate a futuristic space colony. The first two “missions” failed and the structure evolved into a science laboratory.

The University of Arizona gained ownership of the property in 2011 and now operates the facility as an Earth Systems Research Center and tourist destination.

State and federal agencies collaborated with the university and drafted a Safe Harbor Agreement, a voluntary agreement that allows individuals and organizations to keep populations of endangered species and contribute to their recovery.

The introduced pupfish are a part of a backup population meant to safeguard the species from extinction if the wild population declines. 

The entire project took about two years of planning and implementation.

“I’ve been a scientist all my life and every project I ever do it’s to collect data or produce papers. This is the first one we did where we actually built something physical,” said Reinthal. “I really, really enjoyed that.”

Native species: Tiny endangered pupfish return to this lake east of Phoenix after a year’s absence

Habitat loss drives population declines in hardy desert fish

Behind their “cute” faces and chubby bodies, the Sonoyta pupfish are survivors.

Adapted to live in extreme environments, the pupfish are capable of surviving drastic temperature changes, a range of pH levels and low-oxygen water.

“They can survive in 110-degree water, which is wild. And they can handle a lot of salinity,” said Brett Montgomery, topminnow and pupfish specialist with the Arizona Game and Fish Department. “They can exist in springs and streams with all those things that you wouldn’t think would allow fish to survive.”

Despite their hardy nature, the primary threat to the pupfish species has been habitat loss.

The Sonoyta pupfish were listed under the Endangered Species Act in 1986, and today, their total population is about 2,000.

The species was once found south of the border in the Rio Sonoyta, but since groundwater pumping has depleted the river, there has been no observable population in the watershed. 

“A good number of animal species rely on streams like this in the natural world, and they’re valuable places to a large diversity of species, both plants and animals. We need to take care of them,” said Jason Deleeuw, terrestrial biome manager at Biosphere 2.

For more stories about wildlife: Sign up for AZ Climate, The Republic’s weekly environment newsletter.

Habitat is also an educational tool

Deleeuw constructed the desert stream with a local construction company and help from student workers. The stream features several pools to hold the endangered fish and includes native vegetation to emulate their disappearing natural environment. 

About 34,000 fish species are expected to go extinct in the next 25-50 years, according to Reinthal. A recent study co-authored by the International Union for the Conservation of Nature found that 26% of all freshwater fish species were at high risk of extinction. 

Reinthal hopes the population of endangered fish will serve as an educational resource for both university classes and for those visiting Biosphere 2 as a tourist destination.

“It’s a great outreach tool,” said Reinthal. “Biosphere 2 gets about 80,000 visitors a year here, so the public can learn about fish.”

As pupfish settled into their new home right away, establishing territory and chasing each other in circles, the biologists are already planning for future introductions.

Montgomery said he hopes to introduce additional Sonoyta pupfish once the government shutdown ends, and after the pupfish are acclimated, the team plans to introduce the endangered Gila topminnow to the Biosphere 2’s desert stream habitat.

“They make people happy,” said Reinthal. “And I tell my class, if you don’t like pupfish, it means you’re a mean person.”

John Leos covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to john.leos@arizonarepublic.com.

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust.

Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook and Instagram.