Wading through the calm waters of Lake Chichancanab in Mexico, aquarists from ZSL’s Whipsnade Zoo in Bedfordshire were looking for any signs of tiny Mexican pupfish – but sadly, their surveys confirmed their worst fears; six of seven unique pupfish, including the boxer pupfish (Cyprinodon simus), are likely extinct in the wild.

Following the frightening revelation in 2024 that the last remaining wild population of boxer pupfish was feared to be lost, and the only remaining population existed at Whipsnade Zoo, aquarists at the ZSL conservation zoo spearheaded a dramatic effort to save the species from extinction.

Whipsnade Zoo’s team knew that they needed to verify the news with a comprehensive survey of the fish’ only habitat - Lake Chichancanab in Mexico – but in preparation for the worst-case scenario to be confirmed, the team initiated an urgent action plan to bolster the insurance population in zoos, including transporting precious eggs from Whipsnade to Bristol Zoological Society.

Sadly, the survey, conducted in spring 2025, along with ZSL’s conservation partners in Mexico and Bristol Zoological Society, revealed not only a complete absence of boxer pupfish, but of five other species of pupfish endemic to the lake.

Underwater video cameras were deployed, aquarists snorkelled to investigate nooks and crevices, seine netting helped to filter swathes of the lake, and aerial drones were used to scan inaccessible areas; all of which ensured the survey was as thorough as could be. Water samples collected from the lake will be analysed for environmental DNA (eDNA) to officially confirm the disappearance of the six pupfish species.

Alex Cliffe, ZSL’s Assistant Curator of Fish, said:

“As soon as we realised the plight of the Boxer pupfish, we knew we had to act fast; but we had to make sure our actions were led by science and evidence. We had braced ourselves for the worst with the boxer pupfish, but what’s happening in Lake Chichancanab is far more alarming than we imagined.”

“Our initial aim when surveying the lake was to confirm if the boxer pupfish was extinct-in-the-wild. However, once we were there, we sadly discovered only one of the seven pupfish species that inhabit the lake remains – the black lip pupfish.”

It's very likely that the other species of pupfish that were not detected during the survey could be lost forever, as none are cared for in zoos and aquariums.

“Boxer and black lip pupfish are vital to preserving the biodiverse ecosystem of Lake Chichancanab. The decimation of pupfish populations in the lake was likely caused by the introduction of invasive fish species, such as the Mayan cichlid,” said Alex.

“It’s devastating news, but our focus is now on the actions we can take to ensure the survival of the two remaining pupfish species – the boxer and black lip - as we believe that we can reverse the damage already done and safeguard their future.”

Whipsnade Zoo is spearheading a breeding programme for the Boxer pupfish and will be working with conservationists in the United States, where one population of black lip pupfish are cared for at one institution, to establish more insurance populations of the precious fish.

Alex said: “Our short-term goal is to rescue a population of black lip pupfish from their currently imperilled habitat and establish a population in human care in Mexico. Long term, we hope to bring some eggs to Whipsnade Zoo, so we can establish a European breeding programme alongside the boxer pupfish.

“The drastic decline in pupfish numbers highlights that biodiversity is being lost at an astronomical rate, but thanks to the unique conservation expertise of zoos and aquariums, we can make a dramatic difference for those in our care.”

Whipsnade Zoo’s aquarists, as part of global conservation charity ZSL, have previously helped to recover a species once thought Extinct in the Wild. The Mangarahara cichlid, a fish endemic to the river of the same name in Madagascar, was thought to only exist in human care, with just two males left at London Zoo. Following a global search led by ZSL, the species was found clinging on to survival in a tiny tributary, which led to the rescue of the fish and creation of an international conservation breeding programme.

Alex concluded:

“As a world leader in managing and reintroducing extinct-in-the-wild species, and the founders of the Extinct-in-the-wild Alliance, ZSL has a responsibility to drive forward the recovery of the world’s most threatened species.”

“This project to save the pupfish is another reminder of the vital role zoos play in conservation, to claw back species from the brink of extinction, reverse the damage caused, and ensure their protection for the future.”

Every visit to Whipsnade Zoo supports ZSL’s vital work to protect species and restore habitats across the globe. Find out more Whipsnade Zoo | A ZSL conservation zoo.