The tequila fish, which grows no longer than 70 millimetres, disappeared completely from the wild in 2003 following the introduction of invasive, exotic fish species and water pollution.
But more than 1,500 of the fish have now been returned to the Teuchitlan River, in the state of Jalisco in south-west Mexico, thanks to conservationists from Chester Zoo and the Michoacana University of Mexico.
Professor Omar Dominguez, from the university, said: “The tequila splitfin has, for many years, been used by scientists to study the evolution, biogeography and live bearing reproduction techniques of fishes and is a very important species.
“We could not stand back and allow it to disappear.
Not only has Chester Zoo been involved technically and financially, the breeders, which became the founding population for the reintroduction of the tequila splitfin, originated at Chester Zoo
Dr Gerardo Garcia, Chester Zoo
“Successfully reinstating this fish in the wild also offers a wider positive impact. Not only has the fish itself been saved, but the environment it lives in has been restored.
“The springs are now healthy and the community that lives around them can now enjoy this beautiful place again, along with all of the benefits that a healthy freshwater habitat brings.
“Meanwhile, local people, particularly schoolchildren, are fully embracing an ongoing education programme, which is changing the way that many act towards the freshwater environment that surrounds them – something that’s absolutely vital if we’re to ensure long-term change.”
The project started in 1998 when the university received five pairs of the fish from Chester Zoo and founded a new colony in a laboratory.
Experts maintained and expanded the fish population for the next 15 years, until 40 pairs were released into artificial ponds at the university.
After four years there were an estimated 10,000 fish in the semi-natural environment and the colony became the source for reintroduction into the wild.
Dr Gerardo Garcia, Chester Zoo’s curator of lower vertebrates and invertebrates, said: “It is a real privilege to have helped save this charismatic little fish and it just goes to show that with the skill and expertise of conservationists, and with local communities fully invested in a reintroduction project, species can make a comeback from environments where they were once lost.
“This is also a great example of how good zoos can play a pivotal role in species conservation.
“Not only has Chester Zoo been involved technically and financially, the breeders, which became the founding population for the reintroduction of the tequila splitfin, originated at Chester Zoo.
“Without the zoo population keeping the species alive for many years, this fish would have been lost forever.
“It’s humbling to think that a small population, being cared for by aquarists in Chester, has now led to their revival in the wild.”
Experts say the wild population of fish is now thriving and the project has been cited as an International Union for the Conservation of Nature (IUCN) case study for successful global reintroductions.
It is hoped to lead to future reintroductions of other highly endangered fish species.
Dr Garcia added: “With nature declining globally at rates unprecedented in human history – and the rate of extinction accelerating – this is a rare success story.
“We now have a blueprint for what works in terms of recovering these delicate fish species in Mexico and already we’re on to the next one – a new rescue mission for the golden skiffia is already well under way.”