Previously Extinct Fish Successfully Brought Back to Life

A species of fish that previously became extinct in the wild has been successfully bred and reintroduced back into its native habitat. Known as the tequila splitfin, or “zoogoneticus tequila” in scientific terms, the western Mexican fish previously played a key role in the health of its local environment, making this successful reintroduction a major step for wildlife and habitat conservation alike.


When animals become extinct, they are likely gone forever. In some cases, like the Northern White Rhinocerous (2018) or the Splendid Poison Frog (2020) this happens right before our very eyes, while other extinctions are learned about centuries or even millennia after the fact. The Debrief recently reported on efforts to bring back Woolly Mammoths, which went extinct thousands of years ago.

In some rare cases, animals have gone extinct in the wild, while a few remain in zoos or other captive environments. For example, Przewalski’s horse and the Arabian oryx both went extinct in the wild, but conservationists were able to breed enough of the remaining animals in captivity to successfully reintroduce the species back into their natural habitats.

These and other similar, yet rare, efforts inspired the team behind the tequila spitfin’s reintroduction, leading to this successful effort.


University of Michoacan researcher Omar Dominguez first noticed the fish was disappearing from his local river back in the 1990s when he was still a student. By 1998 it was essentially gone, so conservationists from the Chester Zoo in England came to Mexico to try to see if they could help.

First, they bought up a number of tequila splitfin’s that still survived in aquariums and other private collections.  Then, over the ensuing years, they successfully built a specialized pond to help breed the handful of collected fish into a significant number. In 2012, this meant 40 pairs of viable fish. By 2014, that number had grown to 10,000, which Dominguez and the team felt was enough to try to finally reintroduce them to their natural habitat in the local river system.

“They told us it was impossible,” said Dominguez of his team’s many critics in a piece by the Associated Press, “(that) when we returned them they were going to die.”

To increase the odds of success, the fish were kept in cages as they adapted to the river’s natural environment. During this time, Dominguez and his team learned everything they could about microorganisms in the river, local parasites, tequila splitfin’s natural predators and potential issues with other competitors.

“The fish rapidly multiplied inside their floating cages,” the AP piece reports. “Then they were marked so they could be followed and set free.”

By late 2017 the freed population had increased 55%. And in December of 2021, the fish had finally expanded to another part of the river.


Before its “first” extinction, the tequila splitfin helped control the spread of dengue by eating the mosquitos that carry the disease. Although it is still too early to tell what benefits the new batch of reintroduced splitifns may offer the river system, Dominguez says that the river is already noticeably cleaner and there are fewer non-native species flourishing than before.

“The project has been cited as an International Union for the Conservation of Nature (IUCN) case study for successful global reintroductions – with recent scientific studies confirming the fish are thriving and already breeding in the river,” the Chester Zoo said in a statement.

“This is an important moment in the battle for species conservation,” added Gerardo García, the zoo’s curator of lower vertebrates and invertebrates.

Time will tell if the tequila splitifn will continue to thrive, but Dominguez and his team are already working on reintroducing another “extinct” species known as the skiffia francesae back in to the wild.

Now, about those wooly mammoths…..

Follow and connect with author Christopher Plain on Twitter: @plain_fiction