A little river in Mexico is the site of one of 2021’s most heartwarming tales — the reintroduction of a species that had gone extinct in the wild.

We often hear stories about animals going extinct, and they’re always heartbreaking. But, every so often, we get to hear of the reverse: a species that had gone extinct, being reintroduced into the wild. The waters of the Teuchitlán, a river in Mexico that flows near a town bearing the same name, can now boast the same tale.

Efforts by local researchers, conservationists, and citizens, with international support, have successfully reintroduced the tequila splitfin (Zoogoneticus tequila), a tiny fish that only lived in the Teuchitlán river but had gone extinct during the 1990s, to the wild.

Re-fishing

In the 1990s, populations of the tequila splitfin began to dwindle in the Teuchitlán river. Eventually, it vanished completely.

Omar Domínguez, one of the researchers behind the program that reintroduced the species, and a co-authored of the paper describing the process, was a university student at the time and worried about the fish’s future. Pollution, human activity, and invasive, non-native species were placing great pressure on the tequila splitfin.

Now a 47-year-old researcher at the University of Michoacán, he recounts that then only the elderly in Teuchitlán remembered the fish — which they called gallito (“little rooster”) because of its brightly-colored, orange tail.

Conservation efforts started in 1998 when a team from the Chester Zoo in England, alongside members from other European institutions, arrived with several pairs of tequila splitfin from the aquariums of collectors and set up a lab to help preserve the species.

The first few years were spent reproducing the fish in aquariums. Reintroducing these to the river directly was deemed to be too risky. So Domínguez and his colleagues built an artificial pond on-site, in which the fish could breed in semi-captivity. The then-40 pairs of tequila splitfins were placed in this pond in 2012, and by 2014 they had multiplied to around 10,000 individuals.

By now, their results gave all the organizations involved in the effort (various zoos and wildlife conservation groups from Europe, the United States, and the United Arab Emirates) enough confidence to fund further experimentation. So the team set their sights on the river itself. Here, they studied the species’ interactions with local predators, parasites, microorganisms, and how they fit into the wider ecosystem of the area.

Then, they placed some of the tequila splitfins back into the river — inside floating cages. This step, too, was a marked success, and the fish multiplied quickly inside the cages. When their numbers grew large enough, around late 2017, the researchers marked the individual fish and set them free. In the next six months, their population increased by 55%, the authors report. The fish are still going strong, they add: in December 2021, they were seen inhabiting a new area of the river, where they were completely extinct in the past.

It’s not just about giving a species a new lease on life, the team explains. Their larger goal was to restore the natural equilibrium of the river’s ecosystem. Although there is no hard data on environmental factors in the past to compare with, Domínguez is confident that the river’s overall health has improved. Its waters are cleaner, the number of invasive species has declined, and cattle are no longer allowed to drink directly from the river in some areas.

Local communities were instrumental in the conservation effort.

“When I started the environmental education program I thought they were going to turn a deaf ear to us — and at first that happened,” Domínguez said.

However, the conservationists made sustained efforts to educate the locals through puppet shows, games, and educational materials, and presentations about zoogoneticus tequila. Among others, citizens were told about the ecological role of the species, and the part it plays in controlling dengue-spreading mosquitoes.

The tequila splitfin is currently listed as endangered on the IUCN’s red list.

The paper “Progress in the reintroduction program of the tequila splitfin in the springs of Teuchitlán, Jalisco, Mexico” has been published online by the IUCN CTSG (Conservation Translocation Specialist Group). An update on the project has been published in the magazine Amazonas.