Species extinction is one of the most severe, and a truly irreversible, environmental problems facing our planet. Thousands of species have gone extinct in the last 100 years, and many more are at risk. So dire is the situation that it has been named the Sixth Mass Extinction, or Anthropocene Extinction.

Among vertebrates, freshwater fishes are one of the most vulnerable groups. This is because human activities affect freshwater systems broadly and at different levels. The main threats to freshwater bodies and their biodiversity are overexploitation, pollution, modified flow as a result of dam construction, habitat destruction and degradation, and invasive species. In North America alone, there are 700 species of freshwater fishes at risk of extinction, and at least 15 species endemic to Mexico have been lost in recent decades. Many of these extinct or threatened species have very limited distribution ranges, restricted to desert springs or isolated systems like cenotes, natural sinkholes formed when limestone bedrock collapses and exposes the groundwater underneath. Because these species are usually small and inconspicuous, their disappearance often goes unnoticed.

In 2017, Gerardo Ceballos and Lourdes Martinez Estevez coedited a book on threatened freshwater fishes in Mexico, and one species in particular caught their attention: the Catarina pupfish Megupsilon aporus, a relict species that became extinct in the wild in 1994, but had populations in captivity until 2014, when the last individual succumbed to an infectious disease. This beautiful species, endemic to a spring at Bolson de la Sandia in the state of Nuevo Leon in northeastern Mexico, had a unique evolutionary history and became extinct because of water overexploitation for crop irrigation.

Many national and international efforts were implemented to try and maintain and breed this species in captivity. These included collaborations with the Universidad Autonoma de Nuevo Leon, the New York Aquarium, and the Children’s Aquarium at Fair Park in Dallas, Texas.

An article detailing the discovery of the Catarina pupfish, and the conditions that lead to its extinction, has now been published in Oryx—The International Journal of Conservation. To prevent further extinctions, Ceballos, Martinez Estevez and coauthors propose a national strategy to protect freshwater fishes in Mexico. This proposed strategy is part of a broader initiative called ‘Stop Extinctions’ that seeks to reverse the ongoing loss of populations and species worldwide. In particular, the freshwater fish strategy will involve cooperation between scientists and decision makers and will include the participation of local people to safeguard valuable habitats. When possible, it will also include the reintroduction and translocation of individuals.

The extinction of the Catarina pupfish, the most recent one for a freshwater fish in Mexico, is a wake-up call. Conservation efforts must be increased to protect endangered freshwater fishes in particular, and threatened plant and animal species more generally. All threatened species require our help, and we need to recognize that our own fate depends on theirs.

If you would like to read more about this study, ‘The extinction of the Catarina pupfish Megupsilon aporus and the implications for the conservation of freshwater fish in Mexico’ is now freely available until the end of the year in Oryx—The International Journal of Conservation.