The checkered pupfish is a beautiful species of freshwater fish found only in the Media Luna, a 100 square metre spring in the Rio Verde Valley of north central Mexico. It is the only known member of its genus, and is classed as endangered by the International Union for Conservation of Nature (IUCN). In total, there are 140 species in the pupfish family; 37 of those are listed as endangered – one of which is among the top 100 most threatened species in the world – and five, sadly, have already been declared extinct. A further three species have been declared as being extinct in the wild, meaning they now exist only in captivity, in places like London Zoo.
For over a decade, London Zoo has been running a breeding programme for the checkered pupfish out of its Aquarium, focusing on breeding and maintaining a healthy population. The fish’s sole wild habitat is facing a multitude of threats, mostly from human environmental impacts such as the agriculture industry and tourism, with non-native fish species also threatening to destroy the dwindling population. According to London Zoo, the wild population of checkered pupfish is predicted to decline by 50 per cent over the next ten years, making breeding programmes such as theirs absolutely crucial if it is to have any hope of survival.
However, the pupfish has not been an easy fish to save. Breeding fish at the best of times is a tricky business, with particular species needing an exacting set of conditions in order to thrive — temperature, diet, type of water and its mineral balance all need to be accounted for. Although breeding programmes for other species of pupfish proved more successful, the Aquarium struggled to get the conditions for the checkered pupfish right, with populations growing up malformed, or their soft eggs collapsing altogether. It’s here that plaster manufacturer British Gypsum stepped in.
Having looked closer at the difference between the freshwater of the Media Luna and London, the London Zoo staff determined that a massive dose of calcium was required in order to further harden their already hard water. A mineral called gypsum, normally used for fertilizer or in building materials, which is mined by British Gypsum in Brightling, East Sussex, proved the perfect antidote to the fish’s woes. Every couple of years for the past 12, the company have allowed the zoo to fill a van with this vital lifeblood — as a result, the zoo has managed to breed thousands of checkered pupfish, maintaining two healthy colonies of between 50-150 each at any given time.
Unfortunately, the zoo has no plans to reintroduce their colonies back into the wild, given the ongoing threat to their environment. For now, they remain back-up populations, although the zoo may consider reintroduction later down the line if something can be done to stem the tide of human impact. Mexico itself does not have any government-led conservation programme looking out for the pupfish, and London Zoo’s Aquarium doesn’t work on any projects in-country.
The checkered pupfish is not the only fish that owes its survival to London Zoo — in fact, another species only found in the same Mexican spring, the blue tailed goodeid, is also being bred in the Aquarium. The breeding programme is part of the wider ZSL London Zoo Fish Net project, a consortium of organisations such as zoos, aquariums and universities that are working to save species of freshwater fish from the brink of extinction, through breeding programmes and field conservation in a number of target countries around the world. London Zoo’s Aquarium alone is breeding 26 species, including eight species of Mexican pupfish.
However, given that over 60 per cent of the freshwater species assessed by the IUCN are classed as threatened, endangered or extinct in the wild, it’s hard to feel too cheery even at London Zoo’s fantastic efforts.