Conserving the rarest fish on the planet

Conserving the rarest fish on the planet

Unsurprisingly the threats to these exceptional little fish are entirely human-caused. The pressure is increasing for the fish as groundwater pumping, pollution, construction projects, pesticides and non-native species continue to claim more and more pupfish.

Pupfish are a group of ray-finned fish belonging to the family Cyprinodonitodae. They are recognised as the rarest fish on the planet. Their morphology is incredibly unique, and they are the masters of carving out extreme niches in which to thrive. They face a number of human-created threats, but new studies show that they are also an exciting testament to the value of restoration projects.

Pupfish, a bit of introduction, what are they?

These small fish are typically located in incredibly isolated bodies of water across the Americas. One species is more widely distributed across parts of Asia, Africa and Europe, but this species, called Aphanius, is the black sheep of the family. For reference, 40 of the 43 species of pupfish live in Arid environments. For obvious reasons, fish and arid climates are not usually suited particularly well together. These fish have still, somehow, managed to persevere in the hottest and driest parts of America. Their numbers, however, are incredibly low, and almost every species is under threat: 90% of pupfish species are at risk of extinction due to habitat destruction, reduction of ranges and introgression with invasive species.

Rocky body’s of water: Picture of the devil’s hole USFWS pacific south west region

A few key examples of different pupfish species and their habitats

There are a few pupfish species found in Deserts across the Amargosa Valley and Death Valley. These are some of the hottest places on earth. The fish rely on spring ecosystems, small groundwater-fed pools that are beginning to shrink in our warming climate. The devil’s hole pupfish, for example, lives in a single pool located in a cave in the Amargosa Desert. The waters in the devil’s hole are much more stable compared to other habitats of Cyprinodonitodae members, averaging around 33°C and fairly consistent salinity. Amazingly the Devil’s Hole itself only opened up about 60,000 years ago, and it’s thought that the pupfish species living in it could be as young as 1000 years old. Their closest relatives are other Death Valley pupfish that are less well known but have more challenging lifestyles. These other fish inhabit small pools and creeks across death valley in waters up to 45°C and a salinity four times that of the ocean. How is it that these fish can live in such extreme environments?

San Salvador Island: Jesse Allen and Robert Simmon - NASA Earth Observatory

How do pupfish live in these places?

The pupfish have a remarkable trump card that gives them the ability to live in such hostile locations: Pupfish display some of the most rapid morphological diversification found in any animal on the planet. When a pupfish species ends up in a new environment, they can be comfortable and well-adapted in much fewer generations than other animals; this means they’re typically successful in habitats where different species are not, which reduces competition. Pupfish are generalist feeders. They eat plankton, algae, vegetation, and tiny invertebrates, but some have developed into much more niche feeders due to their evolutionary traits. 

Pupfish rarely coexist with one another, although there is a group of three species called the San Salvador pupfish that live in San Salvador Island’s salty lakes. They exhibit one of just two examples of coexistence between pupfish species. They also evolve between 30-150 times faster than any other pupfish, which is the fastest diversification of any fish ever found. One of these three species has evolved to eat nothing other than the other two species’ scales. This trait has only been recognised 14 times in other fish groups, and out of the 1500 ray-finned fish, not a single one eats just scales. The DNA enabling this behaviour is completely novel. With such powerful adaptive capabilities, it’s surprising that they are under such considerable threat. 

Threats to pupfish

Unsurprisingly the threats to these exceptional little fish are entirely human-caused. The pressure is increasing for the fish as groundwater pumping, pollution, construction projects, pesticides and non-native species continue to claim more and more pupfish. 500 devils hole pupfish are reduced to just 35 over the course of 50 years. Many other species have seen similar reductions. The Comanche Springs Pupfish, endemic to west Texas, saw large areas of its habitat completely dried up due to water extraction. Fortunately, as they were on the brink of extinction, a conservation pool was built. New survey methods have shown that this restored habitat has been incredibly successful. Studies on the population are revealing significant growth. 

Conservation efforts are more simple when dealing with small systems like the ones in which pupfish live. Although they are still in very hot water, it’s fantastic to see how attitudes change over time. In the 1970s, there was a social movement called “kill the pupfish” due to the restrictions placed on water extraction from their habitats. Today reservoirs are better protected, and there are many more projects to keep beautiful creatures like these from going extinct.

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