Extreme Evolution

Desert-dwelling fish live on the edge of survival.

If evolution were the X-games, the tiny, tough pupfish would take the gold in the Animal Kingdom competition. Living in shallow desert pools and streams in California, Arizona, and Mexico, these colorful, stubby fish tolerate extreme fluctuations in temperature, salinity, and dissolved oxygen. They live fast, maturing within two to three months from birth, and die young, at the average ripe age of six to nine months. Subsisting mainly on algae, they may spend their entire lives in stagnant, salty ponds as little as an inch deep.

Of the five species native to California, the biggest record holder is the desert pupfish, . The largest pupfish, this two-inch-long leviathan can live in waters from a frigid 40° F up to a scalding 112° F. It can endure the lowest levels of oxygen of any fish species, and a range of salinity from no-salt to twice the salt concentration of seawater.

Despite their ability to thrive in a wide range of environmental conditions, pupfish are severely restricted in range. In fact, they also hold the gold in this arena: Devils Hole pupfish have the smallest known range of any vertebrate in the world, eking out an existence in a single pool in Death Valley National Monument.

 

Charco La Palma Pupfish, Cyprinodon longidorsalis.
This species of pupfish is extinct in the wild. The only survivors are a handful of small populations at public aquaria such as the Steinhart. The vernal pools and desert springs where these pupfish once thrived have been destroyed by cattle grazing and excess groundwater pumping for agricultural irrigation. The fish is roughly 3-4cm long.
Copyright ©2000 Joseph Dougherty

Death Valley
Example of small pool in the desert where pupfish may live.
Charles Weber, CAS Photo Archives. Death Valley National Monument, Badwater, Telescope Peak (Inyo County, California, US)