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.