Death Valley pupfish

The Death Valley pupfish (Cyprinodon salinus), also known as Salt Creek pupfish, is a small species of fish in the family Cyprinodontidae found only in Death Valley National Park, California, United States. There are two recognized subspecies: C. s. salinus and C. s. milleri. The Death Valley pupfish is endemic to two small, isolated locations and currently classified as endangered.

Description
The Death Valley Pupfish is a small, silvery colored fish with 6–9 vertical dark bands on its sides. It has an average length of 3.7 cm, with a recorded maximum of 7.8 cm.

The males, often appearing in larger sizes compared to females, turn bright blue during mating season, April through October. The females, along with premature pupfish, tend to have tanned backs with iridescent, silvery sides. Both males and females have plump bodies with rounded fins, a squashed head and an upturned mouth. The pupfish can withstand harsh conditions that would kill other fish: water that is 4 times more saline than the ocean, hot water up to 116 F, and cold water down to 32 F.

Distribution and habitat
This species is known from only two locations in Death Valley: Salt Creek (subspecies salinus) at about 49 m below sea level, and Cottonball Marsh (subspecies milleri), at about 80 m below sea level. They are thought to be the remainders of a large ecosystem of fish species that lived in Lake Manly, which dried up at the end of the last ice age leaving the present-day Death Valley.

The Salt Creek subspecies is also found at River Springs and Soda Lake, in Death Valley National Park.

Conservation
The Death Valley pupfish has been classified as endangered by the IUCN because of its extremely restricted distribution (if the two extant locations were treated as a single unit, it would be considered critically endangered). Numbers of individuals at the locations are highly seasonally variable, and fluctuate with water level and flow volume. While the entire range of the species is located in a protected area, it may be under threat from accidental introduction of non-native species, local catastrophic events, and excessive pumping of the aquifer that feeds the habitat.