A Devils Hole pupfish is pictured at the Ash Meadows Fish Conservation Facility in Nevada. Scientists recently took captive-bred pupfish from this facility and introduced them into the species' natural habitat in Death Valley National Park. Olin Feuerbacher/U.S. Fish and Wildlife Service hide caption toggle caption Olin Feuerbacher/U.S. Fish and Wildlife Service The Devils Hole pupfish, a critically-endangered species and an icon of conservation, ekes out a precarious existence in Death Valley National Park. There, in the scorching desert, guarded by fences and video surveillance, this fish swims around in a sunken fishbowl made of rock that's been its only natural home for millennia. About a year ago, the population abruptly dropped to just 20 fish. Wildlife managers were so alarmed that, for the first time ever, they decided to release some pupfish that they'd been breeding in a huge tank for over a decade as a kind of insurance policy.…