Climate change is declining the adult population of threatened Devils Hole pupfish, according to a new study led by the University of Nevada, Reno.

The researchers said that the rising temperature of the geothermal water - as high as 93 degrees - in the Nevada desert has reached the threshold of the pupfish's endurance. The hotter water has reduced the egg hatching time during the optimal recruitment periods by one week.

The recruitment period spans around 10 weeks where water temperatures are favorable for egg hatching and adequate food is accessible to feed the young.

The waters are likely to heat up to more dangerous levels due to rising global temperatures. The researchers said that swelling temperatures will further decrease the pupfish's optimal recruitment period by another two weeks by mid-century and disturb the availability of food for young pupfish.

As a result of the extreme environmental changes, only fewer adult pupfish may survive.

"Climate change is making it harder for the Devils Hole pupfish to survive and has most likely contributed to the decline we have seen," said Mark Hausner, a hydrologist at the Desert Research Institute in Las Vegas, Nev., and lead author of the paper, in a press release.

"While the population of the pupfish has declined, we are hoping they are in a period of recovery," Kevin Wilson, aquatic ecologist and a member of the research team from the Pahrump Field Office of Death Valley National Park, said. "Climate change is threatening the already small population size."

Devils Hole is a water-laden limestone cavern in the Ash Meadows National Wildlife Refuge. Its water temperatures and dissolved oxygen concentrations have reached lethal limits for most fish. The iridescent blue, one-inch-long pupfish has lived in the water-filled cavern for over 10,000 years.

Currently, there are 92 Devils Hole pupfish existing in the geothermal pool, down from 171 fish a decade ago and 553 when the fish population counts began in 1972.

"This is a fish that does live in a fishbowl, an incredibly hostile fishbowl, and you can't move the fishbowl," Tyler said. "This is a species that can't adapt or change or leave to go to a better environment, though it's most likely gone through tremendous genetic bottlenecks in its more than 10,000 years of evolution."

The study titled, "Life in a Fishbowl: Prospects for the endangered Devils Hole pupfish (Cyprinodon diabolis) in a changing climate", is published in Water Resources Research, a journal of the American Geophysical Union.