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Fish Discovered Thriving in Extreme Low-oxygen Habitat

Newsweek logo Newsweek 21/1/2019 Aristos Georgiou

Researchers have observed hundreds of fish living in an inhospitable environment where there is virtually no oxygen—an element crucial to the survival of animal life as we know it.

The creatures were spotted deep in the Gulf of California—home to some of the most low-oxygen waters in the world—with the help of a submersible robot, according to a paper published in the journal Ecology.

Read more: Remember Mr. Blobby, the world's ugliest fish? Meet his cousin 

Scientists from the Scripps Institution of Oceanography and the Monterey Bay Aquarium Research Institute (MBARI) say the low levels of oxygen in the habitat the animals were found in would prove fatal for most other fish.

They made their findings during a research expedition conducted in 2015, which was aimed at investigating various deep ocean basins in the Gulf using an underwater remote control vehicle known as Doc Ricketts.

The team also wanted to examine how animals respond to the kind of warmer and reduced oxygen conditions, which may become more common as a result of climate change. The Gulf is a perfect space to do this as its waters vary hugely in terms of oxygen levels and temperature.

One of the robot’s dives in a region known as the Cerralvo Trough revealed a fascinating array of creatures where there should have been very little life at all.

"I could hardly believe my eyes," Natalya Gallo, lead author of the paper from Scripps, wrote on MBARI's blog. "We observed cusk eels, grenadiers and lollipop sharks actively swimming around in areas where the oxygen concentration was less than one percent of typical surface oxygen concentrations.”

Furthermore, data collected by Doc Ricketts showed that the oxygen levels were between one-tenth and one-fortieth of those tolerated by other fish known to live in low-oxygen environments.

“We were in a suboxic habitat, which should exclude fish, but instead there were hundreds of fish,” Gallo said. “I immediately knew this was something special that challenged our existing understanding of the limits of hypoxia [low-oxygen] tolerance."

Surprisingly, the scientists even noticed that the cusk eels and lollipop sharks appeared to have a preference for the low-oxygen areas, despite the fact they had the option of moving to waters where levels of the element were higher.

"Many other types of fish are considered tolerant of low-oxygen conditions," Jim Barry, a scientist from MBARI who led the research expedition, said. "But the fish in these parts of the Gulf are like the winners among a group of elite Olympic athletes."

At present, it is unclear how the fish can thrive in this environment, although the researchers speculate that some of the species may have particularly efficient gills highly adapted to their low-oxygen habitat. Furthermore, the animals display certain characteristics that could help them to conserve energy—and thus use less oxygen—such as being small and having soft, flabby bodies.

The scientists say that further research is needed to understand why so many fish gather in these harsh waters. Currently, various explanations have been proposed, including avoiding predators or searching for food.

© MBARI

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