Even fish sometimes hold their breath in cold, dark and deep water.

Thresher sharks that live near Hawaii spend their days in warm surface waters; But at night, in the depths of the cold ocean, hundreds of meters underwater, they hunt squid and other prey. Researchers on May 22 Science magazine reported that basking sharks may conserve body heat in cold waters by shutting down their gills during deep-water swimming. These animals actually “hold their breath” for almost an hour each time.

Scientists know that whales and other swimming mammals hold their breath in deep water. But Mark Royer“This is the first time such behavior has been observed in a deep-water swimming fish,” says a researcher of shark physiology and behavior at the University of Hawaii at Manoa.

Sharks and other fish are cold-blooded; This means that the heat of the water around them largely controls their body temperature. Fish lose and gain a lot of heat when they breathe through their gills, which take in oxygen from the passing water.

“The gills are like giant radiators strapped to sharks’ heads,” says Royer. For this reason, many shark species in the tropics usually do not go deeper than a hundred meters and tend to swim on the surface of the ocean; Where the water temperature is around 26 degrees Celsius. But tags attached to scalloped basking sharks, a species found in coastal waters throughout the tropics, showed that these animals swim up to 1,000 meters below the water’s surface for up to an hour at night.

At such a depth of the sea, the water temperature can drop up to 5 degrees Celsius. Such temperatures are too cold for tropical sharks; So Royer and his colleagues attached special devices to the backs of sharks gathered for mating in Oahu’s shallow bay to find out how these animals tolerate the cold temperatures of the deep sea.

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