Scientists first discovered fish that can hold their breath: why do they need it

When swimming in cold, deep waters, ridged hammerhead sharks have an unusual way of keeping warm: they close their gills and hold their breath. This unusual behavior has never before been recorded in other fish.

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Mark Royer, a scientist from the Hawaiian Institute of Marine Biology Shark Research Group, noted:

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This was a complete surprise. It was unexpected that the sharks held their breath to hunt like a diving marine mammal. This is extraordinary behavior for an incredible animal.

Hammerhead sharks are ectotherms, or cold-blooded creatures, which means that their body temperature is regulated by their environment. Their gills, which allow them to breathe by absorbing oxygen dissolved in water, are the main points of heat loss throughout the body. Since sharks cannot produce their own heat, they become lifeless and cannot swim if they get too cold. And if the shark stops moving, then water cannot flow through its gills, which can lead to suffocation.