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Rorqual whales have nerves in their mouth that stretch 'like a bungee cord' to help the animals hunt fish. 

The elastic nerves, which can more than double their length, allow the whales to turn their bodies into enormous 'water balloons' as they swallow shoals of prey.

Once captured, the fish are consumed after expelling the water through baleen plates. 

Rorqual whales have nerves in their mouth that stretch 'like a bungee cord' to help the animals hunt fish (illustrated). The elastic nerves, which can more than double their length, allow the whales to turn their bodies into enormous 'water balloons' as they swallow shoals of prey

The volume of water taken in with a single gulp can exceed that of the whale itself.

Dr Wayne Vogl, from the University of British Columbia (UBC) in Canada, said: 'This discovery was totally unexpected and unlike other nerve structures we've seen in vertebrates, which are of a more fixed length.

'The rorquals' bulk feeding mechanism required major changes in anatomy of the tongue and mouth blubber to allow large deformation and now we recognise that it also required major modifications in the nerves in these tissues so they could also withstand the deformation.'

UBC zoologist Dr Robert Shadwick added: 'Our next step is to get a better understanding of how the nerve core is folded to allow its rapid unpacking and re-packing during the feeding process.'

The researchers wonder whether a similar mechanism could be present in other animals, for instance to facilitate the ballooning throats of frogs or the long fast tongues of chameleons.

Co-author Dr Nick Pyenson, from the Smithsonian Institution's National Museum of Natural History in Washington DC, said: 'This discovery underscores how little we know about even the basic anatomy of the largest animals alive in the oceans today.

'Our findings add to the growing list of evolutionary solutions that whales evolved in response to new challenges faced in marine environments over millions of years.'

The research is reported in the journal Current Biology.

Once captured, the fish are consumed after expelling the water through baleen plates. The volume of water taken in with a single gulp can exceed that of the whale itself (illustrated)

Rorquals are the largest family of baleen whales. They feed by gulping large quantities of water and straining crustaceans and fish through short, broad plates. Rorquals range from minke whale up to humpback (pictured) and blue whales. All species have longitudinal grooves in the skin from the throat to the chest

With nine species, rorquals are the largest family of baleen whales. 

They feed by gulping large quantities of water and straining crustaceans and fish through short, broad plates. 

Rorquals range from minke whale up to the blue whale and all species have longitudinal grooves in the skin from the throat to the chest. 

They travel in pods of between two and five and are found in the open ocean.

Those studied by the researchers were obtained from a commercial whaling station in Iceland.