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Last Updated: Tuesday May 17 2005 18:47 GMT

Nut cracking fish is hit at zoo

The pacu fish eating a brazil nut
An amazing fish which can crack a brazil nut in its jaws has stunned visitors at London Zoo.

The fish, called a pacu, uses its strong jaws to break the nutshell and then it carefully nibbles it off so it can get to the juicy nut.

Pacus, from the Amazon, are one of only a few fish anywhere that can do this.

"They're big and round and they look pretty stupid but actually they play an amazing part in the eco-system," a spokeswoman for London Zoo said.

But zoo workers are being cautious. They are training their five pacus to associate brazil nuts with a clicking sound and a keeper with a tea towel wrapped around their arm, otherwise the fish could start biting the staff when they come to clean their tank.

"This way they are not associated with feeding - otherwise their toes would become brazil nuts," the zoo's Dr Heather Koldewey added.

Pacus developed their nutty talent because nuts are a good food source in the Amazon - they fall into the river and float on the surface and the fish have learnt to crack them.

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