Why do pufferfish puff?

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The simple answer - defence - as this superb National Geographic video shows.

It starts by giving a great insight into the natural habitat of Tetraodon mbu, the world's largest freshwater pufferfish.

Juveniles are shown inhabiting a shallow river, which drains into Lake Tanganyika. Their diet is crabs but they must also make sure that they don't end up on the menu of a rather ravenous otter.

Check out the video to see what happens...

Brilliant!