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Last Updated: Thursday May 20 2010 14:20 GMT

In pics: The world's heaviest bony fish

Sunfish in water

Sunfish (or Mola mola) are the world's heaviest bony fish. They can grow to be 3.3m long! The heaviest recorded sunfish was 2,300kg - that's about the size of a white rhino!

Sunfish in water

Sunfish are famous for their strange shape. Some people say they look like a massive fish head with a tail.

Researcher on boat

Not much is known about sunfish but new technology is helping scientists from the University of New Hampshire in America find out more about them.

Sunfish with satellite tag

They've been tagging sunfish with satellite tags to find out where they are and what they are doing. They've found that sunfish can dive to great depths and travel big distances.

Sunfish with satellite tag

Some of the tagged sunfish swam from the northeast American coast to the Caribbean - that's a distance of more than 1,000 miles!