[Photo] Whale sharks are the world's largest fish, growing up to 50ft long. Ralph the whale shark at Georgia Aquarium pictured alongside a ray.

Ralph the whale shark, a star attraction at Georgia Aquarium in the US, has died.

Ralph, one of four whale sharks in the Atlanta aquarium, had not been eating well and had been showing unusual swimming patterns, officials say.

The 22ft-long (6.7m) fish was in effect only "a teenager", and the cause of his death was not immediately known.

Ralph arrived at the aquarium in 2005 from Taiwan, where he had faced becoming seafood.

He and Norton - the aquarium's other male whale shark - arrived together and were joined a year later by two females, Alice and Trixie.

Gasper, one of the aquarium's five beluga whales, was also put down 10 days ago after months of declining health.

Gasper and another 12ft-long Beluga whale, Nico, came to the aquarium from Mexico City, where they had lived in an exhibit surrounded by a large wooden roller coaster.

The aquarium, said to be the world's largest, houses more than 100,000 specimens.

Whale sharks are the world's largest fish, growing up to 50ft long.