A penguin whose break-out from an aquarium in Japan gave him a following around the world is to be formally named after months of being known just by his number, an official said Monday.

Humboldt penguin No. 337 spent 82 days at large in and around Tokyo Bay after bolting his enclosure, evading aquarium staff, an army of public onlookers and even Japan's well-equipped coastguard.

But until his recapture last month and subsequent thorough medical check-up, keepers did not even know what gender the plucky escapee was, and had insisted he did not have a name.

Now officials at Tokyo Sea Life Park have launched a competition asking visitors to think of what the bird should be called.

"We decided to give him a pet name by soliciting ideas and their reasons from visitors," said aquarium official Takashi Sugino.

"This is a special treatment to express our gratitude to the public for providing information on the bird, and also for cooperating with us by listening to our call not to try to capture him," he said.

Visitors are being asked to watch the creature -- now safely back in his enclosure -- before putting their suggestion in a box, Sugino said, admitting the aquarium was expecting a spike in numbers.

Nominations opened on June 15 and will end on July 1, said Sugino, adding "a naming committee comprising the aquarium director, the vice director and keepers will pick the most appropriate name."