Fuji, a Japanese dolphin that lost 75 per cent of her tail due to a mysterious disease two years ago, is jumping once again with the help of what is believed to be the world's first artificial fin.

The 34-year-old dolphin, a resident of Japan's largest aquarium, wears the rubber fin for about 20 minutes a day, allowing her to jump and to swim at the same speed as other dolphins.

"Although she can swim without the artificial fin, the speed is very slow and she certainly cannot jump without it," said Masaya Kowami, a breeder at Okinawa Churaumi Aquarium on the southern island of Okinawa. "Visitors have told us she looks happy."

In 2002, Fuji was stricken by a mysterious disease causing necrosis, the death of cells. To save her life, veterinarians had to amputate three-quarters of her tail with an electronic surgical knife.

"Her physical mobility fell sharply after the amputation," Kowami said. "She got tired easily."

Weeks after the surgery, a veterinarian at the aquarium asked a friend at Japan's largest tire maker for help.

The company, Bridgestone, began working on the fin in 2003 but several samples were either too heavy or loose for Fuji. The current version weighs two kilograms and is 48 centimetres wide.

"The most difficult part was creating the smooth texture of rubber so as not to scratch a dolphin's skin," said Bridgestone spokesman Shinichi Kobori.

"After we created the lightest fin in August 2004, we received a call from the aquarium that Fuji finally jumped."

The fin is kept in one piece by bolts. Her handlers have decided not to keep Fuji's fin on all day, fearing it might fall off and be eaten or destroyed by other dolphins.

With files from the Australian Broadcasting Corporation.