Gasper's problems became apparent in April, when veterinarians noticed a change in his swimming. They discovered the whale had osteomyelitis, a chronic and potentially fatal bone disease. He contracted it, they determined, while living at an amusement park in Mexico. The aquarium removed him from view at the Cold Water Quest gallery.

In public view, he always swam to the front of his tank, blowing bubbles at spectators. He appeared to be grinning, his flippers waving hello.

Since his removal from view, Gasper has been kept in an area adjacent to the public facility. He's had contact with the aquarium's four other belugas, Natasha, Maris, Marina and Nico.

Nico and Gasper are both about 12 feet long, and share the approximate age — 17 years old. They came from the LaFeria de Chapultepec amusement park in Mexico City, where they lived in an exhibit ringed by a wooden roller coaster. When new owners bought the park, they worked with the aquarium to transport the whales to a better environment.

Nico and Gasper arrived in Atlanta in October 2005, with the females joining them soon afterward. The whales were a hit with the public, none more so than Gasper.

In October, aquarium officials announced that Gasper's immune system was weakened — a potentially fatal development. Veterinarians have been giving the whale medicine and fluids, and consulting with their peers about the beluga's affliction.

"We've done everything," Binder said. "The animal is gravely ill."