A Waikíkí Aquarium Hawaiian monk seal has undergone a thorough physical checkup after falling ill over the weekend.

Nukaau, 29, became lethargic and lost his appetite, said Andrew Rossiter, aquarium director.

"He just doesn't seem interested in anything," Rossiter said yesterday. "But when you consider his equivalent to 90-95 years old (in human years), that's perhaps an off day."

Nevertheless the veterinarian wasn't taking any chances and Nuka, as he is called at the aquarium, has been isolated, started on an antibiotic treatment and given a full-body examination Monday night, he said.

The 500- to 600-pound monk seal was anesthetized for the examination in which blood samples and X-rays were taken, Rossiter said.

"He seems to be OK today," he said, adding that the prognosis is guarded until tests results have returned today or tomorrow. "He ate a little today, apparently and is a little bit more alert so hopefully he's on the mend."

Nuka fell ill last year and stopped eating, but treatment by the vet and medication had him feeling better within three or four days, Rossiter said.

Nuka is one of three monk seals at the aquarium. Another elderly male is on display and a young wild seal, KP2, was recently placed there because of cataracts.

KP2 was raised in captivity. He had been released but recaptured with the goal to relocate him this month because he was interacting with humans and had become too rough.

The cataracts means he'll spend his life in captivity. The other two seals came to the aquarium under similar circumstances. One was abandoned by its mother at an early age and the other was starving and injured. None of the three would have survived in the wild, Rossiter said.

But at only 120 to 150 pounds, KP2 remains separate from the two old-timers, he said.

"They're all males and they'll be doing the male kind of stuff, threatening and what have you," he said. "The little guy wouldn't stand a chance."

In captivity the seals are ambassadors for monk seals and give scientists the opportunity to observe their behavior and conduct non-invasive and non-harmful research, Rossiter said.

Scientists are now studying their weight change throughout the year while under a strict diet, he said, adding that researchers will gain information that can help when a wild seal is captured.