ATLANTA - Scientists on Thursday took their closest look ever at one of the world’s biggest fish - with the help of about 50 staffers, a stretcher that could hold a small bus and a hose pumping liquid anesthetic out of two 300-gallon vats.The daybreak examination of Ralph, a 22-foot male who is one of four whale sharks at the Georgia Aquarium, was part of a groundbreaking series of exams on some of the world’s largest fish at the only place outside of Asia where the sharks are on display.

Researchers hope the study will provide new information about an animal that has remained largely a mystery to scientists, despite its massive size and wide-ranging habitat.

“There are huge unknowns out there,” said Ray Davis, vice president of zoological operations at the aquarium. “They’re the largest fish in the ocean and we have the least information about them.”

Ralph and Norton, the aquarium’s other male whale shark, arrived last June from Taipei, Taiwan, where they had been destined to become seafood. They were joined a year later by two females, Alice and Trixie, in their 6 million gallon tank.

Thursday’s poking and prodding session was the latest in a series of exams on the four fish that began in October.

They were given basic exams when they arrived at the aquarium, but the logistics of transporting the giant sharks made it difficult to study them in any great detail, Davis said.

It was Ralph’s third exam. Norton has been examined twice and Alice and Trixie once each.

Around 6 a.m. Thursday, a team of 20 divers used nets to guide the shark into a massive stretcher that hung near the water’s surface from an industrial-sized gantry.

There, a hose pumped a liquid anesthetic into the water around Ralph’s head - making him nearly unconscious for the two-hour checkup.

Once he was under, veterinarians from the aquarium and Mote Marine Laboratory in Sarasota, Fla., took blood samples to test the adolescent shark’s hormone levels and studied the inside of his mouth and gills to learn more about how he digests food. They took DNA samples and used an ultrasound machine, with a small, portable computer screen, to check on his internal organs. They also measured him to track his growth.

At 22 feet, Ralph is still the equivalent of a teenager. Adult male whale sharks can grow up to 50 feet long.

The data will be shared with scientists around the world, including staff at Kaiyukan Aquarium, in Osaka, Japan, which also has a whale shark but does not conduct the same level of scientific study, according to Georgia Aquarium officials.

“So little is known about them,” said aquarium director Jeff Swanagan. “Every time we answer a question, we come up with 25 more questions.”

While Alice and Trixie remained out of sight during the exam, an apparently curious Norton swam within a few feet of the stretcher several times. Once, his tail bumped the netting around the stretcher where several researchers were standing.

At the end of the 2-hour exam, Ralph swam smoothly out of the stretcher, with a team of divers again surrounding him to make sure the effects of the anesthetic had worn off.

More than 3 million people have visited the Georgia Aquarium since it opened last November - far outpacing attendance predictions.

Bankrolled almost exclusively by Home Depot Inc. co-founder Bernie Marcus, the aquarium is considered the world’s largest, with roughly 100,000 fish and more than 8 million gallons of water.

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Georgia Aquarium, http://www.georgiaaquarium.org