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Huge whale shark Ralph gets a once over

By Marsha Walton
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ATLANTA, Georgia (CNN) -- -- Physical exams are a lot more complicated when the patient weighs about a ton. And lives in salt water.

A well-choreographed team of about 50 people, including veterinarians, biologists, engineers, divers and photographers took part in an examination of Ralph, one of four whale sharks at the Georgia Aquarium.

"There are extraordinary challenges. We're talking about the world's largest fish," said Ray Davis, Vice President of Zoological Operations.

"You want to be safe for the animal and the staff handling him," he said.

Ralph is 22 feet long. He's grown six feet since arriving at the aquarium in June 2005.

Divers used nets and ropes to guide Ralph, believed to weigh between 1700 and 2500 pounds, into a sort of floating stretcher. During the exam, engineers could raise, lower, or tilt the contraption so the staff could access the proper body parts.

Anesthesia drugs diluted in nearly 1500 gallons of water were force-flowed into the whale shark's mouth and across the gills during the two-hour procedure.

While Ralph was "out," aquarium veterinarian Dr. Tonya Clauss drew blood for a number of different studies. Scientists know that red and white blood cells are significantly larger in whale sharks than in other sharks, or their relatives, skates and rays.

"In a normal field of view for a smaller shark, you would see 30 to 40 smaller red blood cells. For whale sharks we saw 10 huge cells," said Davis.

Another crucial area of study is the animal's reproductive system. Very little is known about when whale sharks become sexually mature, and exactly how they reproduce. So the blood will also be studied for hormones, to help determine if Ralph is beginning to sexually mature. The same tests are being conducted on his cohorts in the 6.2 million gallon habitat -- Norton, Alice, and Trixie.

Whale sharks are ovoviviparous, meaning that eggs hatch within the mother's body, and then are released. The species is so little studied that researchers did not learn this until 1995, when a female whale shark that had been harvested for food was found to have both eggs and live young inside.

"This female had 350 offspring, that's an extraordinary number, and in different stages of development," said Davis.

Some newborns have been found measuring 21 to 25 inches.

Also during the exam, images were taken under the gill flaps and inside the whale shark's mouth, to add to knowledge about feeding mechanics. A whale shark's mouth can reach four feet across. In the wild, it feeds on sardines, anchovies, mackerel, small tuna, small crustaceans and squids that it strains from the water through its gills. Usually the food consumed is small, because the fish's throat is small and makes a right angle to its stomach. Whale sharks move slowly, and often feed near the ocean's surface.

The medical team also took DNA samples to add to a database of the species, and examined Ralph's gastrointestinal tract.

While the team took extensive measurements to track Ralph's growth, it is considered too dangerous to try to weigh him.

Little is known about the migratory habits of these huge fish. The aquarium has partnered with Mote Marine Laboratory in Sarasota, Florida, to conduct long-term studies of its biology and habitat. Whale sharks are found worldwide, generally about 30 degrees north and south of the equator.

Finding answers to some of the mysteries of this big fish is one of the aquarium's missions.

"Every time we answer a question, we end up with 25 more questions. That's what motivates our team," said Jeff Swanagan, Georgia Aquarium Executive Director.

The World Conservation Union lists the whale shark as a vulnerable species. Heavy fishing of the whale shark in several areas of Asia is believed to be one reason for its population decline.

The Georgia Aquarium has had more than 3 million visitors since it opened a year ago.


Nets and ropes are used to guide Ralph, one of the Georgia Aquarium's whale sharks, into a sort of floating stretcher.



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