Dozens of school kids scramble to look at the glass-walled display tank. They "ooh" and "aah" and send friends cell phone photos of the South Carolina Aquarium's latest attraction, an albino alligator.

As the kids jostle, a metal door opens nearby offering a brief, behind-the-scene view of where the real work occurs at Charleston's most-visited attraction.

It is here, surrounded by sterile concrete walls and the pumps and pipes that keep the display tanks operating, that teams of specialists tend to the aquarium's thousands of fish and other animals.

Theirs is a never-ending vigil to keep the exhibits appearing natural and to learn as much as possible about the animals that inhabit the hidden worlds of South Carolina's streams, rivers, swamps, marshes and the ocean off the coast.

It is a struggle that comes with a cost in time, energy, money -- and fish.

Last year, one out of every three of the more than 9,000 fish for exhibit in the aquarium's tanks died, a total of 3,068 fish, a rate that one national expert says is double that of most other accredited aquariums.

Why so many?

The high death rate is not a reflection of the staff's lack of skill or lack of attention to the health of the fish and other animals. Despite the one-in-three mortality rate, records show that disease caused just one percent of those deaths.

Perhaps the best testimony to the staff's skill is its accreditation by the Association of Zoos and Aquariums, a trade group whose stated goal is to set "rigorous professional standards for animal welfare, veterinary care, wildlife conservation, scientific research, education, expert staffing, and safety."

At its last accreditation in 2007, the South Carolina Aquarium received top ratings for its staff, finances and facilities. Steve Feldman, the association's vice president for communications, said just 210 of more than 2,500 animal exhibitors in the United States achieve accreditation.

So why does the aquarium have such a high death rate?

Fish eating other exhibit fish is the reason. That occurs mainly because one of the aquarium's goals is to mimic the natural environment with multi-species exhibits. In other words, prey and predators share tanks, such as the popular "Great Ocean Tank," which holds 385,000 gallons of salt water and hundreds of fish, including sharks and other predators.

Most visitors don't see fish eating other display fish. Much of that happens after-hours when many of the predators feed.

The aquarium keeps meticulous records of fish deaths and, when possible, conducts necropsies, animal autopsies, to learn the cause, information that is shared with other aquariums and scientists. The records show that 20 percent the fish deaths can be directly attributed to predation - fish eating exhibit mates.

Predation also is thought to be a major cause of two other classifications: "Missing," which accounts for 46 percent of the deaths, and "unknown," 21 percent of the deaths.

Aquarium records show that some larger fish also fall prey, such as sea bass, cobia, snapper and flounder. But species of small fish "low on the food chain" account for much of the missing, unknown and predation categories. Those fish include Atlantic bumper, shiners, minnows, killifish and mullet, often known as bait fish.

The predation occurs despite extensive efforts to minimize it through such measures as regular feedings of everything from chicken and collards to shrimp and salmon to stem the natural desire to hunt, and removing and treating sick or injured fish that attract predators.

"Our multi-species exhibits display natural environment and thus lend themselves to predation. Predation is natural and it can be considered enrichment for the predators," the aquarium records note.

Fish death is a strategy

John D. Hewitt, Director of Husbandry at the Audubon Aquarium of the Americas in New Orleans, said the South Carolina Aquarium's 34 percent death rate for its fish population in 2009 is higher than would be typical for aquariums. "Thirty-four percent, that's up there," Hewitt said.

Many aquariums mimic nature in one or two exhibits, exposing prey to predators. But, Hewitt said, they don't do that to the extent of South Carolina.

Hewitt sits on the Association of Zoos and Aquariums accreditation commission, a position considered the organization's "highest honor." He said that the death rate at the Audubon aquarium is about 15 percent a year, and that most other aquariums he is familiar with have about same, give or take a few percentage points.

At the Audubon aquarium "we do what we can to minimize" predation as a matter of strategy by limiting exposure of prey to predators, Hewitt said.

He has visited the South Carolina Aquarium and was the primary accreditation commission reviewer of its last accreditation. He describes it as "a fine, fine facility," with "top-notch" staff. And adds, "I don't think they are doing anything unethical."

Still, Hewitt said, if he were inspecting that aquarium today he'd tell the staff, "Hey guys, do you really want to keep doing that?" The aquarium is due for accreditation renewal in 2012.

Bob Van Dolah, director of the Marine Resources Research Institute of the state Department of Natural Resources, said the aquarium's death figures surprised him initially. But on reflection, he said, the exhibits do mimic the wild and that the aquarium's death rate probably is less than what occurs naturally.

Beth Nathan, the aquarium's public relations manager, said the facility is comfortable with the way fish and other animals are displayed and the associated costs. She said determining that cost "is unanswerable" because it is part of the overall cost of staff and operations.

"We're confident that our figures reflect the high quality of animal care, nutrition and expert medical care that we provide to all of our fishes. Again, comparing our aquarium to others is not apples to apples - species, habitats, animal management practices and data collection techniques all vary greatly."

Nathan said the effort to reproduce the natural environment provides "an exceptionally comfortable environment and a healthier collection as evidenced by our remarkably low medical case records."

Hewitt said that mimicking nature "makes for a nice exhibit ... while it lasts."

What South Carolina does "is expensive... It's gonna cost you," Hewitt said, "I don't have the budget and staff" necessary to collect all the replacement fish and manage disease, parasites, quarantine and other necessities before the new fish can be placed in exhibits. "Most places can't afford to continue down that road." Ultimately, he said, of display fish, "you want them to be around."

Still, Hewitt said, with many of the predators in aquariums, such as tarpon and snapper, if prey fish are placed with them it doesn't matter how well the predators are fed, they'll still go after the prey. "They're gone in just a matter of time ... predator fish are pretty relentless."

Behind the scenes

Behind the metal doors at the South Carolina Aquarium, specialists continue their tireless effort to maintain the health of the fish collection, even the little fish with a high risk of being eaten by exhibit mates.

Here, behind the scenes, sit 54 of the aquarium's 88 tanks. The other 34 are on view in the public exhibit areas. These 54 tanks occupy several floors and are used for many reasons: as a quarantine for new fish, as a nursery for young fish, for medical treatment, for recuperation of sick or injured fish and for isolation for various reasons, such as to curb aggression -- a practice staffers call "time out."

Jason Crichton oversees the effort as director of husbandry and facilities. The job is especially difficult, he said, because many of the worlds the aquarium replicates are places where "everything eats everything." The faster some illness or injury is found, the easier it is to fix, prevent spread of sickness and head off predation. "Every day, we put lots and lots of eyeballs on the tanks," he said.

Rachel Kalisperis, an aquarium curator, readies a dose of MS-222, a widely-used anesthetic for aquatic animals, near one of the quarantine tanks containing a small school of Atlantic bumper. Just how much to use is not an exact science: It's a range, she said as she and another aquarist prepare to lift a tiny bumper out of the tank and place it in a bucket of water with the chemical.

She needs to sedate the bumper to take a sample of slime and examine it for parasites that the school of fish carried when caught in the wild. The aquarium captures 85 percent of the fish and other animals it displays. If any parasites remain on the bumper after they leave quarantine, an entire exhibit tank could be infected. If the one bumper is free of parasites, then that means treatment in the quarantine tank has worked on the whole school.

The bumper circles the bucket with no indication that the anesthetic is having any affect. Kalisperis adds more MS-222. The fish jumps almost out of the pail, then slowly yields to the chemical. It turns up on one side and stops moving.

Kalisperis lifts the fish in the palm of one surgical-gloved hand - even the fine roughness of a fingertip can be abrasive to fish. She swabs the bumper's side, places the slime on a microscope slide and puts the fish in a bucket of water, free of MS-222.

The fish floats, motionless on its side. MS-222 is a safe anesthetic, but there's always a risk. Seconds pass and still no movement from the fish. Kalisperis jokes that sometimes a fish has to take a hit for the greater good of its fellow fish. But her eyes remain focused on the tiny bumper.

More seconds pass. Finally, movement. The fish rights itself and circles the tank. Kalisperis smiles.