Two divers positioned themselves in the huge tank, down in the swirls of hundreds of fish, waiting for the bonnethead shark to be released. Their job was to make sure everybody played nice.

They weren't worried about the shark; they were worried mostly about jack crevalles -- the real predators. Bonnetheads are relatively docile sharks, said Arnold Postell, South Carolina Aquarium dive safety officer. The aggressive jack crevalles are not always so nice. Aquarium staff had been overfeeding all the fish for a few days to keep everybody placid -- "just to take the edge off," Postell said.

Three bonnethead sharks were introduced to their new aquarium digs on Monday, moved from a nearby holding tank to the two-story high Great Ocean Tank, to take their place among a host of other species found in the ocean off South Carolina. They join 13 other feared sharks that keep visitors gasping at the display window -- nurse sharks, blacktips, sandbar and sand tigers.

The move usually goes smoothly, but there's no real telling.

"New fish are the new guys on the block," Postell said, and not always welcome. "We're just trying to make the introduction as gentle and friendly as possible."

Displaying sharks is a trading game that depends a lot on "chemistry." The last resident bonnethead sharks had to be moved from the tank to another aquarium in the region in 2006, when large sandbar sharks were brought in. Big sandbar sharks eat little sharks, it turns out. The bigger sandbar sharks recently were moved, and the new guys came from the Georgia Aquarium. They get along fine with the smaller sandbar sharks.

Bonnetheads are a type of hammerhead shark and have that classic squished-in-head look. They are one of the shark species that have to move to breathe. They tend to prowl with their mouths open, looking voracious but really just "ram" ventilating, said Shane Boylan, aquarium veterinarian. They are among about 40 shark species that swim in the Lowcountry brine, including the notoriously aggressive bull shark and an occasional great white.

The guys in the aquarium, though, mostly get along.

"None of them are mean. Sandbar sharks have that mean look because of the teeth, but tend to be docile," Arnold said.