INDIANAPOLIS, Jan. 21 (UPI) -- An error in a routine maintenance procedure caused the deaths of 15 bonnet-head sharks at the Indianapolis Zoo's Oceans exhibit, an official says.

Deputy Zoo Director Paul Grayson says the sharks died when a cleaning system released too much ozone into their tank Monday, damaging the sharks' gills, the Indianapolis Star reports.


Grayson said the Zoo uses ozone to help remove unwanted things from the tank water.

"It's great for the health of the fish when you control it," he said. "When it gets high, it can do some serious damage to tissue."

The newspaper says the accident occurred after zoo workers cut power to the tank's sophisticated life-support devices to make a repair. They failed to reopen a valve that regulates ozone after turning the power back on.

Two Emperor Snappers that shared the tank with the sharks suffered no ill effects from the accident.