10 Sharks Die at Pittsburgh Zoo

Ten black-tip reef sharks died at the Pittsburgh Zoo and PPG Aquarium this weekend after dangerous ozone was accidentally added to their water. This isn't the first time sharks have died at the Aquarium. In October 2002, eight sharks died from a variety of causes. Five other sharks died in separate incidents in April and December 2000. According to the Pittsburgh Post Gazette, the accident occurred after the Zoo closed on Saturday during a routine water change which replaces 34,000 litres/7,500 gallons of water with purified seawater stored in a holding tank. The water, which had been sitting for several days, apparently still contained residual levels of ozone which caused problems for the resident fish. The sharks swim near the top of the tank, where the ozone levels were highest, and staff at the aquarium were unable to save them. Almost 100 other animals in the tank were unaffected.