By 3 News online staff
A malfunction at a Chicago zoo has led to the deaths of 54 stingrays, after oxygen levels in their shallow pool plunged.
Staff at the suburban Brookfield Zoo noticed the fish behaving erratically after an alarm which regulated temperature, ozone and oxygen went off, Sky News reports.
The oxygen levels in the tank was restored after around 20 minutes, but it was too late for the four southern stingrays and 50 cownose rays which were kept in a shallow pool where people could touch and feed them.
The Chicago Zoological Society, which runs the zoo, said most of the fish died in the incident on Friday afternoon.
It said staff did "everything possible" to try and save the animals.
The exhibit will be closed for the rest of the US summer season.