A Wellington marine centre has lost more than half of its animals after an act of vandalism.
Overnight on Saturday the Island Bay Marine Education Centre's water system was dosed with pool treatment tablets, a potent form of chlorination for pools and poisonous to most marine life.
Centre spokesperson Julian Hodge said he arrived at the centre on Saturday morning and found dead fish in the reservoir tank.
He said whoever did it knew what they were doing, and described it as a senseless and devastating act of vandalism.
"Whoever did this obviously would have known what the effect might have been, they would have needed to arrive with these sorts of things with them, they would have needed to have lifted the lid on the tank, they probably would have noticed that there were live fish in there and I would suggest that this is a deliberate act."
Mr Hodge said volunteers and the Fire Service worked all day to move the remaining fish to uncontaminated water while they flushed the tank.
The police are investigating.