Offers of time and money have flooded into the Island Bay Marine Education Centre, after an attack by vandals left more than half the aquarium's animals dead.

It is believed chlorinated cleaning tablets, such as those used for swimming pools, were deliberately dropped into an outside storage tank on Friday night.

The tablets flushed through the whole water system, poisoning many of the fish. Centre discovery programme manager Julian Hodge found the damage at 10am on Saturday. Despite immediate efforts to flush out the system with freshwater, about 90 animals, mainly smaller fish species, died. Access to the storage tank was gained by lifting a metal plate, which has since been bolted.

Mr Hodge said aquarium staff had never considered the storage tank would be interfered with.

He thought it unlikely that someone unconnected to the aquarium would have known what the storage tank was, or that it connected to the entire water system. The centre had no security cameras, something else that might be looked into, Mr Hodge said.

But the one positive note of the "devastating" act was the response from the community. "We've had an absolutely phenomenal outpouring of support."

Wellingtonians, and those from further afield, had offered financial support, for improved security or towards a reward for information, and many had volunteered their time.

"People have also been bringing us chocolate fish and scones, which certainly helps at a time like this."

It had been a trying time for staff, with more deaths on Saturday night, including Barney, one of Mr Hodge's favourites - a fish that would jump out of the water if offered food.

"When you see them every day, you get a wee bit attached."

Mr Hodge said the surviving animals would be closely monitored for the next few days, including a brood of octopus eggs, though it was likely more would die by the end of the week.

Island Bay resident Petra Stueben was one of many who visited the aquarium yesterday to offer her support.

She said many locals thought the centre was a great addition to the community, and could not imagine why it would have been targeted, unless it was a prank gone awry or from some long-term resentment over the centre's 2004 plan to build at Te Raekaihau Pt, near Lyall Bay, later prevented by an Environment Court case.

Police are investigating.