An act of vandalism which resulted in the death of almost $30,000 worth of salmon from a Dunedin hatchery has been slammed as a "mindless act of stupidity".

The Dunedin Community Salmon Trust hatchery was struck by vandals over the weekend, resulting in the death of about 180 salmon.

Trust chairman Steve Bennett said the vandals must have climbed a barbed wire fence to get into the hatchery.

"Somebody came in and ... turned off the aerator ... that keeps oxygen in the water [which] keeps these fish alive," Mr Bennett said.

The fish deaths came after a number of other minor pieces of vandalism over the last year and he was at a loss as to why anyone would commit such acts.

"There is actually no benefit for anyone from people killing all these fish.

"It's a mindless act of stupidity and we just want it to stop."

The trust had reported the vandalism to police and he asked the public to report any suspicious activity they had noticed around the hatchery.

The trust, which is a not for profit organisation, releases salmon into Otago Harbour for fisherman to catch.

The fish killed over the weekend were three year-old adults intended to provide eggs for next year's release.

Mr Bennett told Fairfax he estimated the three-year-old salmon, which weighed between 6kg and 9kg, were worth almost $30,000.

The fish killed over the weekend were three year-old adults intended to provide eggs for next year's release,