Archived content: This media release was accurate on the date of publication. 


The desire of a local farming couple to beautify a pond with goldfish has resulted in a major pest fish problem, with a muddy bog all that remains.

Date:  05 February 2009

About eight years ago Roger and Marian Clausen added a large pond, bordered by a patch of natural native bush, to their beautifully landscaped property. After seeing rock pools flashing with large vibrant gold fish in Singapore, the Clausen’s purchased about a half bucket full of “long goldfish” here in New Zealand and released them into their pond to add some life to the clear cool water.

Roger and Marian Clausen.
Roger and Marian Clausen

Unfortunately, there were koi carp amongst the goldfish. The Clausens’ first realised they had a problem when their pond water turned very murky. Then, as water levels in the pond dropped with the summer heat, they noticed the banks of their pond were deteriorating. Although koi carp look very similar to goldfish, they are a noxious species that diminish water quality. They feed like vacuum cleaners, sucking up everything on the pond floor and blowing out what isn’t wanted. “We thought they were beautiful fish when we saw them in Singapore; we didn’t realise how much damage they could do here,” says Mrs Clausen.

Determined to clean-up the pond, Mr Clausen began calling local bodies to find out what to do to get rid of these aquatic assassins. Eventually, freshwater fish expert Logan Brown from the Department of Conservation (DOC) came to the rescue. The pond was drained and a teeming mass of koi carp were scooped out of the mud and destroyed by DOC staff. Mr and Mrs Clausen plan to restore the pond. It will be left to dry out to ensure any remaining eggs are dead before the mud is scraped out. “We’ll be cleaning it up and stocking it with native fish this time,” explains Mr Clausen.

The Clausen’s are not alone; a lot of people may have unknowingly released these noxious pests into their ponds and local waterways. The Department of Conservation hopes to contain koi carp before they spread. “As much as I’d rather not be knee-deep in mud, the Clausen’s have done us a huge favour,” says DOC’s Logan Brown. “We want to eradicate pest fish before they reach a point where they can’t be controlled, but the first step in doing that is knowing where they are,” he explains.

Koi carp.
Koi carp

Koi carp are classified as an unwanted organism. They cause erosion, increase algae, muddy the water, eat the juveniles of other species and destroy the habitat of other fish. “It can be very difficult to tell the difference between these underwater villains and ordinary goldfish,” says Mr Brown. “The main difference in appearance is that koi carp have two pairs of barbels or feelers at the corners of their mouth”. It can be a little difficult catching them to look for barbells, so Mr Brown suggests observing the water quality and clarity. He urges people to contact their local DOC office if they think they have koi carp, or know of any other pest fish species in waterways.


Margaret Metcalfe

Manawatu Base
Phone:   +64 6 350 9700
Fax:   +64 4 471 1117
Address:   717 Tremaine Avenue
Palmerston North 4414
Postal Address:   Private Bag 11010
Palmerston North 4442
Back to top