Date: 29 August, 2012
Banned koi carp found in Northland
One of the two Pahi farm ponds infested with unwanted koi carp.
Biosecurity officials are working to try to contain a large infestation of banned koi carp - one of Australasia’s worst
freshwater pest fish - found in two Kaipara farm ponds.
Since their discovery earlier this month by a farm worker, more than 100 koi have been recovered form one of the ponds
and destroyed in an ongoing joint Northland Regional Council and Department of Conservation operation.
Don McKenzie, the Northland Regional Council’s Biosecurity Senior Programme Manager, says as of today 104 koi – some
more than half-a-metre long and weighing almost three kilogrammes – have been recovered from the large Pahi dairy farm,
near Paparoa.
Just how the banned fish came to be in the two large farm ponds is still being investigated, but initial inquiries
indicate they have been there for several years and before it was purchased by its current owner. Both the owner and
farm staff had been extremely co-operative and the council was grateful for this.
Mr McKenzie says koi are an ornamental strain of the common carp (Cyprinus carpio) native to Asia and Europe, but are
legally classed as both an unwanted organism and noxious species in this country. They are thought to have been
accidentally imported into New Zealand more than 40 years ago as part of a goldfish consignment.
He says the fish’s feeding habits and the havoc it can wreak upon the environment make it well-deserving of its banned
status and reputation as one of Australasia’s worst freshwater pest fish.
“Koi feed like a vacuum cleaner sucking up a wide range of food, including insects, fish eggs, juvenile fish of other
species and a diverse range of plants and other organic matter.
Jack Vallings Nth Polytech student with Pahi koi
When they feed they suck up prey, but blow out what isn't wanted, stirring up the bottom of ponds, lakes and rivers,
muddying the water making it unsuitable for swimming and drinking as well as destroying native plant and fish habitat.”
Mr McKenzie says aquatic plants are dislodged in the feeding process and are unlikely to re-establish, with koi causing
habitat loss for plants, native fish, invertebrates and waterfowl.
“Superficially, koi resemble goldfish but in New Zealand they can grow much larger (up to 10kg and 75cm long) and they
also have two pairs of whisker-like feelers at the corner of their mouth.”
Koi vary greatly in colour, often accompanied with irregular blotching of black, red, gold, orange or pearly white.
Mr McKenzie says a number of the fish caught in Pahi have been female with an autopsy revealing one 2.5kg fish alone had
contained about 250 grams of eggs; roughly 100,000 potential offspring.
At this stage, he estimates the control operation has already cost about $10,000, including “much-appreciated” voluntary
contributions of machinery and labour made by the property owner.
Mr McKenzie says officials have installed a series of nets across all the outflows from the ponds to prevent koi from
escaping into a nearby small creek which flows into the Kaipara Harbour.
At this stage, there’s no indication any koi had escaped from the ponds previously, but given the ponds are prone to
flooding in heavy rain events, that could not be ruled out.
He says with help from farm staff, one of the ponds is being slowly drained in an attempt to net and recover every koi
in it. Water samples would also need to be taken to ensure there was no fish larvae or fry (juvenile fish) in it.
They would then repeat the netting process in the second, smaller pond, although it may not be possible to drain it
because it was used to supply the farm’s stock water. Officials expect to spend up to another several months at the Pahi
site in a bid to ensure all the koi were gone.
Mr McKenzie says koi can survive in very low oxygen levels, in areas where salt and freshwater meet and even out of
water altogether for hours at a time.
“Over the years, we’re aware of several koi incursions in various parts of the region but to date all of these have been
successfully contained or eradicated. We’re keen to continue to keep this very undesirable intruder out of our region.
The Waikato is plagued with this fish and we’d been absolutely despairing if this fish became well-established here.”
Mr McKenzie says anyone sighting what they thought might be a koi in Northland should contact the regional council on
(0800) 002 004 for advice.
Council staff would be happy to visit any landowner who suspected they had seen koi at no charge.
“We just want these fish gone.”
Meanwhile, he says it’s important not to confuse koi’s unwanted status with that of grass carp, which is used for
aquatic weed control, is not harmful and is unable to breed naturally in New Zealand.
Information about koi is available from regional council offices, from its website via www.nrc.govt.nz/nasties or from
the Department of Conservation website via:
www.doc.govt.nz/conservation/threats-and-impacts/animal-pests/animal-pests-a-z/fish/facts/koi-carp/
ENDS