Rudd (scardinius erythrophthalmus)

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


DOC and Northland Regional Council are working together in the battle against pest fish, koi carp and rudd, and need public assistance with surveillance.

Date:  17 April 2019

“The immediate task is surveillance for koi carp and rudd in Northland, making sure we know where populations of these serious pests are. We will also be getting expert advice on our options for eradicating and controlling these pests and where to focus our efforts,” says Amy Macdonald, DOC Freshwater Technical Advisor.

“In Northland we’ve still got the opportunity to protect our waterways from pest fish and stop their spread. We don’t want to end up with koi carp in every pond and river like the Waikato, so now is the time to act.”

“Pest fish upset the balance in our freshwater systems, affecting ecological, cultural and recreational values. Koi carp and rudd are both bad news for water quality so they are also a problem for our agriculture and tourism industries - we’ve all got a reason to work together to stop them spreading and taking over.”

Koi are big and brightly coloured. They breed prolifically, and can have devastating impacts on New Zealand waterways. Rudd are smaller and also prolific breeders; they eat the growing tips of native aquatic plants and can turn lakes into barren algae filled waterways that nobody wants to swim in. Pest fish expert Helen McCaughan from Wildland Consultant’s has flown in from Christchurch to support the operation.

This survey is funded from Budget 2018 in which DOC was allocated $76m over four years to invest in targeted biodiversity initiatives across land, freshwater and marine ecosystems to address NZ’s biodiversity crisis.

This included $4.5mil over four years to be directed to successfully contain key aquatic pest species populations to prevent further spread, i.e. to reduce the likelihood of spread of pest species to sites with high biodiversity values, where it is far more difficult and expensive to control them from. The aim is to contain at least 4 freshwater pests (koi, gambusia, Rudd, hornwort) which are serious freshwater pests that have the potential to expand to other regions of New Zealand.

The new fund will also control invasive aquatic plants that are likely to have a high risk or impact on freshwater biodiversity values, to reduce their impact on river, lake and wetland ecosystems and reduce the likelihood of dispersal to other indigenous habitats.  The aim is to increase reduction of invasive aquatic plants to at least 10 sites per year.

New Zealand’s freshwater ecosystems face a number of threats - pollution, deforestation, loss of habitat, changing land-uses, sedimentation and nutrient enrichment, and the impact of invasive aquatic animals and plants such as koi carp and rudd.

To support this work, DOC and Northland Regional Council are seeking new reports of mysterious fish that could be koi carp or rudd. New reports will be added to the regional pest fish dataset, informing the surveillance in April and May as well as future pest fish work.

How you can help

Report mysterious fish:
Northland Regional Council: 0800 002 004

Identify koi carp

Koi carp superficially resemble goldfish except they grow much bigger and have two pairs of whisker-like feelers, also called barbels, at the corner of their mouth. They are highly variable in colour, often blotchy shades of black, red, gold, orange or pearly white.

Koi carp can often be observed during summer months in ponds and slow flowing water, active during the day swimming close to the water surface. When koi carp feed they stir up the bottom of ponds, lakes and rivers, muddying the water and destroying native plant and fish habitat.

They are opportunistic omnivores, which means they eat a wide range of food, including insects, fish eggs, juvenile fish of other species and a diverse range of plants and other organic matter. They feed like a vacuum cleaner, sucking up everything and blowing out what isn’t wanted. Aquatic plants are dislodged in the process and are unlikely to re-establish. Koi carp cause habitat loss for plants, native fish, invertebrates and waterfowl and degrade water quality.

Identify rudd

Rudd are stocky fish with distinctive red fins and large, shiny scales that range from silver to pale or  burnished orange in colour. Rudd normally grow to about 25 cm, and about 500 g.

As they are the only herbivorous freshwater fish they are the 'possums of the waterways', as the adults feed voraciously on native aquatic plants. They are found in ponds, lakes and slow-flowing streams, they build up to high numbers quickly and destroy the food and habitat for native species.


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