Koi carp are an ornamental strain of the common carp (Cyprinus carpio) native to Asia and Europe. This species is thought to have been imported into New Zealand accidentally in the 1960s as part of a goldfish consignment.

Koi carp were probably initially released into the wild accidentally from private ponds during large scale flooding.  Wild stocks of koi carp were first found in the Waikato River in 1983 by which time they had likely established a breeding population. 

Further illegal introductions have occurred elsewhere, for the purposes of coarse fishing (a traditional British pastime involving the catch and release of certain species including koi carp, rudd, perch and tench) and for ornamental purposes in amenity ponds. Isolated populations have been progressively discovered throughout New Zealand.

Description and life history

Koi carp superficially resemble goldfish except that they grow to larger sizes (in New Zealand up to 10kg and 75cm long) and have two pairs of whisker-like feelers, also called barbels, at the corner of their mouth.

They are highly variable in colour, often accompanied with irregular blotching of black, red, gold, orange or pearly white.

What damage do they do?

When they feed they stir up the bottom of ponds, lakes and rivers, muddying the water and destroying native plant and fish habitat. Koi carp are opportunistic omnivores, whch 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.

Where are they found?

Koi carp prefer still waters in lakes, or backwaters in rivers. They are highly tolerant of poor water quality and contribute to water quality decline.

Koi carp are widespread in Auckland and Waikato. They are spreading into Northland and they have been found in isolated places in Whanganui, Hawke's Bay and Wellington. Koi carp have been illegally released in the Nelson/Marlborough area.

To help stop their spread a containment area between Auckland and Hamilton was created. In the containment area, recreational fishing is permitted, but all koi must be killed when caught. Koi carp outside of the containment area are considered a serious incursion and control options will be investigated.

Legal designation

• Unwanted organism
• Noxious species

Source:  https://www.doc.govt.nz/nature/pests-and-threats/animal-pests/fish/koi-c...