Koi

Koi carp


What does it look like?

Koi carp are an ornamental strain of common carp. Their colour is variable, often a blotchy pattern, which can include black, red, orange, gold and white. They have two pairs of barbels around the mouth. 

Koi carp grow up to around 700mm long. They are bottom-feeding omnivores, planktivorous as juveniles.  Adults mainly eat macroinvertebrates, but also some plant material and fish eggs/larvae.  Koi carp live for approximately 8-12 years in New Zealand.

Still or slow moving freshwater bodies, especially shallow, warm water. The species also prefers well-vegetated areas for spawning. Although they may spend a lot of time in one area, some individuals undertake long distance movements (greater than 20km in some cases), particularly during spawning season.  Tolerant of moderately low oxygen levels.

Why is it a problem?

When feeding, koi carp suck up and expel material from the bottom like a vaccuum, filtering out edible material, which in the process disturbs the substrate (bottom) of a lake or river. Because of their fast breeding and large size, this usually results in constant 'muddying' of the water, with no chance for this mud to settle. As a result, the light levels are reduced, which negatively impacts plant life and other native fish and invertebrates. This also makes for unpleasant swimming at recreational freshwater water sites.

Koi carp are also capable of hybridising with goldfish; there is the potential here then for gene flow to make them more invasive if the offspring were viable.


Rudd


What does it look like?

Rudd were illegally imported into New Zealand in 1967, and widely released into freshwater systems.  Rudd are darker on their backs than on their bellies and have bronze highlights when the light catches their scales.  Their fins are usually bright reddish-orange.  They do not have any barbels around their mouth, a feature that tells them apart from koi carp.  They do not have spines on the front edge of the dorsal fin, but have projections at the bases of their pectoral and pelvis fins.  Rudd are usually 200-250mm long.  Juveniles eat plankton and midges.  Adults are mainly herbivorous but also consume invertebrates and occasionally small fish.

Freshwater, including lakes, ponds, rivers and streams.  They also tolerate periods of exposure to brackish water.

Why is it a problem?

Juvenile rudd are carnivorous, but as adults their diet consists mainly of aquatic plants.  A high-density rudd population could impact on native fish and plant communities, particularly where plant communities are limited.  Rudd are prolific breeders and are known to be invasive overseas.  They may be advantaged by release from native-range parasites.

High fecundity.  Sexually mature at around one year old for male, and around two years old for females.  Spawn in spring-summer, producing around 1000-100,000 eggs.

Control Methods

Please contact the Northland Regional Council for more information if you think you have seen this pest.