red-finned and prolific in slow water

Size
Length: 20–30 cm, Weight: 0.5–1 kg
Lifespan
8–12 years
Diet
Feeds on aquatic plants, algae and small insects. Lives in warm, weedy, shallow lakes and slow rivers. A weedy shallows specialist hiding in thick cover where predators cannot reach easily.
Habitat
Warm, weedy, shallow lakes and slow rivers. The fish of the reed beds. Hides in thick cover where predators cannot reach. Prefers dense aquatic vegetation for shelter and feeding grounds.
Range
North Island, particularly Waikato and Auckland regions. Most common in warm, weedy, shallow lakes and slow rivers. Introduced from Europe. Now established in some North Island lakes as a pest species.
Endemism
Invasive
Main Threats
None. This introduced species is considered a pest in some North Island lakes. Managed by Department of Conservation to prevent spread to other waterways. No natural predators control populations effectively.
Population
Introduced and established in some North Island lakes. Considered a pest species. Competes with native fish for food and habitat. Populations are managed in some areas to prevent spread to new waterways.
Conservation Status
Introduced
The flashy invader of the shallows. It looks like a goldfish crossed with a perch. The body is deep and compressed. Scales are bright silvery-gold. Fins are vivid red-orange. The eyes are striking golden-yellow. A pretty fish. That is exactly why it was brought here in the first place. Vegetarian troublemakers. Rudd feed on aquatic plants, algae and the small insects that live among the weeds. This diet puts them in direct competition with native fish like the giant kokopu and galaxiids. They also hybridise with goldfish. This creates weird mongrel offspring that are even harder to control. The genetic mix complicates management efforts. A classic example of good intentions gone wrong. Someone thought they would look nice in a garden pond. Then the pond flooded. The fish escaped. Now they are in the lakes. They eat the weeds. They make themselves at home. The escape was accidental. The establishment was not. To catch a rudd is to catch a pest in a pretty dress. The fish looks great in a fish tank. It causes chaos in a lake. There is no Māori name because it is not a native fish. European settlers introduced it from Europe as an ornamental species. Today it is the fish of the weed bed. You catch it by accident while fishing for something else. You look at it and think, well, at least it is pretty. The presence of rudd alters the aquatic environment. They strip vegetation that native species rely on for shelter and breeding. The water becomes clearer but emptier. The structural complexity of the weed beds declines. Native invertebrates lose their habitat. The food web shifts. The rudd thrives in the simplified system. It prefers the open water it has helped create. Control measures are difficult. Eradication is rarely possible once a population is established. Prevention of spread to new waterways is the primary strategy. Anglers are encouraged to dispose of unwanted catch responsibly. Do not return them to the water. Do not transfer them to other lakes. The pretty dress hides a destructive appetite. The golden eyes see only the next meal. It carries on.