What does it look like?
Rudd are stocky, deep bodied fish that are darker on their backs than on their bellies and have bronze highlights when the light catches their scales. Colour ranges from silver (juveniles) to pale orange (adults) in colour. They were introduced to New Zealand as an ornamental fish in 1967, initially with a distinctive golden coloration that has not persisted in wild populations. They have distinctive red fins and lack 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. They normally grow to about 25 cm (about 500g) and are highly productive, with females able to produce up to 50,000 eggs per kilogram of body weight. Juveniles eat plankton and midges. Adults are mainly herbivorous but also consume invertebrates and occasionally small fish. They prefer ponds, lakes and slow flowing streams, but can tolerate periods of exposure to brackish (salty) water.
They were introduced into northern areas of Auckland and Waikato, becoming so abundant within the Fish and Game region, that they are now a designated sports fish. Elsewhere, they are classified as a Noxious fish, with isolated populations in Northland, Whanganui, Wellington, Nelson and Christchurch after being illegally released into freshwater systems.
Why is it a problem?
This species was ranked as the ninth highest ranked invasive fish in New Zealand by FRAM (NIWA’s Fish Risk Assessment Model) and also the fourth highest FISK (Fish Invasiveness Scoring Kit) score of naturalised species.
Adult rudd are predominantly herbivorous and feed preferentially on native macrophytes (aquatic plants), while juvenile rudd feed voraciously on zooplankton (tiny aquatic animals).
These feeding habits endanger native plant species, destroy indigenous habitat, remove food sources for native fish and invertebrate species, and potentially impact negatively on water quality by stirring up bottom sediments and muddying the water.
More information
DOC currently manage rudd for surveillance and eradication in all sites outside of the Auckland/Waikato Fish and Game region. Sites are managed to decrease the likelihood of further range expansions.
Related links
Notify Council
If you think you've found this pest, please get in touch with our Biosecurity Team at biosecurity@hbrc.govt.nz or call us on 0800 108 838.
Rules
Section 26ZM of the Conservation Act (1987)
In accordance with the Conservation Act 1987 section 26ZM, no person shall transfer live aquatic life or release live aquatic life into any freshwater. This includes native or introduced fish, plants, and invertebrates. The taking and holding of some organisms requires a special permit from MPI.
More information
