Goldfish (Carassius auratus) were imported early after Europeans settled in New Zealand, although exactly when is uncertain. They were probably introduced by aquarists and pond-keepers as an ornamental species. They were liberated into wild habitats such as Lake Taupō and Lake Rotorua in the 1870s, and by the 2000s were widespread, mostly living in ponds and small lakes, and probably harmless.
Morihana on horseback
Sub-inspector Morrison of the Armed Constabulary released goldfish into Lake Taupō in 1873, after bringing the fish on horseback from Napier. Goldfish became known to Māori as morihana – a transliteration of Morrison’s name. For some time morihana were a food for Rotorua Māori.
Koi or European carp (Cyprinus carpio) were brought to New Zealand in the 1800s, but did not become established in the wild until the 1960s, when ornamental koi were released. They are now abundant in the lakes of the lower Waikato, and present in some other areas, especially the north.
Globally koi carp are a problem. They churn up the beds of wetlands while searching for food, causing environmental deterioration. In New Zealand koi are classed as a ‘noxious fish’ and an ‘unwanted organism’, making their possession unlawful. Nevertheless, they are a target of recreational coarse fishers (who are illegally spreading the fish around the country), because of their size (10 kilograms or more) and fighting ability. Bow hunters look for koi carp in the Waikato wetlands.
Tench (Tinca tinca) were introduced by acclimatisation societies in the 1870s. They lived mainly in some North Otago waters, and did not become widespread or abundant for many decades. Recently, anglers and others have spread tench more widely – often illegally (it is illegal to liberate fish into new waters without approval from the minister of conservation). Tench appeal to coarse fishers because they grow large, are powerful swimmers, and a challenge to catch. In the early 2000s they were widespread, mostly in small lakes. They are classed as ‘sports fish’, so a licence is needed to fish for them.
A fish of ponds and lakes, rudd (Scardinius erythrophthalmus) were smuggled into New Zealand in the 1960s and liberated quite widely – illegally and to provide game for sport (they can reach 2 kilograms). They are common in the hydro lakes of Waikato. Concerns about their potential adverse effects on the environment have led to their classification as ‘noxious fish’, except in the Auckland/Waikato fish and game region, where they are ‘sports fish’ and a licence is needed to fish for them.
Orfe and gudgeon
Orfe (Leuciscus idus) and gudgeon (Gobio gobio) were introduced illegally with a view to establishing populations for anglers. Orfe possibly occur in a single lake near Auckland, although it is uncertain if they are still present. Gudgeon became established in another Auckland pond. Once discovered, attempts were made to exterminate them, and as far as is known, there are now no gudgeon in New Zealand.
Grass carp and silver carp
Grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) were introduced for biological control. It is unlikely either species will reproduce in the wild – all populations were established and are maintained by hatchery production. These carp grow to several kilograms in weight, and are found intermittently around the country.
Grass carp eat large, leafy aquatic plants and in doing so they help control excessive plant growth in ponds and drainage ditches, reducing the need to spray water weeds or use draglines to clean drains.
Silver carp eat phytoplankton (small, single-celled algae that make the water in ponds green and turbid), and were imported to help control it. However, their effectiveness is unproven.