In the late 1800s and early 1900s, British settlers introduced fish of the Salmonidae family – trout and salmon – to New Zealand. Some of these species now form important recreational fisheries. Less well known, and usually much less widespread, are 15 other introduced species. These are known as coarse fish – many have coarser scales than trout and salmon.
Coarse fish found in New Zealand are:
Most belong to Cyprinidae, a family which contains almost 2,500 species, including carps, minnows, and a host of other small fish found across Europe, Asia, Africa and North America.
Coarse fish are caught by anglers with a baited hook attached to a float. Some species have been illegally introduced and spread by anglers wanting to fish for them.
Some species such as goldfish are usually too small to be targeted by anglers. Some very keen coarse anglers aim to catch a variety of species or the largest fish species. A few species, including silver carp and grass carp, do not breed naturally in New Zealand waterways and populations are maintained by releasing fish reared in captivity. It is doubtful whether some species, such as caudo, are established at all, despite records of their presence in New Zealand.
Introduced fish can have four statuses under various pieces of legislation:
Offenders can attract a maximum sentence of five years and/or a fine of up to $100,000. The legal status of some species varies. For example, rudd is only a ‘sports fish’ in the Auckland–Waikato fish and game region, but a ‘noxious fish’ elsewhere. Some species, such as caudo, goldfish and orfe, have no legal status.
Some coarse fish are valued as food (European perch), or for recreational angling (European perch, koi carp, rudd, tench). Some have adverse effects on ecosystems (koi carp, rudd, tench, gambusia), while others are valued for their use in biological control (grass carp and silver carp). When ‘noxious fish’ or ‘unwanted organisms’ are found in contained areas such as ponds or small lakes, authorities sometimes eradicate them using the natural toxin rotenone, known as Derris Dust to gardeners.
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.
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 (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 (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.
A group of exotic species belongs to the family Poeciliidae, sometimes known as the livebearers because they give birth to live young rather than lay eggs. There are five small livebearers in natural habitats in New Zealand – one (gambusia) was introduced for biological control, the others for aquariums.
Gambusia (Gambusia affinis) were introduced, probably in the 1930s, in the hope they would help control mosquitoes. This is unproven in New Zealand, and they may be no more useful than native fish. Gambusia have become increasingly widespread since the 1980s, and are now common from Waikato and Bay of Plenty northwards. A few populations have been reported in the northern South Island, where efforts have been made to exterminate them as they may be detrimental to native fish.
Resembling gambusia, caudo (Phalloceros caudimaculatus) have been reported from waters around Whangārei, but it is uncertain if there are wild populations. Aquarists have stocks that could become established if released into suitable habitats.
Three poeciliids liberated into the wild by aquarists now live in geothermally heated waters in the central North Island. The common guppy (Poecilia reticulata) has been found in streams near Reporoa, the sailfin molly (Poecilia latipinna) in a wetland at the southern end of Lake Taupō, and the swordtail (Xiphophorus helleri) in a stream near Taupō. None of these species is likely to become established in waters of normal ambient temperature, so their geographical range will be restricted. Some were once in the Waipāhīhī Stream, near Taupō, but when water flows were manipulated, temperatures rose and the fish died out.
North American brown bullhead catfish (Ameiurus nebulosus) were introduced for unknown reasons in the 1870s. They became abundant in the lower Waikato River, and were not found elsewhere for many decades apart from small numbers in Lake Māhinapua, near Hokitika, the only confirmed South Island population. Their range increased from the 1980s – perhaps spread by commercial eel fishers who caught them in their fyke nets (large, funnel-shaped nets that trap fish). Intermittent catfish populations are now widespread in northern waters, including Lake Taupō, although how they reached this lake is uncertain. They have spread from Lake Taupō to the series of hydro lakes in the Waikato River.
European perch (Perca fluviatilis) are a desired angling species, brought to New Zealand in the late 1860s. They are classed as ‘sports fish’, so anglers need a licence to fish for them. Perch are widespread but intermittent around the country. Concentrated populations are in the western and southern North Island, around Hokitika, and in the eastern and southern South Island. The fish has firm, white, tasty flesh, and is much the best eating of the exotic non-salmonid species.
McDowall, R. M. Gamekeepers for the nation: the story of New Zealand’s acclimatisation societies, 1861–1990. Christchurch: Canterbury University Press, 1994.
McDowall, R. M. The Reed field guide to New Zealand freshwater fishes. Auckland: Reed, 2000.