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.
Types of coarse fish
Coarse fish found in New Zealand are:
- Cyprinidae family – goldfish, koi carp, tench, rudd, orfe, gudgeon, grass carp, silver carp
- Poeciliidae family – gambusia, caudo, common guppy, sailfin molly, swordtail
- Percidae family – European perch
- Ictaluridae family – brown bullhead catfish.
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:
- sports fish (e.g. perch, tench) – it is an offence to fish for them without a licence.
- noxious fish (e.g. koi carp, rudd) – illegal to possess, breed or release under the Freshwater Fisheries Regulations 1987.
- unwanted organism (e.g. koi carp, gambusia) – illegal to release, spread, sell or breed under the Biosecurity Act 1993.
- restricted species (e.g. silver carp, grass carp) – releases require the approval of the minister of conservation.
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.
Value or pest?
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.