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Pest fish

Pest fish

Updated 3 July 2019 12:32pm


Why are pest fish a problem?

There are a range of pest fish species which present a current or potential problem to the biodiversity of the Wellington region. Many of these species are opportunistic predators eating insects, fish spawn, juvenile fish and a broad range of plants and organic matter. Some of the species are destructive when they feed, filtering through the bottom of ponds, lakes and rivers increasing the turbidity of the waterway, and destroying the habitat of a range of native flora and fauna. All introduced fish species present competition to native aquatic species, and upset the balance of our delicate freshwater ecosystems.

Description and background

Greater Wellington is concerned over the presence or accidental introduction of a range of pest fish species which includes;


  • Brown bullhead catfish (Ameiurensis nebulosis)
  • Gambusia (Gambusia affinis)
  • Goldfish (Carassius auratus)
  • Koi carp (Cyprinus carpio)
  • Rudd (Scardinius erythropthalmus)
  • Tench (Tinca tinca)


Pest fish are often popular pet species, which are accidentally or intentionally introduced into waterways. Koi carp and catfish are common problem species in other parts of the North Island, and there is a high likelihood of their accidental introduction into the waterways of the region.

What can I do?

Male gambusia
Photo: Barry O'Brian

If you suspect you have an infestation of pest fish in a stream or waterway contact Greater Wellington. Always check and clean implements and machinery when moving between waterways, as species

such as catfish are extremely hardy and can survive for hours outside of water. No domestic fish species should be released into the wild. If you have unwanted pet fish contact Fish and Game New Zealand, the Department of Conservation, the SPCA or Greater Wellington.

Additional information can be found at –

Gambusia -
Koi carp -
Catfish -
Rudd -