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Pests and weeds

Welcome to our Pest Hub your go-to guide for advice on pest animals and weeds in Te Tairāwhiti.

Gambusia (mosquito fish)

Poeciliidae - Gambusia affinis

What does it look like?

Gambusia (mosquito fish) are small aquatic fish with a with a stout body, greenish-olive to brownish on the back, grey sides, with bluish sheen and a silvery white belly. The tails are rounded and have one rounded dorsal fin, a very small up turned mouth.

Mature females grow to 6cm and males to 3.5cm. They mature at six weeks old and are short lived but breed rapidly and repeatedly enabling populations to build up to large numbers very quickly. Females give birth to live young and 1 pregnant female is needed to start a new population (around 50 offspring) within 3-4 weeks old. 

Gambusia live in the shallow margins of slow flowing ponds, wetlands and streams, particularly around aquatic plants. They can tolerate poor water quality, high salinity levels and a wide range of water temperatures.

Why is it a problem?

Gambusia are an aggressive species that will build up to large numbers quickly and frequently attack native fish, nipping at their eyes and fins. Endangered galaxiids (whitebait species) and mudfish are especially vulnerable.

These fish spread readily downstream or by deliberate liberations into ponds and dams.

Control methods

Prevention: These invasive fish prey on native species that feed on mosquito larvae.
To make local environments less attractive for mosquitos remember to clean your gutters and other water containers around your home, like paddling pools.

If you have a pond, make it as unfriendly to mosquitoes as possible by creating steep sides and have flowing water, planting plants around the edge to shade the water. This will improve the pond's habitat for other species that feed on mosquitoes.

Control: Please report to Council's biosecurity team if you believe you've encountered this fish species.

More information

Similar species: There are several native species such as those identified as whitebait and freshwater bullies that could be mistaken for the Gambusia due to similar habitat behaviour and size and shape to the untrained eye. 

Current known populations are found in the North Island only. 

Related links

Management programme
Progressive Containment
Pests that are present in our region at numbers or distributions that mean eradication is not possible in the short term, but populations can be contained or reduced over time. These pests are capable of causing adverse effects to the environmental, economic, social or cultural values of the Gisborne/Tairawhiti district.
Rules
Rule 1.10

No person shall intentionally distribute, propagate or dispose of any or all of this pest except at legal landfills or authorised green waste dump sites, or as authorised by a resource consent. 

Progressive Containment

Council will work with landowner/occupier, including developing agreements for the effective management of this pest to protect the values of specific sites.

For more information about this rule, refer to our Regional Pest Management Plan under related links