Gambusia (formerly known as Mosquito Fish)

Gambusia affinis are small fish introduced to New Zealand in the 1930’s from the Gulf of Mexico to control mosquito larvae but, ironically, they are not very good at it! Their ability to control mosquitoes has been exaggerated and they have become pests in many countries around the world. They are very aggressive fish and will attack fish much larger than themselves. This has lead to them being nicknamed “killer guppies”.

Description and Life History:

Gambusia is a small fish with a greenish silvery sheen. Mature females grown to 6 cm and males to 3.5 cm. They mature at six weeks old and are unusual because they give birth to live young. This means that only one pregnant female is needed to start a new population. These features allow Gambusia populations to build up to large numbers very quickly.

What damage do they do?

Gambusia populations quickly expand to out number other species. They attack native fish by nipping at their fins and eyes and prey on their eggs. Whitebait and mudfish species are especially vulnerable to Gambusia, as they inhabit similar habitats.

Where are they found in NZ?

Gambusia prefers the shallow margins of slow flowing ponds, wetlands and streams especially around aquatic plants. They can tolerate poor water quality and a wide range of water temperatures. Gambusia is widespread throughout Northland, Auckland, Waikato and Bay of Plenty. Isolated populations have been found in Hawkes Bay, Wanganui and Nelson.

Native fish such as whitebait, bullies and eels and aquatic invertebrates all feed on mosquito larvae. In addition introduced goldfish and tadpoles and frogs don’t cause as many problems as Gambusia and feed on mosquito larvae.

If you have got mosquito problems:

Empty containers around your home that contain water (saucers, jars, tyres, paddling pools etc) and clear your guttering.
If you have a pond make it as unfriendly to mosquitoes as possible by making the sides steep, having flowing water and planting plants around the edge to shade the water. This will improve your ponds habitat for other species that feed on mosquitoes.

Legal Designation:

Unwanted organism.

Further information can be found here