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Speckled mosquitofish - Phalloceros caudimaculatus

Other common name: one spot livebearer

Mosquito Fish
Photo: Jodi Rowley

INTRODUCTION

Speckled mosquitofish are brightly coloured, hardy and relatively easy to breed. As a result, they are a popular aquarium fish and have been transported around the world by the aquarium trade.

Speckled mosquitofish were recently discovered in a NSW waterway. This raises concerns about the potential impacts of yet another introduced freshwater fish in NSW. Detrimental interactions with introduced pests are considered a major threat to native aquatic biodiversity, and the 'Introduction of fish to freshwaters within a river catchment outside their natural range' is listed as a key threatening process under the NSW Fisheries Management Act 1994.

It is usually extremely difficult to eliminate pest fish once they have become established in the wild. It is therefore vital to prevent noxious pests such as speckled mosquitofish from entering or spreading further in our waterways.

NATURAL DISTRIBUTION AND BIOLOGY

Speckled mosquitofish are native to eastern South America between Brazil and Uruguay.

They are a tiny livebearer (family Poeciliidae) and are similar in size and shape to the related Gambusia holbrooki (plague minnow or mosquitofish), although they are more yellowish in colour. The males are distinctively speckled with irregular black spots and blotches. Females can grow to 6 cm and males to 2.5 cm in length.

Speckled mosquitofish live in still ponds with dense aquatic vegetation. They are hardy and tolerate a wide range of environmental conditions. They mainly eat plant material and sediment. Contrary to popular belief, they do not consume a substantial number of mosquito larvae and have little value in mosquito control.

They give birth to live young rather than laying eggs as most fish do, and produce broods of up to 80-100 offspring.

WHERE ARE THEY IN NSW?

Speckled mosquitofish were first discovered in the wild in NSW in March 2002. Currently the only known population in NSW occurs on Long Reef headland in northern Sydney in a series of ponds that form the water hazards of Long Reef Golf Course. Whilst restricted to this site, they are very abundant.

Previously, speckled mosquitofish had only been recorded in Australia from several isolated locations including a few swamps and drains in the Perth metropolitan area and the Todd River system near Alice Springs. The discovery of the population in NSW is the first record of this species in eastern Australia.

HOW DID THEY GET HERE?

Although the release of unwanted pet fish is the most likely explanation, local aquarium shops do not currently sell this fish.

WHAT ARE THEIR IMPACTS?

There have been no studies on the effects of speckled mosquitofish on Australia's aquatic ecosystems.

However, the closely related introduced Gambusia holbrooki is considered to have had a major impact. Gambusia - which were introduced from the late 1920's to the 1940's in an attempt to control mosquitos - are now widespread throughout many of Australia's freshwater river systems and are regarded as a major pest. They have been implicated in the decline of a number of native fishes and frogs, including some threatened species. Gambusia impact on these animals through predation, competition for food and habitat, direct aggression (e.g. fin-nipping) and the introduction of parasites.

Speckled mosquitofish are also likely to be highly competitive.

WHAT IS NSW FISHERIES DOING?

NSW Fisheries is implementing a plan to manage speckled mosquitofish at Long Reef Golf Course. In August 2002 an attempt was made to eradicate the population using a fish poison called rotenone. Although many speckled mosquitofish were killed during the process, some have subsequently been observed in a few of the ponds. A follow-up survey is planned for 2003 in order to prepare the next eradication attempt.

In addition, speckled mosquitofish have been listed as a Class 2 noxious species in NSW under the Fisheries Management Act 1994. It is illegal to buy and sell speckled mosquitofish, or to keep them in garden ponds or farm dams, without a permit. Heavy penalties of up to $11,000 apply for breaking these rules.

NOTE: Speckled mosquitofish may still be kept in an aquarium providing it is fully enclosed.

NSW Fisheries is also monitoring fish populations in coastal and inland rivers. If any new populations of speckled mosquitofish are discovered they will be monitored, and where possible, action taken to control or remove them.

HOW CAN YOU HELP?

Give unwanted aquarium fish to friends or a petshop, rather than letting them go in the wild (Note: it is illegal to release live fish into NSW waterways without a permit, and heavy penalties apply).

Be on the lookout for new species in your local waterways.


If you find any fish that you think might be speckled mosquitofish or another species not native to the area, freeze the fish whole and contact your local NSW Fisheries office or the Threatened Species and Biodiversity Unit (contact details below).

REFERENCES

Allen GR, Midgley SH, Allen M. (2002). Freshwater fishes of Australia. Western Australian Museum, Perth.

McDowall RM. (1999). Further feral poeciliid fish in New Zealand fresh waters, with a key to species. New Zealand Journal of Marine and Freshwater Research 33:

NSW National Parks and Wildlife Service. (2002). Predation by Gambusia affinis holbrooki - the plague minnow, Draft Threat Abatement Plan. NPWS, Hurstville, NSW.

Welcomme RL. (1988). International introductions of inland aquatic species. FAO Fish technical paper No. 294.

For further information

Helping with protected and threatened species sightings

You can report a sighting by phone on 02 49163877, online, or by downloading the Protected, Threatened and Pest Species Sighting Form icon-pdf115KB and send to:

Port Stephens Fisheries Centre
Private Bag 1, Nelson Bay NSW 2315
Fax: 02 4916 3880
Email: tsadmin@fisheries.nsw.gov.au

Last Updated: March 23, 2006, 11:32 am