Invasive Freshwater Species

There are a number of invasive species that could have a devastating impact on Tasmania's freshwater ecosystems, native fish and plants. Four of the biggest threats are described below.

In Tasmania, the Inlan​d Fisheries Service has responsibility for native fish conservation, pest fish management and freshwater habitat protection.

European carp (Cyprinus carpio)

Not Wanted!Carp were discovered in Northern Tasmania in 1975 and again in 1980, with both incursions being eradicated. Carp were again discovered in Tasmanian waters in 1995, in Lake Crescent and Lake Sorell. Luckily they have not yet been found in any other Tasmanian waters.

Carp have a range of impacts including threatening native galaxias, impacting on recreational fisheries and aquatic vegetation, and causing nutrient enrichment of waterways which can lead to increased algal blooms.

Carp are currently managed by the Inland Fisheries Service​ which aims to contain, and ultimately eradicate carp population Tasmania.

Not Wanted!Eastern gambusia thumbnail

Eastern gambusia (Gambusia holbrooki)

Eastern gambusia (also known as the mosquito or devil fish) were first discovered in Tasmania in 1990, and there are currently several self-sustaining populations in the upper reaches of the Tamar estuary.

The largest identified population is found in the Tamar Island Wetland Reserve Conservation Area, but monitoring reveals that this species is spreading throughout the Tamar estuary. Rapid response if required if we are to stop the spread; gambusia have an enormous reproductive capacity with the average female able to birth up to 450 live young over the summer breeding season.

Gambusia are highly aggressive and can tolerate a wide range of environmental conditions. They are a significant threat to Tasmania's native fish and frogs. Once introduced, it is almost impossible to eradicate without rapid response and persistent, well-coordinated effort.

Gambusia has been implicated in the decline or local extinction of at least 35 fish species worldwide.

Find out more on Eastern gambusia by contacting the Inland Fisheries Service​

Didymo (Didymosphenia geminata)

Not Wanted!Didymo, also called rock snot, is a freshwater algae that is widespread in the Northern Hemisphere. Although not currently in Australia, it is highly invasive and is considered a significant risk. Didymo is a declared List A pest under the Plant Quarantine Act 1997 and its entry into Tasmania is prohibited.

Didymo is found in New Zealand and is causing a major concern for fisheries managers and anglers. It forms dense algal clumps that adversely affect water quality, aquatic invertebrates and fish stocks, and are a hazard for hydro generation, irrigation and recreation.

Didymo poses a significant threat in Tasmania because of the potential transfer from NZ via contaminated fishing and boating equipment.

Find out more: DPIPWE Biosecurity - Didymo (rock snot)

Not Wanted! long-necked turtle - thumbnail

Freshwater turtles

There are more than 20 species of freshwater turtle native to mainland Australia and they are found in most freshwater lakes and rivers. Tasmania has no native freshwater turtles and any freshwater turtle spotted in Tasmania is an invasive species. The Wildlife Management Branch has responsibility for managing the response to sightings of freshwater turtles in the wild in Tasmania.

Captive bred turtles are still sold legally as pets on mainland Australia. Due to their small size, hatchlings are relatively easy to transport and there have been a number of recent incidents where people have been caught smuggling them into Tasmania. It is illegal to import or keep turtles as pets in Tasmania and severe penalties apply.

Read more about freshwater turtles and a case study of the long-necked turtle (Chelodina longicollis).

See other invasive species profiles:

Mammals | Birds | Other species



Invasive Species Branch