Tilapia

Chemicals can be used to eradicate small, isolated populations of pest fish quickly (spot removal) and with a moderate cost, provided that the benefits clearly outweigh any harm to native species and the environment1. There have been a number of attempts to control pest fish in Australia and almost half of these have included the use of chemicals (fish poisons are known as ‘piscicides’). Examples are the successful eradication of carp from Tasmania in the 1970s and from the Cooper Creek drainage in South Australia2.

Presently available piscicide options:

There is no piscicide available that is specific to particular fish species, and in fact, no chemicals are fully registered as piscicides in Australia. Rotenone is the only chemical currently legal to use in Australia to control any pest fish. Rotenone is a naturally occurring chemical, obtained from the roots of several tropical and subtropical plant species. It is widely used as an insecticide and pesticide.
Historically, the states and territories have applied for a ‘minor use’ permit to be able to use chemicals such as rotenone for a specified time and under permit conditions. The current permit for the use of rotenone is APVMA Permit 13011 (Oct 2011-Oct 2020).

Currently available methods of chemical control for pest fish can be used to eradicate small, isolated populations quickly

This permit is held by New South Wales Fisheries and allows the use of rotenone by employees of state and territory government departments responsible for pest fish eradication and persons under their direct supervision. It can be used in all jurisdictions except Victoria.

There are other conditions applied by the APVMA for the permitted use of rotenone to kill pest fish, such that there:

• is a high probability of successfully eradicating the pest fish, with a low chance of immigration or recolonisation
• has been a review of environmental factors that identified benefits outweigh impacts on native species
• is no risk to the health of humans, stock or domestic animals through direct contact or contaminated drinking water
• is generally strong public and political support for the operation.

Table 1: Advantages and limitations of rotenone for spot removal of pest fish populations.

Issues to consider when using rotenone:

Other legal approvals and permits are also required for the use of rotenone (eg Environmental Protection Authority authorisation and Bureau of Animal Welfare animal ethics approval). Rotenone may also only be applied to a water body by certified agricultural chemical users (eg ChemCert accredited users). These requirements may slow response times to critical situations so much that potentiallycontrollable situations may become lost causes. So, it is advisable to be as well prepared as possible in anticipation of chemical control activities. A risk assessment or feasibility study may assist in determining whether a rotenone operation should proceed3.

Considerations may include:

• an accurate estimate of water volume to be treated
• calculations of desired concentration of toxicant, preferably backed by onsite bioassays to account for variability in product
• erformance under different water conditions
• detoxification and cleanup needs (including the removal/disposal of large quantities of dead fish)
• drawdown of the water body if possible to reduce the quantity of toxicant needed
• notification of all relevant government agencies (state and local) and obtaining of necessary environmental approvals
• training of staff and occupational health and safety considerations
• public awareness and notification/consultation.

Other possible options as fish toxins:

A number of other chemicals have been used in certain situations to control pest fish in Australia and overseas4. The most promising of these for widespread use would probably be antimycin, which is used extensively as a piscicide overseas, but has not been registered for use in Australia. Antimycin is comparable in many respects to rotenone with greater toxicity but it is also more expensive.
Another option that has been used successfully is lime, which can be applied to small areas and is especially useful for treating a defined spawning area such as carp eggs in shallow marshlands.

Further information:

1. Sanger AC and Koehn JD (1997). Use of chemicals for carp control. In: J Roberts and R Tilzey (Eds), Controlling Carp: Exploring the Options for Australia. CSIRO Land and Water, Griffith NSW.
2. Hall DA (1988). The eradication of European carp and goldfish from the Leigh Creek Retention Dam. Safish 1998:15–16.
3. Risk Assessments as a Tool for Pest Fish Management. PestSmart Toolkit factsheet, Invasive Animals Cooperative Research Centre, Canberra.
4. Ayres R and Clunie P (2010). Towards a National Emergency Response System for Freshwater Fish Incursions. PestSmart publication, Invasive Animals Cooperative Research Centre, Canberra.
5. Allinson G (in prep). A Strategy for Developing Fish Specific Biocides and Delivery Mechanisms. PestSmart publication, Invasive Animals Cooperative Research Centre, Canberra.