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