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What is the RSPCA’s view on the release of Cyprinid herpesvirus to kill carp?

Article ID: 707
Last updated: 03 Oct, 2017
Revision: 4
Views: 1103

In late 2016, the Australian Government commissioned a two-year research and planning process to determine the feasibility of using a virus (known as Cyprinid herpesvirus 3 or CyHV-3) to control invasive European carp (Cyprinus carpio) in Australia [1,2]. 

The RSPCA recognises the need to control introduced species to minimise their environmental and agricultural impacts where these are validated. However, we argue that the control methods used must be as humane as possible for all species, including fish. The available scientific evidence demonstrates that fish are sentient animals capable of experiencing pain and suffering and must therefore be treated humanely.

In the 1970s, carp spread throughout the Murray-Darling Basin, and are now the most abundant large freshwater fish in this river system. Carp are also abundant in many eastern-draining rivers. Carp can tolerate poor water quality, meaning that they thrive in rivers that are already degraded. For this reason, separating carp impacts from other sources of environmental damage can be difficult.

Despite these difficulties, increased research on the environmental impacts of carp since the 1990s has provided evidence that these fish do real environmental damage. Carp have been found to muddy waters, increase nutrient levels (thereby promoting harmful algae blooms), and reduce abundance of water plants, invertebrates (e.g. aquatic insects and crustaceans), and native fish [3-5]. Therefore, significant reductions in carp numbers could improve the health of Australia’s aquatic ecosystems and the species that inhabit them.

However, the use of disease-causing biological agents such as Cyprinid herpesvirus 3 is contentious due to the potential stress that infected carp might experience before death. Spreading the virus among carp would probably involve catching carp from the wild and inoculating them with virus before release. The welfare risks inherent in these procedures could be reduced if workers adhere to approved standard operating procedures. These procedures should include injecting fish while they are in a stunned condition, and releasing them immediately after inoculation.

The second primary welfare concern relates to stress potentially experienced by infected carp. The virus affects the gills, leading to reduced oxygen intake. Affected fish become lethargic and gasp at the surface with some experiencing loss of equilibrium and disorientation. Death may take several days, with some carp succumbing to parasitic and bacterial infections [6]. Death caused by this virus is therefore likely to involve a level of stress, the extent of which is currently unclear.

An important tool developed by the NSW Department of Primary Industries with input from the RSPCA and funding from the Federal Government is the Model for Assessing the Relative Humaneness of Pest Animal Control Methods [7]. Based on this model, expected welfare impacts resulting from the carp virus are considered to be wide ranging, largely because stress levels in infected carp have not been directly measured. Research quantifying stress levels in infected carp would enable prediction of welfare outcomes for infected carp with greater certainty.

Another welfare consideration relates to potential impacts on non-carp species and aquatic habitats if large numbers of dead fish negatively affect water quality (including oxygen levels) as the carp decompose. These impacts could potentially be managed through implementation of a staged virus release and clean-up strategy, which are both areas of investigation under the National Carp Control Plan [8].

Finally, koi carp - which are popular among fish enthusiasts - are the same species as European carp, and are therefore fully susceptible to the virus [9]. If the virus is released, koi keepers and breeders would need to take precautions to protect their fish from the virus.

In conclusion, the RSPCA recognises the environmental benefits that could accrue from successful carp control. Nonetheless, the RSPCA has some concerns with the use of disease-causing biological control agents which cause avoidable stress to target and non-target species. Research quantifying stress levels in infected carp, along with evidence demonstrating that the environmental impacts of major carp mortalities could be successfully managed would assist in alleviating these concerns.


[1] National Carp Control Plan (2017) www.carp.gov.au

[2] McColl, K. (2016). Final report: Phase 3 of the carp herpesvirus project (CyHV-3). PestSmart Toolkit publication, Invasive Animals Cooperative Research Centre, Canberra, Australia

[3] Vilizzi, L., Tarkan, A.S. & Copp, G.H. (2015). Experimental evidence from causal criteria analysis for the effects of common carp Cyprinus carpio on freshwater ecosystems: a global perspective. Reviews in Fisheries Science and Aquaculture 23, 253 – 290.

[4] Vilizzi, L., Thwaites, L.A., Smith, B.B., Nicol, J.M. & Madden, C.P. (2014). Ecological effects of common carp (Cyprinus carpio) in a semi-arid floodplain wetland. Marine and Freshwater Research 65, 802­­ – 817.

[5] Weber, M.J. & Brown, M.L. (2009). Effects of common carp on aquatic ecosystems 80 years after “Carp as a Dominant”. Reviews in Fisheries Science 17, 524 – 537.

[6] PestSmart Toolkit (2012) Factsheet: Impact of carp in Australia.

[7] Sharp T & Saunders G (2011) A model for assessing the relative humaneness of pest animal control methods (Second edition). Australian Government Department of Agriculture, Fisheries and Forestry, Canberra, ACT.

[8] National Carp Control Plan (2017). Strategic Research and technology Plan

[9] Manual of Diagnostic Tests for Aquatic Animals (2012) Koi Herpesvirus Disease Chapter 2.3.7. OIE World Organisation for Animal Health.

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