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

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 cause 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]. 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 pain and suffering that infected carp might experience before death. 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. Inflammation and damage is also caused to other organs including kidney, spleen, pancreas, liver, brain and the gut. Affected fish stop eating, become lethargic and may show skin lesions as well as excess mucous production, affecting the gills causing suffocation. Death may take 1-2 weeks, with some carp succumbing to parasitic and bacterial infections [4].

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 [5].

Finally, koi carp – which are popular among fish enthusiasts – are the same species as European carp, and are therefore fully susceptible to the virus [6]. 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, although further evidence that the environmental impacts of major carp mortalities can be successfully managed is warranted. The RSPCA also has concerns with the use of disease-causing biological control agents which cause pain and suffering. There is an urgent need to develop more humane control methods to reduce the reliance on such biological agents.