What’s the go with the carp virus?

For many of us in river and waterway management, it’s one of the most asked questions we get from family, friends and the community — “What’s the go with that carp virus?” The recent flooding and subsequent explosion in carp numbers has again seen this question raised beyond just pubs and kitchen tables, to being asked across newspapers and media more broadly.

The problems with carp (Cyprinus carpio L.) are extremely well known within Australia. However, potential solutions to dealing with the invasive species are far more elusive. Since 2016, the Australian Government has been investigating the viability of releasing ~the virus~ to reduce carp populations. Finally in 2022, after 6 years of work, the National Carp Control Plan was presented by Fisheries Research and Development Corporation (FRDC) to the Australian Government for consideration. It is important to note that COVID-19 significantly delayed the delivery of the plan.

If you’ve been paying attention to the mass flooding events within the Murray-Darling Basin, you may have noticed the current ‘boom’ in fish spawning. Whilst great for iconic species such as the Golden perch and Murray cod, there has also been an explosion in populations of carp. With carp numbers climbing, it begs the question: What’s the go with the carp virus?

There are arguments both for and against the release of the carp virus, generating considerable debate between scientists, governments, communities, and conservationists. In this article, we aim to give the latest information on the program, while also sharing some of the potential risks and benefits which have been flagged.

Dozens of carp swim and writhe over one another in an incredibly dense swarm.

Populations of invasive carp have been at problematic levels for years, threatening the wellbeing of native species and the ecosystem more broadly. Image credit: PatternPictures via Pixabay.

But let’s remind ourselves, what actually is the virus?

The virus is known as Cyprinid herpesvirus 3 and is being proposed as a biological control agent to reduce carp populations. The virus has been detected as occurring in more than 30 countries, but never in Australia.

The virus is largely transmitted from physical contact between carp, although it can also survive for up to three days without a host in the water. The virus infiltrates the skin, kidneys and gills of the fish, impacting the carp’s ability to process oxygen and breathe. After a fish is infected, the virus multiplies in the host for around 7 days (depending on the water temperature), with no obvious change in fish behaviour. After this time, it will take 24 hours from the first signs of infection to kill the fish. The signs of disease include reddened gills and darkened skin. Essentially, damage caused to the fish’s gills are what ultimately result in the death of the fish.

What are the risks?

There are some risks, mostly involving ecological consequences, that must be accounted for in reviewing the National Carp Control Plan. These include:

Potentially creating an opportunity for other invasive species, previously suppressed by carp, to increase in abundance. The plan has two research projects established to investigate this topic (research projects 12 and 15).
Sudden major reductions in carp may result in food shortages for some species, such as aquatic birds, who have come to depend upon carp as a food source (research project 12).
Large scale removal of carp biomass (carcasses) poses a logistical challenge.
Possible short-term deterioration of water quality, due to carp carcasses, with the potential to kill native fish and impact potable water for humans.

What are the benefits?

Modelling by the National Carp Control Plan suggests that the introduction of the virus could lower carp populations by 40-60% over a ten year period. This would result in:

Major long-term improvements to water quality, i.e., reduced turbidity.
Recovery of Australian native fish populations.
Recovery of Australian native aquatic plants.
Improved social values for inland river communities.

Dr. Jarod Lyon, Principal Scientist of Applied Aquatic Ecology at the Arthur Rylah Institute for Environmental Research, gives an update on the current state of the virus.

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What now?

The National Carp Control Plan is in the hands of the government and requires further review to determine whether to pursue the release of the virus. Ultimately, the final decision will be made by the Australian state and territory agricultural ministers after a formal review of the plan. The steps of the review are outlined as:

The Fisheries Research and Development Corporation submits the National Carp Control Plan to the federal Department of Agriculture, Fisheries and Forestry (the Department).
The Department then publishes the National Carp Control Plan and supporting suite of documents.
The National Carp Control Plan is then presented to the Environment and Invasives Committee to review and provide advice. Membership of this committee is comprised of representatives from the Australian state and territory primary industry and environment departments.
The National Biosecurity Committee considers the National Carp Control Plan and Environment and Invasives Committee advice, then provides recommendations to the Agriculture Senior Officials’ Committee.
Agriculture Senior Officials’ Committee then consider and endorse the advice recommendations for decision by the Agricultural Ministers’ Meeting.
Finally, a decision is made to whether to proceed with further work towards a release or cease the carp biocontrol program entirely.

Currently, the plan seems to be somewhere between steps 3-5, with the federal Department of Agriculture, Fisheries and Forestry stating that the federal government is working with states and territories to agree on the next steps of the National Carp Control Plan.

It is vital to note that this virus is no ‘silver-bullet’ solution; nor is it likely that any ‘silver-bullet’ solution exists. There are many critical conversations, discussions and debates to be had about the potential implications of this virus, as well as its second-order effects, to fish, biodiversity, and the whole ecosystem more broadly. With recent flooding events, the system being in higher flow introduces yet another factor to consider as to when would be the best time to release the virus.

Charles Sturt University research scientist Ivor Stuart said in a recent ABC article that, “I’d wait until we’d returned to normal flow conditions, then consider whether to release the carp virus in concert or in tandem with a whole lot of other techniques to control carp.”

A very large carp breaks the surface of the water, fins visible just below the surface.

Image credit: Andreas Lischka via Pixabay.

NSW Minister for Agriculture Dugald Saunders stated that, “we supported the findings to undertake further research but we would now like to see the Commonwealth set a date for the release of this virus as soon as possible.”

However, owner of a boutique carp fishing business, Tracy Hill, suggests that carp is an untapped source of protein going to waste. Regarding the virus, she suggests that, “sometimes it’s better the devil you know then the devil you don’t.”

There is also the broad notion that we must consider a range of uncertain environmental outcomes that have yet to be fully explored.

At the end of the day, there remain several bureaucratic processes and committees required to review the latest research to progress this topic towards a decision point of whether to release the virus. Until then, it seems as though we will have to wait and see whether the carp virus progresses to the point where this decision needs to be made — and whether the scientific evidence suggests that the potential benefits outweigh the risks. Before then, it is likely that this will remain a topic of heated discussion around BBQs and dinner tables as we all share our views regarding whether we should ‘let it rip.’

Two cartoon fish have a conversation, one of whom points at a whiteboard which says "NATIONAL CARP CONTROL PLAN: FRDC, DAFF, EIC, NBC, AgSOC." The fish pointing at the whiteboard says, "So the FRDC will submit the NCP to DAFF for them to publish it, while also presenting to the EIC for them to review and advice. The NBC will then consider the plan and advice from EIC, before providing recommendations to AgSOC, for AgSOC to then send it to Ministers for a decision." The other fish replies, "Ah ok. Sorry I asked."

Credit: Masha Artamonova

Resources

European carp numbers spike after record flooding, calls mount to push forward with release of herpes virus (Article – ABC News)
Exploding carp numbers are ‘like a house of horrors’ for our rivers. Is it time to unleash carp herpes? (Article – The Conversation)
The National Carp Control Plan (PDF – Fisheries Research and Development Corporation)
Integrating conventional risk management and population models to assess risks from an established invasive freshwater fish (Journal article – Journal of Environmental Management)
Carp (Cyprinus carpio) as a powerful invader in Australian waterways (Journal article – Journal of Freshwater Biology)
Frequently asked questions about the carp herpesvirus (CyHV-3) (Article – Centre for Invasive Species Solutions / PetSmart)
Cyprinid herpesvirus 3 and its evolutionary future as a biological control agent for carp in Australia (Journal article – Virology Journal)
Cyprinid Herpesvirus 3 (Journal article – National Library of Medicine)

Featured image: The carp is as contentious as it is problematic. Photo credit: Victorian Department of Energy, Environment and Climate Action.

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