Carp, a symptom or a cause of environmental damage?
Australian rivers experience many environmental pressures, of which carp are one. Disentangling carp impacts from other sources of environmental stress can be difficult for two main reasons. First, carp thrive in rivers that are already degraded, and tend to intensify the impacts resulting from other pressures. Second, the 'finprint' carp leave on the environment extends over large areas, and can manifest as sudden shifts between different ecosystem states (e.g. clear vs. muddy water), rather than varying predictably in direct relation to carp abundance. Understanding carp impacts therefore requires large-scale, multi-year experiments.
Despite these difficulties, increased research on carp impacts through the 1990s has provided evidence that carp really do damage river ecosystems. Studies show that carp muddy waters, increase nutrient levels (thereby promoting blue-green algae blooms), and reduce abundance of water plants (macrophytes), invertebrates (e.g. aquatic insects and crustaceans), and some fish. It has also been found that carp increased water turbidity (muddiness) in 91% of surveyed studies, reduced invertebrates in 94%, and reduced macrophytes in 96% of surveyed studies.
Carp impacts also tend to be interlinked. Their bottom-feeding behavior reduces water clarity, which limits sunlight penetrating down to macrophytes on the river bed, which in turn, reduces habitat and/or food for invertebrates, native fish and waterbirds. The cumulative effect of these impacts is to shift ecosystems from a predominantly clear-water state to a murky, nutrient-rich state (‘eutrophication’). Once an ecosystem shifts in this way, reversal can be difficult, meaning that the river will remain muddy for some time, even as carp densities fluctuate in various locations within the system.
Carp are known to:
- Increase water turbidity (i.e. the amount of sediment and other fine matter present in the water, giving it a muddy or dirty appearance).
- Increase nutrient content (especially nitrogen and phosphorus), resulting in outbreaks of potentially toxic algae.
- Reduce the abundance of water plants, aquatic invertebrates, and fish.
- Some research also suggests that carp may reduce populations of water birds, although further evidence is required to be sure.
Carp and habitat damage: cause or symptom?
Australian rivers experience many environmental pressures, of which carp are one. Disentangling carp impacts from other sources of environmental stress can be difficult, for two main reasons. First, carp thrive in rivers that are already degraded, and tend to intensify the impacts resulting from other pressures. Second, the ‘footprint’ (finprint?) carp leave on the environment extends over large areas, and can manifest as sudden shifts between different ecosystem states (e.g. clear vs. muddy water), rather than varying predictably in direct relation to carp abundance. Understanding carp impacts therefore requires large-scale, multi-year experiments.
Despite these difficulties, increased research on carp impacts through the 1990s has provided evidence that carp really do damage river ecosystems. This research included systematic reviews and meta-analyses, which combine and analyse data from all available studies on a particular topic, as well as large-scale experiments. These studies show that carp muddy waters, increase nutrient levels (thereby promoting blue-green algae blooms), and reduce abundance of water plants (macrophytes), invertebrates (e.g. aquatic insects and crustaceans), and some fish species (Vilizzi et al., 2014, 2015; Weber and Brown, 2009). For example, Weber and Brown (2009) found that carp increased water turbidity (muddiness) in 91% of surveyed studies, reduced invertebrates in 94%, and reduced macrophytes in 96% of surveyed studies (Weber and Brown, 2009). A more recent meta-analysis supported these results, finding strong evidence for carp impacts on all the same ecosystem components (Vilizzi et al., 2015).
Carp impacts also tend to be interlinked. Carp feed by sucking sediments from the river bed, filtering out food items and puffing the remaining mud into the water column. This feeding style reduces water clarity, which limits the sunlight penetrating down to macrophytes on the river bed. Fewer macrophytes in turn mean less habitat for invertebrates and native fish. The cumulative effect of these impacts is to shift ecosystems from a predominantly clear-water state (‘oligotrophic’), to a murky, nutrient-rich state (‘eutrophic’). Shifts from one state to another are often termed ‘phase shifts’ in ecology. Once an ecosystem has shifted to a new phase, reversing the change is usually difficult, meaning that the river will remain muddy for some time, even as carp densities fluctuate in various locations within the system.
Australian studies such as King et al. (1997) have also demonstrated carp impacts in Australian waterways. In this study researchers examined effects of carp density on turbidity, phytoplankton (microscopic algae), and nutrients in two billabongs. The study found clear evidence of carp impacts, with the authors reporting that:
In these natural billabongs, high standing stocks of carp caused increases in turbidity and more intense algal blooms.
Finally, a recent study on the lower Murray River used an experimental design with considerable power to detect carp effects, demonstrating that carp can drive phase shifts from clear to dirty water states, with the latter characterised by poor populations of macrophytes and aquatic invertebrates (Vilizzi et al. 2014). Importantly, this study also indicated that carp may cause environmental damage at lower densities than previously considered.
In summary, acknowledging that Australian rivers face degradation from many sources should not preclude carp control. Nor should action to reduce carp impacts diminish efforts to restore waterway health via other means. Rather, an integrated carp control program could provide a springboard for broader river rehabilitation programs, including habitat restoration and water-quality remediation.
King, A.J., Robertson, A.I. & Healey, M.R. (1997). Experimental manipulations of the biomass of introduced carp (Cyprinus carpio) in billabongs. I. Impacts on water-column properties. Marine and Freshwater Research 48, 435 – 443.
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.
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.
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.
How did carp get here?
Perhaps surprisingly, given their present wide distribution and great abundance, carp had a slow start in Australia. During the mid-1800s, approximately concurrent attempts were made to introduce carp in Victoria, New South Wales, and Tasmania. None of these early introductions appear to have resulted in large, self-sustaining populations. Similarly, two attempted introductions in Victoria during the 1870s failed to become established.
Localised populations of carp became established in New South Wales around 1907-1910, following two introductions comprising a total of about 15 carp into an inlet pond above Prospect Reservoir. This strain (genetic variant) of carp, known as the ‘Prospect Strain’ probably maintains a locally-restricted distribution in the area.
The Boolarra strain appears
These early introductions were followed by other releases, some involving up to 50 000 fish, through the 1930s-1950s. However, carp numbers seem to have remained relatively low through the earlier 1950s (Koehn et al., 2000). This pattern of limited geographic spread and relatively low abundance changed when carp produced by Boolarra Fish Farms Pty. Ltd. in Gippsland during the late 1950s were introduced into a reservoir at Morwell, Victoria, in 1960s. Rapid spread of these ‘Boolarra strain’ carp within Victoria ensued, and by 1962 a Victorian state government inquiry had determined that carp should be eradicated.
We’ve got a problem: expansion to the present day
Despite eradication attempts using poisons by the Victorian Department of Fisheries and Wildlife, Boolarra strain carp had gained access to the Murray River by the mid-late 1960s. Extensive flooding in 1974-75, and again during the early 1990s, facilitated the species’ spread. People also aided the spread of carp, through both deliberate translocation, undetected presence of carp among stocked native fish, and the use of small carp as live bait for predatory fish. The latter is thought to be the primary mechanism explaining the presence of carp in several Tasmanian lakes, and in NSW coastal river systems.
What carp control measures have been undertaken and why haven’t they worked?
Commercial fishing fills niche markets for human consumption, fish leather, aquaculture feedstock, bait and fertiliser. Local consumer demand for carp is limited to 50-60 tonnes a year. Demand from these niche markets is not enough to make any significant reduction in the current carp population.
Manual carp removal, including trapping and controlling access to breeding grounds, has seen some success in Tasmania's Lake Crescent and Lake Sorell. Lake Crescent was declared free of carp in 2007 after 12 years of manual removal work. Carp removal work is continuing in Lake Sorell. The cost of the program is in the vicinity of $11 million.
The 'Daughterless Carp' and 'Trojan Y' programs have explored ways to genetically alter fish to produce offspring of only a single sex. This approach does not kill affected fish, but merely pushes a population to extinction by reducing breeding opportunities. But as carp have a lifespan of 35 years, it would take more than a century using this approach by itself to significantly reduce the population. Both show promise, however, and are being investigated as potential long-term control measures in combination with the carp virus.
Various methods have been trialled to control carp, or reduce their impacts in Australia. Primarily these have involved physical removal (e.g. netting, angling, trapping) or poisoning. All of these methods have advantages and disadvantages relating to their effectiveness, ease of use, size specificity (some remove only adult carp), impacts on non-target organisms, and cost. Methods employed for controlling carp and their impacts are summarised within Table 1, and are further discussed below.
Table 1. Carp-control or impact reduction methods used, trialled or under investigation in Australia (modified from NSW DPI 2010).
(Impact on carp population)
|Size specificity|| Impacts on
|Costs/resources||Feasibility/limitations on use|
|1. Community carp fishing competitions/musters/fish-outs (angling)|
Potential to remove large numbers of carp from localised area.
Little long-term effect on populations.
(Gehrke PC, 2010, Norris et al., 2013)
|Size specific - generally targets larger fish, not juveniles.||Non-target species can be released, although not all survive.||Human resource intensive; however, events are often independently organised by community groups.|| High interest from community groups in conducting these types of events.
Increases community awareness.
Ineffective in reducing population numbers or removing residual carp from waterways.
|1. Commercial harvesting (hauling/netting/trapping)|
Potential to remove large quantities of carp quickly in specific locations.
Market forces limit long-term effect on population.
(Graham et al., 2005)
|Dependent on mesh size.||Some bycatch of non-target species.||Self-funding, but only if carp populations and market price allow for a viable, self-sustaining industry. Otherwise fee-for-service.|| Requires consistent supply of large quantities for market to remain viable.
Market returns justify effort only under specific conditions (high carp biomass, proximity to markets, minimal obstructions such as snags).
Currently low viability because of low market price and high costs of fishing.
Not viable for removal of residual carp populations in connected waterways.
Judas-carp technique (where males are radio-tagged and act as 'tracker fish') may enhance effectiveness and efficiency of commercial harvest by targeting spawning or winter aggregations; this would require commitment to a long-term control program.
|Potential to kill discrete populations of carp quickly.||Not size specific.|| Broad-scale application kills virtually all non-target species as well as carp.
Rotenone baits have been trialled but tended to be rejected by carp; the rotenone may also leach out and thus affect non-target species.
| Human resource intensive (planning, application and removal/disposal of large quantities of carp).
| Illegal to use except under and in accordance with Australia Pesticides and Veterinary Medicines Authority (APVMA) permit.
May be feasible to eradicate small, discrete populations under specific circumstances (e.g. new populations) where benefits clearly outweigh harm to native species.
Not suitable for broad-scale use because of impacts on non-target organisms.
Use of baits is not currently feasible without further improvement.
|1. Fishway carp separation cages|
| Potential to remove large quantities of carp and, in some circumstances, eliminate carp from stretches upstream of cages.
Effectiveness depends on the proportion of the carp population that is static vs. migrating. This is unknown for many sites.
|Size specific - generally capture larger carp (>250mm).||Minimal - designed to release native fish and vertebrates.|| Installation cost ranges from $15,000 to $45,000 (or more) per fishway.
Ongoing maintenance is human-resource intensive; requires regular checking and disposal of captured carp.
| Highly feasible where suited to existing fishways, or where new fishways are being designed.
Lack of carp-disposal options may limit feasibility at some sites.
Fish composting technology may be an effective utilisation and disposal method (where feasible and based on resources available from local agencies/groups).
|1. Carp exclusion devices (e.g. mesh screens, 'finger traps') fitted to wetland regulators|
| Carp exclusion devices prevent access of mature carp to wetlands or other spawning grounds.
Potential to substantially reduce carp populations if breeding hotspots are targeted.
|Size specific - generally exclude only larger carp||May affect native fish recruitment by also excluding native species from spawning grounds.||Relatively inexpensive. Requires supporting infrastructure and ongoing maintenance.|| Already installed at many sites in the Murray-Darling Basin.
For maximum effectiveness, requires ecological research to identify recruitment areas for carp and native species.
'Finger traps' may be more effective but are still at prototype stage.
|1. Sex biasing technology|
| In theory could eventually provide total eradication, but technically difficult, and effects would not be seen for up to 100 years due to long generation time of carp.
Effectiveness would depend on many factors, including: heritability; fitness of modified fish; size of carp population at time of release; and number of modified fish released.
|Not size specific.||Not size specific.||Very expensive technology, still under development, total costs unknown.||Unclear. Still many technical hurdles to overcome before ready for laboratory or field trials.
Would initially require stocking of large numbers of fish carrying sex biasing construct.
Would require integrated implementation with other initiatives.
Risk of public non-acceptance of intentional release of modified pests into natural environment. Requires extensive public consultation.
|1. Cyprinid herpesvirus-3 (CyHV-3)|
|Causes mass mortalities of carp - potential to substantially reduce populations (at least until resistance develops).||Not size specific, although juveniles believed to be more susceptible.||Species-specific (McColl, In Prep), but mass carp mortalities post release could have water quality impacts detrimental to native species.||Unknown; still under investigation.||
Strong temperature relationship may impact effectiveness at low or high temperatures. Hybridisation between goldfish and carp could reduce effectiveness.
Risk of resistance from carp dependant industried. Requires extensive public consultation.
Further analysis of the seven identified carp control measures listed in Table 16
1. Community carp fishing competitions.
Recreational fishing events are popular within the Australian community, and such events can enable quantities of carp biomass to be removed from an area, although research suggests that this will not result in a lasting reduction in carp numbers (Gehrke PC, 2010). For example, the mean estimated population reduction by anglers in the Goondiwindi Carp Cull was reported to be 0.5% compared to 13.4% for electrofishing (Norris et al., 2013). Similarly in 2008, anglers in the Goondiwindi Carp Cull removed 40 carp from lagoon habitats in south-eastern Queensland, equivalent to 1.9% of the estimated population, and much lower than the catches provided by other methods (Gehrke PC, 2010). Brown and Walker (2004) demonstrate that unless carp populations can be a reduced by a large percentage, physical removal is unlikely to offer an effective method for carp control. On this basis, Gehrke PC (2010) suggests that low-cost carp angling events provide an effective method for promoting community awareness of issues surrounding carp in the Murray-Darling Basin, but their effectiveness in reducing carp populations and environmental impacts is low (Norris et al., 2013).
2. Commercial harvesting
Graham et al. (2005) summarise predominant commercial fishing methods used for carp, which include electrofishing, hauling, trapping, mesh netting and angling. The limited acceptance of carp for human consumption in Australia limits its market value, with most being sold to produce low-value fishmeal, fish oil, pet food, fertiliser and stock feed. Wilson (1998), cited in Graham et al. (2005) suggested that at the time of writing, fishers needed to catch 5 – 6 tonnes of carp per week (at 80 cents/kg) to make an economic return. This means that the fishery is generally only viable under conditions that allow the removal of large volumes of carp at minimal cost. Another factor limiting the effectiveness of commercial fishing in controlling carp abundance is the increasing cost of production as biomass is reduced.
Whilst electro-fishing is effective for carp removal in areas of high density, it is less effective in deep water, high turbidity or flow, and can be expensive both in terms of capital and labour costs. Whilst non-target species are also stunned during electrofishing, they quickly recover, and mortality levels are generally low under appropriate operating circumstances.
Electrofishing is generally not widely used as a commercial fishing method for carp in Australia, but Graham et al (2005) report that supplies of carp to a processing factory at Sale are regularly supplemented with electro-fished carp from tributaries to the Gippsland Lakes, particularly during drought conditions when carp retreat into the rivers as the lakes become more saline.
A Seine net is a large sock-shaped net with a pair of long hauling lines attached to each side of the open end. The net (including ropes) is ‘shot’ from the boat around a concentration of fish and then hauled back to the boat (or shoreline) by drawing on the lines. The fish will rarely go over or under the lines and are subsequently corralled into the bag (or cod end) of the net.
Seining is one of the most effective methods for catching large quantities of carp (Bajer et al., 2011). Catch records from 2001/02 show that approximately 15 t were caught by drag net from Lake Brewster, after carp were attracted to the hauling area with berley, and up to 1000 t of carp are harvested annually from Lake Wellington, mostly by seine (Graham et al. 2005).
Application of this method is limited to shallow lakes or dams where the substrate is clear of obstructions or where the bottom is relatively smooth, firm, and clear of snags (Graham et al., 2005). Most natural waterways are unsuited to seining as lakes and riverbeds are normally littered with woody debris and other snags (Graham et al., 2005).
Unbaited drum nets were widely used to target native fish prior to discontinuation of commercial fishing in the Murray-Darling Basin in 2003. Larger baited rectangular traps have also been shown to be effective for carp but require easy access to the water. Baited traps are most effective when set downstream in flowing waterways, and when fitted with netting wings to one or both banks to guide carp into the trap. Non-target impacts of trapping can be significant, particularly for air-breathing vertebrates, if not fitted with an escape device or accessible air space.
Mesh-netting was historically the dominant method used for harvesting native fish, in the Murray-Darling. Captured fish can be damaged through scale loss and meshing injuries, and air breathing vertebrates can also become entangled. However Graham et al. (2005) report that setting mesh nets in shallow water and frightening fish towards the net can effectively enable carp to be targeted whilst having minimal impact on non-target species.
The Judas carp technique (wherein males are radio-tagged and act as ‘tracker’ fish) may enhance effectiveness and efficiency of commercial harvest by targeting spawning or winter aggregations which contain populations of sexually mature carp (Gilligan et al., 2010). This method has been trialled in Lake Cargelligo in the lower Lachlan catchment and in Tasmania with some success, however is most useful in areas of low carp abundance (Bajer et al., 2011).
There are no piscicides available that are specific to common carp, and 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, and it is widely used for this purpose. Rotenone interrupts cellular respiration in gill-breathing animals by blocking the transfer of electrons in the mitochondria. Acute exposure to toxic levels reduces cellular uptake of blood oxygen, resulting in increased cellular anaerobic metabolism and associated production of lactic acid causes blood acidosis (Fajt and Grizzle, 1998).
Historically, Australian 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, including that there:
- is a high probability of successfully eradicating the pest fish, with a low chance of immigration or recolonization.
- 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.
Researchers have attempted to develop a carp-specific targeting method using rotenone, through integrating it into floating pellet baits. This method was found to be unsuccessful due to low buoyancy and palatability (Gehrke, 2003). Further development and testing would be required (and a separate APVMA permit approved) before rotenone baits could be utilised to target carp populations. Although it is a potential option to eradicate discrete new populations of carp in some limited circumstances, rotenone is not appropriate for use to control carp on a large scale.
4. Fishway carp separation cages
Carp separation traps that exploit jumping behaviour in carp have been implemented at numerous locations throughout the Murray-Darling Basin. Trials with these devices on the Murray River revealed that these traps were effective in catching carp and passing native fish, with 88.8% of carp caught, 99.9% of native species passed, and catches of up to 5 t per day in some instances. It is clear that their effectiveness can be variable (Table 2), with catch per unit effort across seven installations reported to be 14.7kg per week, or 1.4 carp per day (Pers Comm. Matt Gordos). For this reason the NSW Department of Primary Industries no longer recommends the installation of carp separation cages at remote, un-manned locations.
Table 2. Carp separator trap effectiveness at several sites within the MDB (Gordos, M. unpublished).
5. Exclusion device
Carp exclusion devices can prevent access of mature carp to wetlands or other spawning grounds, having potential to substantially reduce carp populations if breeding hotspots are targeted. However such methods are size specific, generally excluding only larger carp, and may affect native fish recruitment by also excluding native species from spawning grounds.
Exclusion devices are relatively inexpensive and are already installed at many sites in the Murray Darling Basin, however requires supporting infrastructure and ongoing maintenance. For maximum effectiveness exclusion devices requires ecological research to identify recruitment areas for carp and native species. This information will assist in determining appropriate deployment locations. 'Finger traps' may be a more effective technique, though are still at prototype stage.
6. Daughterless carp technology
In theory the species specific daughterless carp technology could eventually provide total eradication of common carp, however effects would not be seen for up to 100 years due to the long generation time of carp. The effectiveness of daughterless carp technology would depend on many factors, including: heritability; fitness of modified fish; size of carp population at time of release; and number of modified fish released. It is very expensive technology that is still under development with the total costs unknown. There are still many technical hurdles to overcome before daughterless carp technology is ready for laboratory or field trials. Daughterless carp would initially require stocking of large numbers of genetically modified fish and would require integrated implementation with other initiatives. There are risks of public non-acceptance of intentional release of genetically modified pests into the natural environment and would therefore requires extensive public consultation.
7. Cyprinid herpesvirus-3 (CyHV-3)
The species-specific cyprinid herpesvirus causes mass mortalities of carp with potential to substantially reduce wild populations, at least until resistance develops. The virus is not size specific, although juveniles are believed to be more susceptible. The strong relationship between temperature and the virus may reduce the effectiveness of the virus at low or high temperatures; furthermore hybridisation between goldfish and carp could reduce the virus effectiveness. There is also the risk of public non-acceptance of the intentional release of a biocontrol agent. As is the case with daughterless carp technology, CyHV-3 requires extensive public consultation. Challenges may also arise as a result of resistance from the ornamental koi carp industry, koi enthusiasts and commercial fishers. Furthermore, mass carp mortalities as a result of the virus release could have water quality impacts detrimental to native species.
BAJER, P., CHIZINSKI, C. & SORENSEN, P. 2011. Using the Judas technique to locate and remove wintertime aggregations of invasive common carp. Fisheries Management and Ecology, 18, 497-505.
BROWN, P. & WALKER, T. I. 2004. CARPSIM: stochastic simulation modelling of wild carp (Cyprinus carpio L.) population dynamics, with applications to pest control. Ecological Modelling, 176, 83-97.
FAJT, J. R. & GRIZZLE, J. M. 1998. Blood Respiratory Changes in Common Carp Exposed to a Lethal Concentration of Rotenone. Transactions of the American Fisheries Society, 127, 512-516.
GEHRKE PC, S. P. S., MATVEEV V, AND CLARKE M 2010. Ecosystem responses to carp population reduction in the Murray-Darling Basin. Canberra, Australia: Murray-Darling Basin Authority.
GEHRKE, P. C. 2003. Preliminary assessment of oral rotenone baits for carp control in New South Wales. Managing invasive freshwater fish in New Zealand. Wellington New Zealand: Department of Conservation.
GRAHAM, K. J., LOWRY, M. B., WALFORD, T. R. & WALES, N. S. 2005. Carp in NSW: Assessment of distribution, fishery and fishing methods, NSW Department of Primary Industries, Cronulla Fisheries Centre.
MCCOLL, K. A., SUNARTO A., SLATER J, BELL K, ASMUS M, FULTON W , HALL K, BROWN P, GILLIGAN D, HOAD J, WILLIAMS N, CRANE M 2016. Cyprinid herpesvirus 3 as a potential biological control agent for carp (1 Cyprinus carpio) in Australia: non-target species testing. Journal of Fish Diseases. Doi:10.1111/jfd.12591
NORRIS, A., CHILCOTT, K. & HUTCHISON, M. 2013. The Role of Fishing Competitions in Pest Fish Management. In: CENTRE, I. A. C. R. (ed.). PestSmart Toolkit Publication. Invasive Animals Cooperative Research Centre, Canberra.
Why a virus?
CSIRO research and overseas lived experience in the 33 countries which have the virus present in their rivers has shown the carp virus has potential to quickly reduce the fish's population, and suppress it for many years. A number of other methods have been tried to control carp in recent decades without widespread success.
CSIRO experiments on Australian carp show that exposure to the carp virus generally results in mortality rates of 70-100%. Carp that survive infection continue to carry the virus, which can reactivate and infect other carp.
The carp virus alone will not completely eradicate carp - some carp will inevitably survive, and over time populations would rebuild. Therefore, continuing investigation of complementary control measures, such as those that aim to alter carp reproduction biology, is important to ensure that we can take advantage of large population declines following a future virus release.
How does the virus work?
The carp virus is highly contagious and specific to carp and is most effectively transmitted through carp-to-carp contact. The virus will also survive in water without a host for approximately three days. If the virus is released in Australia, it is expected to initially kill more than 70 per cent of infected carp. Carp that survive will carry the virus for life and, when stressed, may eventually succumb to disease. They will also continue to pass the virus on to uninfected carp. This is expected to help control carp populations for many years after the initial release.
Water temperature: Overseas, the virus is most effective when water temperatures are 18°C to 28°C. At temperatures above 30°C or below 15°C carp can become infected but not die. When temperatures return to the effective range the virus can be reactivated and fish can develop signs of disease.
Signs of infection: The virus damages the kidneys, skin and gills of carp. Damage to the gills is the primary cause of death. After a carp is infected, the virus multiplies in the fish for seven to 12 days, depending on the water temperature. During this time the fish will develop signs of disease, including darkening of the skin and reddened gills. Infected fish will die as soon as 24 hours after these signs develop.
What will everything eat when carp numbers are significantly reduced?
Some Australian native species including Murray cod, Eastern water rats, cormorants and long-nosed fur seal prey on the pest fish species carp. Consequently, there is a need to understand what might happen if carp numbers are significantly reduced following possible implementation of the National Carp Control Plan.
Though there are only few studies which have examined the importance of carp as a food source in Australian ecosystems, available research suggests that they do not comprise a large part of the diet of most species. This is partly because juvenile carp often live in different habitat types to predators such as adult Murray cod. Also, carp quickly grow to a size that is too large for most predatory species to eat.
A recent Queensland study demonstrated that reducing carp numbers can cause subsequent explosions in biomass levels of other native prey items including zooplankton and small-bodied native fish. This work indicates that reducing carp numbers may increase food available for predatory species, not decrease it. This, in turn, may result in healthier populations of species which eat these prey items, including popular native angling species.
Carp make up a significant proportion of the biomass of fish in many Australian rivers (Harris et al., 1997, SRA Unpublished Data, Lintermans, 2007), and potentially significant reductions in carp abundance and biomass levels if the National Carp Control Plan is implemented have prompted some to ask the question "what will species that currently prey on carp eat?". The insinuation is that without carp, these species might not have sufficient food available and starve. But what does the available research say?
Whilst there is not a significant body of research available on the contribution that carp make to the diet of native Australian species, what information does exist suggests that they generally do not form a significant dietary component. In fact, Koehn et al. (2004) suggests the rapid expansion of Carp within Australia may have been assisted by lack of predatory pressure. This is largely because the rapid growth rate of carp enables them to quickly reach a size that precludes their consumption by most predators (Koehn, 2004)
Nevertheless, some species of native fish, waterbirds, and charismatic fauna do prey on carp to some extent. In particular, Australia’s largest predatory freshwater fish, the Murray cod, has been shown to predate upon Carp. A dietary study by (Ebner, 2006) found 35% of Murray cod sampled (all cod >500mm total length) contained Carp. Similarly, Baumgartner (2005) found Cyprinidae spp. (Carp and Goldfish) constitute up to 25% of Murray cod prey occurrence in cod sampled from the Murrumbidgee River. Examination of Murray cod stomachs from Rivers of the Southern Murray Darling Basin found <7% of Murray cod stomachs sampled contained Carp (Doyle et al., 2012). Carp up to 410 mm total length have been recorded in stomach of large Murray cod. Doyle et al. (2012) attributes the low occurrence of Carp in the diet of Murray cod to the variation in the habitat utilisation between early life stages of Carp, that primarily inhabit shallow floodplain-type habitats, and Murray cod that prefer main channel habitats.
Golden perch and Australian bass also consume small Carp, though infrequently, and each species would be incapable of consuming adult Carp due to their gape size limitations (Ebner, 2006, Doyle et al., 2012). The critically endangered Trout cod has also been shown to predate Carp, however Carp made up <1% of their prey (Baumgartner, 2005).
Terrestrial vertebrates that have been shown to predate upon Carp and other Cyprinids include feral cats (Jones and Coman, 1981), the Eastern water rat (Woollard et al., 1978) and cormorants (Miller, 1979), however in each instance Common carp constitute a small proportion of the diet. Hughes et al. (1983) suggests Carp within billabongs may provide a reliable food source for Australian Pelicans. Koehn et al. (2004) suggests with few effective predators, sequestered detrital carbon, rather than passing up through subsequent trophic levels of macroinvertebrates and smaller fish (Bunn and Davies, 1999), may become ‘locked’ away from the trophic chain for the lifespan of a Carp (up to 35 years) (Bănărescu and Coad, 1991).
So some native Australian species do prey on carp. However it is important to note that native species which currently prey on this pest species have not always relied upon them for food. In years gone by when carp were absent or in much lower numbers in Australian waterways native prey items including zooplankton, invertebrates, small fish, biofilms were more abundant. Ebner et al. (2006) suggests major shifts in prey availability have influenced the ecology of Murray cod and the structure and function of the food web in the rivers of the Murray-Darling Basin. The decreased diversity of native prey species provides opportunity for Murray cod to exert a larger per capita effect on Carp (Pimm, 1982, Ebner, 2006). However in microcosm trials both Murray cod and Golden perch consumed Carp relatively infrequently compared to native prey species (Doyle et al., 2012). There are very few published studies which provide an insight into potential alterations to food web dynamics that may result from significant reductions in Carp biomass within Australian aquatic ecosystems. Prey switching of Carp’s dominant predator, the Murray cod, may exert increased pressure upon other native species and decapods, though the ecosystem will eventually reach a predator/prey equilibrium (McColl et al., 2014). Furthermore, the reduction of Carp may allow the proliferation of native prey items of predatory species including Murray cod returning the ecosystem closer to its former state before the proliferation of Carp in the 1960s. Indeed the findings of Gehrke et al. (2010) showed that after a significant reduction in Carp biomass within several experimental wetlands the biomass of small-bodied native fish increased by up to three times the biomass of Carp removed. In the Queensland study, carp biomass was reduced within two of four lagoons, removing 43% and 33% of carp biomass, 34 and 26 kg per hectare respectively. The other two lagoons remained untouched, for comparison. In the two lagoons where carp were controlled, native fish biomass increased by 90 kg per hectare, roughly three times the biomass of carp removed. Added to this, large zooplankton populations (e.g. Boekella and Daphnia) increased 10 times and populations of aquatic insects and crustaceans also boomed. In the two lagoons where nothing was done, populations of native fish, zooplankton, aquatic insects or crustaceans did not change. What this work suggests is that native fish are much more efficient in their use of food resources than carp (producing three times the biomass) and that removing carp will likely increase the food available for predatory fish and waterbirds, not decrease it. This should ultimately lead to bigger, healthier populations of popular native angling species and waterbirds.
Banarescu, P & Coad B (1991). Cyprinids of Eurasia. Cyprinid Fishes. Springer.
Baumgartner LJ (2005). Effects of weirs on fish movements in the Murray-Darling Basin, University of Canberra.
Bunn S & Davies P (1999). Aquatic food webs in turbid, arid-zone rivers: preliminary data from Cooper Creek, western Queensland. A Freeflowing River: the Ecology of the Paroo River, 67-76.
Doyle K, Mcphee D & Wallter G (2012). Can native predatory fishes control invasive carp in south-eastern Australia. In: G., H. K. (ed.) Forum Abstracts: Cap management in Australia - State of knowledge. Canberra: Invasive Animals Cooperative Research Centre.
Ebner B (2006). Murray cod an apex predator in the Murray River, Australia. Ecology of Freshwater Fish, 15, 510-520.
Gehrke PC, St Pierre S, Matveev V, and Clarke M (2010).Ecosystem responses to carp population reduction in the Murray-Darling Basin. Project MD923 Final Report to the Murray-Darling Basin Authority
Harris JH, Gehrke PC (1997). Fish and rivers in stress : the NSW rivers survey, Cronulla, NSW, NSW Fisheries Office of Conservation and the Cooperative Research Centre for Freshwater Ecology, in association with NSW Resource and Conservation Assessment Council.
Jones E & Coman B (1981). Ecology of the Feral Cat, Felis catus (L. ), in South-Eastern Australia I. Diet. Wildlife Research, 8, 537-547.
Koehn JD (2004). Carp (Cyprinus carpio) as a powerful invader in Australian waterways. Freshwater Biology, 49, 882-94.
Lintermans M (2007). Fishes of the Murray-Darling Basin : an introductory guide, Canberra, Murray-Darling Basin Commission.
McColl, K, Cooke, B & Sunarto, A (2014). Viral biocontrol of invasive vertebrates: Lessons from the past applied to cyprinid herpesvirus-3 and carp (Cyprinus carpio) control in Australia. Biological Control.
Miller B (1979). Ecology of the Little Black Cormorant, Phalacrocorax sulcirostris, and Little Pied Cormorant, P. melanoleucos, in Inland New South Wales I. Food and Feeding Habits. Wildlife Research, 6, 79-95.
Pimm SL (1982) Food webs, Springer.
Woollard, P, Vestjens, W & Maclean L (1978). The ecology of the eastern water rat Hydromys chrysogaster at Griffith, NSW: food and feeding habits. Wildlife Research, 5, 59-
Will the virus affect other species?
Over the past eight years, CSIRO has undertaken experiments to test whether other species can contract the virus. In these experiments, non-target species were exposed to the virus by direct injection and / or in a water bath. All non-target species were exposed to 100-1000 times the amount of virus required to cause disease in carp. Non-target species tested included 13 native bony fish species, one introduced fish species (rainbow trout), lampreys, freshwater yabbies, two frog species, two reptile species (a lizard and a freshwater turtle), chickens, and mice. None of these species were infected or affected by the virus.
In addition the carp virus has been present in Israel, Europe, Asia and the UK for several decades, and is now found in 33 countries. It has not infected any other species in these countries where it is circulating in river systems.
Tested non-target species were selected to represent the range of animals inhabiting the geographical areas in which the carp virus. Importantly, tested fish species represent all orders of freshwater and estuarine fish that could potentially be exposed to the virus. To clarify this, ‘order’ is a scientific term describing a fairly broad level of relatedness For example, human beings are classified into the order Primates, along with apes, monkeys, lemurs, lorises and tarsiers. Carp are classified into the order Cypriniformes, and there are no native Australian fish of this order. The Australian fishes most closely related to carp are the various catfish species in the order Siluriformes. Two catfish species (the eel-tail catfish, Tandanus tandanus, and the salmon catfish, Neoarius graeffei) were therefore tested, and found to be non-susceptible.
Further susceptibility testing covering representatives of the fish orders Synbranchiformes (swamp eels), Osteoglossiformes (the ‘bony tongues’, including the valued sporting fish saratoga), and Beloniformes (needlefishes, including garfish). Representatives of these orders are present in small areas along the margins of the proposed virus release areas. Similarly, two freshwater fish species found only in the southern corner of Western Australia will also be tested, reflecting their conservation significance in that state.
A closer look at the carp virus and comparison with other viruses provides further confidence that the risk of mutation, that may allow it to infect other species, is low. Firstly, the carp virus stores its genetic information as DNA. DNA is a stable molecule, meaning that mutations are rare, and usually repaired by in-built mechanisms. Therefore, mutations big enough to enable infection of a new host are rare in DNA viruses. Secondly, the carp virus has a large, complex genome (the set of genetic instructions). Such viruses are even less likely still to mutate than those with smaller, simpler genomes. Finally, neither of the two viruses introduced to Australia for rabbit control (the myxoma virus, which causes myxomatosis, and the calicivirus) have infected new species, despite having been in Australia for 66 and 21 years respectively. This augurs well for the carp virus which, like the myxoma virus, is a large, complex DNA virus
Informing possible release
When and where might the virus be released?
The carp virus will not be released before the end of 2018.
During 2017, the NCCP will embark on a large program of research and consultation. The two key components of this program will be: a series of scientific projects conducted by independent researchers at Australian universities; and, a series of community engagement forums (i.e., town hall events) across areas affected by carp.
At the end of 2018, the NCCP will make a formal recommendation on the best way to control carp impacts in Australia. This recommendation will be a document called 'The National Carp Control Plan'. It will be based on the results of the research projects funded by the NCCP and the input from communities during the consultation process.
If it is recommended that the carp virus form part of a suite of carp-control measures, and formal approval is granted, the carp virus may then be released. In that case, the initial release sites and specific pattern of release would follow the results of relevant research funded under Research Theme 3: Informing possible implementation.
How do we know that carp won’t just develop immunity and rebuild?
Based on lessons learnt from past use of viral biocontrol agents for invasive vertebrates, and on mathematical modeling, the carp virus will likely have the greatest impact in the first few years after release. After that, effectiveness may be diminished - but not lost - as virus and host adapt to each other. Earlier modeling suggested that carp populations may recover to 30 - 40% of present levels within a decade of virus release.
The release would therefore need to be complemented by secondary control measures to ensure enduring results. Genetic strategies are being carefully considered under the NCCP to work synergistically with the carp virus. These strategies would skew the sex ratio of the remaining carp population after release of the virus. As abundance of one sex diminished, so too would the whole population. New generations of more virulent, but still natural, strains of the carp virus may also be investigated.
Of course, any strategy to manage carp impacts will be most effective if supported by efforts to promote ecosystem recovery through habitat restoration, native fish restocking, restoring native fish migration pathways, and addressing water quality concerns.
How will a clean-up be planned?
Like any worthwhile endeavour, controlling carp and their impacts in Australia presents some challenges. How to kill the largest number of carp possible, whilst maintaining water quality for use by people, stock, and native species is one such challenge. The team responsible for developing the NCCP recognise the importance of this task, and are employing a multi-faceted approach to develop effective clean-up strategies.
The first step in planning the clean-up is gaining an in-depth understanding of the issue. Several research projects will be commissioned under the NCCP to develop this understanding, including:
- Reviewing fish-kill clean-up methodologies world-wide.
- Conducting a scientific risk assessment for the entire process of carp biocontrol using the virus, including the clean-up phase
- Improving estimates of carp abundance and distribution through a multi-method biomass study
- Understanding potential impacts on water quality, including the risk of blue-green algae blooms and strategies for their avoidance
- Working with river managers to develop water release strategies that assist possible release and clean-up
Results from this research will be provided to a Critical Issue Advisory Group comprising experts from areas including logistics, commercial-scale harvesting, and large-scale human and animal-health responses. These experts will assist in developing detailed strategies for rapidly responding to carp mortality events, including identifying equipment and personnel needs.
Like any worthwhile endeavour, carp biocontrol presents some challenges. Maintaining water quality for use by people, stock, and native species is one such challenge. The NCCP recognises the importance of this task, and our approach to developing a practical, effective, and flexible clean-up strategies is outlined below.
Learning from the past
Fish kills in freshwater ecosystems occur world-wide, with many causes (e.g. Monette et al., 2006; Hoyer et al., 2009; Polidoro and Morra, 2016). Research on fish kills has tended to focus on identifying causes (e.g. Thronson and Quigg, 2008; Moustaka-Gouni et al., 2017) and ecological consequences (e.g. Starling et al., 2002; Sayer et al., 2016) of fish deaths. Nonetheless, published and unpublished case studies consider clean-up action to protect water quality following fish kills (La and Cooke, 2011). Researchers will be engaged under the NCCP to systematically survey fish-kill clean-up methods worldwide, providing insights into what works, what doesn’t, and likely challenges and ensure that past experience informs proposed approaches.
Intuitively, we can all understand that major carp mortality events entail some risks to water quality. However, understanding the exact nature and magnitude of these risk may require a specialised approach. Research commissioned under the NCCP will include a scientific risk assessment quantifying risks associated with the proposed carp biocontrol program, including the clean-up. Hayes et al. (2007) provide an overview of the methods used in scientific risk assessment.
Biomass estimates: how many carp are there, and where are they?
Successful clean-up requires understanding carp abundance and distribution at several spatial scales, from continental through to particular habitat types. The NCCP will commission a multi-method biomass study, providing the most accurate picture ever developed of carp distribution and abundance in Australia. Methods used will include:
- capture-recapture studies
- acoustic and radio-tagging
- collation and statistical interrogation of all pre-existing carp abundance datasets
- physical measurement of carp biomass when lakes and wetlands are drained as part of ecological remediation works
- environmental DNA (e-DNA, a suite of methods that enable detection of a species and estimation of its abundance based on DNA shed into the water)
This multi-method approach will enable cross-checking and triangulation, enhancing the accuracy and rigour of resulting biomass estimates.
An ecosystem perspective on clean-up requirements
Planning the clean-up requires knowledge of the virus’s behavior in wild carp populations, including seasonal patterns of viral latency and re-emergence (Eide et al., 2011; Xu et al., 2013). To enable this understanding, an epidemiological model of the carp virus’s behaviour across all 29 river catchments of the Murray-Darling Basin will be developed. The model will identify optimal seasons, locations, and release strategies for the virus, and in so doing will also pinpoint times and places where carp mortality events are likely, allowing for response planning.
Hydrological models, developed and tested over many years, will also examine the effects of varying levels of carp biomass on dissolved oxygen levels in a range of aquatic habitat types. Mosley et al. (2012) provide an example of a similar modelling process. These models will be complemented by detailed experimental studies in real ecosystems (see Boros et al., (2014) for an example of this kind of experiment). Additional research may also explore nutrient interception pathways in freshwater ecosystems, identifying options for avoiding blue-green algae blooms. Together, these research projects will enable response planning that safeguards water quality. For further reading in these areas, Brookes et al. (2005) discuss nutrient interception pathways, while Carmichael and Boyer (2016) review health impacts of blue-green algae.
How to eat an elephant: compartmentalising clean-up
Successful control of a pest species over a large geographic range can be logistically challenging, and this is certainly true of carp control in Australia. Common carp are now present in every Australian state and territory except the Northern Territory, making up more than 80% of fish biomass in some river systems, and up to 93% in some areas (Harris and Gehrke, 1997). Logistically, it would impractical to seek to employ a simultaneous pest control strategy for common carp across the species’ distribution; a phased approach is required.
The need to phase any release and clean up strategy also presents some clear challenges. In particular, how to compartmentalise such a large, geographically, climatically and hydrologically diverse landscape. The world’s largest rat extermination program in South Georgia offers some useful insights here. The aim of this program was to eradicate brown rat (Rattus norvegicus) from a 170km long, 10-40km wide sub-Antarctic island 1400km east of the Falkland Islands through introduction of 183 tonnes of poison over 224 square miles (580km2). Through robust metapopulation research of the target species (Robertson and Gemmell, 2004) it was learned that the island’s unique climate and topographical attributes resulted in several isolated rat populations separated by large glaciers. This knowledge enabled development of a staged program for implementation, in which the island was divided into a number of treatment zones, which were treated individually (Figure 2). Using this staged, methodical strategy the project team were able to progressively move across the island, treating rats in each zone, testing effectiveness in each zones before moving on until eventually the entire island was treated successfully. This is a noteworthy accomplishment clearly considered impossible by some in 1980 (Poncet et al. 1980), who reported brown rats to be “an established part of the wildlife of South Georgia”, and also reported that “no management procedures would be possible to reduce or control the existing rat population even if this were thought desirable”. The successful outcome delivered in spite of earlier pessimism highlights the value of adopting an evidence-based strategy, coupled with a ‘can do attitude’ when tackling significant pest control challenges.
Figure 2. Glaciers enable South Georgia to be divided into discrete zones for the purpose of rodent control (Figure reproduced from Poncet and Poncet 2009).
While there is no evidence of genetic structuring of carp in Australia, the discontinuous nature of Australia’s Murray-Darling Basin resulting from extensive installation of flow regulating infrastructure may offer a means via which the release of CyHV-3, and subsequent clean-up of carp biomass may be logically compartmentalised and phased (see Figure 3). Under the National Carp Control Plan opportunities are being explored to utilise these assets to separate waters into discrete treatment zones, enabling carp to be treated within each zone in a staged manner.
Figure 3. Dams and weirs present throughout the Murray-Darling Basin (in green). Opportunities will be explored to use these compartmentalise reaches into zones, enabling progressive treatment for the control of carp (source: Murray-Darling Basin Authority)
Many Australian rivers are highly regulated, with locks, weirs, and dams controlling water movement (Growns, 2008). The NCCP is working with river managers to identify ways that flows can be manipulated to assist release and clean-up and maintain water quality.
Boots on the ground: the logistics
Results from these research projects will show us what needs to be done. Expert help will then be enlisted to work out how we do it. The NCCP will form a Critical Issue Advisory Group composed of experts from areas including military and transport logistics, commercial carp harvesting, and large-scale human- and animal-health responses. These experts will develop detailed strategies for rapidly responding to carp mortality events, including identifying equipment and personnel needs.
Boros, G., Takács, P. & Vanni, M.J. (2015). The fate of phosphorus in decomposing fish carcasses: a mesocosm experiment. Freshwater Biology 60, 479 – 489.
Brookes, J.D., Aldridge, K., Wallace, T., Linden, T. & Ganf, G.G. (2005). Multiple interception pathways for resource utilization and increased ecosystem resilience. Hydrobiologia 552, 135 – 146.
Carmichael, W.W. & Boyer, G.L. (2016). Health impacts from cyanobacteria harmful algae blooms: implications for the North American Great Lakes. Harmful Algae 54, 194 – 212.
Eide, K.E., Miller-Morgan, T., Heidel, J.R., Kent, M.L., Bildfell, R.J., LaPatra, S., Watson, G. and Jin, L. (2011). Investigation of koi herpesvirus latency in koi. Journal of Virology 85, 4954 – 4962.
Growns, I. (2008). The influence of changes to river hydrology on freshwater fish in regulated rivers of the Murray-Darling basin. Hydrobiologia 596, 203 – 211.
Harris, J.H. & Gehrke, P.C. eds. (1997). Fish and rivers in stress: the NSW rivers survey. NSW Fisheries Office of Conservation and the Cooperative Research Centre for Freshwater Ecology, in association with the NSW Resource and Conservation Assessment Council.
Hayes, K.R., Kapuscinkski, A.R., Dana, G., Li, S. & Devlin, R.H. (2007). Introduction to environmental risk assessment for transgenic fish. In Environmental risk assessment of genetically modified organisms, Vol 3. Methodologies for transgenic fish (Kapuscinski, A.R., Hayes, K.R., Li, S., Dana, G., Hallerman, E.M. & Schei, P.J., eds), pp. 1 – 28. CAB eBooks, http://www.cabi.org/cabebooks/ebook/20073267247
Hoyer, M.V., Watson, D.L., Willis, D.J. & Canfield Jr., D.E. (2009). Fish kills in Florida’s canals, creeks/rivers, and ponds/lakes. Journal of Aquatic Plant Management 47, 53 – 56.
La, V.T. & Cooke, S.J. (2011). Advancing the science and practice of fish kill investigations. Reviews in Fisheries Science 19, 21 – 33.
Monette, S., Dallaire, A.D., Mingelbier, M., Groman, D., Uhland, C., Richard, J-P., Paillard, G., Johannson, L.M., Chivers, D.P., Ferguson, H.W., Leighton, F.A. & Simko, E. (2006). Massive mortality of common carp (Cyprinus carpio carpio) in the St. Lawrence River in 2001: diagnostic investigation and experimental induction of lymphocytic encephalitis. Veterinary Pathology 43, 302 – 310.
Mosley, L.M., Zammit, B., Leyden, E., Heneker, T.M., Hispey, M.R., Skinner, D. & Aldridge, K.T. (2012). The impact of extreme low flows on the water quality of the lower Murray River and Lakes (South Australia). Water Resource Management 26, 3923 – 3946.
Moustaka-Gouni, M., Hiskia, A., Genitsaris, S., Katsiapi, M., Manolidi, K., Zervou, S-K., Christophoridis, C., Triantis, T.M., Kaloudis, T. & Orfanidis, S. (2017). First report of Aphanizomenon favaloroi occurrence in Europe associated with saxitoxins and a massive fish kill in Lake Vistonis, Greece. Marine and Freshwater Research 68, 793 – 800.
Polidoro, B.A. & Morra, M.J. (2016). An ecological risk assessment of pesticides and fish kills in the Sizaola watershed, Costa Rica. Environmental Science and Pollution Research 23, 5983 – 5991.
Poncet, S., Poncet, L., Poncet, D., Christie, D., Dockrill, C. and Brown, D., (2011). Introduced mammal eradications in the Falkland Islands and South Georgia. Island invasives: eradication and management. IUCN, Gland, Switzerland, pp.332-336
Robertson, B.C. and Gemmell, N.J., (2004). Defining eradication units to control invasive pests. Journal of Applied Ecology, 41(6), pp.1042-1048.
Sayer,, C.D., Davidson, T.D., Rawcliffe, R., Landgon, P.G., Leavitt, P.R., Cockerton, G., Rose, N.L. & Croft, T. (2016). Consequences of fish kills for long-term trophic structure in shallow lakes: implications for theory and restoration. Ecosystems 19, 1289 – 1309.
Starling, F., Lazzaro, X., Cavalcanti, C. & Moreira, R. (2002). Contribution of omnivorous tilapia to eutrophication of a shallow tropical reservoir: evidence from a fish kill. Freshwater Biology 47, 2443 – 2452.
Thronson, A. & Quigg, A. (2008). Fifty-five years of fish kills in coastal Texas. Estuaries and Coasts 31, 802 – 813.
Xu, J-R., Bently, J., Beck, L., Reed, A., Miller-Morgan, T., Heidel, J.R., Kent, M.L., Rockey, D.D. & Jin, L. (2013). Analysis of koi herpesvirus latency in wild common carp and ornamental koi in Oregon, USA. Journal of Virological Methods 187, 372 – 379.
Will the virus affect humans?
Three primary lines of evidence enable us to be very confident that the carp virus won’t affect humans.
First, a report to the European Commission by the Scientific Committee on Animal Health and Welfare found that there is no evidence of ANY fish virus ever being transmitted to humans.
Second, researchers have attempted to culture the carp virus on human cell lines, and cell lines of other primates (i.e. apes and monkeys) without success. In other words, even deliberate and concentrated attempts to infect human and other primate cells with the carp virus have been unsuccessful.
Third, the virus’s history in carp aquaculture globally provides a practical demonstration of the carp virus’s inability to infect humans. People in thirty-three countries where carp virus is present have been repeatedly exposed to the carp virus without a single documented case of infection by the virus. This exposure has included clean-up from virus outbreaks, when workers have close, repeated contact with carp that are shedding large quantities of the virus. In addition infected fish are regularly eaten and the absence of infections under these conditions provides confidence that the virus is not transmissible to humans.
There are multiple lines of evidence demonstrating that CyHV-3 will not infect humans:
- The virus has been described since the 1990’s and is now present in over thirty-three countries. Fishers, aquaculturists and Koi enthusiasts come into contact with the virus on a regular basis through interaction with water and/or fish carrying virus particles, and no adverse effects have been documented.
- A significant though unquantified proportion of carp sold internationally for human consumption are vaccinated with a weakened strain of the virus, and no human health concerns have been raised in relation to consumption. Israel alone produces 5 – 6,000 tonnes of carp per annum for human consumption, of which the majority is vaccinated (Pers Comm. Arnon Dishon.)
- Carp aquaculturists in some countries harvest farmed carp immediately upon observing clinical signs of CyHV-3 and sell infected fish at a reduced price (Pers. Comm. Ayi Santika). Despite this no human health concerns have been raised in relation to human consumption.
- There are no documented instances of closely related CyHV-1 (carp pox virus), or CyHV-2 (goldfish hematopoietic necrosis virus) causing issues for humans.
- McColl et al. (2016) have tested mice as a model mammal species and confirmed that the virus did not replicate within inoculated mice.
- Dishon (2007) attempted to infect cell cultures of homoeothermic, mostly mammalian origin both at 37°C and 22°C which did not result in either cytopathic effect or presence of virus by PCR. Cells included embryonic chick cells (CEF), XC (a rat cell line), HeLa (human cell line) and CV-1 (monkey origin cell line). Importantly, there has been no evidence of any fish virus causing disease in humans (European-Commission, 2000).
- All fishers, aquaculturists, researchers, fisheries managers and community groups surveyed from Indonesia, the United States, United Kingdom, Israel and Japan during a recent international study tour confirmed that they have never experienced any health issues, including respiratory, skin, eye or oral irritation/sensitisation as a result of contact with the virus in either its wild or attenuated form.
DISHON, A. 2007. Cyprinid Herpesvirus Type 3, Modified Live Virus Product code 1443.20 VS Memorandum 800.109 MS & MCS testing report submission.
EUROPEAN-COMMISSION. 2000. Health and Consumer Protection Directorate-General, Scientific Committee on Animal Health and Animal Welfare, 2000, Assessment of zoonotic risk from Infectious Salmon Anaemia virus.
MCCOLL, K. A., SUNARTO A., SLATER J, BELL K, ASMUS M, FULTON W , HALL K, BROWN P, GILLIGAN D, HOAD J, WILLIAMS N, CRANE M 2016. Cyprinid herpesvirus 3 as a potential biological control agent for carp (1 Cyprinus carpio) in Australia: non-target species testing. Journal of Fish Diseases. Doi:10.1111/jfd.12591
How can the community get involved?
During the two years of the NCCP’s development, the NCCP project team will speak to stakeholders and visit regional centres to provide updates on the progress of the plan and gather community feedback.
The project team wants to understand your local waterways, what's important about them and how you use them, and your concerns and questions so that they can be addressed in the plan.
The NCCP team has been meeting regularly with communities members and interested groups across the carp distribution areas and we will be conducting an initial round of regional workshops and public meetings across the seven participating states and territories. The regional workshops/public meetings will be held in appropriate locations within 29 identified regional natural resource management areas likely to have an interest in this project.
The following regional NRM areas have been identified as having carp within their boundaries and will be a key focus of the NCCP team.
- Queensland Murray Darling Committee Inc.
- Condamine Alliance
- SEQ Catchments
New South Wales
- Central Tablelands Local Land Service
- Central West Local Land Service
- Greater Sydney Local Land Service
- Hunter Local Land Service
- Murray Local Land Service
- North Coast Local Land Service
- North West Local Land Service
- Northern Tablelands Local Land Service
- Riverina Local Land Service
- South East Local Land Service
- Western Local Land Service
Australian Capital Territory
- ACT NRM
- Corangamite Catchment Management Authority
- Ease Gippsland Catchment Management Authority
- Glenelg Hopkins Catchment Management Authority
- Goulburn Broken Catchment Management Authority
- Mallee Catchment Management Authority
- North Central Catchment Management Authority
- North East Catchment Management Authority
- Port Phillip and Westernport Catchment Management Authority
- West Gippsland Catchment Management Authority
- Wimmera Catchment Management Authority
- South East Natural Resources Management Board
- South Australian Murray Darling Basin Natural Resources Management Board
- Swan - Perth Region NRM Inc.
- NRM South
These public information sessions will be held in the evening and give community members the opportunity to hear first-hand from the project team about the background, context and desired outcomes of the NCCP as well as the proposed approach towards its development. It is important these public information sessions position the impact of carp as a ‘whole of community’ issue and, as such, encourage all members of the community to opt in to the discussion. Importantly we will want to hear directly from community members about what is important to them.
How can I keep up to date on the latest info?
Register your details at the bottom of our homepage to keep up to date on when we will be in your region.
For more information, or if you would like someone to speak to your community group, contact the National Carp Control Plan team via the contact us page or call 1800 CARPPLAN.