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Pacific Oyster Mortality Syndrome (POMS)

Mass mortality in cultivated Pacific Oysters

Pacific Oyster Mortality Syndrome (POMS) is a disease of Pacific Oysters (Crassostrea gigas; also known by Magallana gigas).

What is POMS?

POMS is caused by a virus known as Ostreid herpesvirus -1 microvariant (OsHV-1 µvar). This virus affects Pacific Oysters and does not affect the Sydney Rock Oyster (Saccostrea glomerata) or the Flat Oyster (Ostrea angasi). There are no human health or food safety concerns with POMS, it cannot be transmitted to humans. Consumers can be confident of the quality of oysters in the marketplace.

How does POMS affect oysters?

Pacific Oysters affected by POMS experience rapid and mass mortality. Mortality of up to 100% can be experienced in cultivated oysters within days of infection. The highest mortalities (between 60%-100%) occur in juvenile oysters (3-6 months in age), however all life stages have been recorded as susceptible.

wild pacific oyster
A wild Pacific Oyster (Crassostrea gigas)

Where does POMS occur?

The first reported POMS mortality outbreak was in France in 2008. Since then, POMS has been detected in the United Kingdom, Ireland, the Netherlands, Spain, Italy, Asia, New Zealand and Australia.

POMS was first confirmed in Australia in NSW in November 2010. In January 2016, oyster mortalities confirmed to be caused by POMS occurred in Tasmania. In February 2018, POMS was confirmed in the Port River of South Australia.

In NSW, POMS has been confirmed in three Pacific Oyster producing estuary systems, Botany Bay/Georges River, Hawkesbury River and Brisbane Water. POMS has also been confirmed in wild Pacific Oysters in Sydney Harbour/Paramatta River, where oyster farming does not occur. It is not known how POMS first arrived in NSW.


OsHV-1 µvar first detected

Botany Bay/Georges River

November 2010

Sydney Harbour/Paramatta River

January 2011

Hawkesbury River (including Patonga Creek)

January 2013

Brisbane Water

February 2013

Immediate reporting of these mortalities resulted in rapid action by NSW DPI to investigate the cause and implement controls on the movement of oysters and oyster cultivation equipment from these areas to help prevent further spread of the disease.

POMS status of NSW Estuaries

What drives disease outbreaks?

POMS is a seasonal disease where clinical infection and mortality is most prevalent during the summer months. Once POMS is introduced to an estuary system, impacts generally persist on an annual basis. In NSW, mortality occurs once water temperatures reach and sustain a minimum 21°C, although in Europe, a lower threshold temperature of 16°C has been reported. Studies in Europe found that POMS was detectable in oysters after mortalities ceased, which indicates that surviving oysters can act as carriers of the virus. At this stage, there is still a lot to be learned about the lifecycle of this virus.

Reporting of suspected POMS mortalities

Any unexplained or significant mortality of wild or cultivated oysters should be reported to NSW DPI. POMS is a notifiable disease and if suspected, must be reported to NSW DPI. Oyster growers are required to report unexplained mortality by aquaculture permit conditions. Collect as much information as possible, including any photographs of the mortality, an estimate of how much mortality is occurring, when the mortality was first seen, the waterway, nearest town and any other identifying features.

To make a report, complete one of the following:

See, report and protect

NSW DPI can investigate the mortality event. If required, NSW DPI can coordinate the submission of samples to the State Veterinary Diagnostic Laboratory at NSW DPI Elizabeth Macarthur Agricultural Institute to exclude or confirm disease.

What is NSW DPI doing?

Management is in place in NSW to minimise the risk of further spread of POMS.

POMS Biosecurity Zone

NSW DPI has established a POMS Biosecurity Zone under the NSW Biosecurity Regulation 2019. In this zone, POMS affected areas are described and restrictions apply on the movement of oysters and oyster cultivation equipment. Oysters and equipment may only be moved between affected areas. The movement of oysters from affected areas to any other unaffected NSW waterway is not permitted. Oyster cultivation equipment may only be moved to other unaffected POMS waterways if it has been treated in accordance with strict biosecurity measures.

Moving equipment out of POMS affected areas

Strict biosecurity measures are described in the Biosecurity Order (Permitted Activities) 2019. These must be followed to allow for oyster cultivation and research equipment that has been used in POMS affected areas to be cleaned and decontaminated before it can be safely used in other unaffected waterways.

How does the QX biosecurity zone interact with the Pacific oyster mortality syndrome (POMS) biosecurity zone?

Oyster and oyster cultivation equipment movements are permitted in accordance with the rules of both the QX and the POMS biosecurity zone - both biosecurity zones apply and must be read together.

The POMS biosecurity zone has some complex rules that still restrict inter-estuarine movements of oysters even though those movements may be permitted under the QX biosecurity zone. If a movement would be permitted between estuaries under the QX biosecurity zone but not the POMS biosecurity zone (or vice-versa), the movement is prohibited.

Control Order restrictions on importing oysters from Tasmania

The Biosecurity (Pacific Oyster Mortality Syndrome) Control Order 2021 is in force. This control order provides restrictions on the importation to NSW of oysters and oyster cultivation equipment originating from Tasmania, to reduce the risk of spread of POMS from infected areas of Tasmania into unaffected areas of NSW.

Responding to new outbreaks

A procedure has been developed that outlines the management actions and legislative provisions that may be used in response to suspected or confirmed outbreaks of POMS in NSW waterways where POMS has not previously been known to occur.

Increasing access to disease resistant stock

NSW DPI has been working with industry to develop protocols to support approved NSW oyster growers to access specially bred disease resistant hatchery produced Pacific Oyster spat (juvenile oysters) in Tasmania.

POMS disease resistant Pacific Oyster broodstock are held in Tasmania. Following the outbreak of POMS in Tasmania in February 2016, the initial NSW Control Order restricted access to products produced using these broodstock, with the exception of movement into POMS affected estuaries under a specific protocol.

Since that time, NSW DPI has worked with the oyster industry and the Tasmanian Government to support access to Tasmanian oyster spat through implementation of strict biosecurity protocols so that they could be safely imported into and cultivated in NSW POMS unaffected estuaries.

In 2018, NSW DPI worked with Pacific Oyster growers in the POMS unaffected estuaries of the Clyde River and Shoalhaven/Crookhaven rivers to address a shortfall of available spat (juvenile oysters) for cultivation, due to the Control Order restrictions. Following an independently led comprehensive risk analysis relating to the risks and risk mitigation options available, NSW DPI was able to develop a protocol to provide access to stock from Tasmania for these estuaries and safeguard the NSW industry against introduction of POMS into unaffected areas.

A precautionary three-year temporary outward movement restriction was enforced on these NSW receiving estuaries while active surveillance was implemented to confirm the protocol was working. The surveillance was completed in 2020 and 2021, involving laboratory analysis of 640 oyster samples. The surveillance program was completed in March 2021, which found no evidence of OsHV-1 µvar in these estuaries.

On 27 August 2021, an updated Control Order was published in the NSW Government Gazette to revoke the temporary movement restrictions on the Clyde and Shoalhaven/Crookhaven rivers, returning these estuaries to normal business.

What you can do to help

NSW DPI encourages anybody that observes suspected aquatic disease events to report them so they can be investigated. Fish Care Volunteers, recreational fishers and community groups can assist by reporting any observed mortality outbreaks in wild Pacific Oyster populations.

Cleaning boats, trailers, kayaks fishing gear and other equipment before moving to another waterway can greatly help reduce the spread of aquatic diseases and pests. Read how via this aquatic hygiene factsheet and Make 'clean' part of your routine.

To make a report, complete one of the following:

Resources and further reading

Factsheets and information:

Information for restaurants:

NSW Legislation:

Published papers:

  • Petton B, Destoumieux-Garzon D, Pernet F, Toulza E, de Lorgeril J, Degremount L, Mitta G (2021) The Pacific Oyster Mortality Syndrome, a polymicrobial and multifactorial disease: state of knowledge and future directions. Frontiers in Immunology 12:630343
  • King WL, Siboni N, Williams NLR, Kahlke T, Nguyen KV, Jenkins C, Dove M, O’Connor W, Seymour JR, Labbate M (2019) Variability in the composition of Pacific Oyster microbes across oyster families exhibiting different levels of susceptibility to OsHV-1 µvar disease. Frontiers in Miccrobiology 10:473
  • Whittington RJ, Liu O, Hick PM, Dhand N, Rubio A (2019) Long-term temporal and spatial patterns of Ostreid herpesvirus 1 (OsHV-1) infection and mortality in sentinel Pacific oyster spat (Crassostrea gigas) inform farm management. Aquaculture 513:734395
  • de Kantzow M, Hick P, Becker JA, Whittington RJ (2016) Effect of water temperature on mortality of Pacific Oysters Crassostrea gigas associated with microvariant ostreid herpesvirus 1 (OsHV-1 µVar). Aquaculture Environment Interactions 8:419-428
  • Hick P, Evans O, Looi R, English C, Whittington RJ (2016) Stability of Ostreid herpesvirus-1 (OsHV-1) and assessment of disinfection of seawater and oyster tissues using a bioassay. Aquaculture 450:412-421
  • Paul-Pont I, Evans O, Dhand NK, Rubio A, Coad P, Whittington RJ (2014) Descriptive epidemiology of mass mortality due to Ostreid herpesvirus-1 (OsHV-1) in commercially farmed Pacific oysters (Crassostrea gigas) in the Hawkesbury River estuary, Australia. Aquaculture 422-423:146-159
  • Jenkins C, Hick P, Gabor M, Spiers Z, Fell S, Gu X, Read A, Go J, Dove M, O’Connor W, Kirkland P, Frances J (2013) Identification and characterisation of an ostreid herpesvirus-1 microvariant (OsHV-1 µ-var) in Crassostrea gigas (Pacific oysters) in Australia. Diseases of Aquatic Organisms 105: 109-126