Bonamia ostreae

In May 2017, MPI detected the flat oyster parasite Bonamia ostreae on flat oyster farms in Stewart Island. Find out about the parasite and what we're doing to try to control its spread.


Bonamia ostreae is a parasite that can be fatal for flat oysters. It has been in New Zealand since 2015 in the Marlborough Sounds and Nelson. In May 2017, the Ministry for Primary Industries (MPI) detected the parasite on flat oyster farms in Stewart Island. This was the first time it had been found in another area of New Zealand.

No food safety risk

There is no food safety issue from eating oysters with Bonamia ostreae. Fresh, good quality New Zealand oysters continue to be safe to eat.

What MPI is doing

As a result of the detection of Bonamia ostreae on Stewart Island, MPI has reissued a Controlled Area Notice. This legally restricts movements of some shellfish species, including their spat, into and out of Nelson, Marlborough Sounds, and Stewart Island. It also legally restricts movements of farm equipment and vessels out of Stewart Island to limit further spread. On 12 June 2017 MPI delivered a Notice of Direction to flat oyster farmers in Big Glory Bay in Stewart Island and Marlborough requiring the removal of all flat oyster stocks.  

Note that the Notices of Direction are subject to change, and are to be used as examples only.  People in receipt of a Notice of Direction from MPI in relation to removal of oysters from Big Glory Bay and Marlborough should refer to the Notices issued directly to them by MPI.

You may need a permit

If you're moving shellfish stock within the requirements of the Controlled Area Notice, you may need to get a permit by completing the application form.

Increased surveillance

Extensive sampling to date has not found Bonamia ostreae in wild (Bluff) oysters in Foveaux Strait. However, MPI is continuing its sampling and is increasing its surveillance.

What recreational fishers can do to prevent the spread

Don’t throw shellfish, their waste or shells overboard.

The risk of Bonamia ostreae spreading to flat oysters increases if any shellfish, or their discarded shells and waste, are moved from one area to another in the water. This risk is particularly high in Big Glory Bay and Paterson Inlet.

Here’s how you can protect our wild oysters from Bonamia ostreae:

  • Don’t throw shells or shellfish waste overboard.
  • Return undersized or excess shellfish back to where you collected them.
  • Dispose of shells and shellfish waste at home or in a landfill.
  • Clean your fishing gear after you’ve finished collecting.
  • Keep your boat hull clean. 

How to spot infection

Generally, signs of the disease caused by Bonamia ostreae, which can often go undetected, are:

  • poor condition
  • gills that appear corroded
  • yellow discolouration of the gills and mantle.

Flat oyster farmers and harvesters who see these signs in oysters, or mass mortality, should call our Exotic Pest and Disease Hotline – 0800 80 99 66.

Compensation for losses

There are provisions for compensation under the Biosecurity Act 1993. If you can prove financial losses arising from MPI's exercise of powers under the Biosecurity Act, and your loss resulted from damage or destruction of property, or from restrictions placed on the movement or disposal of your goods – you can claim compensation for those losses.

Compensation is funded from a special appropriation from Parliament requiring, in some cases, Crown Law endorsement and Cabinet approval.

The Act gives clear grounds for compensation but the losses must have actually occurred and can be verified, and you have been unable to mitigate the losses by taking every step that is reasonable in the circumstances.

Affected parties have to apply for compensation. 

The amount paid depends on what verifiable losses have incurred as the result of any direction by MPI. Each situation will be different and every claim has to be assessed on a case-by-case basis. MPI's compensation team will assess claims under section 162A of the Biosecurity Act.

If you have questions about compensation email:

Welfare and support

The welfare of people affected by the response is important to us. We understand that many people may be worried about the activities and impacts associated with the Bonamia ostreae response. Stress and anxiety affect people differently – ask for help early.

Some groups that may be able to help include:

Help and information for fishers, oyster farmers and people affected by biosecurity responses' [PDF, 1.3 MB]

Who to contact

If you have questions about Bonamia ostreae:

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