A deadly oyster disease has been found in one of the largest estuaries in New South Wales. 

Key points:

  • The deadly QX disease has been detected in Port Stephens estuary for the first time
  • Movement restrictions are in place for oyster stock and equipment
  • The NSW chief vet has confirmed QX does not pose any risk to human health

It is the first time that QX (Queensland Unknown) – a seasonal disease affecting Sydney rock oysters – has been found in Port Stephens, but previous outbreaks have crippled growing regions elsewhere.

After a report of oysters experiencing poor growth, samples were taken and sent to the Elizabeth Macarthur Agricultural Institute (EMAI) with tests confirming the presence of QX.

NSW chief veterinary officer Sarah Britton said QX was a very complex disease.

“It’s a protozoa that has an intermediate host that has a whole lifecycle that happens and it gets into the oyster and tends to reproduce and sporulate and it gets in their digestive system and it basically starves them and they don’t do very well,” she said.

Dr Britton said infections of QX were more likely to occur earlier in the year around March to April.

“We’re probably at the very end of where this intermediate host would be very active for this disease,” she said.

A woman with glasses and a collared shirt smiles.

NSW chief veterinary officer Sarah Britton says QX was very complex.(

ABC: Hugh Hogan

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Biosecurity direction restricts oyster movement

The Department of Primary Industries has placed movement restrictions on the Port Stephens oyster industry while it investigates the presence of the disease further.

There are concerns the presence of QX in Port Stephens will have a major impact on the whole state.

“It’s one of our biggest areas for oyster production and has hatcheries and nurseries and research facilities, and a lot of stuff happening in that estuary,” Dr Britton said, adding that growers in other regions should monitor oysters for any signs of the disease.

“There is no risk to human consumption with this particular disease, so the main thing we’re trying to do is it minimise risk to other estuaries and keep the disease out of as many estuaries as we can.”

Farmers waiting on tenterhooks

Port Stephens oyster farmer Don Burgoyne said the possibility of QX has “hung over our heads”. 

“Every estuary has a chance of something like this happening,” he said.

The estuary is home to more than 40 oyster farmers, but stock is also sourced from the region by outside growers.

“We’re all waiting on tenterhooks really just to see how things develop,” he said. 

Don Burgoyne stands next to Tilligerry Creek at his oyster farm.

Don Borgoyne said the impact on the local industry could be devastating.(

1233 ABC Newcastle: Robert Virtue

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Mr Burgoyne said judging from past QX outbreaks, there could be a significant impact on the region.

“It absolutely decimated the industry in the George’s River and the Hawkesbury. They couldn’t continue. Each year it kills 90 per cent of your oysters, so you just can’t continue,” he said.

Since those outbreaks, researchers have been working on breeding QX-resistant oysters.

Macleay farmer turns to QX-resistant oysters

Three hours north of Port Stephens, David Smith, who farms on the Macleay River, knows how tough a QX outbreak can be.

“It’s an absolutely devastating event for anyone to go through,” he said.

“We heard about the outbreak in Port Stephens on Friday and to be honest I didn’t sleep all Friday night just worrying for those fellas.”

Oyster farmer David Smith in front of water.

Farmer David Smith turned to QX resistant oysters after losing $500,000 worth of crop to the deadly disease in 2020.(

ABC Mid North Coast: Hannah Palmer

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After he lost $500,000 worth of stock to QX in March 2020, he turned to QX-resistant oysters developed by the DPI, and just in time.

“We’ve had QX come back this year on our river and that was a direct result of the floods,” he said.

Mr Smith referred to the devastating virus as the ‘slope of hope’ it takes years to recover from an outbreak.

“You bring your oysters in and anything that’s closed you assume is alive and you put them back in, then you check on them a month or so later and another 50 or 60 per cent of them are dead,” he said.

“Not only do you lose your current year oyster, which is your cash flow, but you’re losing next year’s cash flow too, because, what we saw in oysters under 12 months old we saw a 70 to 75 per cent mortality rate.” 

Oyster shells.

Farmers say it takes years to recover from losses caused by the QX disease.(

ABC Mid North Coast: Hannah Palmer

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Before QX hit the Macleay River there were 25 oyster farmers, Mr Smith said now he is one of 10.

“The scale of oyster farms in Port Stephens is off the charts, compared to our river here,” he said.

“My thoughts go out to all those farmers. It’s a challenge mentally and physically to deal with this event.

Posted , updated 

Safe to eat but disease a deadly blow to oyster growers
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