Updated Fri 24 Jan 2014, 11:55am AEDT
Oyster farmers in the NSW Hunter region's Port Stephens estuary are in limbo after a mystery kill wiped out millions of their oyster crop.
Several hatcheries of Pacific oysters have been hit and some have perished altogether.
Geoff Diemar has worked in the industry for more than six decades.
He has lost about 10 million oysters, including all of next year's crop.
"This is the first time I've ever seen any catastrophic event like this with Pacific oysters," Mr Diemar said.
"It's very devastating and humiliating because the biggest problem is we can't find out what is causing these mortalities in the oysters.
"We don't know how to plan, we don't know how to go forward."
Seafood grown in the area has been declared safe to eat but the New South Wales Department of Primary Industries has been unable to find a cause, despite carrying out more than 1,200 tests.
Aquaculture division manager Ian Lyall says they have been able to rule out Pacific oyster mortality syndrome, which has devastated hatcheries in the Georges River and Hawkesbury River over recent years.
"We can't get a lead on some action that may be causing this with Pacific oysters," Mr Lyall said.
"We are continuing with our investigation and working with other agencies and as a last resort we're looking at what's called a transmission trial to see if there is a transmissible disease that can be detected.
"That could take a couple of months for us to complete that work and that could be the last throw looking at what is causing these events in Port Stephens."
The mystery deepens because the native Sydney rock oyster, which grows nearby, has not been affected.
That species is more disease resistant and the NSW Government has long promoted it to farmers as a better choice than the introduced Pacific variety.
Mark Salm from the NSW Farmers' Association says the mortalities could act as a catalyst for growers to move away from the Pacific oyster altogether.
"It wouldn't be to their detriment," Mr Salm said.
"The Sydney rock oyster is an outstanding oyster with a wonderful shelf life to work with on your farm, out of the water and management of the oyster is a lot easier."
He has also hinted at possible financial assistance for affected farmers.
"If they can't connect it to any sickness of other sorts caused by some organism, it could come down to a natural disaster," he said.
Mr Lyall says the department is working to help farmers.
"Contract farmers while they have a downturn to give them employment while they recover and that would be removing derelict lease infrastructure from the past," he said.
There are also hardships exemptions from paying certain fees that farmers can apply for.
Farmers are set to meet in the coming weeks to map out a way forward.
