Researchers looking to develop a Sydney Rock Oyster which would grow fatter faster, have unwittingly discovered a strain that is immune to the diseases Q X and Winter Mortality.

Q X which originates from Queensland has hit oyster leases in northern New South Wales, while Winter Mortality affects oysters in the state's cooler waters.

The project to come up with a fast growing larger oyster began 20 years ago.

Since then farm lobby group New South Wales Farmers set up the Select Oyster Company to market the brood stock to commercial operators.

"It was a good coincidence that the disease that existed in the estuaries where the breeding program was conducted.

The by-product was that selecting larger oysters they were also selecting survivors of the disease," the company's operating manager Emma Wilkie explained.

"So the disease resistant became a by-product that has actually now developed into the main trait that they would select for today."

The bonus of an immune oyster that is fatter and develops quicker than the traditional Sydney Rock Oyster means that they could be available as a "plate grade oyster" in a year and a half compared to a "wild oyster" which can take up to three and a half years.

"It depends on the condition of the estuary at the time, sometimes food sources are very high, water temperatures are a little higher than previous years and handling by the farmer."

The brood stock is being managed in five different New South Wales' estuaries to "condition them" enabling hatcheries to do a "production run" which results in larvae which grows into spats and then sold to nurseries and farmers.