The Pacific oyster is native to Japan with production concentrated in China and the US. Sydney Rock Oysters and Angasi (flat) oysters are native to Australia and shells have been found in ancient Aboriginal middens.
Oysters are bivalves and feed by filtering algae and other nutrients from the sea water in which they live. One oyster can filter at least 0.25 ML of water. In NSW alone, farmed oysters can remove over 1 million tonnes of suspended material, mostly phytoplankton, in their lifetime.
For best growth an oyster needs relatively clear water with a salinity less than 35ppt, pH between 6.75 to 8.75, temperature between 14 - 30oC (Sydney Rock) and 10 to 18oC (Pacific), and low concentrations of metal compounds.
Most oyster species change sex during their life. An adult female oyster releases between 20 to 40 million eggs and a male, hundreds of millions of sperm at spawning. Larvae settle on a hard surface to mature. Commercial production relies on relocating settled larvae (spat) to various culturing methods.
Oysters are not fed or treated with any chemicals throughout their lifetime in the water or after harvest. In their lifetime they will be graded and culled a number of times.