Native oysters have a rough shell that is yellow, pale green or brown in colour, sometimes with bluish, pink or purple markings. The two halves of a native oyster’s shell are different shapes. One half is a deep cup and is cemented to the seabed, while the other is flat and forms a lid. Individual oysters can vary widely in shape too, especially when crowded together in dense beds.
The shell shape is a good way to distinguish native oysters from Pacific oysters, which compete with the native oyster for space and food. Native oysters have rounder shells with smoother edges, while their Pacific relatives have a more elongated shell with deeply grooved edges.
All native oysters start out as males, and throughout their lives change back and forth from male to female. A single female oyster can produce 2 million eggs. Although usually up to about 11cm long, native oysters can grow to more than 20cm and can live as long as 20 years.
Native oysters can be found down to a depth of 80m on just about any type of seabed from bedrock to mud. They are also tolerant of wide range of wave and tidal conditions, and live in sheltered bays as well as exposed coasts. They can tolerate the reduced salinity that occurs when fresh and seawater mix, and so can be found in estuaries.