Are there male and female oysters?

Yes, the two sexes are separate in this species of oyster. This means that at any one time, an oyster is either male or female; but in rare cases, both male and female sex organs are present. Interestingly, they can change sex during their lifetime from one to the other and possibly back again. The change is thought to be related to environmental conditions; femaleness being favoured in locations and years with good food supply.