Sex in Oysters Sex in Oysters Birds do it, bees do it, and oysters do it too, but in a different way. Oysters are marine bivalves that live on the bottom of the ocean by cementing themselves permanently to a hard surface. They do not actually mate as most terrestrial animals do. Instead, oysters broadcast their gametes in the water, and fertilization takes place outside of their bodies.
Oysters also have two separate sexes, males and females.
Juvenile oysters usually mature as males first and then change to females later in life. Occasionally, one oyster can function as both female and male at the same time, a condition known as hermaphroditism. The coexistence of separate sexes, sex-change, and hermaphroditism within the same species raises an interesting question. Involvement of genetic factors was suspected, but supporting evidence has been scarce. Furthermore, the sex-ratio of a family is primarily determined by the father, but not the mother.