A force of 26 to 30 pounds is required to tear off the muscle of the oyster. Mechanical disturbance, change in illumination or presence of irritating substances are sensed by two rows of tentacles which convey the stimulus through nerves to the muscle which closes the shell. The oyster has only an anterior muscle. The oyster has no means of attacking other animals and protects itself only by closing the valves tightly and remaining hermetically sealed. If undisturbed, O. virginica may remain in good condition for about four months in air at a temperature a few degrees above freezing.
Oysters feed on minute algae and other microorganisms.
O. virginica and other oysters may change sex during the winter. Young O. virginica are predominantly males, but toward the end of the first year some of them change into females and a one to one ratio is established. Also present are sodium, potassium, calcium, magnesium, chlorine, bromine, phosphorus and sulphur as well as many heavy metals including iron, copper, zinc, manganese and iodine. Oyster farming is ancient. Long before the Christian era the Chinese were cultivating oysters and Romans successfully used artificial methods of growing them.