Are they alive?
Yes! If you ate a dead oyster it would not be a pleasant experience.
Oysters are perfectly adapted for living out of water for long periods of time. They are used to being exposed to the air at low tide two times a day. Oysters develop good seals on the edges of their shells (valves) to hold in seawater.
The adductor muscle (like the muscle eaten as scallops) pulls the valves of the oyster closed and this muscle is strengthened by holding the valves closed twice a day at low tide. If the oyster were to die and be eaten, the experience would be memorable for how bad the oyster would taste. The adductor muscle relaxes when the oyster dies and the shuckers are trained to listen for signs that the oyster is not alive. We have a saying behind the bar: “If in doubt, throw it out.” I have tossed out many a good oyster that I was not 100% sure was good. Oysters should smell fresh when opened. They should be moist with the natural liquor (seawater) inside the shells. They should not appear to be dried out or shriveled up. When opening the oyster, my staff and I know if something is not right.
How do oysters have sex?
Think hot tubs. Rising water temperatures trigger the oyster into developing gonads. The gonads release the sperm or eggs into the water. Fertilization is external (except for flat oysters).
For at least 10,000 years (at least) oyster growers have placed structures (cultch) such as oyster shells in specific locations to catch the natural spawn of native oysters. Many times these structures are then moved to areas more favorable to accelerate oyster growth (faster currents bringing more alga to eat). In the last 70 years scientists have worked to discover how to make shellfish spawn by environmental cues controlled by the scientists/farmer in an oyster hatchery. Over the years it was discovered that oysters work much like humans; get the adult oysters into a hot tub and watch what happens. It turns out that raising the water temperature 10 Celsius per hour for several hours gets the oysters to release their gonadal material. Boys usually go first, emitting strong blasts of milky sperm. As the females filter the sperm they in turn release their eggs into the seawater. Fertilization is external. In nature almost all the offspring die because when they settle to the bottom 10 to 14 days after spawning, the bottom does not have clean cultch for the oyster to set upon. In hatcheries, oysters spawn in tanks of seawater where the tank either has bags of whole oyster shells or has ground shell on the bottom of the tank. With these optimal conditions the survival rates are greatly increased. Six male and six female oysters can produce over 15 million larvae in one day!
* Flat oysters breed internally. Sperm is taken into the female and she holds her seed until she thinks conditions are optimal. Then she ‘spits’ out the seed, commonly called ‘spat’.
How many kinds of oysters are there?
There are five species of oysters available, some in very limit supply. There are Miyagi oysters. This is the most available oyster on the west coast and goes under many regional or grower names. There are east coast oysters from many regions of the Atlantic coast. There is the Kumamoto oyster. Finally there are the rare flat oysters, the Olympia and the French Belon (see Flat oysters).