Oyster Farming: Some Terms

OYSTER SCIENTISTS AND WATERMEN AND FARMERS throw around a lot of terms they find familiar and the rest of us find odd. When we order oysters on the half-shell, we don't spend much time thinking about cultch and larvae, seed oysters and spat set, diploids and triploids. But the people who grow oysters for a living spend a lot of time thinking about these terms.

Oyster life cycle. Copyright John Norton

Spawning erupts when male and female oysters release sperm and eggs into the water where sperm can fertilize eggs and create larvae which float and feed before becoming spat.

Larvae are the free-swimming organisms created by spawning.

Spat set results when free-swimming planktonic larvae undergo metamorphosis and settle on to some kind of hard substrate, usually an oyster shell. Once they set and stick they become baby oysters and are called spat.

Cultch is any kind of hard material or substrate that oyster larvae can use for settlement. Oyster shell is the most commonly used cultch, but almost anything hard will work and has, including sticks and bushes, balls, and pieces of concrete from old bridges and ballpark structures.

Spat-on-shell results when spat attach to shells. Shells with a lot of spat can be moved and planted on the bottom as seed oysters.

Remote setting tanks allow farmers to create seed oysters by putting larvae spawned in hatcheries into tanks located on land near their lease grounds. The tanks hold shucked shell that has been cleaned and aged and is ready for setting.

Seed oysters can take the form of multiple spat-on-shell or they can take the form of one spat attached to one tiny chip of a shell.

Cultchless oysters are created when spat attach to a single small chip of shell. They are typically grown out in cages, bags, or floats which can protect them from predators like blue crabs or cownose rays. They produce nicely cupped oysters for the half-shell trade.

Bottom culture is the term for growing oysters by planting shell to catch natural spat set or spat-on-shell along the bottom of the Bay. This type of farming requires a Submerged Land Lease. More than 80 percent of current leases for oyster farming in Maryland are for bottom culture.

Off-bottom or water-column culture is the practice of using cages, bags, or floats to hold oysters in the water rather than on the bottom for most of their growout stages. This form of farming requires a Water Column Lease.

Triploid oysters are sterile oysters that cannot reproduce but can grow much faster than natural (or diploid) oysters. Nature gave oysters two sets of chromosomes, but scientists developed techniques for packing oysters with three sets of chromosomes (triploids). Triploids cost more, either as larvae or seed oysters, but grow to market size sooner.

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