How They’re Grown

Aquaculture oysters are grown in cages, in bags on racks, in floats and spat-on-shell bottom planting. Oysters grown in cages/racks/floats are generally destined for the more lucrative half-shell market, while spat-on-shell oysters are usually grown for the shucking market.

Cultured oyster production can be viewed as a 3-step process – hatchery; nursery; and grow-out to market size.

The first step begins onshore in a hatchery, where adult oysters are encouraged to spawn and produce baby oysters.  During this hatchery stage, oysters of all ages (broodstock, larvae, and post-set juveniles) are fed a diet consisting primarily of cultured micro-algae and then a mixture of cultured algae and natural algae.

  • Mass culture of algae to be used as food.
  • Oysters in a spawning trough for production of eggs and sperm. Fertilization occurs externally within the spawning trough water. Fertilized eggs will be collected on fine mesh screens and transferred to culture tanks with static water and aeration. Over the next couple weeks, the eggs will develop into planktonic larvae, become ready to settle (set), and attached to a solid surface to begin their existences as a non-mobile oyster.
  • Developing oyster eggs.
  • Oyster eyed-larvae competent to set.
  • Downweller units are used to set eyed-larvae and rear the earliest settled oysters. Downwellers are cylinders, open on one end with the other end covered in a fine mesh. Microcultch (very small pieces of oyster shell) are placed into the downwellers and competent to set eyed-larvae are introduced to the cylinders. Water is air-lifted into the cylinder via the pipe through the cylinder wall, flows downward through the microcultch on the bottom and back into the downweller trough. Eyed-larvae will settle upon the individual pieces of microcultch creating single oysters for further culture.
  • This ball of eyed-larvae contains many millions of competent to set oysters. Wrapped in a moist covering and held in a refrigerator, eyed-larvae can survive several days and still be able to settle and attach to cultch. These eyed-larvae can be used for single oyster production or spat-on-shell.
  • Recently set, individual juvenile oysters ready for further growth.
  • This is a setting tank used for the production of spat-on-shell oysters. Oyster shells are contained within the tank; ambient water is pumped into the tank and aerated. Eyed-larvae are introduced into the tank and allowed to settle onto the oyster shells. After a few days in the tank, ambient water is flowed through the tank to feed the newly set oysters before they are removed for planting.
  • Newly set oysters on the inside of an oyster shell from the spat-on-shell production method. The second stage of production is the nursery phase where newly settled (set) oyster are raised to a larger size to be planted in the natural environment for grow-out to market size. The nursery stage can occur either onshore, on floating structures, or in the ambient waters.
  • Constructed similar to the downweller units, this is an upweller cylinder for juvenile oyster growth. With this cylinder, water is introduced into the trough holding the cylinder, passes through the juvenile oysters sitting on the bottom mesh screen and exits through the pipe at the top of the cylinder. Ambient water is pumped into the trough to bring in naturally produced food (algae), passes through the oyster mass (which feeds on the algae), and then exits through the top pipe back into the trough and out via an overflow pipe back to the natural waters.
  • This is a floating, paddlewheel operated upweller. The paddlewheel pushes water through the upweller containers (instead of cylinders they are rectangular boxes) in the same manner as onshore upwellers that utilize pumped water from an adjacent water source.
  • Juvenile oysters from a nursery upweller ready for planting for final grow-out to market size. The final stage of production is the grow-out phase, when larger “seed” oysters (~8-12 mm in length) grow to their final market size (>~70-mm). Depending on the desired market (half-shell or shucking), seed will be grown is some sort of protective device (cage, rack bag or float) or placed directly on the bottom (spat-on-shell production). In Virginia, the most common grow-out method used is on-bottom cages.
  • Raising a bottom cage full of oysters.
  • An oyster cage with the top removed to access the oysters inside. During the grow-out phase, cages will be raised several times for normal husbandry practices and to harvest market-size oysters.
  • Regardless of the production method, the desired result is a well-shaped, tasty treat.
  • Single oysters ready for market.
  • Cluster of oysters from spat-on-shell production ready to head to the shucking house.

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Virginia Seafood

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Virginia Seafood
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Virginia Aquaculture Oyster Growers