Coastal Aquaculture and Mariculture (2+1)

Unit 7 - Culture of Molluscs and Seaweeds

7.3.2. Culture methods

The suitable sites and culture methods are almost similar to edible oyster. Cages are stocked with seed oyster and suspended from the rafts or long lines in protected bays. Oysters are allowed to grow for four months when they become ready to receive nucleus.

The oysters from cages are brought to the laboratory for implantation of nucleus. They are kept in glass troughs containing filtered seawater. A few menthol crystals are sprinkled into the troughs to anesthetize the oysters. After one hour the oysters are ready to receive the nucleus.

Graft tissues are prepared by sacrificing a few oysters. Pieces of mantle are cut, cleaned and trimmed to 3x2mm pieces. They are smeared with weak eosin solution to avoid deterioration.
Nuclei are made from chank shells of shells of freshwater mussels. Nuclei range in size from 2-8mm.

The anaesthetized oysters are mounted on a stand. An incision is made at the base of the foot and a canal is cut through the gonad. A graft tissue is first implanted into the gonad through the canal followed by insertion of nucleus using special instruments made for the purpose. Depending on the size of the oyster and the nuclei, 1-8 nuclei can be inserted into the same oyster.

After implantation of the nuclei, the oysters are acclimatized in the laboratory and returned to the farming sites, but this time they are placed in frame nets which have compartments for individual oysters. The frame nets are suspended from the rafts/long-lines for development of the pearl.

The outer epithelium of the graft tissue grows over the nucleus and forms pearl sac in about a week. The pearl will form in about 3 months. The time of harvesting depends on the size of the pearl required. 3-20 months are required to produce pearls of 3-8mm respectively. Six months are required to coat nacre 0.2mm thick.
The oysters are harvested after the formation of required size of pearls. They are sacrificed to recover pearls. The harvested pearls are bleached in hydrogen peroxide to remove any blemishes.