Two important aspects are involved in oyster culture i.e. the production of seed and the rearing of the oyster spat to marketable size.
There are two ways to obtain oyster spat for culture, collecting natural seed which are usually available in large numbers during peak spatfall seasons and artificially propagating the seed. In the first method the major difficulties are the selection of suitable spat collectors (cultches) and timing. A great variety of materials are being used among the selected Asian countries to collect spat. These range from empty Placuna placenta (windowpane) shells, empty oyster shells, coconut shells, mussel shells, asbestos sheets, bamboo poles, lime-coated tiles, PVC tubes and polyethylene ropes and nets. The choice of cultch material is not only dependent on its availability, but also on the species intended for collection. It has been shown that different oyster species have preferences as to the materials on which to settle. Among the cultches available the most popularly used are empty oyster or windowpane shells, because they are cheap and readily available.
The most critical phase for spat collection is the timing of placing the cultches in the pre-selected areas. Although, spatfall occurs throughout most of the year in many tropical countries, the bulk of spat are usually collected during the peaks of the spatfall seasons, which vary according to species and geographical location. Placing the collectors at the right time is extremely important if large numbers of spat are to be collected. In fact, prolonged permanence of the cultches in the sea usually cause them to become less efficient as result of fouling from other organisms such as barnacles, ascidians and algae and sedimentation. In addition, setting the cultches at the wrong time means also the loss of considerable labour effort, as well as possibly missing the peak spatfall period all together, due to the unavailability of freshly prepared collectors.
Methods commonly used for farming oysters are the bottom or broadcast method, the stake method, the raft method, the long-line method, and the rack method employing either shellstrings or trays. In the bottom method, oyster shells, stones, gravel, cement bars, etc. are scattered on intertidal areas with suitably firm bottoms for attachment and growth of seed until they reach marketable size. The stake method consists of driving bamboo or palm poles into the soft bottom of intertidal flats. A variation of the stake method is the use of cement structures such as the stone-bridge method used in China and the cement poles and pipes methods used in Thailand. Usually poles are fixed singly or in bundles spaced 0.5 to 2 m apart. The rack method consists of bamboo stakes (or other materials) supporting rows of horizontal poles from which strings of shells are hung. Trays with wooden or iron frames and nylon screens may also be hung from or placed on the racks. The raft and long-line methods are completely off-bottom and subtidal. Rafts are generally constructed with bamboo poles and when additional floatation is needed, styrofoam blocks, plastic or metal drums, etc, are used. The long-line method basically consists of a series of floats arranged in a row connected to one another by one or two parallel synthetic ropes, from which the oyster strings are hung.
Oysters are usually harvested in 8 to 12 months, however, the growth period is mainly determined by the marketable size required, and on the geographical latitude where such culture is practised. In the Philippines C. iredalei are harvested in 8 to 12 months and production values reported range from 4–8 MT/ha in the bamboo stake method and 10–15 MT/ha in the shellstring method. In China 60 MT/ha are produced on average using the bamboo stake method, whereas 30 MT/ha are commonly obtained from the stone bridge method. In Thailand and Malaysia, yields of 18– 19 MT/ha are obtained using the bottom and stake culture methods (Davy and Graham, 1982).
