1. CULTURE OF MOLLUSCS AND SEAWEEDS

2. OYSTER CULTURE Two groups of oyster are cultured
Flat oysters – Osrea spp
Cupped oysters – Crossostrea spp 
Are filter feeders - mainly on plankton and suspended detritus
In tropics - spawn throughout the year
The larvae pass through trochophore and veliger and metamorphose to spat and settle on solid surfaces
Flat oysters
Cupped oysters

3. Culture techniques:
Spreading clean oyster shells called cultches on the bottom- Most primitive method
The spat settle on the empty oyster shells and grow
This is method is known as bottom culture
In 1673 a Japanese culturist Gorohachi Koroshiya discovered that oyster spat also settle on bamboo poles erected in - off-bottom culture techniques.
Four methods of off-bottom culture
Raft culture - most productive and commonly used
Rack culture
Long line culture and
Stake culture.
Long line culture

4. Raft culture:
Collection of spat for natural spat settlement areas and grow-out for market
Spat collection:
Spat collectors - empty oyster shells strung on GI wires suspended from rafts or long lines; or lime coated tiles stacked on racks
They are set in collection areas and left over their till spat grow to cm
They should be set during the period of maximum spat fall
If set out early barnacles and undesirable organisms settle. If they are set out late spat collection will be scanty
Plankton samples should be analysed, when maximum spat are available spat collectors should be set out

5. Growing to market size:
Site selection:
The farming area should be in sheltered places like bays, fjords etc. free from strong wave action
Tides should be sufficient and frequent to change water
Salinity should be ppt and temperature 15-30oC
They area should have sufficient phytoplankton as food for the growing oysters
The area should be free from industrial, agricultural and domestic pollution

6. The rafts are made of bamboo poles tied together using strong polythene ropes
They are suspended using floats made of used empty cans or Styrofoam floats coated with cement
Rafts of size 16x25m are generally used
One month old spat attached to oyster or scallop shells from collection areas are restrung on galvanised wires 20cm apart using bamboo/plastic spacers
500 to 600 wires with spat can be suspended from each raft
The spat are allowed to grow to marketable size of 30-60g individual weight
Duration of culture will depend on water temperature
In Japan it takes around 6 months for the oysters grow to marketable size
Rafts
Oysters on galvanised wires

7. Long line culture:
In Northern Japan where wind and wave action is heavy
Unlike rafts the long lines can withstand more water agitation; also cheaper than rafts
Pair of ropes 45-75m long is attached to a pair of floats on both side and anchored
Rens with empty oyster or scallop shells containing spat are attached to the long ropes
The spat are grown to marketable size similar to those in the rafts

8. Each ren on a raft or long lines yields about 6 kg in 6-8 months
It works out to 140 tonnes of whole oysters or 20 tonnes of oyster meat
The main problem - fouling by barnacles, mussels and algae which affect the growth of oyster by competition for food space and oxygen
Periodic manual cleaning of rens should be carried out remove the fouling organisms

9. Oyster culture in India
Rack and tray culture method for growing the cupped oyster Crossostrea madrasensis – in Tuticorin centre of CMFRI
Trays made of metal rods and nylon net; measuring 90x60x15cm is placed on wooden platform fixed in shallow mud flats
2 rows of 10 trays were place on each platform
Spat collected on empty oyster shells were placed in each tray
The oysters grew to 90 mm in 12 months yielding about tonnes/ha of whole oysters
Commercial farming of oysters in not yet undertaken in India