By FoF, BAU

2. Introduction
Pearl is a natural gem and is produced by a mollusk which
have a worldwide demand and have been exploited from
the time immemorial.
The entire trade was totally depending on the natural pearl
resources causing heavy of damage to the natural
populations.
To produce a pearl by the pearl oysters hit required at least
3 to 4 years under natural conditions.
In 1907 Tokichi Nishikawa produced the first spherical
cultured marine pearl in the oyster and the pearl culture
industries started flourishing with a master touch of
Mikimoto and several others.

3. The success in developing the technology of pearl
production was achieved only in 1973 when the first batch
of spherical cultured pearls was produced at Central
Marine Fisheries Research Institute.
The world trade of cultured pearl is reported to be over
US$ 3 billion per year.
The major pearl producing countries are Australia, Tahiti,
Indonesia, Japan and China.
India is one of the major importers of pearls importing
pearls worth US $ 4 million every year to meet the growing
domestic market demand.

4. Method of pearl culture
Pearl culture operations can be divided into three
categories which are
(1) collection/hatchery production,
(2) on growing and
(3) pearl culture.
Each phrase of production permits a degree of
specialization by farmer and allows people of different
income and different technical expertise to get involved in
cultivation.
Collection/ hatchery production
The pearl oyster industry relies on spat collection at
natural production atolls where spat is abundant, during
the warm season (November to May).
Farmers place their collectors, made of black shade mesh

5. Spat oysters are left on collectors for 1 year till 4- 5cm in
length where they are big enough to be grafted, and skip
the on growing process altogether.
Some of the spat are produced in hatcheries
 To induce spawning, oysters are held overnight at 20 0
C,
and then transferred to a raceway with the seawater
temperature at 30–32 0
C.
 Spawning oysters are removed individually into individual
containers.
 Larvae are reared in static water exchange systems where
water is changed every 2-3 days.
 At day 20, when most of them reach 150μm, they are
transferred to seawater settlement tanks.

6. On growing
 Hatchery grown juveniles are put into the sea on the material
which they settled upon.
 The material is hung from long lines in areas of calm water.
 The spat are left to grow for 2 years till an average size of 90
mm.
 A hole is then drilled through the posterior ear and the oysters
are hung down in pairs on a down line.
Pearl culture
Pearl culture involves the
implantation of a spherical nucleus together with a piece of
mantle tissue (Saibo) from a sacrificial oyster, into the gonads.
The mantle tissue grows around the nucleus and secretes
nacreous deposits to form a pearl.

7.  At a minimum size of 100mm, the preoperative pearl
oyster undergoes a weakening process for 40 days for the
muscular and gonadal epithelium to disintegrate.
 The oysters are then returned to the sea and placed in
calm conditions.
 Cells in the pearl sac secretes nacre onto the outer surface
of the nucleus and cultured pearls are harvested when
nacre are 1 mm thick after 18-24 months.

8. Farming methods
Raft culture
Most suitable and appropriate one to farm the oysters in
the sheltered Bays.
Wooden poles lashed with coir ropes and floated with the
help of buoys moored by 2 to 4 anchors tied by means of
15mm nylon ropes.
A raft of 6 x 5 m is found to be more ideal for the pearl
oyster, culture and can accommodate 80-100 cages of
40 x40 x 10 cm in size.

9. Raft culture
Raft culture

10. Collapsible or long line raft
 Comprised of 16 to 20 empty PVC barrel (200 litre
capacities) arranged in a row or 4 rows connecting one
another by a chain stretched, and anchored to all the ends.
 Between, the gaps, the pearl oyster cages are suspended.
 Suspended cages get entangled during the rough weather
and get damaged due to hitting with one another.

11. Collapsible or long line raft

12. Rack System
 3" dia GI pipe materials or 5 ̋ bottom casurina or eucalyptus
poles erected at a depth of one metre into the soil in the
sea with 2 to 3 m depth of water column at low tide.
 The poles are cross connected by means of wooden poles
and tied by means of coir ropes.
 Accommodate 80 to 100 cages per compartments
 Can be extended to a long distance more than 200 m from
the shore to a depth of3 to 5 m into the sea.
 Very convenient for the operation and also to attend the
farming work easily.

13. Rack System

14. On bottom culture
 Possible only on the rocky sea bottom or artificial bottom
 In an area of 100 x 3 m, 300 oyster cages can be kept.
 Can be applied as a temporary means to accommodate the
wild collected oysters before farming into off shore rafts.

15. Management methods
 Although pearl culture is extensive with little control over
weather, the use of management methods can drastically
increase productivity and result in higher profitability.
 Therefore, management of culture system such as site
selection, settlement, feeding, stocking density and pearl
culture technique is essential.
Site selection
 Site selection is the most critical factor affecting pearl
oyster productivity and spat collection, as the oysters
spend most of their growing time exposed to water
elements.
 Site selection must take into account important water
quality parameters like temperature, salinity and turbidity.

16. Optimum growth for P. margaritifera occurred at 23-28 0
C
 Under 14 0
C, larvae did not develop into veliger.
 Temperature also affects byssal attachment, with the
highest rate at 180
C.
 Higher temperatures accelerate nacre deposition
 Salinity plays an important in larvae development.
 Survival of P. imbricata larvae was highest at 32 and 35 ppt
and at 29-35ppt,
 Turbidity also has an influence on growth and survival of
oysters.

17. Settlement
Settlement of larval spat is
affected by various factors.
Types of substrate also influence larvae settlement.
Depth and chemical cues also affect spat recruitment,
with an intermediate depth of 60-90 cm
Feeding
 Optimum diet for P. margaritifera larvae was found to be
1:1 mixture of Pavlova salina and Chaetoceros simplex and
dried Tetraselmis suecica and commercial yeast L-10,
Microfeast.

18. Stocking density
 For nursery culture at more than 100 individuals/ tray ,
100 individuals/ tray after 3 months, 50/tray from the 4th
month onwards
 At 30% stocking density is the optimum method for
culturing P. margaritifera.
Pearl culture techniques
As the oyster grows, growth rate reduces progressively
The sooner the nucleus is implanted, the greater is the
rate of nacreous deposition, and the shorter is the time
to obtain a marketable pearl .

19. Problem and their solution in pearl culture
Predation
Predation of oyster spat and
juveniles can result in massive loss in productivity.
Removal spat collectors at a shorter period 3-4 months
instead of 6 months, when mean size is 15mm and reared
in panel nets.
Spat can be covered with mesh, and a mesh size of 3 mm
improved spat survival of P. maxima while not fouling so
easily.
For juvenile culture, ear hanging and 24 pocket juvenile
panel nets were the preferred method, showing highest
growth and lowest fouling and mortality from predators.

20. Biofouling
Stunted growth and shell
deformities are caused by biofouling organisms like
barnacles and polychaete worms.
Cleaning also affect survival rates, frequent cleaning
every 4 weeks resulted in high mortality forP.
margaritifera.
Diseases
 Oyster diseases have the potential to affect productivity.
 Pearl oyster P.maxima suffered high mortality in
Australia in 1996 due to the bloom of algae
Trichodesmium erythraeum.

21.  However, another commonly occurring oyster disease,
the reddening of abductor muscle caused by infection in
P. fucata can be prevented by lowering the temperature
of water to less than 190
C.
Genetics
One of the worries of
selection through inbreeding is loss in genetic diversity,
which may lead to inferior growth and survival.
 The future of pearl oyster aquaculture lies in genetic
selection, which can create faster growing oysters,
resistance to diseases and production of higher quality
pearls.

22. Conclusions
Pearl farming is an attractive business venture because of
the high value of the final product.
 In recent years, pearl prices have fallen significantly,
especially for smaller, lower-quality pearls.
 With the exception of the grafting process, pearl farming
is a relatively simple form of aquaculture because pearl
oysters do not require artificial feeds, complicated farm
structures or constant attention.
 If properly managed, pearl farming will not harm the
environment and can increase the wild pearl oyster
population over a period of years.
 For these reasons, pearl culture may be the best
opportunity for business development.

23. THANKS
TO ALL