edible and pearl oysters

NIDHIYA KOTTAYI
III SEM
MSC. MARINE BIOLOGY
CUSAT

INTRODUCTION
The molluscs are an important group of shellfish and
are exploited along the Indian coasts
The term "oyster" has been applied to more than 400
different mollusks world-wide, including such non-
food species as the pearl oyster.
Edible varieties include some 70 species. Only a
small percentage of these are grown commercially.
The edible oyster, popularly known as 'Aali' in Tamil
and 'Muringa' in Malayalam,
 sedentary bivalve

The flesh is encased by two shell valves,
The lower valve is cemented to the substratum and the upper
valve acts as a lid.
The hinge mechanism connecting both valves, allows the valve
to open or close
The animal feeds by filtering the microscopic organisms in the
water which pass through the gap between the two valves.
 The flesh of oyster is highly nutritious containing 8-10% protein
and 2% fat, in addition to minerals like calcium, phosphorus, zinc
and iodine.
Edible oysters occur attached to hard substrata in the
intertidal areas, backwaters, muddy bays, lagoons, and
creeks along the east and west coasts of India

As early as in the first century B. C, the
Romans were first to culture the edible oysters.
 Then Japan developed various methods for
farming the edible oysters.

TAXONOMY
Kingdom : Animalia
Phylum : Mollusca
Class : Bivalvia
Order : Ostreoida
Family : Ostreidae

RESOURCES AND DISTRIBUTION
Six species of oysters found in Indian waters
The Indian backwater oyster Crassostrea madrasensis
The Chinese oyster Crassostrea rivularis
The West coast oyster Crassostrea gryphoides
The Indian rock oyster Saccostrea cucullata
The Bombay oyster Saxostrea cucullata
The Giant oyster Hyastissa hyotis

EDIBLE OYSTERS FOUND IN OTHER REGIONS OF
THE WORLD
•Pacific oyster,= Crassoatrea gigas
•Portuguese oyster= Crassostrea angulata
•European oyster= Ostrea edulis
•American oyster= Crassostrea virginica
•Australian Rock oyster=Crassostrea commercialis
•New Zealand oyster =Crassostrea glomerata
•Olympian oyster= Ostrea lurida

Crassostrea madrasensis
•Outer surface of shell valves
has numerous foliaceous
laminae with sharp edges
•The left valve is deep,and the
right one slightly concave
•Hinge is narrow and elongated
•Outer shell surface is grey,
green or light purple depending
on the area of collection due to
presence of detritus, algae etc

•This species grows to a size
of 212 mm, the larger ones
occurring in estuarine
systems.
•It is a typical euryhaline
species
•Temperature range 22.8 –
34.5 °C
•Salinity 7.2 – 34.1 ppt
(Kripa, 1998
•It is found in Orissa ,
Andhra pradesh ,Kerala,
Karnataka,
Andaman&Nicobar,
Tamilnadu.Also in Pakistan,

Crassostrea gryphoides (SCHOLOTHEIM)
•The shell valves are
elongate and thick.
•Left valves cup- like
•Hinge area is well
developed and has median
groove with lateral elevations
•Roundish and broad in
shape
•Whitish or greyish externaly

• The species grows to a size of 170
mm
• Occurs in the intertidal zone and
down upto a depth of 7 m
•C. gryphoides occurs along North
Karnataka, Goa and Maharasthra

Crassostrea rivularis (GOULD)
•Large, roughly rounded, flat
•Thick shell cavity with a shallow shell
•The left valve is thick and slightly concave ,
the right one is slightly larger
•Adductor muscle scar is oblong and white
• The species grows to a size of 150 mm
•Inhabits the intertidal zone of coastal waters and creeks.
•Salinity – 15- 30 ppt
• It occurs in the creeks of Kutch, Aratada- Creek, Poshetra
Point, Port Okha, Dwarka and Porbundar in Gujarat and at
Mahim, Ratnagiri and Jaytapur in Maharshtra. Outside India
it is distributed along Pakistan coast

Saccostrea cucullata(BORN)
•The shell valves are trigonal or pear
shaped
•The left valve is deep or moderately
deep
•The right valve is flat or slightly
convex and covers the left one like a
lid
•The hinge is straight , moderate in
size and devoid of teeth
•The margins of both valves have
well developed angular folds
•Colour of outer shell– pale white,

•It grows up to 20cm
•It is distributed in the marine environment
in shallow coastal waters and creeks.( up
to 5m depth)
•Salinity -- 10.4 – 34.1 ppt
•The species enjoys a wide distribution and
is found in East Africa, India, Pakistan,
north western Australia and Philippines
•In India it occurs at various places along
both the east and west coasts and around
Andaman and Lakshadweep Islands

Crassostrea virginica
•Colour is white or brown and is
grows up to75mm
•Hinge line without teeth in the
adult.
•Shell margins smooth.
•temperatures between 15.5
and 20°C,salinity is 10-28 ppt.
• Larvae will not settle and metamorphose into
spat when salinity is less than 6 ppt (Wilson et al.
2005).
•C .virginica is native to the eastern seaboard and

Crassostrea gigas
•It is externally rough and sharp
with radial folds.
•It’s shape varies with the
environment, where it attatched
•The two valves of the shell are
slightly different in size and shape,
the right valve being moderately
concave.
•Shell colour is variable, usually pale white or off-
white.
• Mature specimens can vary from 80 mm to 400 mm .
•The optimum salinity 20 to 35 ppt, can tolerate
salinities as high as 38 ppt;
• It can withstand a range from -1.8 to 35°C.

BIOLOGY
Edible oyster is sedentary animal usually
elongate with highly variable shape.
 The animal is attached to the substratum by
lower left valve which is cup-shaped
Food of oyster mainly consists of diatoms and
detritus.
 Generally the oysters are filter feeders.
The oysters obtain food by collecting particles
suspended in the water column.
 They are also known to absorb dissolved
organic matter from the water through the
surface of gills, palps and mantle.

•Sexes are separate
• Hermaphrodites also occur
•Oysters spawn throughout the year with 2 peak periods
in
April-May and August-September.
•The peak period varies from place to place, depending
on environmental factors.
•In Kerala Coast, the peak spawning occurs during
postmonsoon months (September-December)
• At spawning, eggs and sperms are discharged directly
outside into the water where fertilization and
subsequent development takes place.
• The larvae are pelagic.
•When the larvae attain pediveliger stage, they begin to
crawl with the help of foot and settle on suitable
substratum.
•This process is called spatting or setting and the young
oyster is called spat or seed oyster.

NUTRITIVE VALUE OF ONE OYSTER
40.8 calories.
Carbohydrate -10.2 grams
fat calories -10.4 grams
protein calories -20.2 grams
Vitamin B12 (120 percent of your daily
recommended value)
Rich in three minerals: zinc, copper and
selenium
(33-55% of daily requirement)
Complete protein (having all the amino acids in
the proper proportion)

EDIBLE OYSTER CULTURE
•Oyster farming has a long history and the
Chinese practiced oyster culture before the
Christian era
•Bardach et al. (1972) stated that ―Marine
aquaculture may well have begun with oysters,
which were cultivated in Europe during Roman
times
•In India , work on oyster culture was taken up
during 1970 at the Tuticorin Research Centre of
CMFRI, Tuticorin

CRITERIONS FOR SITE SELECTION
Wave/wind action..
 Information regarding wave and wind pattern of
occurrence and intensity is usually useful to determine
whether a site is suitable or not.
Salinity.
Oysters thrive best in brackish- and full strength
seawater.
Optimum range is about 17–26 ppt .
Areas which are prone to flooding or surface run-offs
should be avoided.
Natural food supply.
There should be an abundant supply of phytoplankton.
Plankton sampling and analysis may serve as a good
guide in determining the productivity of the area.

Availability of broodstock/seeds.
The best area, as far as this criterion is concerned, is one which
has a natural population of the species to be cultured.
Transportation of broodstock or seedling is difficult and costly,
especially if the distance from the source to the farming area is
more .
Pollution.
It is important that the culture area is free from any form of
pollution.
Areas which are endangered by chemical, industrial or domestic
effluents should be avoided.
Oysters are filter-feeders and have the capacity to absorb and
accumulate heavy metals (such as zinc, copper and mercury) and
pathogenic organisms.
Water depth.
Water depth should be sufficient for the selected culture
method(about 2-5 m depth)
Post-harvest and marketing facilities
 Oysters are highly perishable, and since local demand is largely

The technology of oyster farming consist of two
important phases
1)collection /production of seed oysters
2)growing the seed oysters to marketable size.
Seed collection from wild
 The seed required for culture is met either from
natural spat collection or through hatchery system.
For collection of spat from nature, suitable spat
collectors or cultch materials are provided at
appropriate time.
The spat collectors should be able to retain the
oysters till they reach marketable size or up to the size
at which they could be scrapped for further rearing.

SPAT COLLECTION
•The seed requirement for culture of oyster is met either from
natural spat collection or through hatchery rearing
•For collection of spat from natural grounds, suitable spat
collectors or cultch materials are provided at appropriate time
which may be oyster shells, coconut shells, asbestos sheets,
mussel shells or other materials.
•The choice of spat collectors depends on the culture method
adopted, materials availability, economical and practical
considerations.
•The spat collectors should be rough, free from slime, without any
secretion of resins and strong to retain the oysters.
• Lime coated tiles and oyster shell are suitable for large scale spat
collection.
•The tiles are arranged in trays and are placed on racks, where as
oyster shell are arranged on a nylon rope of 1.50m,length,as strings
and placed on racks.

For efficient spat collection the
farmer should know the:
(a) spat setting season
(b) the sites to collect sufficient spat
for stocking in the grow-out ponds.

SEED PRODUCTION THROUGH HATCHERY
SYSTEM
Selection and holding of broodstock
 Oysters of length ranging from 60-90 mm are ideal and
30% of them should be 60-75 mm in order to have assured
availability of males.
25 oysters are selected, cleaned and placed on synthetic
twine on a PVC frame in a 100 I fiberglass tank and
precooled
seawater (at 20°C - 22°C) is filled in the tank and aerated.
Mixed algae with cell concentration of 1.5-2 million cells/ml
is given as food daily .

Induced spawing
The conditioned oysters are induced to spawn by
trasferring them to seawater with temperature of 34-
35°C.
This sudden change of water temperature stimulates
spawning in oysters.
Once spawning is completed, the oysters are
removed from the tray.
Larval rearing
The fertilized eggs undergo cleavage within 45
minutes.
At the end of 4 hours, the eggs attain morula stage
and begin to swim and at 20 hours, 'D' shelled larval
stage is attained.
Isochrysis galbana is provided as larval food. The
rearing density and feeding protocol for the various

stage Rearing density
(larvae/ml)
Algal cells/ day
D shaped 5 3000-4000
Umbo 3 4000-5000
Eyed stage 2 5000-8000
Pediveliger 2 10,000-12,000
On 18-20th day the larvae settle down as spat.
 The cultch material provided is oyster shell
valves for attached spat or polythene sheet for
production of cultchless or free seed.

Spat settling and seed production
For cultchless seed, oyster shell grit or
polyethylene sheets are provided as spat
collectors.
 The oyster shells are cleaned, hole is drilled
centrally in the shell valves and are provided in
the larval rearing FRP tanks for spat settlement.
Once the larvae attain eyed stage, the spat
collectors are uniformly spread in the bottom of
the tank and the released larvae settle on the
shells.

GROW- OUT CULTURE
The Grow out culture technique is broadly divided into
1) on-bottom
 In the on-bottom culture, the seed oysters are
grown on the ground.
 This method is substrata-specific and the area
should be free from silting and predators.
2)off-bottom culture
 Off-bottom methods, the advantages lie in better
growth and good condition of the meat.
 The methods involved in off-bottom culture are
(1) rack & tray, (2) rack & string, (3) stake and (4)
raft (5)long –line method

ON-BOTTOM CULTURE
A firm and stable bottom is required
Is either intertidal or subtidal area directly on hard
substratum.
In intertidal ,minimum 16hrs submergence is
suggested to ensure quality.
Oyster seed attatched to the collectors are planted on
the bottom.
Farmers collect spat on concrete pipes, later
transferring the juveniles to grow-out pipes, cementing
them in place.
Spat density is 2000-10,000 per ha.
The average production is 45 oysters per pipe, or
75,000 per 0.16 ha
A market-size oyster is 7 cm and a few can be
harvested between four and five months of age.

•Advantages
•Less labour to maintain the culture
•Lower capital and maintenance expenses as no
nursery or grow-out structures are required
•Less labour in moving shellstock to new areas because
structures are not involved
•Generally, fewer permits are required for bottom culture
than off-bottom culture
Disadvantages
• Higher rate of siltation
•Less rapid growth and less meat yield
•Growth takes place only one side of the mother shell
•Higher rate of predation

OFF- BOTTOM CULTURE
It is the culture of oysters in some type of mesh
container (basket, bag, cage, etc.) that is held
above the seafloor.
Oysters grown this way are typically hatchery-
reared single set oysters instead of clumps of
oysters normally found in the wild.
 The container provides protection from
predators and eliminates burial in sediment.
 Suspending oysters in the water column
improves growth rates due to improved water
flow.

This systems take advantage of the
availability of food (single cell algae called
phytoplankton) throughout the water column.
They have the following potential advantages
over other production methods like bottom
culture:
1. Promote faster growth;
2. Increase survival
3. Allow control of fouling (e.g.,
barnacles, overset oysters, mud worms)
4.Improve shell shape and appearance
5. Increase product consistency.

OFF- BOTTOM CULTURE METHODS
1.Rack and string (ren) method
2. Rack and tray method
3. Stake culture
4. Raft culture
5. Long line culture

RACK AND STRING (REN) METHOD
This method can be practiced in areas having 1-2.5 m
depth.
The oyster spats collected on shells are made into
strings having six shells using 5-6 mm synthetic rope.
A string can hold six shell valves having 80-100 spat
& 3-4 string are enclosed in a velon screen bag.
The bag suspended from racks for nursery rearing.
After 2 months, the velon screen bags are removed,
the strings are suspended from the racks in the farm.
 Rack-and-string method is mainly advocated for
oyster culture in shallow esturies, bays and backwaters.
A series of vertical poles are driven into the bottom in
rows and horizontal bars are connected on the top of
the poles.

A rack covering 80 sq.m. area holds 90 strings
and 125 racks in a ha.
Oyster shell rens made of 5-6 empty cleaned
oyster shells string in 5 mm thick nylon rope and
positioned 10 cm apart are suspended from the
racks.

At the end of 7-10 months, each string may weigh 7 to
7.5 kg.
 The production of oyster is estimated at 80 ton/ ha.
The mortality is about 45 per cent.
The meat yield is about 10%.
The farmers of Kollam region have adopted it.
The CMFRI is maintaining rack and ren oyster farms for
Research and development for two decades in Tuticorin
Bay and since 1993 in the Ashtamudi Lake .

RACK AND TRAY METHOD
The nursery reared single spat
(cultch-free) measuring about 25
mm are transferred to trays of
size 40 x 40 x 10 cm
 Density is 150 to 200 spat /
tray.
The tray is knitted with 2 mm
synthetic twine of appropriate
mesh size and is suspended
from the rack.
Once the oyster reaches 50
mm length they are segregated
and transferred to rectangular
tray of size 90 x 60 x 15 cm

These trays are placed on the rack which
occupies 25 sq.m area and holds 150-200
oysters
The average growth rate of oyster is 7 mm/
month
 At the end of 12 months, the oyster attains
an average length of 85 mm.
The production estimated is 120 ton/ ha/
year which when compared to string method
is higher, however the production cost is quite
high.

STAKE METHOD
Stake method is adopted if the substratum of
the culture site is soft and muddy.
In this culture method, stakes with one nail on
the top end and two nails on the sides are driven
into the substratum .
These nails hold the shells with spat.
 The stakes are placed 60 cm apart
 In this method, the nursery rearing of spat is
carried on the same stake.
Initially for 2 months, the spat is covered with
velon screen till a size of 25-30 mm.
 They reach marketable size in10 months
The production is estimated to be 20 ton/ ha/

Casurina or eucalyptus poles act as stakes
and level support to the spat, set on shells.
The stake culture is suitable for shallow
waters.
Studies on stake culture is of oysters were
conducted at Tuticorin and hatchery raised
spat , set on oyster cultch , were used.
 Nursery and grow out culture are carried on
the same stake
Each stake holds 3-4 oyster shells with
attached spat
The number of oysters on the shell cultch
vary from 15-20/stake(density )

RAFT METHOD
 In this system oysters are suspended from floating
rafts.
 Raft is the most suitable farm structure in sheltered
bays where the depth is 5m and more
Rafts are constructed using bamboo or wooden
poles and are floated with empty oil drums or wooden
barrels.
 Once raft is positioned by anchors, shell strings with
attached oyster spat are hung from the raft for further
growth.
An alternative to the raft is the long line method
whereby a series of small floats are joined by synthetic
ropes and the line is anchored at both ends.
 Spat set only on the under sides of the tiles& count

The trays or strings are suspended from the rope.
The size of the raft varies however rafts of size 6m x
5 m are found to be quite suitable.
PVC pipes instead of wooden poles and Styrofoam
floats in place of barrels may be used.
 In India, raft culture method not been tried so far.

LONG LINE CULTURE
In this system long ropes or cabels are
anchored at each end and are supported at
each end.
Long lines of 50-100m length are easy to
manage.
Double long line comprising one line on
either side of the floats are also used.
Oyster strings are hung from long lines.
Long lines withstand rough sea conditions
better than rafts
Spat set from about 100 no.per line.

OYSTER CULTURE IN OTHER COUNTRIES
CHINA
Bivalve culture in China has a long history .
 Currently it occupies an important position in
modern mariculture.
 Several species of edible oysters are found in
Chinese coastal waters, however only Crassostrea
plicatula and C. rivularis are cultured on a large
commercial scale.
Oyster production data are available from 1983
During 1997, China produced 23,28,568 t of
oysters, ranked first, and far ahead of other
countries.

CULTURE METHOD
Bottom method
The oyster C. rivularis is cultured mainly
on the bottom of estuaries of low salinity.
A number of cultches are typically used
such as gravel, cement plates, cement bars
and oyster shells.
 As many as 30,000–38,000 cement bars
and 1,00,000– 1,40,000 cement plates are
laid down per hectare.
The growth period ranges between 7–12
months and yields vary from 30–80 t/ha.

Stake method.
In the northern and eastern parts of Fujian, the
bamboo stake is the typical culture method adopted
.
The coastal areas in these regions tend to be soft
and muddy.
Stakes 1.2 m long and 1.5 cm in diameter are laid
down in bundles (4–5 stakes/bundle) in mid-tidal
flats just before the spatfall peaks.
 The bundles are regularly spaced in rows.
 Usually 1,50,000– 1,80,000 stakes per/ha are
used as collector.
The spats settling in May reach marketable size in
11–15 months, and those in September, 16–18
months.

Stone-bridge method:
This method is prefered for sandy muddy bottoms
and is extensively practised in the southern part of
Fujian.
Bridges made of stone bars measuring 80×20×8
cm are used to collect spat on mid-tidal flats in May
and June .
Usually an average of 15,000 stone bars are laid
per hectare
Growth period ranges from 7–12 months and yields
vary from 30–80 t/ha.

Raft method:
The raft method has been recently introduced,
especially in South China, where potential damage
by typhoons has limited oyster culture to the
traditional bottom method.
Raft culture is becoming increasingly important,
mainly due to the fact that higher yields in a
shorter period are obtained when compared to
bottom culture.
An 84 m2 raft produces the same yield in 2 years
as 667 m2 of bottom culture does in 4 years .
In addition, well constructed rafts tend to
withstand heavy action of waves and wind.

JAPAN
At least 8 species are involved
But by far most important is the Pacific
oyster
(Crassostrea gigas)
Methods of culture
Raft culture
Stake culture
Tetsuao SEKI (Japan Fisheries and
Technology Association) reported a
production of 662,000 tonnes in 2010.
(FAP 2010 Yearbook B-53).

PHILIPPINES
There are four species of oysters cultivated: Crassostrea
iredalei, Crassostrea cucullata, Crassostrea malabonensis
and Crassostrea palmipes.
Of these four species, C. iredalei is the most commercially
desirable because it grows at a faster rate to a larger size
and has straight shell margins which make them easier to
open
Methods of culture
Stake method
Hanging method –
the cultches installed in the oyster plots consists of oyster
shells strung in polyethylene ropes of a certain length
depending upon the height of the water column where they
are to be installed.
Holes are punched at the centre of the oyster shells by
means of a nail.

Other methods
Broadcast method
Lattice method
Hanging method

REPUBLIC OF KOREA
Crassostrea nippona, C. echinata, Ostrea
denselamellosa and O. revularisare found
along the coast of South Korea
Pacific oyster (Crassostrea gigas) is of
commercial importance
60% contribute oyster among mollusc
Methods of culture
Bottom sowing culture
Stake culture
 Hanging culture.

FRANCE
•Important species cultivated are
Crassostrea gigas and Ostrea edulis
Methods of culture :
on-bottom culture,
off bottom culture
suspended culture.

Suspended culture (5%),
is done by hanging oysters fixed on
ropes or in baskets from special frames
(tables) in the Mediterranean lagoons or
on lines in the open sea

OYSTER CULTURE IN INDIA
Current status
A number of oyster species occurs in Indian waters
. S. cucullata, a purely marine form, is predominantly
found in shallow areas with rocky substratum.
The native Indian oyster (C. madrasensis) occurs
throughout the coast of India, whereas the other
two Crassostrea species are restricted to the
northwest coast regions and have not been reported
so far anywhere on the east coast .
 C. madrasensis dominates the entire east coast and
Kerala.
It is also found in various localities of Karnataka
State. C. gryphoides is mainly present along the
Maharashtra coast and in several localities of Goa
State.

C. rivularis occurs along the coast of Gujarat State
and to a lesser extent along the coast of Maharashtra
State.
S. cucullata occurs all along the Indian coast,
however only the settlements along Maharashtra and
Gujarat coasts are large enough for exploitation.
 Oyster fishing grounds along the west coast include
Dahanu creek, Jaytapur, Versova, Satpuri, Alibag,
Boiser, Marve, Ratnagiri, Cuff Parade, Mahd, Utsali,
Navapur, Aramra creek, Gagwa creek, Gomati creek
and Azad island.
Oyster culture in India is not as well developed as in
other Indo-Pacific countries, however it has received
considerable interest within the last decade or so.

The Central Marine Fisheries Research
Institute (CMFRI) under the Indian Council of
Agricultural Research (ICAR) is the main
institution involved with bivalve culture.
Through applied research aimed at
developing suitable and low-cost culture
methods and through training and
demonstration courses they are trying to
popularize oyster farming.
Small oyster beds exist in Kerala and
Karnataka, but little exploitation occurs.
Along the east coast, exploitation
concentrates in the backwaters of Orissa, in
Gokulapalli (Andhra Pradesh) and in

Small scale bottom culture of oysters by transplanting
the spat from the natural beds has been practised for
some time along the west coast.
Oyster culture at Tuticorin and some experimental
culture carried out at Athankarai estuary ,
Bheemunipatnam backwaters, Andhra Pradesh , Mulki
estuary , Goa and Cochin backwaters indicated good
prospects for oyster farming along the Indian coasts.
Apart from bottom culture techniques the rack method
has been developed and successfully practised at
Tuticorin.
Each rack can accommodate 20 rectangular trays
which have a holding capacity of 3,000–4,000 oysters .

A variety of techniques and cultch materials have been
tested in India.
Cultches tested were oyster shell rens, coconut shells,
lime coated asbestos sheets, mussel shells, Velon screen
and polythene liner sheets, PVC tubes and lime coated
tiles.
Among the above coated materials, tiles are preferred
due to the high setting rate, although more expensive than
oyster and coconut shells.
A new dimension has been given to oyster culture by the
successful production of seed of the C. madrasensis at the
Tuticorin Research Centre hatchery.
 Conditioning is carried out by supplementing the diet
such as Chaetoceros affinis, Skeletonema
costatum, Thalassiosira subtilis, Isochrysis
galbana and Chlorella salina .
Spawning has been accomplished by thermal stimulation

OYSTER CULTURE IN KERALA
The Kerala state government promotes oyster
farming among the coastal fishers by providing
financial assistance and subsidies.
The brackishwater Fish Farmers Development
Agency (BFFDA) provides Rs.1,500 per a unit of 500
rens.
The profit from a farm ranges Rs.2,500 to 25,000
depending mainly up on the density of spat fall on the
rens.(Marine fisheries information service, CMFRI
The oysters are heat shucked and the meat is
purchased by the Aquaculture Development Agency
in Kerala and marketed.
The participation of women is high in several
farming and postharvest activities.

GROWTH
•Growth of oyster is generally measured by
volume, length or weight.
•Oyster growers measure volume by the number of
oysters required to fill a standard box.
•Length of oyster is measured usually with a
caliper
•The growth of oysters varies from place to place
and depends on food availability and
environmental conditions, particularly salinity and
temperature

HARVESTING
•Oysters reach harvestable size (above 80 mm)
within 10-12 months.
• They are harvested when the condition of meat
reaches high value.
•Harvesting is done manually

DEPURATION
•During depuration the shellfish are placed in cleaning
tanks under a flow of filtered seawater.
•In this system 10-20% of the seawater is continuously
replaced in the tanks and the oysters are held for 24
hours. As a result the bacterial load of the shellfish is
reduced.
•During depuration at the end of 12 hours the water in
the tank is drained and the oysters are cleaned by hosing
a strong jet of water to remove the accumulated faeces.
•Again the tanks are filled with filtered seawater and the
flow is maintained for another 12 hours.
•At the end of this period, the tanks are drained again
and flushed by hosing water.
• Finally the oysters are held for one hour in 3 ppm
chlorine seawater.
•Then the oysters are washed once more in filtered
seawater and kept ready for marketing.

TRANSPORT AND STORAGE OF LIVE
OYSTER
 Oysters can survive out of water for several days,if
carefully handled and kept moist and cool.
 However, it is desirable that the oysters reach the
consumer market within three days of harvest, if they
are to be in prime condition.
 Experiments indicate that live marketable size oysters
packed in wet gunny bags can safely be transported
for 25 - 30 hours without mortality and in good
condition.
 Small holding tanks having filtered seawater or
artificial seawater and provided with adequate
aeration, would keep the oysters alive for a few days
at the whole salers premises

 Shucked oysters require cooling and safe
storage temperature to arrest bacterial and
enzymatic decomposition.
 Shelf life is influenced by storage
temperature as shown below:
TEMPERATURE(⁰C) SHELFLIFE(DAYS)
12 3-5
8 7-8
1 16

SHUCKING
 Shucking is the process of removal
of meat from depurated oysters .
The oysters, after depuration are
kept in boiling water for 2-3 minutes
and transferred to shucking table.
Using a stainless shucking knife
between the valves, the valve is
removed and meat is flipped into the
container by cutting the base of
adductor muscle.
 The meat thus collected is
processed in salt and citric acid
solution and packed-in 2 kg slabs for
freezing.
After thawing the frozen meat, the

DISEASES AND PARASITES
•In oyster farming system, pests, parasites and predators
cause considerable loss of stock.
• 'Dermo' a dreaded disease caused by a fungus Perkinsus
marinus inflicted heavy mortality among East American
oysters.
• Gill disease and shell disease attributed to pathogenic
fungus, caused heavy mortalities among Japanese and
European oysters.
•A disease caused by the haplosporidian parasite Minchinia
nelsoni (formerly known as MSX) was responsible for heavy
mortality in American oysters.
•Whereas predation by this gastropod occurred in the
oysters cutlvated either by rack and string or stake method.

PREDATORS AND FOULERS
•Crabs, fishes, starfishes, polychaetes and
gastropods are the predators that affect the
oyster population
•Predation is generally size specific and
young oysters are more vulnerable than
grown-up oysters.
•However, fouling organisms such as
barnacles, ascidians, other molluscs and
algae are considered mainly a nuisance.
•Sponges , annelids, and bivalves are known
to cause shell damage to oysters

FOULING IN OYSTER
TRAYS
BIOLOGICAL FOULING
CONTROL; SEA
URCHIN

CONTROL OF FOULERS
•Physical
pressure pumps and special nozzles, and
air
drying in the sun.
•Chemical
Exposure for 1-2 hr to freshwater , to
copper
sulphate (1-2%) solution and giving brine
bath,
are some of the chemical methods
• Biological
Green sea urchins are used to remove

OYSTER UTALISATION
Shells
•The empty oyster shells contain 52-55%
calcium oxide and are used in the manufacture
of calcium carbide, lime and cement.
•The shells crushed to suitable size are used as
poultry grit

EDIBLE OYSTER PRODUCTION IN INDIA IN
10 YEARS( CRASSOSTREA MADRASENSIS)
YEAR PRODUCTION
(TON)
2003 800
2004 800
2005 900
2006 1500
2007 2150
2008 2400
2009 1450
2010 3200
2011 4058
2012 4202SOURCE; FAO

PROBLEMS AND PROSPECTS OF OYSTER FARMING
•Sudden changes in hydrological parameters,
mainly salinity cause much damage to the
oyster population
• At a 50% drop from the ambient salinity level
feeding is affected
•first followed by slow degeneration of tissues
and cessation of the gametogenesis.
•Further drop in salinity totally prevents the
oyster from feeding and eventually it dies.

•Similarly higher saline condition of above 40
ppt affects the feeding of the oysters
•Pollution plays an important role in oyster beds
•Considerable quantity of industrial waste
waters, agricultural run-off, dust from thermal
power stations and oil enters the sea
•Oysters, particularly accumulate certain heavy
metals and cause health hazards to those who
consume them.
• Hence assessment of the level of pollution has
to be made before starting culture work

FUTURE RESEARCHPRIORITIES
•In the culture of normal diploid oysters, time
of harvest depends on the spawning
season.
•The oysters could be harvested only during
prespawning periods to maximise return.
•The triplold oysters with enhanced meat
weight and condition factor are harvestable,
irrespective of the spawning seasons.
•For better yield, production of triplold oyster
seed and culturing the triplolds has vast
potential.

INTRODUCTION
•Pearls are classified by
gemologists as cultured
stones.
•They are not “inorganic”
as most stones are but
“organic”
• Fewer than 20 species
of the 8,000 mollusks
produce pearls

•The world’s main pearling grounds were
depleted in the 18th century due to constant
demand
•By the beginning of the twentieth century
most of the world’s pearl-producing mollusks
were in immediate danger of extinction
•Pearls are made of NACRE
•A natural substance produced by
mollusks that also costs the inside of the
animal’s shell (also called “mother of
pearl”)
•Nacre is made up mostly of calcium
carbonate in the form of the mineral
aragonite and held together by crystal layers
called conchiolin

ECONOMIC IMPORTANCE
•Billion dollar retail industry
•Sold all over the world
•Price depends on rarity and quality
•$50 Pair of freshwater pearl earings to $100,000
strand of South Sea pearls.

Taxonomy
Phylum : Mollusca
Class : Bivalvia
Order : Pterioida
Family : Pteriidae
Genus : Pinctada
( Roding-1798)

MAJOR PEARL OYSTER SPECIES
Pinctada fucata (Gould)
The hinge is fairly long and its ratio to the
broadest width of the shell is about 0.85 and that
to the dorsoventral measurement is about 0.76.
The left valve is deeper than the right.
Hinge teeth are present in both valves, one each
at the anterior and posterior ends of the ligament.
The anterior ear is larger than in the other
species, and the byssal notch, at the junction of
the body of the shell and the ear, is slit-like.

 The posterior ear is fairly well developed.
 The outer surface of the shell valves is reddish or
yellowish-brown with radiating rays of lighter
colour.
 The nacreous layer is thick and has a bright golden-
yellow metallic lustre .

Pinctada margaritifera (Linnaeus)
The hinge is shorter than the width of the shell and has no teeth.
The anterior border of the shell extends in front of the anterior
lobe.
The byssal notch is broad. The anterior ear is well developed
while the posterior ear and sinus are absent.
The posterior end of the shell meets the hinge almost at a right
angle. Shell valves are moderately convex.
Externally, the shell is dark grayish-brown with radially
disposed white spots.
 The nacreous layer is iridescent with a silvery lustre except
distally where it is black.

 This pearl oyster is also known as the Black-lip pearl oyster
due to the dark marginal colouration of the shell.
 The width of the nacreous region at the hinge is about 2/3
that of the broadest part of the valves .

Pinctada chemnitzii (Philippi)
 The hinge is almost as long as the antero-posterior
measurement of the valves.
 The posterior ear is well developed and the convexity of
the valves is less than in P. fucata.
 The anterior and posterior hinge teeth are present.
 The posterior ear and the posterior sinus are well
developed.
 The shell valves are yellowish externally with about four
or more light brownish radial markings from the umbo
to the margin of the shell.
 The growth lines of the shell are broad. The nacreous
layer is thin and bright, while the non-nacreous layer is
yellowish-brown .

Pinctada sugillata (Reeve)
 The hinge is considerably shorter than the antero-posterior
axis of the shell with a ratio of 1:1.3.
 The anteroposterior measurement is almost equal to the dorso-
ventral measurement.
 The anterior ear in both valves is small and the byssal notch is
a moderately wide slit.
 The anterior ears are slightly bent towards the right. The
posterior ear and sinus are poorly developed.
 The convexity of the valves is not prominent, especially that
of the right valve.
 The hinge teeth are small and the posterior one is slightly
elongated. The shell valves are reddish-brown with six
yellowish radial markings .

Pinctada chemnitzii Pinctada
sugillata

Pinctada anomioides (Reeve)
 The hinge is shorter than the width of the
broadest region of the antero-posterior
axis of the shell with a ratio of 1:1.2–1.5.
 The hinge and dorso-ventral axis have a
ratio of 1:1.4.
 Hinge teeth are absent or poorly
developed.
 The anterior ear is moderately developed
and the byssal notch at its base is deep.
 The posterior ear and sinus are absent.
 The shell valves are translucent and
externally yellowish or grayish.
 Some shells have faint radial markings.
 The nacreous layer is slightly iridescent
.

Pinctada atropurpurea (Dunker)
 The shell is roundish and its hinge narrow.
 The valves are thin, translucent and moderately convex.
 A poorly developed anterior hinge tooth is present in some
oysters.
 The shell valves are copper colour

Distribution
Pearl oysters of the genus Pinctada are widely distributed in
the world.
They occur in several seas of the tropical belt and in the sub-
tropical region.
Although a number of species of pearl oysters have been
identified, only a few have been found to produce pearls of
good quality and commercial value.
Of these, P. maxima, P. margaritifera and P. fucata stand out.
 The gold/silver-lip pearl oyster P. maxima occurs along the
north coast of Australia, Burma, Thailand, Indonesia,
Philippines and Papua New Guinea at depths ranging from
low tide level to 80 m.

 The black-lip pearl oyster, P. margaritifera is widely
distributed in the Persian Gulf, Red Sea, Sudan, Papua New
Guinea, Australia, French Polynesia, Indonesia, Andaman
and Nicobar Islands, Southwestern part of the Indian Ocean,
Japan and the Pacific Ocean.
 The occurrence of this species is sporadic along the coasts of
mainland India.
 The pearl oyster P. fucata is distributed in the Red Sea,
Persian Gulf, India, China, Korea, Japan, Venezuela and
Western Pacific Ocean.
 In the Indian waters six species of pearl oysters occur but
only P. fucata has contributed to the pearl fisheries in the Gulf
of Mannar and Gulf of Kutch.
 In the Gulf of Mannar, the pearl oysters occur in large
numbers on the submerged rocky or hard substrata known as
paars.

 The paars lie at depths of 12 to 25 m off the Tuticorin coast
along a stretch of 70 km. In the Palk Bay, P. fucata occurs
sporadically on loose sandy substratum attached to
submerged objects in littoral waters.
In the Gulf of Kutch, the pearl oysters are found as stray
individuals on the intertidal reefs known as khaddas.
 In the southwest coast of India at Vizhinjam, Kerala coast,
large numbers of spat of P. fucata have been collected from
mussel culture ropes.
 The blacklip pearl oyster, P. margaritifera is confined
mostly to the Andaman Islands where it is common in some
places.
 From Lakshadweep, settlement of spat of P. anomioides
has been observed on the ridges of rocks and corals.

Biology
Food and feeding habits
 The pearl oyster is a filter feeder.
 Minute food organisms in the water, enter inside the mantle
cavity along with water current passing though the narrow slit
formed by the inwardly directed edges of the pallial lobes.
 These are carried towards the branchiae which act as fine
strainers arresting every particle in the water current.
 The food particles collected thus are carried by the cilia to the
crest of the branchial lamellae and from there they are directed
by the labial palps into the mouth.
 The labial palps have the ability to reject unwanted materials
like mud particles.
 Unicellular organisms including infusorians, foraminifers and
radiolarians have been found in the stomach of pearl oyster.

 Minute embryos and larvae of various organisms, algal
filaments, spicules of alcyonarians and sponges were
also observed.
 The presence of diatoms, flagellates, larvae of
lamellibranchs, gastropods, heteropods, crustacean
nauplii, appendages and frustules of copepods, spicules
of sponges and unidentified spores, algal filaments,
detritus and sand particles were also noted in the
stomachs and intestines of cultured P. fucata collected
off the coast of Tuticorin.
 Oysters from natural beds were also found to contain the
same organisms in their stomach and intestine.

Reproduction
 In pearl oysters, the sexes are separate although hermaphrodite
conditions have been observed in some individuals.
 Change of sex takes place in some oyster towards the end of
spawning.
 Based on the external appearance, microscopic examination
of smears and histological studies, five developmental stages
have been distinguished in the gonads of P. fucata off
Tuticorin coast.

PEARL OYSTER FARMING
Selection of culture sites
In any farming activity, culture site selection is of
paramount importance.
 Technological and economic considerations play a major
role in the selection process.
 A careful appraisal of the habits of the organism to be
cultured would give a resonable level of confidence on the
tolerance limits within which the various environmental
parameters can vary.
 Due consideration has to be given to possible effects of
fluctuating water flow, primary production, siltation, etc. in
order to obtain the optimum level of growth and production
of high quality pearls.

 Unsuitable levels of environmental factors such as salinity,
water temperature, cold water currents and other factors
such as red tides, hydrogen sulphide and pollution by
industrial and domestic effluents are serious hazards to
pearl culture.
 Sheltered bays are ideal locations for pearl oyster farms.
 They offer good protection to the culture structures such as
rafts and cages.
 Shallow coastal waters where the sea is calm most of the
year can also be considered as a suitable site.

Environmental conditions
Temperature
In temperate regions, the water temperature plays an
important role in the biological activities of pearl oysters.
 In Japan, the optimum temperature for oyster growth has
been found to be between 20–25 °C.
 A temperature below 13 °C causes hybernation.
 Below 6 °C, the oysters die.
At temperatures above 28 °C, the oysters show exhaustion.
 The thickness of the pearl layers are affected by the minute
changes in water temperature during the day and also vary
considerably according to the season of the year.

 The deposition of calcium stops at a water temperature of 13 °C.
 In the Gulf of Kutch, the oysters grow vigorously in winter months
when the seawater temperature ranges between 23–27 °C.
 A slight decrease in temperature triggers spawning in oysters in the
Gulf of Mannar.
 The growth-temperature relationship is presumably valid only up to a
certain temperature for optimum growth.
Salinity
 Pearl oysters tolerate a wide range of salinity from 24–50 ‰ for a
short duration of 2–3 days.
 Salinities of 14 ‰ and 55 ‰ may cause a 100 % mortality among
the oysters.
 The effect of salinity on the growth of pearl oyster has not been
clearly investigated.
 However, it appears that pearl oysters tend to prefer high salinities.
 Oysters raised in such salinities produce pearls with a golden tint.

Bottom
Gravelly bottoms are suitable for pearl oyster farming, while
sandy or muddy bottoms should be avoided.
 Repeated culture on the same ground leads to some extent
the deterioration of pearl quality.
 The chemical and physical state of the sea bottom is
affected by the organic substances discharged from the
oysters and fouling organisms.
 Periodic removal of such accumulated substances from the
bottom of the culture grounds often increase production as
well as quality.

Depth
The optimum depth for farming pearl oysters is around 15
m.
 At greater depths, even if the rate of nacre deposition is
slower, pearls of high quality with a pinkish colouration are
obtained.
Silt load
Pearl oysters generally prefer clear waters as high turbidity
levels will affect their filtration efficiency.

Water current
 Tidal amplitude and currents must be sufficient in order
to allow replenishment of oxygenated water and fresh
plankton and flush away waste materials.
 In strong water currents the formation of the pearl
layers is usually fast, but the quality of pearls produced
is affected.

Primary productivity
The condition of a specific culture ground depends
primarily on the chemical constitution of the seawater and
on the species and amount of plankton present.
 Rich nutrients discharged by rivers into the sea are
responsible for high primary productivity.
The oysters probably derive their chief source of conchiolin
from the nitrogen substance of the plankton.
 The organic matter and calcium dissolved in the seawater
are directly absorbed by the food consumption cells.
 The calcium passes through the mantle to be deposited on
the surface of the shell or pearl in the process of their
formation.
The presence of trace metals in small quantities influences
the colour of the nacre.

Supply of oysters
In pearl oyster farming, oysters collected from the
natural beds or reared from naturally collected or
cultured spat are used.
 In the Gulf of Mannar, several pearl banks are
distributed off Tuticorn at a distance of 12–15 km
and at depths of 12–25 m.
 Pearl oysters from these beds are collected by skin
and SCUBA diving.
 In the Gulf of Kutch, the pearl oysters are found on
the intertidal flats and the population is sparse.
Collection is done by hand.

 In Japan, oyster spat are collected by submerging
bundles of cedar twigs near the water surface during the
peak larval settlement season.
 Hyzez films and old fish nets are also commonly used
as spat collectors.
 Almost the entire requirement of oyster supply to the
pearl culture industry is met by this type of spat
collection.
 Spat collection attempts in India have not been
successful, and this may be due to the distance of the
pearl oyster beds from coastal waters.

 Attempts have been made to collect the natural spat of
P.fucata from the costal waters of Veppalodai,Tuticorin and
Vizhinjam Bay using materials such as coconut and pearl
oyster shells,tiles,spit bamboo reapers and frilled nylon
ropes(Nayar et al.,1978;Victor et al.,1987;Achary
,1983;Appukuttan,1987)
 Achary and Thomson (1993) designed a double layered
hapa of 1 m3 size and covered by 2 mm nylon mosquito
net.The hapa containing 25 P.fucata brood stock, was
suspended in the Vizhinjam Bay during the spawning season
and 3125 pearl oyster spat were collected in August 1988.

Silver lip oyster spat collected
in rope collector
Spat pearl oyster attached to
spat collector (Southgate and
Lucas, 2008)

 Alagarswami (1991) rightly stated that “it has been
experienced that spat collection ,as done in japan,cannot
be succesful in india to raise a pearl oyster resource of
commercial value”
 However, India has recently succeeded in producing
pearl oyster seed under hatchery conditions, there by
providing the industry with a more dependable source of
oysters.

 Seed of P. fucata, were produced in 1981 in the laboratory
through hatchery techniques at the Central Marine Fisheries
Research Institute at Tuticorin.
 The technology developed is helpful in overcoming the
problem of insufficient supply of mother oysters for cultured
pearl production.
 The hatchery methods developed are simple to adopt and
inexpensive.
The pearl oyster hatchery of the CMFRI at Tuticorin has
facilities for oyster conditioning, maturation and spawning, as
well as larval and spat rearing

 Oyster broodstock are maintained at a water temperature
ranging from 25–28 °C in a controlled room.
 They are fed with a mixed algal diet at a ration of 4 l per
oyster/day.
Pearl oysters with maturing gonad fed with the above food
for 45 days will spawn with a 30 % response.
 The matured oysters can be kept for a prolonged period at
25–28 °C, while spawning of these oysters can be stimulated
by raising the water temperature by few degrees. (from 28.5
°C to 35.0 °C)
 Spawning of pearl oysters can also be effected by
chemical stimulation(hydrogen peroxide in combination
either with normal seawater or alkaline seawater (pH 9.1) is
used in inducing spawning.)
 Fertilization takes place externally in the water medium

larvae duration
trochophore 10 hour
Veliger/D larva 20 hour
umbo 10-12 days
Eyed stage 15 th day
pediveliger 18 th day
Plantigrade stage 20 th day
spat 24 th day(300 um size)
Alagarswami et al (1987) observed that larval density of 2
nos/ml gaves faster growth and highest spat settlement

 The spat are reared in the hatchery for about two months.
By then they shall have grown to 3 mm or more. They are
then transferred to the farm in velon screen netcages with a
mesh size of 400 μm.
 Mortality may occur if spat measuring less than 3 mm are
transplanted.
The oyster spat attain an average size of 40–45 mm in 12
months.

Oyster spat on shellOyster spat on micro clutch

Rearing methods
Raft culture
Raft culture is considered to be
one of the most suitable farming
methods in sheltered bays.
 The size of the rafts can be
altered according to the
convenience of the situation.
 A raft of 6×5 m in size can be
easily constructed and floated
with 4 buoys

 These logs are arranged as per the requirement and lashed with coir
ropes.
 Floats are attached to the raft to give buoyancy.
 The floats can be sealed, empty diesel drums of 200 l capacity with
fibreglass coating, mild steel barrels painted with
antisaline/anticorrosive paints or FRP styrofoam floats.
 Unit raft system is found to be convenient and well suited to the
Indian sea conditions.
 Rafts are moored with anchors at opposite sides with tested quality
chains and their direction is decided according to the prevalent wind
direction at the specific site.

A) Culture raft constructed with teak
poles; (B) A FRP styrofoam buoy; (C) A
mild steel buoy, and (D) Oyster long-
line culture system.

Long-line culture
In the long-line culture
method, spherical or
cylindrical floats which are
connected by horizontal
synthetic rope or chain are
used.
 The oyster cages are
suspended from the ropes.
This system is good for open
sea conditions.

 In another method of hanging, a
hole is drilled near the hinge of
the pearl oyster.
A small thread is put through the
hole, which is then tied to a straw
rope coated with tar.
The straw ropes are hung from a
raft.

On-shore tank culture
 Large concrete tanks constructed on the shore with the
holding capacity ranging from 75 to 150 tons of seawater
can also be used for rearing the oysters.
 The preferred depth of the water is 3 m to get the normal
growth in oysters.
Under this system, feeding the oysters/juveniles with
cultures of phytoplankters is needed.
 A stocking density of 125nos/sqm is maintained.

Stocked oysters are supplemented with mixed culture of
Chaetoceros spp. Cell concentration in the rearing medium is
maintained at 75,000 cells/l in the tank.
 Daily 25% water exchange is required.
 By this method an average growth of 50 mm in 6-7 months
from a stocking size of 5.0 mm is achieved.

On-bottom culture
 Sea bottoms with a granite or coral stones composition can be
used for on-bottom culture.
 In the Tuticorin Harbour Basin where the breakwater has been
constructed with granite stones, the protected portion of the
breakwater is used for culturing mother oysters.
 1 m of water is available below the low water mark.
 Due to constant circulation of seawater, settlement of fouling
organisms is poor and inconsistent.
 However, it has been noted that the growth of the mother
oyster is slower in on-bottom culture compared to the growth
of oysters cultured in raft.

Rearing containers
Culture of mother oysters
 Box cages, measuring 40×40×15 cm, are used to rear mother
pearl oysters.
 The size of the mesh varies with the size of the oysters to be
reared.
 The frames of the cages are made up of 6 mm mild steel rods,
coated with anticorrosive paints or coal tar.
 Box-cages are useful in general mother oyster culture.
To trace the history and performance of individual oysters,
frame nets are used.

 The frames, measuring
60×40 cm each with five
compartments, meshed and
hinged at one end, open as a
book.
 The oysters are arranged in
rows and held in the
compartments when closed.
 The space available in
between the two frames is
about 10 mm which is
sufficient for the oysters to
open their valves for feeding
and respiration.

Juvenile rearing
 Juvenile pearl oysters are reared in netcages.
 Synthetic fabric of velon screen bags whose sides are stretched
with a steel rod in the form of a prism are used for rearing of
juveniles.
 The mesh size of the screen depends on the size of juveniles to
be reared.
 The mouth of the bag is tied with a synthetic twine which
facilitates opening or closing when required.
 To provide further protection from predators the bags are
placed in old nylon fish net bags.
 Clogging by silt and by the growth of fouling organisms can
be prevented by periodical replacement of the velon screen bag
which can be cleaned, sun-dried and reused.

Spat of up to 2 cm in size
are reared in these small
netcages.
 Box-cages which are
used for rearing mother
oysters can also be used
for juvenile rearing by
providing an additional
velon screen cover inside
the cage.
(C) A netcage for rearing oyster spat of 3–10 mm in
size and (D) Rearing netcage covered with velon
screen.

BIOFOULING AND PREDATION
 Major problems in pearl oysters farming are caused by
biofouling organisms which settle and grow on the
oyster shells, by boring organisms which riddle
through the shells making them weak and friable, and
by predators which feed on the oysters.
 Singly or in combination, these organisms can cause
heavy mortality to the farm stock through
physiological stress and diseases.
 The removal of foulers, borers and predators is a
labour intensive activity.

•Biofouling organisms
Barnacles , Ascidians , Bryozoans,
Molluscs . Sponges
• Boring organisms
Sponges , Polychaetes , Molluscs
•Predator organisms
Perches , Rays , Starfish, Octopus

Small tunicates that compete
with oyster spat.

Control measures
Fouling
 The most effective method of controlling fouling growth is
by cleaning the oysters, cages and farm materials regularly.
 Suspending the oyster cages at depths below 5 m during the
peak barnacle settlement period usually reduces the degree of
settlement of this organism.
 In addition, periodical exposure of the oysters to sun light for
a few hours results in the killing of the larvae of most
undesirable settlers.
 Fresh water, brine and chemical treatment are also found to
be effective.
 Finally, the peak spawning and settlement season of major
fouling organisms can be also avoided by timing the
introduction of the new spat stocks in the farms.

Boring
 The boring polychaetes are easily killed by
immersing the oysters in freshwater for about 6
hours.
 The oyster shell valves infested with boring
organisms can also be brushed with 1 % formalin,
dipped in freshwater and returned to the sea.
 The above treatment is found to be effective against
sponges and Martesia sp. and partly against Polydora
sp.
 At a concentration of 78 %, brine has been shown to
kill all polychaete species within 8 hours.

Predation
 Periodic monitoring of the culture facilities and manual
removal of the predators is the only way of containing
predation on the oysters.
 Oyster spat can be additionally protected from fish by
covering the rearing cages with old fish net.

PEARL CULTURE
 Pearl culture is an art concerned with biological production of
one of the finest gems, the pearl, nature's perfection of beauty
and splendour.
 It is produced by mantle (i.e., the skin) of pearl oysters in
response to irritations caused by external or internal stimuli
such as sand grains, molluscs eggs, parasites, detritus, and other
foreign particles
 The credit for the development of modern pearl culture goes to
Japan.
 They developed and perfected the techniques of pearl culture in
the marine pearl oyster in the early part of the present century,
starting from the initial success achieved by late Mr. Kokichi
Mikimoto in 1893.

 The Japanese marine cultured pearl production has dropped in
the recent years from 127 tonnes (all-time) in 1966 to 34 tonnes
in 1973 which has been stabilised at that level in subsequent
years.
 The annual freshwater cultured pearl production has been
around 7 tonnes recently.
 Pearl culture has spread to other countries, in all cases with the
Japanese help perhaps with the exception of China.
 Australia has a sizable production but the other countries in
South-east Asia such as Burma, Philippines, Malaysia, Thailand
and Indonesia have very modest production limited by the
availability of pearl oyster resource.

 The major species of pearl culture in Japan is Pinctada
fucata from the sea and Hyriopsis schlegelii from the lake.
 In Australia and South-east Asian countries it is the silver-
lip pearl oyster Pinctada maxima.
 The black-lip P. margariiifera forms a small component at
some centres as also black-winged pearl oyster Pteria
penguin.
 Round pearls are produced in P. fucata, while both round
and half-pearls are produced in P. maxima.
 Pearls produced in the freshwater mussels are largely
baroque.

PEARL CULTURE IN INDIA
 India has one of the highest demand for pearls for setting in
jewellry, and is particularly famous for its pearl oyster
resources which yield superb pearls.
 The pearl oyster fisheries are located in two main areas:
1) in the Gulf of Mannar off Tuticorin coast and
2) in the Gulf of Kutch on the northwest coast of the country.
 The pearl oysters are found in two different environments in
the two localities, at depths up to 23 meters in the Gulf of
Mannar, in the intertidal zone in the Gulf of Kutch.
 These bivalves form large beds on hard substrata in the Gulf
of Mannar, while they are sparsely distributed in the Gulf of
Kutch.

 After surveying the pearl oyster resources and fisheries in the
two Gulfs at the beginning of the century, Hornell (1916)
recommended that in order to maintain pearl fisheries profitably
it was necessary to develop techniques to induce the Indian
pearl oysters to form pearls by artificial means.
 In response, the then Madras Government Fisheries
Department carried out preliminary research at the Marine
Biological Station in Krusdai Island, Gulf of Mannar.
 Research focused mainly on the biology and ecology of several
species.
 The oysters were reared in cages and induced to form pearls.
 That work managed to produce only two poorly shaped pearls
and a half-pearl attached to the shell.
 Efforts in Gujarat did not meet success either.

 In October 1972 the Central Marine Fisheries Research Institute
started a pearl culture research project at Tuticorin.
 Success came in July 1973 when a perfectly spherical pearl was
produced.
 This breakthrough was achieved by introducing a graft of the oyster
mantle in the gonad of an adult specimen together with a shell bead
nucleus.
 This is a delicate operation.
 Following this success an Ad-hoc Research Scheme on pearl culture
under the Indian Council of Agricultural Research (ICAR) was
implemented (from 1973–78) by the CMFRI in association with the
Department of Fisheries, Government of Tamil Nadu. During this
Research Scheme, production of cultured pearls by multiple
implantation was successfully achieved.
 Several aspects of pearl formation and pearl oyster biology and
ecology -- highly important for successful pearl culture -- were
investigated.

 The CMFRI also succeeded in artificially spawning
Pinctada fucata, rearing of larvae, and producing seed in
the laboratory by hatchery techniques.
 This breakthrough is very important in light of the
difficulty in obtaining sustained supplies of oysters from
natural banks for culture purposes.
 Recently the CMFRI also produced seed of the black-lip
pearl oyster, Pinctada margaritifera which produces the
highly valuable black pearl.

 To follow-up on the development of pearl culture
technology, the Tamil Nadu Fisheries Development
Corporation and the Southern Petro-chemical Industries
Corporation Ltd. established in 1983 a company to produce
cultured pearls, with the farm at Krusadai and the nucleus
implantation centre at nearby Mandapam.
 The CMFRI is making efforts to promote the pearl culture
technology by conducting short- and long-term training
programmes.
 Scientific and technical personnel from fisheries institutes
in all of the maritime states as well as from the Fisheries
Faculties of Agricultural Universities are given the
opportunity to be trained in these programmes.

CULTURE SYSTEM
Culture operations
Major work is in the sea involving pearl oyster
collection and farming.
 Manpower needs and inventory items vary according
to the scale of the operation.

THE SURGERY
 The two items needed to induce the formation of a
cultured pearl are a piece of mantle and a nucleus.
 The mantle piece, taken from a donor oyster, is grafted
into the gonad of the recipient oyster, along with a
spherical shell bead nucleus.
 The different steps followed in the operation are:
(1) selection of oysters
(2) preparation of graft tissue
(3) conditioning of oysters
(4) pearl oyster surgery and
(5) post-operation care.

Surgical instruments
Knife
 The knife has a blade 9 cm long and a wooden handle 11 cm
long.
 The width of the blade is 1.2 cm at the base and 1.5 cm near the
tip.
 The anterior portion of the blade is slightly curved
corresponding to the curve of the oyster shell, so that the blade
can be easily inserted between the two shells in closed
condition.
 The blade is made by hand forging and finished by filing and
grinding.
 The knife is used to open the unconditioned oysters by sharply
cutting the adductor muscle without touching the mantle lobes.

Scissors
 This is a pair of straight surgical scissors of 10 cm length.
 It is used for cutting a long and narrow strip of mantle from
its edge.
 The cutting edges are sharp and the tips are finely ground so
as to enable quick cutting of a strip before the mantle
withdraws under the stimulus of contact.

Forceps
 The forceps is usually 14 cm long.
 The two components are filed and are provided with
serrations and finely ground points at the tips.
 The material near the joint is ground to proper size to
get required mild tension after due hardness is
imparted.
 It is used to lift the mantle strip from the shell, to hold
it while cleaning and trimming and to reverse the strip
on the wooden block.

Spatula
 The spatula is 17.5 cm long, with a round handle of 13 cm
length and 4 mm diameter and a blade 4.5 cm in length and
8 cm in width.
 The required springiness is given to the blade by grinding
and the edges are smoothened out.
 The spatula is used to remove dirt on the mantle strip and to
smoothen the folds on it.
 It is also used to gently lift back the mantle, labial palps
and gills of the oyster during surgery so that the foot and
the main body are exposed.

Scalpel
 The scalpel is flat and 17 cm long, the length of the
blade portion being 3.5 cm.
 The scalpel is produced by forging from bar stock or
blanked from sheet metal and the actual size and
shape are obtained by filing and grinding.
 The instrument is then heat treated to get high
hardness.
 The 2 cm broad cutting edge provided at the end has
a delicate curve and is smooth and sharp.
 The scalpel is used for trimming the mantle strip on
both edges, to remove unwanted tissue and to sharply
cut the tissue into small bits of the required size.
 It is also used in place of scissors to cut strips from
the mantle.

Oyster stand
 The stand is used to hold the oyster in
a stable position, so that the operator's
hands are free to perform the surgery.
 It consists of two parts, the base and
the clamp.
 The base consists of a wooden board,
to which is screwed a metal square
plate, 4.5 cm wide.
 A vertical tube of 15 cm in length and
1 cm inner diameter is welded to the
basal plate.
 The tube has a collar at the top
provided with a threaded hole for
fixing a bolt to hold the shaft of the
clamp tightly in position.

Shell speculum
 The shell speculum is used to keep the oyster open for
the duration of the operation.
 The instrument is 14.5 cm long and consists of two
components, which are made by forging from round bar
stock to proper size and shape.
 Each component has a long straight portion and an arc.

Retractor
 It is a slender, flat rod 15
cm in length, provided with
a sharp bent hook at the
tapered end.
 The retractor is used to
hold the foot of the oyster
in a stretched position
during the operation.

Lancet-cum-graft lifting needles
 There are three such needles. Each needle consists of an
elongated spindle-shaped aluminium handle in the middle
(6.5 cm long), with a lancet and a graft lifter, each 5.5 cm
long, at the two ends.
 The lancet is a thin (2 mm) stainless steel tapered shank
with its tip slightly curved and flattened to form an
elliptical blade.
 The edge of the blade is rendered smooth and sharp.
 The graft lifter is similar to the lancet, but the tip is
provided with a sharp, pointed spur.
 The lancet is used to make a sharp incision at the base of
the oyster foot and to cut a channel through the tissues of
the gonad up to the site chosen for nucleus implantation.

Nucleus-lifting needles
 These are similar in construction to the needles
described above, but are provided with hemispherical
cups at both ends of the shanks.
 There are three such needles, each with two cups at the
ends.
 The cups are of different dimensions to enable lifting
of nuclei (spherical shell beads) of 2–8 mm diameter
range.
 The cup shoe is initially drawn by hand forging and
finished to dimensions by pressing with iron balls of
proper size in the cold condition.

PEARL FORMATION
Natural pearl formation
 The principal causative factor in pearl formation in a pearl
oyster is the presence of a nucleus.
 It can be of organic or inorganic origin, such as parasites
adults or larvae, molluscan eggs, decaying parts of plants,
sand grains, epithelium or blood cells of the same animal, etc.
 These tiny particles or organisms enter the oyster when the
shell valves are open for feeding and respiration.
 These foreign bodies may become embedded between the
shell and mantle.
 In response to this stimulus, the foreign body is invaginated
by the outer epithelium of the mantle and a pearl-sac is
formed around it.
 Pearls are not produced without the formation of the pearl-
sac.

 The pearl-sac is derived from the internal or external
layer of the epithelium of the mantle or of the gill plates.
 The epithelial cells of the pearl-sac secrets the nacre
which becomes deposited over the foreign body, forming
a pearl in due course of time.
 These pearls are produced either within the mantle, in
other soft tissues of the oyster, or between the mantle,
and the interior surface of the shell.
 Such pearl production is accidental and occurs very
rarely.
 They are generally small and irregular.
 Large and spherical pearls are still rarer to find.
 When the extraneous matter becomes fixed to the shell,
only the exposed portion becomes covered by the pearl-
sac resulting in a blister pearl.

Process of pearl formation. (A) round and half-natural pearls; (B) half-cultured
pearl; and (C) round cultured pearl with an artificially implanted nucleus.

Cultured pearl formation
 Cultured pearls are formed in a pearl oyster, thanks to human
interference.
 In any pearl formation, two things are required, the outer
epithelium of the mantle lobe and core substance or nucleus.
 It was found that cut pieces of the mantle epithelium would
provide the pearl secreting cells and that processed shell beads
would be accepted by the oyster as the foreign body.
 Through careful surgery, the mantle piece graft tissue and the
shell bead nucleus are implanted together, side by side, into
the gonad of the oyster.
 The oysters are then returned to sea for further growth. The
outer epithelial cells of the graft tissue proliferate and
rearrange themselves over the shell bead nucleus, forming a
pearl-sac.
 The inner epithelium and connective tissue of the mantle
disintegrate and become absorbed by the surrounding tissue.

 The cells of the pearl-sac derive their nourishment from the
surrounding tissues and soon reassume their function of nacre
(mother-of-pearl) secretion which is deposited over the nucleus in
the form of concentric micro-layers.
 The nacreous matter consists of thin alternate layers of aragonite
and conchiolin deposited around the nucleus.
 The conchiolin is organic in nature and consists of
mucopolysaccarides.
 It forms the binding layer for the aragonite crystals.
 The aragonite layers are 0.29–0.60 mm thick and are made of
calcium carbonate in the form of highly laminated crystals.
 In cultured pearls the nacre quality and the process of pearl
formation are the same as in the formation of natural pearls.
 Cultured half-pearls are produced by affixing many nuclei on the
inner surface of the shell valves.
 The outer epithelium of the mantle forms the pearl-sac on the
free surface of the nucleus and the halfpearl is formed.

1. Selection and preparation of host
Healthy and adult oysters,preferably those above 45 mm
size,are selected for the production of cultured pearls.
Oysters collected either from natural pearl beds,or from
culture systems.
Gonad of the oyster is the ideal site for the insertion of the
foreign particle ( nucleus) to induce pearl formation.
The inactive or resting phase of the oyster,just after
spawning,is the ideal time for the insertion of nuclei.
Since this phase is short in duration,maturation must be
delayed by keeping the oysters under low temperature.
If only ripe specimens are available,their maturation is
accelerated and they are induced to spawn by keeping them
in warm temperature.
Later, these oysters are used for nuclear insertion.

2. Preparation of graft tissue
Graft is a piece of mantle epithelium, introduced in to
culture oyster before the surgical implantation of the
nucleus.
It is used to wrap the nucleus before implantation.
Graft is obtained from a healthy donor oyster.
The oyster is opened carefully and its mantle is removed.
The dirt and mucus,caught on the mantle,are removed using
the blunt edge of a scalpel.
A mantle strip is then cut away.
It is a gain cut in to 2x3 mm squares.
The mantle strips are kept in sterilized and filtered sea
water.
It is better to use the graft mantle tissue within 10-15
minutes after preparation.

3. Preparation of nucleus
Nucleus is the foreign particle introduced in to recepient
oysters for stimulating them to produce pearls.
Deposition and binding of nacre take place most
satisfactorily around calcareous particles.
There for, the nacreous layer of molluscan shells is most
ideal for the preparation of nucleus.
The shell is made in to small spherical beads of 2 to 3
mm diameter using machines.
These beads may be polished slightly, but never very
smoothly.

4. Implantation of the nucleus
Implantation is the insertion of nucleus into an ideal site of a
recepient or host oyster.
Many host oysters are made ready for this operation.
They are placed in a plastic basin,with the hinge ( dorsal )
portion of their shell directed downwards.
Sea water is then poured slowly into the basin for fully
immersing the oysters.
A little amount of menthol powder may be sprinkled over the
water.
The shell valves of the oysters start to open in a few minutes.
A wooden plug or key is then placed between the valves to
keep them open.
The conditioned oyster is mounted on a stand and nucleus is
inserted.
There are three methods of nuclear implantation,namely
mantle cavity insertion,mantle tissue insertion and gonadial
insertion.

a. Mantle cavity insertion
Nucleus is inserted between the mantle and the shell.
Mantle epithelium secretes nacreous substance over
around the nucleus and a pearl develops attached to the
inner surface of the shell.
The pearl formed by this method is a hemispherical
blister pearl.

b. Mantle tissue insertion
A small incision is made in the mantle of the recipient
oyster and the nucleus is inserted into that incision.
The nucleus is kept in piece of graft mantle before
insertion,in order to stimulate nacre secretion.
The graft tissue is made into a bag like structure with the
help of a cotton thread.
The thread is removed after insertion and the incised
region is applied with antibiotics to prevent microbial
infection.
Nearly round pearls are produced by this method.

c. Gonadial insertion
 Gonad is the most ideal site for nucleus implantation.
 The success rate and the secretion of pearly material
are very high in this method.
 Further,superior quality pearls are produced by
gonadial insertion.
 A sharp incision is carefully made on the gonad.
 The graft mantle tissue from the donor is then inserted
into the gonad.
 This is followed by nuclear insrtion.

The nucleus is placed in contact with the outer epithelium
of the graft mantle tissue.
The oyster is then taken out of the stand and the plug is
removed.
The number of nuclei to be inserted depends upon the size
of the nucleus.
Two to five nuclei are inserted,when they are 3mm or less
in diameter; only one nucleus is inserted,when it is larger
than 3mm.

ANTIBIOTICS
Antbiotics have been used as a means of improving
hygeine during nuclei insertion
Reduce post operative mortality
Antibiotics can be applied to the instruments and to
the oyster tissue during operation or the nuclei can be
coated with an antibiotic
Neomycin (10% oxytetracycline)

POST-OPERATION CULTURE
Culture conditions
 Freshly operated oysters should be reared undisturbed for a
few days.
 If kept in the laboratory, they should be placed in plastic
troughs or FRP tanks, where seawater is allowed to flow
gently.
 If no flow-through system is available, the seawater has to
be changed frequently to overcome the narcotizing effect of
menthol.
 When normalcy is resumed, the oysters slowly re-open
their valves and commence their pumping and filtering
activity.

 If the sea is not calm, it is desirable to rear the operated
oysters under laboratory conditions till the wound heals
completely.
 The normal duration of wound healing is only a day or
two.
 However, if the surgery is rough or the incision is large,
the nucleus could slip out of the oyster, if cultured in
rough waters.
 In Japan, newly operated oysters are hung in deep and
calm waters for a period of 2–3 weeks, by which time
they recuperate fully.
 Afterwards they are hung as in normal culture practices.

 The farming methods described for the mother oyster
culture are followed for the nucleus implanted oysters
All cages containing the implanted oysters are stitched
with velon screen of 1.5 mm mesh at the bottom to collect
the rejected nuclei
The number of oyster per cage is reduced by about 50% ie
50 nos/cage so as to provide better growing conditions
Good quality pearls are produced when oysters are
cultured in 5-10 m depth
Strong sunlight result in poor quality pearls

 Indian waters due to favourable water temparature ,
nacre secretion is continuous and the pearl grows fast
They reach marketable size in 3-4 months with 2-3
diameter nuclei ,and 15 -18 months with nuclei of 6-7
mm diameter(Alagarswami,1991)
PEARL HARVEST: the oysters are brought to the
shore ,opened individually to collect the pearls and are
killed in the process

The rate of pearl growth in relation to the size of oysters, as obtained at
Tuticorin, is as follows:
Oyster
size (mm)
Nucleus
diameter (mm)
Thickness of
nacre (mm)
Duration of
culture (days)
40–50 3 0.609 388
40–50 4 0.692 402
50–60 3 0.929 395
50–60 4 0.732 404
60–70 5 0.590 318

 Quality commands a premium price in pearls.
 The success of the pearl culture industry depends on
the high rate of production of quality pearls.
 Therefore, considerable attention is paid to this aspect.
The value of a pearl is decided by its quality, size,
shape, colour and lustre.
 Exceptional pearls command special premium price
 . Being a product of biological origin, individual
variations are bound to occur in each and every pearl

 The secretion of the mantle or the pearl-sac, which leads
to the formation of the pearl, may be organic or inorganic
in origin, or a combination of both, with unpredictable
and subtle variations in structure and composition.
 The final product may range from the finest to the trash
due to such variations. Even under the highest possible
human control, the quality of cultured pearls cannot be
controlled absolutely, but can be considerably improved
through appropriate care in surgery and during farming.
 Only the size and shape of the cultured pearls are under
the control of the pearl culturist.

 However, the colour and lustre, which depend on the secretion
of the pearlsac, can also be improved to some extent by proper
understanding of individual biological and physiological factors
as well as the environmental conditions of the culture farms,
which influence the formation of pearls
To achieve a high rate of production of quality pearls, the
following factors are required to be taken care of:
Oyster selection
 Large oysters, in terms of size and weight should be selected.
 They must be free from a heavy fouling load and blisters
caused by sponges and polychaetes

 The oysters should be healthy as can be judged from the
colour of the visceral mass and gills.
Narcotization of oyster
 The amount of menthol required to narcotize, and the
duration of narcotization should be carefully adjusted
depending on the volume and weight of the oysters.
Graft tissue preparation
 The graft tissue is one of the most critical factors in
controlling the rate of pearl production.
 The donor oyster should be of the desirable size with a well
developed and healthy mantle.
.

 Extreme care should be taken in selecting, stretching,
cleaning, trimming and cutting of the donor mantle tissue.
Good water quality and correct level of the chemical agents
should be used in maintaining the tissue pieces
Implantation
 The nucleus implantation is one of the most important
factors in cultured pearl production.
 Its success greatly depends on the selection of the correct
site and skill of the technician.
 The positioning and orientation of graft tissue in contact
with nucleus is also critical and should be carried out with
great skill and patience.

Multiple nucleus implantation requires still greater care and
patience.
Oyster convalescence
 Oysters can be made to recover from the effect of
narcotization through periodic changes of water or gentle
flow-through.
 Sufficient time must be allowed for the incision wound to
heal before taking the oysters to the sea for further farming.
Tool maintenance
 The tools must be sharp, rust-free and should have been
either sterilized or suitably cleaned and sun-dried
.

COLOR OF PEARLS
 Different molluscs produce pearls of different colours.
 The colour of a pearl is usually similar to the colour
of the shell nacre of the mollusc which produces it;
this character is genetically controlled.
 This is very clearly shown by Pinctada margaritifera
(black or steel grey), P. maxima (silvery white),
abalones (green) and freshwater mussels (pink).

Status of pearl culture
 The world production of cultured pearls was
estimated to vary between 226.7 to 276.6 t valued
between 992.8 and 1029.8 million USD in 1993 (
fassler ,1994)
 Japan is the largest producer and also the largest
importer of raw pearls
 Japan continues to dominate the production of
marine cultured pearl with china,french
polynesia,indonesia and australia fast emerging as
important pearl producers.
 Cultured pearl production at 127.46 t peaked in
japan in 1966 and declined to a low level of 34.43 t
in 1973.
 China is world leader in the production of fresh
water pearls.

REFERENCES Algarswami,K & Meiyappan,M.M.(1989)
Prospects and problems of Management and
Development of Marine molluscan resources
(Other than cephalopod) in
India,CMFRI,Cochin,India,pp 250-259
Angell ,C .L. (1986). The biology and culture
of tropical oysters. International centre for
aquatic resource and management, pp 8 – 46
Appukkuttan,K.K.,Velayudhan,T.S.,Kuriyakos
e,P.S.,Laxmilatha,P.,Kripa,V. &
Narasimham,K.A.(1993) Farming experiments
and Transfer technology of Bivalve culture
along the south-west coast of
India,CMFRI,Cochin,India,pp 24-26

references Muthiah,P.,Ramadoss,K.& Appukkuttan,K.K.
(1998) Edible oyster hatchery and culture,
Central Marine Fisheries Research Institute ,
Cochin, India,pp 129-133
Narasimham,K.A. (2005) Molluscan Fisheries
Of India, pp 40-80, B. R. Publishing
Corporation,New Delhi
Pillay ,T.V.R. (1990) Aquaculture:Principles and
practices, pp 470-488 ,Marston book services
Ltd.,oxford
Pillai,V.N. & Menon,N.G.(2000) The edible
oyster culture,CMFRI,Cochin,pp 786-797
Thangavelu,R.(1991) Technology of oyster
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