I
INDIAN COUNCIL OFAG.RICUL.TUBAL Rf:$EARCH NEW DELHI .
PRODUCTION OF
CULTURED PEARLS
DR K. ALAGARSWAMI
Director
Central Institute of Brackishwater Aquaculture
Madra~
¥
~3r.jI
leAR
PUBLISHED BY
PUBLICA nONS AND INFORMAnON DIVISION
INDIAN COUNCIL OF AGRICULTURAL RESEARCH
KRISffi ANUSANDHANBHAVAN,:NEW DELHI 110012
First printed: January 1991
Director (P & J)
Chief Editor
Editor
Associate
Technical Officer (Production)
Associate
Chief Artist
Cover Design
DR
V.S.
BHATI
S. N.
TATA
R.R.
LOKESHWAR
ARUNA
T.
KUMAR
1.B. MEHRA
K.B.
GUPTA
M.K.
BARDlfA,"!
SURESH DHAWALE
All Rights Reserved
© 1991, by the Indian C:ouncil of Agricultural Research, New Delhi
Price: Rs 41.00
Laser Typeset by Instaprint, A3 Commercial Complex, Janakpuri, New Delhi 110058
Printed at The CL'TIlral Eleclric Press, A-12/l, Naraina InduSlrial Area, Phase I, New Delhi 110028
and puhlished hy Shri G.S. Agrawal, Under-Secretary, for the Publicalions
and Information Division, Indian Council of Agricultural Research,
Krishi Anusandhan Bhavan, Pus., New Delhi 110012
FOREWORD
PEARLS have fascinated man ever since these were discovered. The process of their
formation in the oyster has been a subject of conjecture by the ancient philosophers
and naturalists. The Chinese developed a practical approach in the 12th century
A.D. to produce pearly Buddha images from the freshwater mussel. The Japanese
solved the mystery by experimentally producing blister pearls in 1893 and free,
spherical pearls in 1907 from the pearl oyster. A new term 'cultured pearl' was
coined to distinguish the Japanese pearls from the 'natural pearl' produced by the
wild oysters. They took the technology to dizzy heights of an industry producing
127 tonnes of pearls in 1966.
The Indian pearl fisheries date back to time immemorial and were compared
at one time with the Persian Gulf fisheries for the production of the finest Oriental
Pearls; In many parts of the world, the fishery for the natural pearls has been
depleted due to over-exploitation, pollution of water or diseases. In India, it has
become more and more irregular during the last two centuries and there has been
no production of pearls since 1961. In this context, the development of tcchnolo gy
for pearl culture at the Central Marine Fisheries Research Institute (CMFRI) of the
ICAR in 1973 and the subsequent research achievements to date have great
significance and deserve our highest appreciation. My personal role, during my
brief tenUI~e as the Director of the CMFRI, has been to initiate a research project
on pearl culture and provide the required support to Dr K. Alagarswami and his
team members. The break-through came immediately within six months after
launching the project.
The soundness of our technology for the production of good quality cultured
pearls has been tested commercially. The pearl oysters are now produced in
hatcheries and this development is a major technological breakthrough iii the
breeding and domestication of tropical marine bivalve molluscs. One aspect
which remains te be developed is the large-scale production of shell-bead nuclei,
a mechanical engineering proc.ess, which should be taken up seriously so that the
technology of the production of cultured pearls becomes totally indigenous. The
tropical conditions of our seas enable a faster turn over of pearls than the period
required for producing t\1em in temperate waters. The Andaman and Nicobar
Islands and the Lakshadweep with their numerous lagoons, bays and inlets could
provide Idea~. conditions for pearl culture. The pearl trade of India is of a
considerable magnitude involving import, processing, domestic sale and export.
Therefore, full advantage should be taken in using the indigenous technology for
further commercial production in suitable areas.
This publication on the production of cultured pearls is indeed a valuable
addition to the Indian literature on science and technology and includes some
important references on the subject Its treatment in 12 chapters gives a wide
coverage of the resources, technologies, industry and current devcloplnent in
iv
PRODUCTION OF CULTURED PEARLS
pearl culture. It deals with pearl culture at the global level and also describes fully
the work carrie!i out in India. Besides the marine pearl culture on which the work
has been largely based, the publication has also touched upon the freshwater pearl
culture -.yhich has a great scope in the country.
Dr K. Alagarswami, presently the Director of the Central Institute of
Brackishwater Aquaculture, has spent about 15 years of his illustrious career of
research on pearl culture. He has written this publication with great care. I am sure
his technical competence and professional ability will be well appreciated by the
readers.
The Indian Council of Agricultural Research, is to be complimented for
commissioning this publication on a subject of common interest and of much
technical value. I have no doubt that this Bulletin will have a large audience of
scientific workers, prospective entrepreneurs in the pearl culture industry and all
interested persons. It will surely be cited widely as an important reference on pearl
culture.
SZ. Qasim
ACKNOWLEDGEMENTS
IT gives me great pleasure to record my gratitude to various organizations and
individuals who helped me in the course of the development of pearl culture
technology at the Central Marine Fisheries Research Institute. The Indian Council
of Agricultural Research supported the •• Scheme on Pearl Culture" during 197378 and, subsequently, the research projects on pearl culture and pearl oyster
hatchery at the Central Marine Fisheries Research Institute. For the contributions
made in these fields, the ICAR awarded the Hari Om Ashram Trust Award for
Agricultural Research for 1976 to me and the lCAR Award for Team Research in
Agriculture (for the biennium 1985-86) to my colleagues and myself.
Dr M.S. Swaminathan, F.R.S., the then Director-General of the ICAR,
showed a keen personal interest in developing this technology at the the C:MFRl
in 1972 and gave the necessary impetus. Dr S.Z. Qasim, the then Director of
CMFRI, was responsible for creating for the first time a research programme on
pearl culture in the Institute and providing all support and encouragement. The
breakthrough in the technology was achieved during his tenure. Afterwards, for a-brief period during 1974-75, Dr R. V . Nair, Director, helped main tain the progress
of the project. Later, Dr E.G. Silas, during his stewardship of the Institute for a
decade from 1975 to 1985, gave top priority to this programme, which facilitated
the vital breakthrough in the hatchery technology, besides making an overall·
progress in the projects. Since September 1985, DrPS. B.R. James, Director, has
given further thI1lst and added a sea ranching programme aiming at the revival of
the pearl oyster beds in the Gulf of Mannar. Dr P. V. Dehadrai, Deputy Director~
General (Fisheries), Indian Council of Agricultural Research, gave support and
encouragement to th,is publication.
The involvement of the CMFRl in 1972 in pearl culture research would not
have been possible but for the permission generously given by the Government of
Tamil Nadu, for directly collecting pearl oysters from the Gulf of Mannar.
Subsequently, the Department of Fisheries of Tamil Nadu collaborated with the
CMFRI in the ad-hoc Scheme on Pearl Culture. The joint venture commercial
project taken up by Mis Tamil Nadu Fisheries nevelopment Corporation Ltd and
Mis Southern Petrochemical Industries Corporation Ltd in 1983 drew the technical
know-how from the CMFRI, and the Institute got feedback information in
problems faced by them. Utilizing the experience gained by the scientists and
officials in the training courses organized by the CMFRI, the Government of
Gujarat has been carrying out a Research and Development project in pearl
culture, and the Central Agricultural Research Institute for Andaman & Nicobar
Islands and the Department of Fisheries of Lakshadweep have been trying pearl
vi
PRODucnON OF CULTURED PEARLS
culture in the island territories. Put together, these efforts have enriched our
knowledge and have emphasizeq the importance of practical considerations that
are required in launching pearl culture projects at different centres.
My scientist associates, Dr A.C.C. Victor, Shri A. Chellam, Shri S. Dharmaraj
and Shri T.S. Velayudhan, have stood together wJth me as a team and worked with
untiring devotion and dedication. It gives me great pieasure La record my
appreciation and gratitude to these scientists. Shri A.D. Gandhi, Shri 1. Antony
Pitchai (since retired on superannuation), Shri Soosai V. Rayen, Shri Dasman
Fernando, Shri K. Shanmughasundaram and Shri K. Srinivasagam provided
excellent technical assistance to the projects. The Officer-in-Charge of Tuticorin
Research Centre, Shri K. Nagappan Nayar (up to 1986) and Shri S. Mahadevan
(since 1987), have given administrative and logistic support to the projects. Smt
N. Ambika, Junior Stenographer, CMFRI, Cochin, diligently and carefully typed
the nlanuscript, and Shri K. Sankaran, Artist, drew the illustrations of this
publication. I thank them all for their valuable help.
lowe my deep gratitude to my wife Sm! A. Lakshmi, who has stood by me
through the difficult period of heavy demand on my time for the project and for
the completion of this manuscript as well.
I am grateful to the Indian Council of Agricultural Research for assigning
the work of preparation of this publication.
CONTENTS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Foreword
Acknowledgements
Introduction
The theory of pearl
Distribution, ecology and biology of pearl oysters
Pearl fisheries
Pearl oyster breeding
Pearl oyster farming
Production of cultured pearls
Structure and composition of pearl
Freshwater pearl culture
Cultured pearl industry
Recent developments in pearl culture
Transfer of technology and strategy for pearl culture in India
References
Appendix I
iii
v
1
3
15
22
38
48
59
77
82
8S
93
98
104
109
CHAPTER!
INTRODUCTION
PEARL is a very fascinating subject associated with nature's mystery. It is counted
among the nine gems and has been treasured since the earliest human civilization.
In its purest and simplest form, pearl is a beauty adored whereas the rest of the
gems are appreciated only after they are cut and polished to bring out their beauty.
Pearl has been a subject of folklores allover the world and is also a subject of one
of the most modern sciences - genetic engineering. The Vedas, the Bible and the
Koran speak on pearls giving one of the highest places for it, associating it with
purity, virtue, chastity and wealth, the greatest attainments a human can achieve.
The philosophers, poets and scientists have treated the pearl in their own way.
From the commoner to the emperor, cutting through the levels of society, pearl has
been an object of adornment. The price of pearl ranges from a few pennies to
thousands of pound sterling depending upon the size and quality. And yet, the
pearl is produced by a lowly mollusc as a pathological product in the depths ofthe
oceans. While science has unravelled the mystery of pearl to a very large extent,
much remains to be explored.
Pearls produced by the pearl oyster from the Persian Gulf and the Gulf of
Mannar are the famous Orient Pearls. Those produced by the freshwater mussel
in European rivers are the Occident Pearls. With the discovery of new continents,
migrations of people and development of trade, pearls came to be collected in
several other parts of the world such as the Central America, Caribbean Sea, Gulf
of California, Indo-Australian Archipelago and the Western Pacific. All these
were natural pearls accidental in the animals. Collection of pearl oysters was
termed as pearl fishery or pearling. It was organized under the control of the
governments. In the recent. years, the pearl fishery has gone into oblivion due to
various reasons. Some of them are depletion of stocks due to pollution and
diseases, and shift of interest due to growth in economy in other areas. The natural
pearls that circulate in the world trade today are those produced decades back and
there has been no great nett addition to the old stocks. The last Indian pearl fishery
of Gulf of Mannar was conducted in 1961 and there has been none subsequently.
The collections from the Gulf of Kutch ebbed out in 1966.
The cultured pearl became a phenomenon consequent to the advent of pearl
culture in Japan in the early part of the present century; What was accidental in the
oyster was converted into 'asking rates' of production through manipulation of the
process of pearl fonnation. Pearls which were produced in a few number were
produced in tonnes and made available much cheaper and to every woman who
desired them at affordable cost. That has at least been the motto of the late Kokichi ,
Mikimoto of Japan; the Pearl King and the Father of Pearl Culture industry.
2
PRODUCTION OF CULTURED PEARLS
The art of pearl culture has entered the realm of science to correct the skews
of commercial production and to improve the quality. The present stage is full of
challenges - to add new regions, take additional species and to develop modem
techniques. Apart from extension of pearl culture which has its own problems, the
basic aspects of mother-of-pearl secretion by the animal, biomineralization,
crystallization and growth into patterns of nacre offer great scope for investigations.
Tissue culture, genetic manipulation and crystallography are being given considerable
importance in attempts to improve pearl quality. The future of pearl culture lies
in these areas.
The failure of Indian pearl fishery was recognized as early as the beginning
of the present century. James Hornell, a noted British marine biologist who
worked both in Ceylon (now Sri Lanka) and India, stated that "the only
economically sound way of making the Indian and Ceylon pearl fisheries
permanently and regularly remunerative is to concentrate upon the inducement of
pearls by artificial means in comparatively limited numbers of cultivated pearl
oysters and to avoid all expensive attempts to control the comings and goings of
oysters upon the natural beds in deep water" (Hornell; 1916). It has been a long
way since then with confidence lostor gained. When the first phase of uncertainties
of technology for several decades (Devanesen and Chidarnbaram, 1956; Devanesen
and Chacko, 1958) ended. the current phase started with the breakthrough in
technology (Alagarswarni, 1970, 1974; Alagarswami and Qasim, 1973) and
further achievements in several areas of pearl culture (Alagarswami, 1987 a, b).
A commercial production attempt has been made, though not fully successfully
due to problems inherent to a new venture. The technology is not to be faulted as
good-quality cultured pearls have been produced. It is the logistics which require
to be looked into to make pearl culture a commercially viable proposition in India.
As HoUyer (1984) pointed out, pearl culture is a long-term investment and big
profits can be made in a successful culture operation as there is still a great demand
for pearls.
CHAPTER 2
THE THEORY OF PEARL
THE English word pearl is derived from the Latin pirula which means pear. Pearls
are often pear-shaped and hence the name. In other European languages, pearl is
named from similar derivatives - parel or paar/ in Dutch, perle in French and
perla in Italian and Spanish. The Greek name margaritae (margarita of the
Romans) for pearl is, according to etymologists, derived from the old Oriental
languages - Persian mervarid, Babylonian mar-galiler, Sanskrit manjari-h and
Semitic margun (Bolman, 1941).
PEARLS IN ANCIENT TIMES
Since the dawn of human civilization, pearl has been an object of adoration.
The beauty of the pearl, as extracted from the oyster from the sea or the mussel
from the river, enchanted the early man and has continued, over the millennia, to
be closely associated with man, revered in worship, considered as a symbol of
purity and serenity, adored as precious gem and held as a barometer of wealth.
Pearls are mentioned in the earliest of the Indian Vedas, the Rig Veda.
Chinese literature, believed to belong to 2200 B. C., mentions pearl gifts. Ancient
Persian Kings' palace at Shushan, when excavated recently. yielded pearls which
belonged to the 4th century B.C. and are supposed to be the oldest of its kind in
existence. The Indian epics Ramayana and Mahabharatha mention pearls and also
indicate inclusion of pearl-divers in the army units in times of war. The Hebrew
literature, the Bible and the Koran speak. of pearls in glorious terms.
Pearl reached its zenith in the Roman empire as can be gleaned from the
writings of Pliny. He wailed over the fact that the coffers of the empire were being
emptied to pay in gold [or the import of pearls from Persia and India. The
emperors, nobles, wealthy and the commoners alike were crazy of pearls. .
The Roman extravaganza is matched in the Tamil Sangam literature of 4th
century A.D. which states in a passage that Korkai (an ancient port in Tamil Nadu)
belonged to the Pandya king who possessed a beautiful chariot to which were
yoked beautifully trotting horses, whose hoof marks could not be traced on the
ground covered with the cool-rayed pearls (Arunachalam, 1952). In the .6th
century B.C. King Vijaya who conquered Sri Lanka is said to have included rich
offerings of pearls among the presents to his father-in-law, the Pandyan King of
Madurai. Megasthenes, the Greek Ambassador at the court of Chandragupta
Mauryaduring 3rdCentury B.C. and in much later years Marco Polo (1260-1300
A.D.), Ibn Battuta (1325-1354 A.D.) and several other travellers have left glorious
accounts of the pearl fisheries of India and Sri Lanka.
4
PRODUCTION OF CULTURED PEARLS
The pearls of Cleopatra are legendary. At a banquet she is said to have
wagered Mark Antony that she co~ld give the most expensive dinner. She
removed one of her large matched pearl ear-rings, crushed and dissolved hin wine
and drank the costliest potion. Pliny estimated that those pearls then were worth
60 million sesterces, or 1,875,000 ounces of fine silver.
MYTHS ABOUT NATURAL PEARLS
The most fanciful idea among the folklores of yonder days is that pearls are
the tears of Nereids (sea nymphs). A Japanese legend has it as follows: On a
fullmoon night, a beautiful princess was tom away from the arms of her lover on
the banks of Ago Bay by the evil spirits, and the tear drops rolling down the rosy
cheeks of the queen of night from the heavens turned to treasures in the green
waters of Tatoku. The Atharva Veda states that when the oceans roared against
Paranjaya with lightning, therefrom was born this golden drop (of pearl). Aelian,
a Latin writer of first century A.D., stated that pearls were formed by a lightning
flash entering the opened shells of oysters.
Pliny the Second (69 A.D.) wrote in his book "Historia Naturalis" on the
origin of pearls thus: "The pearl-oyster gapes in spring, catches the dew, by which
the oysteris fecundated; the pearl is the product derived from this. The pearl is fullgrown, when the purity and clearness is influenced by the purity of the received
dew. When the fecundation has happened during the stormy weather, the pearls
are pale; in that case they are originating from heaven and not from the sea. The
pearls are cloudy or equal coloured, when the heaven is clouded or clear during
fecundation. Because they are in relation with heaven, it is not to wonder, that they
are friends with the sun, by which they are coloured reddish and lose their white
colour, as it is with the human skin". He further added that •'Pearls consist of
multiples of the same pile ate layers; they form a callous skin, from which they are
cleaned by the people". The theory of Pliny follows the general fanciful view as
held in India that pearl is formed when the oyster receives a drop of dewar rain.
Starting from the 16th century several theories on pearl formation which are
not entirely speculative, were put forth by more modem writers. The three
methods generally referred to in these competing theories were: (1) sand grain
irritation, (2) pathological secretion, and (3) stimulation caused by the presence
of a parasitic worm.
BIVALVB MOLLUSC
Structure
Before proceeding further with the discussion on how pearl is formed"it
would be necessary to understand the general structure of a bivalve mollusc with
the example ofpearJ oyster. It consists of a pair of external shells or valves and a
soft body (Fig.l). The shells are joined together on the dorsal side by the hinge
which permits the opening and closing of the valves. The mantle is a thin skin
5
THE THEORY OF PEARL
h
am
Fig. 1.
Dorso-ventral section through the pearl oyster Pine/ada/lICata. am, Adductor
muscle; dg, digestive gland; g, gill; gn, gonad; h, hinge; i, intestine; ro, mantle;
pm, pedal muscle; sh, shell; st, stDmach.
which hangs on either side of the soft body of Lhe animal, attached to the inner
aspect of the shell by the adductor and oLher smaller muscle bundles on the one
hand and to the soft parts of the body on the other; however, on the ventral aspect
the mantle lobes are free from any attachment. The mantle is responsible for the
secretion of the shell right from the early larval stage.
Shell structure
The shell is composed of 3 layers, viz. the outer periostracal layer, the
middle prismatic layer and the inner nacreous or mother-of-pearllayer (Fig.2).
The periosLracal layer is composed of organic $ubstances (conchiolin). The
6
PRODUCTION OF CULTURED PEARLS
Fig. 2.
Transverse section of bivalve shell showing the three layers.
cL Conchiolin layer (periostracum); pI. prismatic layer; nl, nacreous layer.
5
pe
Fig. 3.
Radial section (diagrammatic) of shell edge and mantle margin of
bivalve mollusc showing the site of shell mineralization.
e, Outer epithelium of mantIc; m, mantIc; n, nacre; pe, periostracum;
pI, prismatic layer; s, site of mineralization.
prismatic and nacreous layers are formed by inorganic calcium carbonate in the
form of calcite or aragonite crystals. The epithelial cells of the mantle secrete the
organic and inorganic substances of the sheU (Fig;3).
Pearl, which t:tymologically arises from the word 'pear', is nothing but the
THE THEORY OF PEARL
7
formation of a free object of that shape (and its variations from sphere to baroque)
composed essentially of the calcium carbonate crystals of the aragonite form.
There is a close similarity between the nacreous layer of the shell and of the pearl
produced in the pearl oyster.
Formation of pearl
In the simplest way, it may be stated that a pearl is formed when a foreign
body, such as a grain of sand or a parasite, lodges itself into the soft tissue of the
pearl oyster. Since the oyster cannot always get rid of this irritant. it protects itself
by secreting nacreous substance that gets deposited over the foreign body in thin·
microlayers. thus forming a pearl. Since only the outer epithelial cells of the
mantle are capable of secreting nacreous substance the chances of pearl formation
are limited only to those cases where the foreign body is in contact with the mantle
epithelium. The mantle epithelium at the point of contact of foreign body
undergoes changes. The outer epithelium regenerates a new layer of cells which
spreads over the foreign body and covers it completely. This layer is called the
pearl sac. The pearl-sac epithelium secretes nacre around the foreign body which
becomes the nucleus of the pearl. The pearl oyster 'learns' to live with the
encysted pearl. The pearl grows in size as the oyster grows.
As to the nature of the foreign body that acts as the irritant it may be of
organic or inorganic origin. Sand grain is the common inorganic material that
finds an entry into the pearl oyster. The larval forms of parasitic cestodes and
trematodes, and minute planktonic organisms form the organic core material
around which pearls are formed.
Blister pearl
Pearl formation may take place when the foreign body lodges itself between
the shell and the mantle. Such situations lead generally to formation of attached
or blister pearls on the surface of the shell. The foreign body is attached to the shell
by the secretion of the mantle and with continuous depositions of nacre around the
foreign body, a blister pearl is formed (FigA).
Free pearl
Under certain other conditions, the foreign body gets embedded in the
connective tissue of the mantle. The invading body as it breaks through the outer
epithelium of the mantle carries a few epithelial cells which would regenerate and
grow into a complete pearl sac around the foreign body. As a result of secretion
of nacre a free pearl is formed.
Besides on the shell and in the mantle, pearls are found in other soft tissues
of the pearl oyster such as the adductor muscle, gills and pallial muscles. Since
nacre secretion is possible only in the outer epithelial cells of the mantie, it has to
be deduced that the foreign body, during its sojourn inside the oyster, should have
carried a few epithelial cells of the mantle or should have corne in contact with a
8
PRODUCTION OF CULTURED PEARLS
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THE TIlEORY OF PEARL
9
few detached epithelial cells that might be found floating in the vicinity of the
mantle. When it finally ge~ embedded in the soft tissues, these few cells would
grow by poliferation leading to the formation of the pearl sac.
Pearl without nucleus
Given this accepted theory of pearl formation with a pearl sac and a nucleus,
the term 'pearl without nucleus' would seem to be a contradiction. It is supposed
that the size of the nucleus may even be as tin y as a few microns. It is possib Ie that
a few decayed blood cells or epithelial cells might provide the basis for pearl
formation but subsequently disintegrate totally. Such pearls, when cut and
examined, would not reveal any nucleus and would appear to be formed entirely
of mother-of-pearl layers without a recognizable nucleus.
CULTURED PEARLS
The Greek philosopher Appollonius (2nd century B.C.), in his description
on how pearls are produced in the Persian Gulf, narrated that the fishermen would
render the sea smooth by flooding it with oil. Then they would dive and, holding
out a small container of an aromatic herb, would induce the oyster to gape. Into
this opening they would insert a long hollow pin and draw off the pearl-making
liquid which would then be placed in iron moulds whence it would solidify into
a pearl (Abbott, 1972). He had impleaded man's intervention in the production of
pearl.
Pearl Buddha teChnique
The Chinese were the first to produce pearly objects in molluscs since the
12th century A.D. They used, a species of mussel in the rivers and lakes. Mussels
of about 20 em length were collected from Lake T~u in Central China and placed
in bamboo cages. By means of a forked bamboo stick, small pellets of hardened
clay and small outlines of Buddha made of tin were inserted between the shell and
the mantle. The cages were left in the canals and pools for about one year after
which the mussels were opened. The objects inserted were found to have received
a coating of nacre and attached to the shell (Fig.S). The tiny raised pearly Buddhas
were sawed off the shell and.,sold in the temple markets (Abbott, 1972). This
practice continued in China for a long time without any change.
Pearl culture attempts in Europe
Carl von Linnaeus, aSwedishnaturalist, claimed in 1761, to have discovered
a process by which pearl could be produced artificially in the freshwater mussel.
He wrote that in the course of five years he was able to produce in any mother-ofpearl shell, the size of one's hand, a pearl as large as the seed of the common vetch.
He submitted the process to the State Council of Sweden, which set up a 'Secret
Committee' in 1761 to look into the claim. The Committee recommended an
10
Fig. 5 .
PRODUctION OF CULTURED PEARLS
Production of nacre-coated images of Buddha in the Chinese freshwater mussel
in the 12m Century. (After Simkiss and Wada. 1980)
award of 12,000 dollars which was not actually paid. But the process was bought
by a Gennan merchant Peter Bagge for 6,000 silver dollars but was never put to
usc (Simkiss and Wada, 1980). The pearls so produced by Linnaeus had been
deposited in the Linnaen collections. Herdman and Hornell (1906) stated that the
'secret process' of Linnaeus consisted merely in piercing the shell and inserting
a small fragment of calcareous matter kept in position by a fine silver wire. The
hole was then sealed and the mussels left for a number of years before opening
them and removing the pearls.
As early as 1857, E.F. Kelaart, in his' 'Introductory Report on the Natural
History of the Pearl Oyster of Ceylon" observed that when a grain of sand or the
larva of an insect (meaning perhaps a helminth parasite) is introduced between the
mantle and the shell, it will become covered over with the pearly secretion. In his
last report of 1859, Kelaart, corrOborating the observations of A. Humbert,
suggested that it may yet be found possible to infect pearl oysters in other beds
with these worms, and thus increase the quantity of pearls (fide Herdman and
Hornell, 1906).
Several workers found a relationship between the pearls found in the
European mussel Mytilus edulis and the occurrence of Distomid parasitic worms
(Gamer, 1863; Dubois, 1901; Jameson, 1902,jide Herdman and Hornell; 1906).
Expe[iments are stated to have been conducted to artificially infect the mussel
with the parasitic worms to improve pearl production, the whole process having
been referred to as 'margarose artificieJle' . However, these aLtempts did notresult
TIlE THEORY OF PEARL
11
in artificial production of pearl s as could be "justified by lhefacts" (/ide Herdman
and Hornell, 1906).
Pearl culture in Japan
Finally, it was the Japanese who succeeded in solving the mystery of pearl.
Kokichi MikimolO was the flrst among nine children of a noodle-seller living on
the banks of Ago Bay. He worked in his father's trade and also as a green grocer.
Later, moving to Tokyo, he traded in marine products. Professor Keikichi
Mizukuri of the Tokyo Imperial University, who had known the Chinese pearl
Buddha technology, had informed Mikimolo of the process. Mikirnoto set his
mind on producing pearls in the Japanese pearl oyster akoya gai. He gathered them
and set them out in guarded areas in the bay in 1888. He inserted all conceivable
materials like bits of shell, coral pieces, bits of metal and ground-up fish scales
between the shell and the mantle of the oyster. He was not successful in the
beginning, and a red tide took toll of his oysters in 1892. Undaunted by this
crushing misfortune, he tried again and, on 11 July 1893, he found blister pearls
in five of his oysters (AJagarswami, 1970).
Later, while producing such blister pearls on a large scale, Mikimoto also
started experimenting with free pearls. In 1907 Tokichi Nishikawa, a scientist at
the Misaki Marine Biological Laboratory of Tokyo Imperial University, had
concluded that a free pearl was formed when the shell-secreting cells of the mantle
tissue migrated into the body of the oyster under the stimulus of a foreign body.
He saw that these cells divided and surrounded the foreign body forming the pearl
sac which secreted the resulting pearl. At the same time Tatsuhei Mise, in May
1907, applied for a patent on his spherical pearl method andon the needle used for.
inserting the n uclcus. In 1913, Nishikawa succeeded in experimental production
of spherical pearls and, after his premature death that year, his assistants, the Fujita
brothers started commercial production of free, spherical pearls. Sukeyo Fujita
went over to the South Pacific and Masay Fujita to Shikoku island of Japan where
they continued their pursuit of commercial production of cullured pearl. By 1919,
Mikimoto himself achieved success with round cultured pearls and patented his
method. Thus the modern technology of culture of free pearls was evolved by the
efforts of Nishikawa, Mise and Mikimoto. Commercialization of the process was
started by the Fujita brothers and Mikimoto (Cahn, 1949).
In 1919, Mikimoto sent some of his pearls to London for sale at 25% less
than the cost of natural pearls. This caused a flutter in the European jewel market
and the business denounced the cultured pearl as fake. The newspaper London
Star, datelined 4 May 1921, stated that certain merchants were selling Japanese
cultured pearls so skilfully made that without cutting them in half it was
impossible to distinguish them from the natural pearls. The London Chamber of
Commerce said that it was determined to treat the Japanese products as a fake
because its appearance in the market had caused changes in the prices of natural
pearls. The problem was solved in favour of cultured pearl only after scientists had
12
PRODUCTION OF CULTURED PEARLS
examined the process and the product, and gave the verdict recognizing the
cultured pearl on its own merit (Shirai, 1970). From that day, the cultured pearl
never had to look back.
PEARL-PRODUCING MOLLUSCS
By I he theory of pearl formation, it can be stated that any mollusc, bivalve
or gastw[1od, which has the mother-of-pearl layer on the inner aspect of its shell
is capable of producing a pearl by scientific definition. However, pearl as a jewel
is produced only by a few species of molluscs. Some of the pearl-producing
molluscs ru-e listed here.
Marine pearls
Pearl oysters: The prime species of pearl oysters from the sea are Pinetada
fucata, P. margariLifera and P. maxima (Figs 6-9). These produce the finest
Fig. 6.
Indian pearl oyster, Pinctadafucala.
pearls. There are several other species such as P. chemnitzii, P. sugillata, P.
atropui"purea and P . anomioides which neither form a resource nor produce pearls
of any commercial value.
Winged oyster: PUria penguin produces pearls rarely.
Windowpane oyster: Placenta pLacenta produces seed pearls of very small
size. These are used for their medicinal properties and not considered as gems as
THE THEORY OF PEARL
Fig. 7. Black-lip pearl oyster, Pi.nctada margaritifera.
Fig.8. Silver-lip pearl oystel, Pinclada maxima (exterior
of shell). (Shell: Courtesy Dr E.G. Silas)
13
14
PRObucnON
OF CULTIJRED PEARLS
Fig. 9. Pine/ada maxima (interior of sheIl). (Shell:
Courtesy Dr E.G. Silas)
they are porcellaneous and translucent.
Sea mussel .' Mylilus edulis. Perna viridis and Perna indica produce small
seed pearls occasionally but these are not considered gems.
Giant clam : Several species of Tridacna contain pearl formations of
occasionally large size, as big as a golf ball, but they are porcellaneous without
mother-of-pearl.
Gaslropods: The abaJone Haliotis produces multicoloured irregular pearls
with nacreous layers sometimes with strong iridescence, especially red and green
colours. Several other genera such as Cassis. Strombus. Trochus. Turbo and
Xancus contain occasional pearl formations.
Freshwater pearls
Just as the marine pearl oysters of the genus Pinclada, freshwi;ter mussels
belonging to Unionaceae are considerably important for production of pearls.
/-/yriopsis schlegelii of Japan and Cristaria plicata of China, a large number of
species belonging to Quadrula. Pleurobema. Tritogonia and Megalonais of the
USA, and species of Unio of Europe arc the more notable species. Parreysia
corrugala and Lamellidens marginalis of SouLh Asia, though not of the same
prominence as the foregoing species, produce pearls of some value.
CHAPfER3
DISTRmUTION, ECOLOGY AND BIOLOGY OF
PEARL OYSTERS
DISTRIBUTION
THE dislribution of major species of pearl oyster in the world is largely confined
to the Iropical belt from the Tropic of Cancer to the Tropic of Capricorn (Fig.l0).
However, in cerlain areas the distribution extends outside this limit as in the case
of Japan where Pincradajucata var. martensi; is seen up to 37° IO'N latitude.
Pinctada/ucata (Gould)
The Indian pearl oyster was formerly known as P. vulgaris and the Japanese
pearl oyster as P. martensii. Both these species have now been synonymised under
P. juca/a. The Japanese scientists prefer to denote Lhelr species as P. jucala
marlensii.
The three main areas of distribution are Japan, the Indian subcontinent and
the Persian Gulf. In the Indian re gion it occurs in the Gulf of Mannar (off the coasts
of Tamil Nadu in India and off Sri Lanka) and in the Gulf of Kutch (coast of
Gujarat). The natural pearls produced by P .jucata in Gulf of Mannar and Persian
Gulf were the famous 'Lingah' pearls or Oriental pearls.
In Australia, the species has been recorded in Northern A ustralia, Shark Bay
in the west and Sydney in the east. Hynd (1955) reported the presence of large beds
off Groote Eylandt in the Gulf of Carpentaria at 12 fathoms depth. These
resembled the famous beds of Gulf of Mannar_ It is also reported from the Banten
Bay of Indonesia (Unar et al., 1982), Recent reports show that this species occurs
in Guangdong and Guangxi provinces of China (Zhong-Qing, 1982).
P. jucata occurs from the intertidal area, as in Gulf of Kutch (India) and
Moreton Bay (Australia), to depths up to 12 fathoms as in Gulf of Mannar (India)
and Gulf of Carpentaria (Australia). It grows up to 9 em in shell height The
maximum lifespan is about 7 years.
Pinetada margaritifera (Linnaeus)
Commonly known as the blaCk-lip pearl oyster, the species has a very wide
dislribution girdling the tropical belt of the world. It occurs in Tuamotu-Gambier
Archipelago (French Polynesia), Papua New Guinea, Torres Strait (Australia), the
Philippines, Indonesia, Thailand, Malaysia, Andaman and Nicobar Islands (India),
Persian Gulf, Gulf of Oman. Red Sea (Sudan), Gulf of Mexico, Panama Coast and
Gulf of California. Within the species, several regional varieties have been
recognized, e.g. cuming ii (Indo-Auslralian Archipelago and South Pacific),
16
PRODUCTION OF CULTURED PEARI..S
~
.
-I
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,
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DISTRIBlITION, ECOLOGY AND BIOLOGY OF PEARL OYSTERS
17
persica (persian Gulf), erythraensis (Red Sea) and mazatlantica (Gulf of Mexico
.
and Gulf of California).
The 'black-lip pearl oyster occurs from the intertidal region as in the
Andaman-Nicobar Islands (India) to depths up to 22 fathoms as in Torres Strait
(Australia). The species grows to about 17 cm in shell height and heavy specimens
are known to occur.
Pinctada maxima (Jameson)
This is the largest and the best of all the pearl oysters in the world and is
known as the gold-lip or silver-lip pearl oyster depending on the colour of shell
nacre. The distribution of this species is rather restricted to Australia (north, west
and east coast), Papua New Guinea, China (Hainan Island). the Philippines,
IndoneSia, Thailand and Burma (Mergui Archipelago). It is also expected to occur
in Andarnan and Nicobar islands.
The species occurs from low tide level on reef flats to about 40 fathoms
depth as in Australia, although commercial catches come from 5-30 fathoms
depth. It grows to about 28.2 em in diameter, weighing up to 5.5 kg a pair of
shells, although the average weight may be about 2.3 kg a pair (Bolman, 1941;
Hynd,1955).
Minor species
As already stated, the species of pearl oysters other than the 3 mentioned
above are not considered very important from the standpoint of pearl production
although they produce pearls occasionally. The species are listed here.
Pinctada a/bina carcharium (Jameson) occurs in Shark Bay (Western
Australia) in the intertidal grassy beds up to a depth of2 fathoms. Pearls produced
are light yellowish, light brownish, light greenish or light pink with strong
iridescence (Bolman, 1941; Hynd, 1955).
P. a. sugillata (Reeve) occurs in Australian waters and Gulf of Mannar
(India). It grows up to 11 cm (Hynd, 1955).
P. maculata (Gould) is found in the reef flats and rock pools in northern
Australia; also in the lagoons 4-5 m deep in Tuamotu Archipelago (French
Polynesia) along with P. margaritifera.
P. chemnitzii (PlJilippi) is known from several regions including Australia
and India.
P. imbricata (Roding) is from MargaritalslandofVenezuela and Bermudas.
Pearls often have no mother-of-pearl1ustre, are white, light pink or yellow and
translucent (Bolman, 1941).
.
P. anomioides (Reeve) andP. atropurpurea (Dunker) are the other 2 species
recorded from Indian waters, besides P.jucata, P. margaritifera and P. chemnitzi
(prashad and Bhaduri, 1933; Rao, 1970).
18
PRODUCTION OF CULTIlRED PEARLS
ECOLOGY OF PEARL OYSTERS
Pearl oysters are truly marine forms and do not occur in estuaries or
backwaters. At the global level, the distribution is influenced by temperature, the
oysters being confined to the tropic belt but extending into sub-tropic in certain
areas. In Japan, pearl oyster occurs in the sub-tropical regime up to 35° lO'N
latitude on the Pacific coast and 37° lO'N latitude on the Japan Sea Coast. The
northern limits are determined by the warm currents 'Kuroshio' and 'Tsushima'
where the coastal water temperature generally does not fall below lOoe in winter.
In Gulf of Mannar the annual range of temperature is about 25°_32° C.
Pearl oyster tolerates certain amount of dilution in salinity for short spells.
In the Gulf of Mannar the general salinity regime is from 30 to 36 ppt. However,
during a heavy north-east monsoon salinity may drop to as low as 15.69 ppt in the
inshore waters due to heavy land run off but would not cause oyster mortality if
it is for a short duration of 1 or 2 days.
.
Turbidity, that is the amount of matter in suspension, is a factor which
influences the life of pearl oyster. It prefers clear waters. High turbidity would
interfere wilh its rate of filtration upon which depends its intake of food and
oxygen availability. Besides, the larval life of oyster requires clear seawater for
successful completion of its pelagic phase, settlement and metamorphosis to adult
form.
Pearl oysters are associated with coral reefs and island ecosystem. They are
attached with their byssal threads to live or dead corals, rocks, other molluscan
shells like Pinna, calcareous algae, sponges or other hard substrate. Where they
form extensive beds, they are found in bunches attached to one another. The pearl
banks in the Gul f of Mannar are known as 'paars' and the intertidal beds in the Gulf
of Kutch as 'khaddas'. Herdman (1906) estimated that the fauna and flora of the
pearl banks of the Gulf of Mannar comprise a whole assemblage of more than
2,700 species of animals and 200 species of plants. The nature and densi ty of such
a dynamic surrounding have a profound effect on the well being of the stock of
pearl oysters. Sponges, starfish, molluscs, crustaceans, annelids, coelenterates
and fishes among the fauna, and the luxuriant growth of different species of red,
brown and green algae dominate the pearl oyster beds (Mahadevan and Nayar,
1967). Among these, the weaving mussel Modiolus spp., octopus, predatory
fishes like Balistes, serranids, rays and skates, boring polychaetes and sponges,
predatory gastropods, crabs and lobsters are considered notable enemies of pearl
oystercausing death and destruction either by direct aggressive action orindirectly
in the struggle for existence (Nayar and Mahadevan, 1987).
BIOLOGY OF PEARL OYS1ER
The life of pearl oyster is greatly influenced by the environmental conditions
19'
DISTRIBUTION, ECOLOGY AND BIOLOGY OF PEARL OYSTERS
in which it lives. The same species would show differences in the values of
parameters such as. growth and reproduction when grown under different
environmental situations.
Reproduction
The sexes of pearl oyster are separate, but the males and females cannot be
distinguished from the characters of the shell. The Indian pearl oyster P.fucata
attains first sexual maturity when it is about 15.5 mm, i.e. when about 3-4 months
old. Peak spawning of oyster population is seen about twice a year under the
influence of monsoon conditions, although some amount of spawning. takes ylace
throughout the year. On the Sri Lankan coast of Gulf ofMannar, the species, under
wild conditions, has been ~ported to spawn during May-July (south-west monsoon)
and again during November-January (north-east monsoon) (Herdman, 1906)_ On
the Indian coast of the gulf, the species spawns during April-May and Septem berOctober (Hornell, 1916). However, under farming conditions in Tuticonn Harbo].lf
basin, Chellarn (1987) found spawning during June-September 1980, December
1980, February 1981, July-August 1981, and November 1981. These data would
indicate regional and year-to-year variations, as also differences under wild and
farming canditions. Considered generally, the integrated temperature-salinity
profile which shows changes, however, small they be, from month to month would
influence the development of gonad and spawning.
Life-history
.
The male and female pearl oysters release their spermatozoa and ova,
respectively, into the sea and the eggs are fertilized. The number of eggs released
by each female oyster in a reproductive season runs into a few millions. The egg
size is about 47.5 J.lffi. The fertilized ovum goes through embryonic development
and, at tbe end of about 20 hours, the typical bivalved 'veliger' larva emerges. It
measures about 67.5 J.lIll x 52.51-1.m and begins to lead an independent life. It feeds
on minute micro-algae found in the sea. The form and structure of various organs
of the larva change as it developsthrough the straight-hinge, urn be and pediveliger
-{ :u-e carried
stages. Fo~ about three'weeks the larvae live in the column w
of
by the currents away from their original place of product
survival through this period of pelagic phase are rather'
which reaches the 'pediveliger' stage at the end of this pe
the sea bottom and begins an exploratory phase to locatesettle down. It settles on algae, corals, rock etc" and cree
for a while. If it is not satisfied, it leaves the substra'
again. This exercise is repeated many times until the l'
attaches itself to the substratum wilha few horny th'
secretes from a gland and metamorphoses to a forr
'n
20
PRODUCTION OF CULTURED PEARLS
This baby pearl oyster referred to as pearl oyster' spat' measures about 300 J..Ul1 or
O.3mm.
From this stage, the struggle for survival continues further amidst dangers
of sand drift, smothering by the carpet-like growth of small weaving mussels,
competition by fouling and boring organisms which find the pearl oyster shell an
ideal place to live on, and predation by starfish, fish and octopus. Very very few
live up to the old age.
Growth
The growth potential during the first year of the life of pearl oyster is high.
The growth rate decreases from the second year onwards. At the Krusadai Island
in the Gulf of Mannar, Devanesen and Chidambarm (1956) estimated the growth
of Pinctadafucata as follows: end of first year 45 mm, second year 55 mm, third
year 60 mm, fourth year 65 mm and end of fifth year 70 mm. The corresponding
estimated weights were 10,30,45,60 and 70 g. For the same species in the Gulf
of Kutch, Narayanan and Michael (1968) estimated the growth as follows: first
year 44.05 mm, second year 61.68 mm, third year 76.20 mm, fourth year 81.62
mm, fifth year 85.15 mm and sixth year 86.65 mm.
Tracing the growth of P.fucata produced in the hatchery and later transplanted
to the sea, CheUain (1987) observed the oyster to reach a modal size of 47.5,64.5
and 75.0 mm at the end of the first, second and third years, with corresponding
weightsof8.3, 31.6 and 54.4 g. The estimated maximum sizeofthe oysteris about
SOmm....
.
Food and feeding
Generally, the bivalves which feed by filtration are wasteful feeders, and the
pearl oyster is no exception. The animal lies on the seabed with the shells open
exposing the body to the flow of seawater. Forward currents are set in by the
rhythmic movement of the minute cilia on the gill filaments. The micro-algae
which are found floating in the immediate vicinity are wafted by the ciliary current
towards the mouth which is surrounded by a pair of labial palps. The micro-algae
and other particulate matter get entangled in minute mucus sheets produced by the
gills. These food-laden mucus sheets are directed, into the mouth opening of the
oyster by the labial palps.
The mechanism of selection of food items to be sent into mouth by the above
process is not efficient. As a result several organisms which cannot be digested by
the pearl oyster are invariably seen in the stomach and intestine. Herdman (1903)
noted that uniCellular organisms including infusorians, foraminifers and radiolarians
formed the food of the pearl oyster of Gulf of Mannar, but the stomach contents
also included minute embryos, larvae of various animals, algal filaments, and
~cyonarian and sponge spicules. Chellam (1983) reported the presence of
-'""
DISTRIBUTION, ECOLOGY AND BIOLOGY OF PEARL OYSTERS
21
diatoms and flagellates which formed the food. He also noticed larvae of
JamelJibranchs, gastropods and heteropods, crustacean nauplii and appendages,
frustules of copepods, spicules of sponges and unidentifiable spores which
apparently are not of any food value for the pear~ oyster and, therefore, passed out
of the alimentary canal as pseudofaeces. Some of the organisms such as the
lamellibranch larvae would pass out alive.
CHAPTER 4
PEARL FISHERIES
for pearls, or pearling has been practised for several centuries in many
parts of the world. In some cases, as in India and Persian Gulf, the practice is from
time immemorial. Besides for pearls, fishing used to. be conducted for the shells
of some species of p_earl oysters such as the gold-lip or silver-lip (Pinetada
maxima) and the black-lip (P. margaririjera) which have been commercially
valuable as raw material for the manufacture of buttons and fO.r mother-of-pearl
inlay work. With the advent of plastics in the 1950's, the shell-button industry
suffered a setback. But this waS more than compensated with the introduction of
pearl culture in some of the countries such as Australia and the Philippines .
FISHING
. PEARL FISHERIES OF INDIA
Gulf of Manna;
Ancient rererences. The IndifID and Sri Lankan pearl fisheries in the Gulf
of Mannar.based on the common speciesPinctadajucata, produced the true orient
pearls of the finest quality, along with those of the Persian Gulf. The origin of the
pearl fisheries of the Gulf of Mannar which were in vogue even 2,000 years ago
is not on record. However, some· accounts of these fisheries are known from Pali
writings referring to the presents of pearls from King Vijaya to Pandyan King of
Madura (550-540 B.C.), writings of Pliny, "Periplus of the.Erythraean Sea",
Ptolemy (163 A.D.), Marco Polo (1260 - 1300 A.D.), Friar Jordanus (1323 -1330
A.D.) and some of the Tamil literature such as 'Madttrai Kanchi' and 'Silappadhikann'
(1st or 2nd centUry A.D.). The pearl fisheries came to be recorded in more detail
with the advent of Europeans to the Indian subcontinent
Recent works. The credit for having chronicled the Indian pearl fisheries of
the recent period goes to Mr James liomell. a noted British Marine Biologist who
became the fIrst Director of Fisheries of the erstwhile Madras Presidency. His
treatise on "The Inman pearl fisheries of the Gulf of Mannar and Palk Bay",
published in Madras Fisheries Bulletin, Vol. 16, in 1922, and other earlier
publications give a. comprehensive account of the history, topography nomenclature
and inspection of the Indian pearl banks of the Gulf of Mannar with other details
on the pearl oyster and pearl formation. The historical perspectives were supplemented
by Arunachalam (1952). Further scientific knowledge_'on the pearl banks was
added by Devanesen and C.hidambann (1956), Devanesen and Chacko (1958),
Baschieri-Salvadori (1960, 19q2), FAD (1962). Mahadevan and Nayar(l'973) and
Alagarswami et ai. (1987).
Control of the resource. During the 16th century, the history of the pearl
23
PEARL FISHERIES
fishery was intricately connected, on the one hand, with the ruling powers the
Nayaks of Madura, Nawab of Carnatic, and the Portuguese with their battles for
controlling the land and sea, and, on the other. with the Paravas who traditionally
exploited the fisheries and the Moors who had an interest in pearl fishing largely
for trade. The pearl fishery seems to have been prosperous under Portuguese
control (1524 - 1658). Often armed ships had to escon the pearling boats to give
protection against piracy. The rights then passed on to the Dutch in 1658 and
subsequently to the British in 1796. With their unprecedented control over the
pearl fisheries and sovereign rights over the adjoining areas, the British Government
abrogated the privileges previously enjoyed by the local rulers. After Independence
in 1947, the rights and control over the pearl fishery have been exercised by the
Government of Tamil Nadu.
The paars. Hornell (1922) listed a total number of 72 pearl banks, known
as 'paars' , grouping them into 54. from Pamban Karai Paar in the north at the head
of Gulf of Mannar to Manapad Periya Paar in the south (Fig.ll). 'Paar', by
definition, is a patch of hard ground of very low profile. the surface of which
consists of rock fonned of corals and shells to a certain extent and to a large extent
by calcrete-compound of sand and organic remains cement.ed to a continuous
mass by calcium carbonate. These paars lie roughly in line parallel to and at a
distance of 10 - 16 nautical miles from land. Majority _ofthem are located between
8° 20 'N and 9° 00 'N latitudes within 78° 15 'E and 78() 25 'E longitudes. Those
which lie north of 9° 00 'N latitude are not considered important from the point of
view of pearl oyster settlement. From 8° 35 'N an inner series is recognizable at
15-70 m depth. whereas the outer series is located at 20 -23 m depth (Nayar and
Mahadevan, 1987). These rocky grounds are of varying areas ranging f.rom a few
hundred square metres to a few square kilometres.
Fluctuations and yield. The Britlsh Governor Van Imhoff once queried
•'whether there in not more of glitter than gold about the Pearl Fishery" (Hornell,
1922). This is not without truth. From 1663 to this date, in 325 years, there have
been only 38 pearl fisheries, including the recent grand series of seven fisheries
from 1955 to 1961. During the 20th century till date, the fishery was conducted in
1900,1908,1926,1927,1928,1955,1956,1957,1958, 1959, 1960 and 1961. Iq
the remaining years pearl fishery could not be conducted as the paars contained no
oyster or did not contain oysters in fishable quantities. The gap Of unproductive
period extended for 27 years between 1928 and 1955, and a similar 29 years so far
since 1961 with no sign of prospects for a pearl fishery in the coming few years.
The 1955 - 1961 series has been conSidered the best among the pearl fisheries on
record. The yield of pearl oyster was as follows :
Fishery year
1955
1956
1957
1958
No. of oysters fished
3,508,967
2,129,05i1
ll,175,214
21,476,514
24
PRODUCTION OF CULTURED PEARLS
1959
1960
1961
16,428,298
16,175,839
15,360,928
Among the 72 pearl banks, only a few have sustained pearl oyster populations
yielding 10 fishery in some years, and most of the banks have not yielded to any
fishery at any time. The productive beds during the 1955-61 series were Tholayiram
(all seven seasons), Kodamuthu Karuwal (three seasons), Rajavukku Chippi
Choditha (three seasons), Poonthottam (two seasons), and Saithombathu, Dudu,
Karai Kodamuthu, Kodamuthu and Koothadiar (one season each). In general, the
recorded pearl fisheries would show that Tholayiram paar, Kodamutlm group and
Karuwal group have been relatively more consistent in the production of pearl
oyster than the others.
In 1914, a freak pearl fishery came up in the Pa1k Bay, off Tondi, yielding
about 0.5 million pearl oysters. Economically it was not a successful fishery as the
oysters were not the same as the Gulf of Mannar ones in quality.
Pearl fisheries have always been considered as a source of revenue 10 the
Government which came through licensing of boais , sale of the Government share
of oysters and the rentals for the sheds. The gross revenue from the fisheries during
the 1955-61 series has been: 1955, Rs 1,46,000; 1956, Rs 45, 454; 1957, Rs
1,68,807~ 1958, Rs 4,74,067; 1959. Rs 8,74,000; 1960,2,15,267; and 1961, Rs
2,88,860. Against this revenue, the expenditure in organizing the fishery has been,
respectively, Rs 48,000, Rs 4,877, Rs 22,264 for the years 1955 through 1957.
Decision-making on pearl fIShery. The pearl fishery is declared by the
Department of Fisheries based on the results of inspection of the beds, the details
of which have been briefly given by Mahadevan and Nayar (1973). Inspection of
the pearl banks is carried out by the departmental officers and staff, including skindivers. Three sets of parallel dives are made throughout the length of the paar.
Each diver is assumed to cover an area of 2.5 m2 per dive: Based on the number
of oysters collected per dive and the area of the paar, the standing stock of oyster
is computed.
As the second step, the age of oysters as collected above in each paar is
ascertained. If more than 60% of the oyster population in a bed is estimated to be
3 years (about 60 mm shell height and 45 g weight) and more of age, the bed is
considered fishable. It has been seen by experience that oysters above three years
in age give satisfactory pearl yield.
The third step involves estimation of the pearl yield. The oysters collected
during the inspection from each paar are allowed to rot in a pot for a week. Then
they are washed and the pearls are collected. These are sorted out, graded. weighed
and assessed for value. If the value of pearls thus obtained works out to more than
Rs 30 per 1,000 oysters (1955-61 price), then it is considered feasible to exploit
the bed commercially.
Based on the results obtained at the three steps, the Government takes a
25
PEARL FISHERIES
".J.
••••
D."I
F ernand 0 3)
adutha marlkan ~.;
...\
........
(_) ValPor perlya
Tutloorln' .
G U L F
OF
Rala"uk Itu.ohlppl
lothlttla
.. ,.} (.",
MANNAR
H ')Kudol'lluthu
.:;0:::0
Soith kudomufhu
,•.f.} Poonthottom
f'" ... ~..
r·:.rJ.·
·0.:
.•..,
....
()Manapad
''\,.\..... , ...... """,') Monapad perlyCi
.~
... ~. ....
I·····...... .' ".- ...... ' .. ..
:...... .
..
30'
Fig. 11. Distribution of pearl oyster beds (paars) on the Indian side of the Gulf of Mannar.
26
PRODUCTION OF CULTURED PEARLS
decision whether to declare a pearl fishery or not during that year. The pearl
fishery i? conducted with Tuticorin as the base of operation.
Conduct of pearl fishery. When the Department of Fisheries has taken a
final decision to hold a pearl fishery, it is widely announced with dates and the
names of pearl banks. A pearl fishery camp is organized at Tuticorin by putting up
temporary ~heds. The fishermen register their canoes. Pearl fisheries are usually
held during the fair weather season when the sea is calm and the clarity of seawater
is good so that the divers can visually see the pearl oysters at the depth of the beds.
The season is generally dqring February - May but the number of fishing days is
regulated based on the estimated population of the oysters on the beds. Pearling
was done for 44 days in 1955, 18 days in 1956,51 days in 1957,55 days in 1958
and 62 days in 1959. The number of canoes registered was46,48, 86, 150, 150 and
150 through the fishery of 1956 to 1961, and the number of divers engaged were
457,733,945, 1,600, 1,821 and 1,392 during the same period.
The canoes are towed by Government's power boat to the pre-detennined
pearl bank early in the morning and the divers will work on the beds till early
afternoon. The divers do not use even masks up to the last fishery and had no
underwater breathing aids. By holding their breath, they would descend to the
bottom with the help of a stone attached [0 a life-line prud out from the canoe, the
oysters by hand picking, deposit them in a bag tied. to their waist, and when they
have just enough breath to come up, they would surface. After taking some rest
they would dive again. Each dive would last for a maximum of about 90 seconds.
The divers, afthe end of the day's work would return to the shore. The divers get
one-third of the pearl oysters collected arid the Govemment the rest. The divers
are free to sell their share the manner they like; and the Government's share is
auctioned late in the evening in lots of 1,000 oysters.
Pearl col1ection. Up to this point no one knows what is inside the oystera pearl or blank. The oyster keeps its shells closed so tightly that one cannot open
it without the help of a sharp knife. For dealing in bulk, the oysters are placed in
gunny bags and are left to rot for a week on the shore. They are then washed in
water and the pearls collected. The putrefied meat is dried in the sun and carefully
checked for 'dust' pearls. The system ohotting of pearl oysters in the open areas
often resulted in outbreaks of cholera in the vicinity. People braved these hazards
in trying their luck! It would appear worthwhile repeating Governor Van Imhoff's
query "whether there is not more of glitter than of gold about the Pearl Fishery".
There is no account of the pearls obtained in any pearl fishery and as such
it is not possible to assess the real economic value of the fishery. Ranganathan
(1964) and Chacko (1970) reported that the Indian pearls range in size from that
of fine mustard to that of a pea, from a fine round sphere to mass of irregular
concretion in shape and from pink to black lead in colour. These pearls are
classified in the Bombay pearl market as (i) •Jeevan' to refer to pearls of uniform
shape. bright lusti~, rosy. pink or pinkish white or rosy tinge; (ii) 'Gholwa' to
pearls nearly round. bright colour or varying shades; (iii) 'Ghat' to small irregular-
PEARL FISHERIES
27
shaped ones; and (iv) 'Masi' to very small ones. Nearly 85% of the pearls obtained
are of 'Gholwa' type.
Some highlights of the recent series are available from the Administration
Reports of the Department of Fisheries, Government of Tamil Nadu. In 1958, a
French exporter of Orient pearls from Bombay attended the fishery. Unprecedented
quantity of pearls flowed into the market. The biggest and perfect pearl obtained
in 1958 was one of7 carat and the next largest one with good lustre and yellowish
brown colour was of6 carats. Baroque pearls and blisters up to 23 carats were also
collected. The total turnover of pearl busin'ess in the entire fishery was estimated
to be not less than Rs 1 million.
. '
Gulf of Kutch
..
In the beginning of the present century, the pearl fishery of Gulf of Kutch
was under the control of Jam Saheb of Nawanagar and the fishery was conducted
under certain unique rules (Hornell, 1909). The fishermen received 118m of the
value of pearls in cash, 1/40th in cloth and 1/20th in food. In addition, two prizes
were given to the two villages producing the most valuable collection of pearls.
In 1926, a separate department called 'Moti khata' was established to manage the
fisheries. With the merger of Nawanagar State with the Indian Union in 1948, the
pearl fishery came under the control of the Fisheries Department of the State
Government.
There are about 42 important pearl oyster reefs, known as 'Khaddas', in the
intertidal area of the Gulf of Kutch bordering the coastline of Jamnagar District,
about 24,000 ha from Sachana in the east to Ajad in the
covering a total area
West (Fig. 12)'(Easwaran et al., 1969; Pandya, 1974). A typical 'Khadda' consists
of a hard bottom of coral and rocky frame~ork with an admixture of mud and sand.
Pearl oyster of the species Pincladafucata are attached to the rocky substratum
here and there amidst other fauna and flora. The pearl oyster beds are situated in
the intertidal zone, the distance from coastline ranging from I to 5l;m.
The pearl fishery is conducted on days of good ebb tides during the southwest monsoon"generally after one or two good showers. The fIshermen wade
through the' beds and pick up oysters with hands. Modifying the, system of
remuneration to the fishemien, the Fisheries Department paid 25 paise for every
oyster collected during the 1966-67 fishery.
Easwaran et ai. (1969) reported that the Kutch oysters fetched a price higher
than the Mannar oysters, According to them, while the value of 1,000 oysters was
only Rs 25 in Tuticorin and Rs 22 in Sri Lanka, it was Rs 250 in Jamnagar ..
However, the higher price may be due to the rarity of pearl oysters in the Gulf of
Kutch as compared to Gulf of Mannar. From 1950 to 1967, the average number
of oysters fished per sejlSon was about 17,000 in th~ Gulf of Kutch as compared
to several million in a season in productive years in the Gulf of Mannar. The
density of population as estimated by Pandya (1974) was about 1- 6 oysters per
hectare.
of
28
PRODUCTION OF CULTURED PEARLS
PEARL FISHERIES
29
The Gulf of Kutch fishery used to be held almost every year or alternate
years from 1913 to 1939. Subsequently, it was held every 3-4 years. There have
been 25 pearl fisheries during 1913 to 1967, the last one being 1966-67 Season
yielding about 30,000 pearl oysters. The highest value of pearls realized from the
fishery was Rs 61,693 during 1943-44. After 1967, no pearl fishery has been
conducted in the Gulf of Kutch due to paucity of oysters on the khaddas.
Current status of pearl oyster resources of India
In the survey camed out in theGulfofMannarduringDecember 1958-May
1959, a season of successful pearl fishery, Baschieri - Salvadori (1960) es timated
the pearl oyster population density at 132 oysters/m2 in the northern sector
(Fernando, Nagarai and northern and central parts of Tho Iayiram) , 74 oysters/m 2
in the central sector (southern part of Tholayiram, Kuthadiar, Melonpalhu,
Vadaonpathu, Saithonpathu, Pulipundu, Kudamuthu and northern Karuwal) and
large quantities of both adult and young oysters in the southern sector (poonthottam
and Manapad). In the post-fishery period, the pearl oyster beds had immediately
entered into the unproductive phase. Oysters were very fare or altogether absent
(Sambandarlloorthy, 1966; Mahadevan and Nayar. 1967; Chacko and
Sambandamoorthy, 1969).
SCUBA (Self-Contained Underwater Breathing Apparatus) diving was
introduced in India for the survey of the pearl banks for the firs ttjm e in 1958 under
the auspices of an F AO Technical Assistance programme which had been
continued by Indian experts (Mahadevan and Nayar, 1982). Since 1975 regular
survey of the pearl banks of Gulf of Mannar was conducted using SCUBA. Some
of the beds, especially those in the northern group of the central sector which are
relatively shallower (5 - 7 fathoms) than the others, showed some modest
production from 1975 -76 to 1985 -86. During this period, fora total diving effort
of 595 hours in various paars, 239,000 oysters were fished, giving an overall yield
rate of 400 oysters ;hour. The total diving effort and the yield rates in some of the
paars from each of which over a thousand oysters were collected are given in
Tables 1 and 2.
There has been some revival of pearl oyster in some of the pearl banks of
Gulf of Mannar during 1975 to 1986 but none of them was consistent in yield
except perhaps Devi, Kurichan, Nagarai and Fernando paars. The shallow
shoreward paars have never yielded to pearl fisheries in the past. The classical
paars which had led to the magnificent pearl fisheries of 1955 - 61 such as
Tholayiram; Kodamuthu, Karuwal, Rajavukku, Chippi Choditha, Poonthottam
and Koothadiar paars had not shown any sign of revival during the above period.
While the northern group of shallow paars gave an yield rate of 526 oysters!hour
for a total effort of 441.67 hours of diving the southern group ofdeeper paars gave
an yield rate of 44 oysters!hour for a total effort of 153.33 hours. The little
collection that came from the latter group was essentially from Tholayiram (601
hr), Karuwal (83/hr) and Saith Kodamuthu(23!hr).
30
PRODuCTiON OF CULTURED PEARLS
Table 1. Overall paar-wise yield rates of pearl oyster from
different paars in Gulf of Mannar during 1975 -76
to 1985 - 86
Name of
the paar
Diving effort
in hours
Yield rate
NO.}hollf
Nagarai
80.13
1,572
Utti/Uduruvi
Vaipar Periya
4.00
41.78
Kurichan
40.30
27.00
669
345
318
308
300
98
83
60
Fernando
Devi
Van Thiro Arubagam
220.00
13.60
Karowal
15.72
Tholayrram
73.35
Data fr<>ID Alag~rswami et 01. (1987)
Table 2.· Overall seasonal yield rates of pearl oyster from
various paars of Gulf of Mannar during survey in
the recent years
Season
1975-76
1976-77
1917 -78
1978 -19
1979 - 80
1980 - 81
1981- 82
1982- 83
1983 - 84
1984- 85
1985 - 86
Diving effort
in hours
81.00
120.03
67.22
110.23
56.52
35.09
46.25
44.36
Nil
42.45
8.25
Yield rate
No./hQur
15
267
183
326
217
3
2,164
829
319
. 30
Data from AJagarswami el 01. (1987).
The 1986 - 87 season has shown a virtual absence of pearl oyster in the
.
northern group of paars which had been surveyed.
A major factor that emerged from thesurvey of pearl banks during 1975 86 was the incursion of pearl oysters of species other than Pinctada jucata
(Alagarswami, 1977). These non-fucata species comprising P. sugilJata, P.
anomioides, P. atropurpurea and others are not quality oysters for pearl production;
they are relatively flat-shelled, smaIIer in size and the nacre is generally of poor
quality. These pearl oysters, collectively referred to as 'fiat' oysters, had not
31
PEARL FISHERIES
Table 3. Percentage contribution of P.jucata and 'flat' oysters
in the pearl banks of Gulf of Mannar during 1975-86
Season
1975-76
1976-77
1977-78
1978-79
1979- 80
1980- 81
1981- 82
1982- 83
1983 - 84
1984- 85
1985 - 86
Average
P·fucata (%)
'Flat' oysters (%)
79.18
ZO.82
68.25
31.75
82.37
93.68
93.01
49.50
100.00
100.00
No data
85.58
76.31
89.64
17.63
6.32
6.99
50.50
Nil
Nil
No data
14.42
23.69
10.36
Data from Alagarswami et al. (1987).
figured in any of the pearl fishery reports or survey reports in the past. They were
noticed for the f"lrst time in 1975 (Table 3). Some of these not-sa-useful species of
pearl oysters have made incursions in the pearl banks causing a species 'pollution'
on the commercial value of the resource.
Another notable feature of the period was the predation of pearl oysters by
gastropods such as Cymatium cingulaturn and Mure.x virge!1eus, leading to heavy
mortality of the stock (Chellam et al., 1983).
Over the decade, the size of pearl oysters collected from the different pearl
banks has been consistently small. The mean size of pearl oyster from 1975 -76
to 1985 - 86 has, respectively, been 24.5,33.9,24.7,34.8,32.0,19.6.29.5.47.7,
22.1,30.5 and 29.0 mm. The crops from various beds consisted almost entirely of
less than one-year-old oysters, thereby indicating that the stock resulting from the
spawning of a year did not survive to the next year, with very few exceptions, and
that these stocks have no use for natural pearlproduction in fishery.
The Gulf of Kutch beds have not shown any improvement since 1968
although some oysters could be gathered from here and there (Pandya, 1974).
A phenomenon witnessed in the recent years is the settlement of pearl
oysterson the breakwaters of Tuticorin Harbour and on spat collectors laid in the
Vizhinjam Bay (Alagarswami, 1977; Achary, 1983; Appukuttan. 1987). However,
the species composition of pearl oysters in such coastal areas is quite varied with
a very small percentage of Pinctadafucata. The major cOlllPonents are the 'flat'
oysters as seen in the recent years in some of the beds of Gulf of Mannar, It has
been experienced that spat collection, as done in Japan, cannot be successful in
India to raise a pearl oyster resource of commercial value.
32
1>RODucnON OF CULTURED PEARLS
Ranching of pearl oysters
Interest has been evinct:?d by fishery scientists to sea-ranch certain species
of fish and shellfish which have shown dwindling of stocks due to overfishing or
other man-made causes. Sea-ranching of abalones in Japan on a commercial scale
is a typical example of such attempts. This has not only improved abalone harvests
in their natural grounds, but also created new fishing grounds by transplantation.
The pearl oyster in the Gulf of Mannar has shown very wide fluctuations and it
merits attention to see whether the resource can be revived by ranching laboratory/
captive-reared stock of young oysters.
Although the concept of 'ranching' of marine animals is fairly recent,
Herdman had suggested as early as 1906 that transplantation of young' strikes' or
broad oysters from useless or unreliable paars to other productive paars may be
attem pled in the Sri Lanka pearl banks. Hornell (1916) su ggested rehabiIita tiD n of
the outer series of pearl banks by transplanting the scattered oysters found in the
shallow areas around the reefs and islands in the Gulf of Mannar.
The ability to produce pearl oyster in the hatchery in quantities required
gave a new opportunity for attempting ranching of Pinctadajucata in the Gulf of
Mannar. Pearl oyster spat are reared in the hatchery facility until ~hey reach a size
of 3 - 5 mm and then transferred to the fann in the harbour basin. When they have
attained a size of 10 -15 mm, they are allowed to settle on synthetic fibres of old
fishing nets, velon screen fabric and tufts of mono filaments. These materials with
the spat are placed in large cages covered with synthetic webbing and taken to the
paar in the Gulf of Mannar. The cages are lowered down to the sea bottom, placed
in the hollows and secured to coralline projections.
It is expected that these young pearl oysters would grow in the natural
habitat and propagate by spawning, thereby providing an augmented population
in the paars. However, the factors contributing to natural mortality such as
predation, sand drift, and mat formation of weaving mussel cannot be controlled
and survival and propagation of sea-ranched pearl oysters would depend on
prevalence of a set of favourable factors as required for successful population
build-up in nature.
PEARL FISHERIES OF OTHER REGIONS
Sri Lanka
The pearl fisheries of Sri Lanka were once famous as those of the Persian
Gulf, producing the true oriental pearls, and contributed much to world production
of natural pearls. The pearl banks are located off the north - west coast in the Gulf
of Mannar and the beds are known asPeriya paar, Cheval paar, Periya paar karai,
Modragam paars, Muttuvarattu paar, Chj)aw paar, Alantura paar, Karativu paar
and a n urn ber of smaller paars. The secoTld to fifth named paars have been the most
valuable pearling grounds. These are from 12 to 22 km from the shore and at
depths from 6 to 9 fathoms. The species is PinctadaJucata which was referred by
PEARL FISHERJES
33
the name P. vulgaris for a long time in the scientific literature.
Herdman's (1903 - 1906) "Report to the Government of Ceylon on the
Pearl Oyster Fisheries of Gulf of Mannar" is a masterpiece on the subject of
fishery, biology of pearl oyster. ecology of pearling grounds and associated fauna
and flora. The pearl fisheries of Sri Lanka have been subject to similar fluctuations
of fortune as in the case of Indian pearl fisheries. Hornell (1916), examining the
fishery data from 1669 to 1904 on both sides of the Gulf of Mannar, found that the
Indian pearl fisheries have mostly either preceded or followed the Sri Lankan
pearl fisheries. This led him to propound the theory of mutual dependenc!! of tile
two sides for successful fisheries. He staled that such regularity of alternative
succession extending over 75% of the fisheries held on the Indian side appears to
be more than a coincidence and lends weight to an opinion that the beds on the
opposite sides of the Gulf of Mannar confer reciprocal benefits upon one another
and that the Sri Lankan banks are frequently replenished from those off the Indian
coast and, conversely, the latter obtain most of their deposits of spat from the Sri
Lankan side.
Sri Lanka followed similar procedures of survey and conduct of fishery as
in India. The divers were partly from India and Arab countries. In the 1925 fishery,
out of 1908 di vers in 125 boats engaged during the peak. period, only 157 were Sri
Lankan divers and the rest were Arab and South Indian (particularly from
Tuticorin) divers. The Sri Lankan pearl fisheries, at one time, were leased out to
London Syndicate for 25 years. In 1958, a pearl fishery was organized, after a gap
of33 years, for the fir'st time by dredging using two 13.5 m (45 feet) mechanized
boats 'Canadian' and 'North Star'. It was highly successful. The fishery ended up
with a collection of 4.5 million oysters from a single paar, viz. South - west Cheval
Paar, in 53 days. This led Sivalingam (1961) to reason out that with proper
incentive to the crew, it will be possible to fish a quarter million oysters with the
help of two boats of the above size in aday which is equal to the work of 1,400 men
per day if divers are employed. The practice of dredging was continued subsequently
in the pearl fisheries yielding about one million oysters in 1960 and aboul400,OOO
oysters in 1961. Subsequently, no pearl fishery has been conducted in Sri Lanka
due to paucity of oysters.
Pearls obtained from the Sri Lanka pearl fisheries have been generally
small. Kunz and Stevensen (1908) stated that the quantity of seed pearls (very
small ones) obtained in Sri Lankan pearl fishery exceeds that of an yother in the
world. In no fishery in the world is the average size of pearls secured smaller, nor
is the relative number greater than in that of Sri Lanka. Jt is rare that one is found
weighing over 10 grains; thenumber weighing less than 2 grains is remarkably
large. The oyster samples obtained in 1957 gave an average pearl yield of 6.42
carats valued at an average of Rs 58.44 per 1,000 oysters (Sivalingam, 1961).
Herdman (1905) observed that, of the 1,491 oysters of over 3 til years old
collected from 6 pearl banks, 106 oysters (7.1 %) yielded a total of 130 cyst pearls
and 205 oysters (13.8%) contained muscle pearls. Thecyst pearls are the ones that
34
PRODUcnON OF CULTURED PEARLS
are valued. The percentage of total pearl-bearing oysters was 20.9%. Giving the
weight of pearls, Herdman (1905) recorded that, of the above.production, 43
largest cyst pearls weighed 2.055 g, averaging 0.048 g/pearl, and the aggregate of
72 small cyst pearls and 484 muscle pearls weighed 2.965 g averaging 0.005 g;
pearl. These figures would show the common type of natural pearls to expect from
a pearl fishery. It is rarer to find a pearl of real worth.
Persian Gulf
The most important pearl fisheries contributing to about 85% of the world
production of natural pearls had existed in the Persian Gulf (Bolman, 1941). The
pearling areas were Kuwait, Bahrain, Dubai, Bushire, Charak and Lengeh in the
Persian Gulf and Muscat in Gulf of Oman. There are more than 120 pearling
grounds in the Gulf of which 60- 70 rich banks are around Bahrain (Chidambaram,
1958). Most of the beds are found about 48 km north and north - east of Bahrain
ata depth of about 12 fathoms. Someofthe banks areas far away as about 160km
from the coast. The most common species is Pinctada Jucata although some
workers referred to this species as P. radiata. Rarely, P. margaritifera is also
collected. After 1952, Bahrain did not conduct any pearlfishery as the di vers were
more gainfully employed in the oil companies. Presently, Bahrain is engaged in
scientific investigations on increasing the frequency of occurrence and improving
the size of natural pearls (K. Nagappan Nayar, Personal Communication).
,Red Sea
The Red Sea pearl fishery was of greater importance before the opening of
Suez Canal but has since fallen in significance. Pearling grounds are found in the
Farasan Is .• Dahlak Is., Dongonab Bay and off liddah and Sabya of the Arabian
coasLIn the Dongonab Bay along the coast of Sudan, the shells of P. margaritifera
used to be fished from 8 - 15 fathoms; Crossland (1957) and Reed (FAO, 1962)
had developed techniques for spat collection, nursery rearing and grow-out
culture of this species in Dongonab Bay and the shell trade depends on production
employing these techniques.
The pearls of the Red Sea oysters are whiter than those from the Persian Gulf
and the lustre is stronger (Bolman, 1941).
Australia
The mother-of-pearl shell.of the silver or gold-lipped pearl oyster P. maxima
was formerly the mainstay of the Australian pearl fishery. Natural pearls were
only an added incentive but were not the prime motive for pearling operations.
Australia met about 85 % of the mother-of-pearl shells demand of the world in the
hey days of the shell-button industry.
The pearl fishery was concentrated in Thursday Island in the Torres Strait
off the Capv York peninsula of Queensland. off Broome in Western Australia and
PEARL FISHERIES
35
off Darwin in Northern Territory. The pearling grounds occur up to a depth of 45
fathoms. In the 1930s the Japane,se attempted to produce mother-of-pearl nuclei
for their pearl culture industiy from P. maxima shells which did not tum out to be
successful. Since the establishment of pearl culture farms in 1956 under Japanese
collaboration, live oysters are collected by luggers and transported to the farms
located at several far-off centres. The oysters are placed in wire baskets which are
then stacked underwater in carrier tanks built into the hold of transport ships.
Seawater is circulated through the tanks only when the ship is moving by a venturi
system that pipes water through the hull to the surface of the tanks. Water drains
from the tanks through the holes in the bottom. The Western Australian pearling
industry is Australia's third most valuabiefishing industry (pass etal., 1987). The
live-shell tonnage for culture use in Australian farms increasedf_rom 5 tonnes in
1956 to 368 tonnes in 1966.
The pearls of P. maxima have mostly a white colour with a silver white
strong gloss but the fine iridescence of the oriental pearls is missing (Bolman,
1941).
The Philippines
The entire Sulu Archipelago is one extensive pearling bank and is considered
the largest and the most prolific in the Philippines. Other known fishing banks are
Davao Gulf and Illana Bay in, Mindanao, Cagayan, Palawan, Cuyo, Bohol. Cebu,
Bantayan, Masbate, Ilacaon, Gigantes, Guimaras Is., Ba1asan, Estancia; Mas inIac
Bay in Zam bales. western and northern coasts of Samar, Cape Engano, Polillo Is.
and the Balan group (Mantilla and Dimeo, 1952 - 53). P. margaritifera is more
widely distributed than P. maxima. It is common at depths of 2 - 30 m.
The mother-of-pearl shell fishery in the Philippines started only with the
American regime in the countl'y for export of shells to the USA. Later, button
industry was established in the country and 86% of the sheUs produced went into
the manufacture of buttons and the rest exported as raw material. According lo
Martin (1952 - 53), Sulu pearls were well known in foreign markets like
Singapore, Paris andLondon. The Philippine beds yielded afar greater percentage
of pearls than the Australian and Celebes pearl fisheries. Pearls from this region
range in colour from a while of camphor to a bronzy - greenish black.
Gulf of California
The pearl banks in the Gulf of California are principally located near the
is1ands of Cerralvo, Espiritu and S. Jose, extending from the La paz Bay to the
cluster of Carmen Islands of Baja Californian coast. The beds again are found on
the eastern side of the. Gulf in the islands of Tiburon and Aniel de Ia Guardia.
Pinclada margaritijera var. mazatlantica is the main species. The fishery has
been both for pearls and the shells. Light or dark lead, black or greenish black
pearls are produced by this oyster (Bolman, 1941).
36
PRODUCTION OF CULTURED PEARLS
Gulf of Panama
In the Gulf of Panama, the Archipelago de las Perlas and the islands of Say
Jose, Charios and San Miguel had once formed important pearling grounds which
had more or less been exhausted due to overfishing by incessant di ving operations.
The shells formed the Panama shells of the trade including those from La Paz and
Nicaragua. The natural pearls of P. margaritifera are multi-coloured of almost
imperceptible colour tones fading into one another. Thenoted Tararequi pearls are
among these. It is stated that Emperor Charles V (1500 - 1558) once purchased
two of these Tararequi pearls, one 31 carats and the other 26, paying in gold 650
times the weight of these pearls (Shirai, 1970).
Venezuela
The islands of Cubagua and Margarita in the Caribbean were once considered
very important for pearl in g and pearl trade. According to Bolman (1941), the nice
pearl named 'Peregrina' was found here in 1560. This pearl is light yel10wish and
more or less pear shaped, weighing 134 grains. In the more recent years, besides
the islands of Margarita and Cubagua, the Araya peninsula and Cabecera Isla
Coche have been exploited for pearls and shells (Salaya and Salazar, 1972). The
most common species of pearl oyster in Venezuela is Pinctada imbricata which
is stated to resemble P.fucata.
Other regions
Besides the major and notable pearl fisheries mentioned above, several
other countries had pearling in their waters.
The Mcrgui Archipelago of Myanmar; Moluccas and Celebes of Indonesia,
the notable region for the so-called black pearls; Papua New Guinea; Manihiki
Islands, Society Islands (Tahiti and Papeete), Polynesian islands and Melanesian
Islands in the Pacific; Ago Bay in Japan and Madagascar are some of the regions
where diving for pearls and shells had been in vogue.
FRESHWA 'fER PEARL FISHERIES
The freshwater pearl mussel fishery of the USA is several centuries old. The
fishery is believed to have become intensive after the finding of the famous
'Queen Pearl' weighing 93 grains, in the state of New Jersey in about 1857
(Bolman, 1941). There are up to 24 species of pearl-producing fresh water mussels
in the Tennessee and Mississippi river valleys, including the four well-known
species Quadrula, Pleurobema (three-ridge shell), Tritogonia (pig-toe shell) and
Megalonais (washboard shell). The colours of the pearls are red, pink, reddishbrown, brass, purple, Jigh t greenish or steel. Pollution of the ri vers by agricultural
pesticides has affected production of these mussels. According to Ward (1985),
there were over 300 natural pearl dealers in the 1920s. Their number came down
to six by the 1950s and to none in the 1980s and, with no supply and no market,
PEARL FISHERIES
37
the natural pearl business is dead. Now these shells are only source for the
manufacture of 'kaku', the shell-bead nuclei for marine pearl culture in Japan.
The other region for natural freshwater pearls has been Europe with mussels
of species of Margaritana, Unio and Anodonta. In the UK the mussels, which were
once. important, occurred in Wales, Cumberland and Scotland. The USSR,
Sweden, Norway, Germany and Austria had pearl fishery. The average number
produced by these mussels amounted to about one pearl per 100 mussels (Bolman,
1941). Freshwater pearls lose their colour, Iustre and iridescence sooner than the
marine pearls. Due La pollution and other man-made changes of the environment,
European freshwater pearls have entirely disappeared from the trade.
CHAPTER 5
PEARL OYSTER BREEDING
IN com mon with bivalve molluscs, the pearl oyster has a reproductive strategy by
which several millions of eggs are produced by every single mature femcJe and
trillions of sperms hy every sjngle mature male. Providing for the high mortality
of eggs, larvae and young ones, and death due to predation and old age, the species
finally establishes an equilibrium level of population in its area of distribution.
However, interference by man in exploiting the stocks and unpredictable changes
in the environment.11 conditions, coupled with occasional outbreaks of diseases,
would reduce the pGpulation to suhequilibrium levels or even threaten the very
existence of the species in the area. Recalling the status of pearl oyster stocks in
the Gulf of Mannar, it is evident that they are acted UPOIl more by unfavourable
factors than favourable ones, leading to near absence of oysters on the beds for
decades at a stretch. The Indian pearl oyster Pincladafucata, therefore, forms a
classical example where benign research is needed to rehabilitate the resource ..
This effort would also provide for the commercial needs of pearl culture. lL would
start with the breeding of pearl oyster under controlled conditions.
Farming oflhe edible species of oysters (Crassoslrea virginica and Ostrea
edulis) is several centuries old in the USA and E'Jrope. Motivated by the lack of
adequate and timely supply of seed for the oyster industry, formal research was
begun over a century ago to spawn the oyster under controlled conditions and to
improve on the chances of survival of the larvae and juveniles (Brooks, 1880).
Early attempts by several workers in Europe and the USA in the early decades of
the present century met only with partial success (Wells, 1920; Cole, 1937). The
technology towards hatchery production of seed of the oysters and other bivalves
blossomed with the advent of a greater understanding of the conditions controlling
maturation and spawning of these animals, and the food and water quality
requirements of their larval stages (Loosanoff, 1945; Loosanoff and Davis, 1963).
Commercial hatcheries for oyster seed production came to bq established in the
sixties in toe USA, Canada, the UK, France and Japan. The technology was good
for the temperate and sub-tropical species. The technology for tropical species still
eluded success [or a long time un til AQUACOP succeeded in French Polynesia for
oyster and mussel (AQUACOP,1977, 1979) and the Central Marine Fisheries
Research Institute in India for the pearl oyster (Alagarswami et ai., 1983b).
The quest for hatchery technology for the Indian pearl oyster was motivaled
by the well-deserved qlJestion posed by the Indian pearl fishery managers: Ofwhal
use is the technology of pearl culture if thcrearenopearl oysters in the natural
beds? This led to the formulation of a research project at the Central Marine
39
PEARL OYSTER BREEDINu
Fisheties Research Institut.e on development of hatchery tec hnology for the
production of seed 9f pearl oyster in 1978 which gave the a.nswer in 1982
(Alagarswami el al., 1983b).
HATCHERY ESTABLISHMENT
The hatchery establishmcntconsists offacilitics for supply of good seaw ater,
aeration, maturation and spawning of oysters, live aJgal production, larval rearing
and s_!)at rearing CFig.13). These aspects a.re brielly descr ibed i n th e followin g
pages.
'.1
.'t
/
Fig. 13 . Pearl oyster hatchery tacility for breeding, larval rearing and spat production.
Seawater supply
It is the plentiful supply of seawater of good qualily that determines the
success of hatchery production of pearl oyster seed. The water should be [rec from
pollution as the larvae are very sensilive to even small amounts of pollutants.
Waler drawn [rom the sea is passed through sedimentation tanks and filtration
units and stored. Before use it is further filtered through a series of cartridges so
that all particulate matter down to about 3}J.lll is removed. It is then passed tllrough
germiCidal ultraviolet irradiation so that the bacteria are destroyed. Temperature,
salinilY and pH of the water should be within the optimum ranges. and large
variaLions in any of these parameters would result in failure of hatchery operation.
40
PRODUCTION OF CULTURED PEARLS
Aeration
Supply of dust-free and oil-free compressed air is an essential requirement.
Larval rearing may be done under static conditions with change of seawater on
alternate days. However, towards the end of the larval pha'ie and for the spat, and
for broodstock maintenance, adequate aeration is required to make up for the
consumption of dissolved oxygen by the larvae, spat and adults.
Maturation and spawning of oyster
The natural population of pearl oyster in the Gulf of Mannar has two peak
spawning periods coinciding with the monsoon cycle (north-east and south-west
monsoons). However, it is not uncommon to see oysters in different stages of
maturity in any given month. In the temperate waters as in Japan, the same species
has a single well-defined reproductive season in a year and no gametogenic
activity can be seen in the animals outside the season. This is because the higher
temperatures which cause the development of gonad, maturation and spawning
occur only during summer (June-August). However, in a hatchery system,
broodstock has to be maintained in active reproductive phase throughout the year
to enab1e year-round operations for seed production. Therefore, outside the
normal reproductive sea.')on, these hatcheries develop the broodstock by temperature
manipulation, i.e. by slowly raising the temperature of seawater in which the
animals are mainlained from ambient condition to temperatures required for
gonad maturation and then for spawning. For example, temperature is raised from
abollt 10° C (winter temperature) to about 24°C (summer temperature) in steps
over aperiodofabout3 months and then to about 28°C in which the oysters would
spawn. Such practice is common in shellfish hatcheries in the USA, Canada and
Europe.
However, in the tropical situation as in India where the seawater has an
annual temperature range of about 25°_32° C, temperature by itself is not the key
factor in controlling the reproductive cycle. It has been seen that plentiful supply
of food for providing the energy for reproductive growth and some manipulation
of temperature within the range of 25°-32° C helps in taking the pearl oyster to
maturity and spawning,
For larval production both natural spawning and induced spawning in the
laboratory are made use of. Oyster which are fully mature spawn spontaneously
on many occasions when they are brought from the natural beds or from the farm
and placed in seawater. In all cases, the males initiate spawning first. When a
single oyster starts spawning, the chemical substances present in the gametes
induce others to follow resulting in mass spawning in a majority of the oysters in
the tank, However, to ensure spawning at the required time, the mature oysters are
induced to spawn through physical or chemical stimulation. Oysters placed in tris
buffer solution at pH 9.0 for 1-2 hours and later transferred to normal seawater
spawn with a success rate of about 78%. Similarly injection of 0.2 ml N/10
ammonium hydroxide at the base of the foot elicits satisfactory spawning
PEARL OYSTER BREEDL'IlG
41
response. Mature oysters would also spawn on thermal stimulation when maintained
for a day ?t 24 0 C and then the temperature is increased gradually to 32.0~ C
CAlagarswarni et al., 1983a). In induced spawning, it should be ensured that, as
soon as spawning is noticed, the oysters are transferred from the medium to normal
seawater so that the sperms and eggs are not subject to any physiological stress and
remain viable at fertilization.
Live algal production
The larva of pearl oyster, called veliger, in its earliest stage measures about
67.5 J.ll11 x 52.5 )lffi and requires food. The mouth opening of the larva is so small
that it needs food which is smaller than 10 J!ffi in size. Certain microalgae,
particularly flagellates, which are motile, devoid of a cell- wall and do not produce
toxic metabolites, satisfy the dietary requirements of the larvae. One of the crucial
functions of the hatchery is to mass produce live algal cells in required quantities
La feed the larvae.
Isochrysis galbana. Pavlova lutheri, Chromulinajreiburgensis and Dicrateria
sp. are the microalgae generally used as food for the pearl oyster larvae (Fig. 14).
Among these, the first two species are invaluable. These algae are mass cultured
in 20-litre carboys or in 1OO-litre perspex tanks in appropriate nutritional medium
(Walne, 1974), under sufficient illumination (1,000 - 1,500 lux) and photoperiod
(12 hours light and 12 hours darkness). cool temperature (23 0 - 25 0 C), and under
aseptic conditions. Small quantities of stock culture inoculated into mass culture
tanks multiply and bloom on days 4-5 depending on the species and is harvested
when growth has reached the exponential phase. Algal culture with aconcenlration
of 1-2 million cells per ml is gi yen as food to the larvae at appropriate ration with
25 -50 cells ~ of larval rearing medium.
Larval rearing
The main function of a hatchery is to rear the tiny larvae to the stage when
they set and metamorphose into the form ofthe adult pearl oyster, a process which
takes about 16 -20 days from the time of fertilization of the egg. TheD-shape or
straight-hinge veliger(size 67.S!J.ffi x 52.5).Un) larvae emerge through embryonic
development of fertilized eggs in about 20 hours (Figs 15,16). Healthy larvae are
separated from the others and are reared in filtered and sterilized seawater in
fiberglass tanks, being fed once a day with adequate supplies of microalgal food.
The rearing density is kept at 2-5 larvae / ml. The seawater is changed on alternate
days after collecting the larvae on a sieve. Antibiotics are added to the larval
rearing medium where required to prevent bacterial and fungal diseases. The
veliger reaches the umbo stage measuring 135).lm x 130}.Lm between days 9 and
10 (Fig. 17). Up to the end of umbo stage the larva remains in the column water
and swims about with the help of the muscular, ciliated veil or velum. With thl'!
development of foot, it reaches the pediveliger stage (size 200 ~ x 190 J..lm) and
soon settles down on a substrate specially provided as collectors or on the bottom
42
PRODUCTION OF CULTURED PEARLS
Pavlova
\utheri
Isochrysis
galbana
Chaetoceros indicus
Chromulina
freibergensis
Dicrateria
inornata
Pig. 14. Live microalgal food organisms used in the feeding of pearl oyster larvae in
hatchery. (Courtesy: Dr C.P. Gopinalhan)
PEARL OYSTER BREEDING
Fig . 15. Eggs of pearl oyster (mean size, 47.5 !J.m).
Fig. 16. D-shape veliger larvae of pearl oyster (mean size, 67.5ll1T1 X
52.5
~m).
43
-l4
l'RODUCIlON OF CULTURED PEARLS
Fig. 17. Umbo larvae of pearl oyster (mean size, 135
~ X
Fig. 18. Early spat of pearl oys ter ( size of 0.3 mm).
130/-Lm).
N : ARL OYSTER BREEDiNG
45
or sides of the lank after an cxploratory pha~e of swimming with thc velum or
cra'lVling with the foot, .scouling for a suitable s.pot. The brief frec-swimming
larval phase comes to an abrupt end once for all dUfing the life of the pearl oyster
and, on setUing down, il <lltachc s itself to lhe substratum by secreting l.l horny
substance in the form of threads , culled byssal threads, which have an adhesive
end. The larva metamorphoses lhrough a series of morphological changes and
aLlains Lhe shape and form of adult. although the size is aboul300 }-lm only (Fig.
18). This Lransformed young oyster is ca lled 'spat', a terminology wn ieh is loosely
used umil it reaches about 2 em shell height (Figs 19,20). The spat, ac;; £lIsa the
adulloysters, are capab le of discard ing the buneh ofbyssallhreads, moving a lillie
away from the spot wit h the help of foot, and refixing themselve s by secreting
fresh threads.
S uecess in larval rearing and spa t production depends on a variety offactors.
Water quality is the prime factor that influences production. Water temperature,
sa linity, hydrogen-ion concentration and dissolved oxygen shou ld be in Lhe
oplimum range. The pipeline should be of good quality p. v.c. ma terial and [lIsling
Fig. ] 9. Juv eni les of Pinelada fuca1a, reared in hatchery.
46
PRODUCTION OF CULTURED PEARLS
Fig. 20. Juveniles of Pine!ada margariliJera. reared in hatchery.
metal parts should not be u~ed. Parallel standby waterline should be provided for
use when the mainline needs maintenance. The tanks should be of material that
would not leach in seawater and should be clean. Use of detergents should be
avoided for cleaning. The environment inside the hatchery should be free from
dust and insec ts. The algae given as larval food shou 1d be free from con lamination.
Feeding schedule and ration should be precise to avoid decay of .excess algae.
Larval growth is not uniform even uncl.er the best 0 f circumstances due to genetic
heterogeneity. Mortality rates tend to be high due to their delicate nature and
sensitivity to changes in environmental parameters. A spat production rate of up
to 50% can be achieved under ideal conditions, but an average of 25% may be
considered satisfactory. For example, in rearing in 1 tonne lank with 500 lilIes of
seawater, at a larval density of Simi, the initirularvaJ population is 2.5 million. At
50% the tank: would yield 1.25 million spat, and at 25% 0.625 million spar. In
general practice, these figures are a little difficult to achieve when larval rearing
is done under ambient conditions. Hatchery operations may be avoided in seasons
when many of the factors are unfavourable.
Rearing of spat
The spat at first seltlement are too smrul and fra.g ile for transplantation LO the
farm and need rearing in the hatchery atleast until they reach about 3 mm size.
Good seawater, aeration and adequate amount of mixed algal food are the main
requirements. These young oysters can consume a larger variety of species of
PEARL OYS7ER BREEDING
47
algae and diatoms. Natural blaoms afmixcdphytoplankt.on are raised in large outdoor tanks by adding nutrients to seawater which has been filtered so as to relain
only the phytoplanktanicorganisms. These organisms come to bloom and arc used
as food far the spat When the spat reach about 3 mm in about a monrll's time, they
are carefully collected from the L;'lnks, placed in fine-meshed velon screen neLS
with a protective covering and transplanted to the farm . Nets of higher mesh sizes
and regular fruit baskets with holes arc used as the spat grow. When about 25 mm
they are laken out and grown in regular baskets. During this early period growth
potential j.e; the highest Hence nursery rearing of spat should be done under
optimum conditions of depth, wat<;rflow and foorl availability an0 the least
problems from sill, fouling organisms and predators. The young oysters fall prey
to carnivorous fishe-s, crabs, predatory gastropods, octopuses and slarfishes and
areas where these are abundant should be avoided. If unavoidable, these enemies
should be pe.riodically removed and destroyed .
CHAPTER 6
PEARL OYSTER FARMING
of oysters is a major activity of pearl culture. It is carried out in the bay
or lagoon or in the open coastal waters. Since the te rritorial sea is the property of
state, the wa ter area for fanning has to be leased. All COUll tries which have an
establishe.d pearl culture industry have laws for leas in g out the water bodies La the
farmers or companies. Appropriate slructures are floated in the waLer area for
holding the pearl oysters.
The farm will also have a shore eSlabli shment with fa ci lities for all landbased work. The facilities include a laboratory for oyste r surgery, pearl colleclion
centre, pearl grading and processing unit, farm stores , cage-cleaning yard and a
mechanical workshop . The farm will have bOals for transport of workers, oyslers
and farm materials. In the Japanese farm s, hUlS are e recled on the rafts for workers
to carry out periodic shell cleaning operations. In Australia, floating surgeries <.lre
established for nucleus implantation on the oysters.
Pearl oyster farming is divided into two phases, viz. mother-oyster culture
and post-operative culture. Mother-oyster culture deals with raising of stock from
spat collection and rearing them up to a s ize suitable for nucleus implantation. In
Japan this phase of culture is carried out independently by farmers who are
e ngaged exclusively in raising the slocks. When the oysters reach about 20 g in
weight, the farmers sell the stock to pearl cul turi sts. The laLter rear the oysters for
a few more months until the arri val of the season for surgery. After the nucleus
implantation, the oysters are subjected to a brief period of convalescence and then
reared in the farm until harvest. This phase of farming for pearl production is
termed post-operative culture. Generally the farming techniques are the same in
both the phases except for the additional care taken in rearing the pearl-bearing
oysters.
FARMING
FARMING TECHNIQUES
The simplest technique used by Mikimoto in the beginning of his experiments
was to collect oysters from the natural beds engaging women divers, popularly
known as 'Ama san', and broadcast them on the sea bed in a demarcated area near
the shore. The oysters suffered heavy mortality due to predation and covering of
sand and silt. Later, techniques were developed to grow the oysters in the water
column well above the bottom. This can1e La be known by various names such as
off-bottom culture, hanging culture, suspended culture, raft culture and long - line
culture. Placing the oysters in nets, baskets or cages gave protection against
predation. A hole was drilled on the anterior ear of the s hell and ten or more of the
PEARL OYSTER FARMl NG
49
oyslers were connecle d by a vinyl strin g passing throug h the holes at inte rva ls of
7 or 8 em. Thi s w as call ed a pearl strin g. ThG string was wo und ar ou nd a rope o r
bamboo pole hung verticall y fro m a raft.
Ra ft cul t ure
B ask ets. Mode rn tec hniques do not vary muc h i n principle. Howeve r, l he
des ign and materials of th e structures have ch a nged. T he baskets or c<.Iges are of
different materia ls and des igns. Plas tie-comed o r pa int-treated mil d s teel rods of
6 mm diameter form the solid frame whic h is covered wi th synthe tic webbing of
appropriate me sh siz e to hold the oyster s witho ut d.ropping. T he ba.sket w ill have
a lid of similar making . The strucLural vari ati ons a re: (a) in size and shapl.; recwngu}ar, square or round; (b) in volum e of space - flat as in pearl ne t or th ree
- dimensional as in regular baske t; and (c) in th e numbe r o r compa.nm enls with in
the structure - single or multilayered. The choi ce is of on e of spe ci es in volvcd,
depth of operation and convenience of the farmer. Oy ste rs are scg rega led in
different size groups . The numbe r of oy sters p e r baske t varies according to lhe ir
size. An example for the Indian p earl oyster P-fu. cata would be thal a square basket
of 40 em x 40 cm x 10 em can hold 125 oyste rs of 35- 45 mm s ize , 100 of 4555 mm , 75 o f 55-60 mm and about 50 in the case of larger oys te rs.
Rafts. The baskets are hung from rafts which are moored in the sea (Figs
2 1-24). The raft is made of wooden poles placed parallel and across, and las hed
Fig. 21. Preparation for SCUBA - diving on board research boat in the pearl
banks of Gulf of Mannar for pearl oyster C{)llection.
50
PRODUC110N OF CULTURED PEARLS
Fig. 22. Raft in the Gulf of Mannar for fanning of peaTl oyster.
with rope to form a rigid frame of an overall size of 6 m x 5 m. A couple of planks
are attached to the raft to enable the workers to walk on during inspection. Empty,
air-tight barrels of about 200-1itre capacity are attached on the under side of the
comers of the raft so that when it is floated on the sea only the barrels remain
parLially submerged and the poles are clear of water. The raft which is constructed
on the shore is taken to the se..1. and towed by a boat to the site selected for farming
the oysters. The raft needs anchorage to prevent its drifting and is moored by two
anchors of appropriate design and weight with lengths of anchor chain. Variations
in this floating structure are severa1. PVC pipes may be used in the place of wooden
poles and styrofoam t10ats in the place of barrels. T he unit rafts may be attached
serial ly and anchored at selected points when the farm is in a calm bay as in the
case of Japanese pearl culture farms or moored individually when the raft is to be
located in the open sea as under the Indian conditions.
Long-lines
Long - lines with a series of large hollow floats in a row attached to strong
ropes and suitably anchored are more suitable for open coastal waters . The baskets
with oysters are suspended from the strong rope of the line. The floats give the
buoyancy and keep the line without sinking. While rafts are rigid and hence are
liable to break under strong winds and waves, the lines are tlexible and can tide
over rough sea conditions. Long~line culture is practised in the inland sea of Japan.
Il is also currently used in Sudan for the rearing of black-l ip oyster.
51
PEARL OYSTER FARMJNG
Fig. 23. A pearl oyster frame net loaded with oysters for hanging from raft.
Underwater platforms
Underwater platforms are used jn deeper lagoons a .tn1ti~ .y.ase o (black-lip
pear) oyster farming in French Polynesia. Oysters in
~~&e su1;~~q from
these platforms . Galvanized wireweld trays sup
~d' off bAltom by ~~~ rete
blocks have been used i.n the Red Sea for P. marg !fjf~~f:.i{f!-:"!'f. l'
;..o~ \
j . , ~~~
~
.,!~
\ ~.T~,?:G ", " ,..
.,~'....
<:>,
.:;.
u·r:..; .
\~.'.
" . '/P,
, . "'.'~ '
.....
.
-' ,
f.
"" 1<
.....!J.t"j
'. ' \lv'~ . ~
,(10
~
52
PRODUCTION OF CULTURED PEARLS
Fig. 24. A pearl oyster basket with oysters.
Choice of technique
It is important to choose the right technique of farming La suit the site.
Generally raft culture is good for calm bays. Long-lines are ideal for turbulent sea
conditions. Underwater platforms are suited for moderately deep lagoons. It is
often difficult to make a decision on the right technique. Trials and experience can
guide in making final decisions.
ENVIRONMENT AL CONDITIONS
The success of pearl oyster farming and pearl production depeFlds largeJy on
the environment in which the oysters are teared. The oyster wholly depends on
seawater for all its life functions such as osmoregulation, respiration, nutrition and
reproduction. It does not require any external supplies from man; the deliberate
dumping of domestic, agro-chemical and industrial pollutants into the sea only
harms the oyster. Therefore, the set of environmental conditions has to be ideal
and this should be ensured while selecting the site for the farm.
Topography
Areas sheltered from strong winds and waves are preferred to open coasts.
Pearl oyster farms in Japan, the Philippines and Australia are located in sheltered
PEARL OYSTER FARMING
53
bays, the surrounding hills and islands giving protection against strong winds. The
coastline of India is more or less straight withou t much indentation. The effects of
both the south-west and north-east monsoons are felt in the coastal waters and the
sea is turbulem in some part of the year. Year-round open-sea farming, therefore,
becomes difficult to achieve. The Gulf of Mannar in India where pearl culture
work is concentrated so far has been found to be mocicralely acceptable in the
absence of better locations on the coast of the mainland. The small islands such
as Krusadai, Pullivasal, Manauli, Hare, Nallatanni tivu, Karaichalli, Vilanguchalli
and Vantivu give some protection. In Gulf of Kutch, the 'khacldas' are open
intertidal stretches with high tidal amplituue. Embankments will require to be
erected in the channels to sheller the oyster farm. However, the Andaman and
Nicobar Islands have many areas which provide ideal conditions for pearl oyster
farming (Alagarswami, 1983). The lagoons of some islanus of Laks~ladwccp,
especially Bangaram, would seem to be favourable (Alagarswami el al., 1989).
Hydrographic conditions
Depth is an important factor in rearing pearl oyster. In Australia, farms arc
located in a high tide depth of 18 fathoms c= 33 m) with a maximum of 34 feet C=
10.4 m) rise and fall of tide (Hancock, 1973). In Japan, the depth range of bays
where farms are located is 4.3 - 10.0 m and minimum depth preferred for the rafL<;
is 5 m (Alagarswami, 1970). Sea bottom should preferably be gravelly or
sufficiently hard if there is an admixture of sand. Muddy bottom shou Itl be avoided
as suspended silt would harm the oyster by choking the gills and affccting the rate
of filtration. Walercunent which is essential should be mild (less than I knot) to
continuously carry away the biological waste material from the farm and to bring
in fresh seawater with sulTicient amount of dissolved oxygen and food materials.
Strong current will lead to reduced metabolism and stunted growth of oyster. Tidal
flow and range should be moderate. RepeaLed culture in the same grounds often
deteriorate the quality of thc pearl. Accumulation of biological waste of the
oysters on the scahottom and consequent degradation of the ecosystcm would lead
to pollution problems causing diseases and rnorlality of oysters.
Some of the standard environmental parameters to be considered are
temperature, salinity, hydrogen-ion (PH) concentration and nutrient salIS. Temperature
is important in many respects, particularly in regulating the metabolic ratc of the
animal, controlling the reproductive cycle as in sub-tropical and temperate waters
and inOuencing the quality of pearls. The Japanese pearl oyster has its most
suitable range in 18° - 25°C. In winter, sea surface temperature drops down to
10°C and oyster enters into hibernation; when it is above 25°C the oyster shows
signs of cxhaustion. Deposition of calcium carbonate stops at 13°C or I()wer and
the oyster perishes at 6°C. In areas of pear} culture where winter temperature goes
below 1DoC, oysters are shifted to other areas where higher temperature prevails.
In the Indian seas the temperature is high throughout the year. In the Gulf of
Mannar the lowest sea surface temperature is about 23.8°C and the highest
54
PRODUCTION OF CULTURED PEARLS
33.5°C, the monthly averages ranging from 25.9° to 31.5°C (Victor and Velayudhan,
1987). As observed both in the Gulf of Mannar and Gulf of Kutch, oysters. show
a higher growth rate in winter months in the lower range of temperature. Higher
temperature within the ambient range helps in faster growth of pearl. But very fine
layers of nacre which improve the lustre of the pearl are deposited at lower
temperatures. Hence pearl harvest is done in Japan during winter when the quality
is at its best.
Salinity needs consideration when the farm is located in areas near to the
mouth of rivers. The salinity of the Gulf of Mannar would normally vary from 30
to 35 ppt. Even heavy rains in the open sea would not bring about any large
variations in salinity in view of constant mixing of sea water that takes place by
currents and tides. However, heavy discharge of freshwater by rivers in spate
during monsoon would considerably lower the salinity of the coastal waters in the
region of its flow. In an instance of Novem ber 1977, due to floods, the salinity of
the coastal waters in the Gulf of Mannar came down to as low as 15.69 ppt.
However, the oysters tided over the unfavourable conditions as, within a day, the
salinity rose to 26.53 ppt. Prolonged spells of low salinity would cause mortality
of oysters.
The pH should be around 7-8. In open sea conditions. the value is generally
steady. In the fann at Tuticorin, the annual range is 7.7-8.3. Within the ambient
range, the lower pH is preferable at the time of pearl harvest. Value of 7.3-7.5 in
winter ill the Japanese bays is considered favourable for pearl collection as the
quality of pearl in this range is good.
Calcium is basic to the formation of shell and pearl. The oyster derives its
requirements for calcium metabolism from the seawater as well as from the body
fluids via the mantle. The nonna1level of calcium in the seawater is about 400 mg!
litre. In the Ago Bay of Japan, the calcium level ranges from 390 to 407 mg/ litre
(Matsui, 1985). In Tuticorin Bay it ranges from 316 to 454 mg! litre. Lower levels
of calcium would lead to fornation of thin shells and poor quality pearls.
Nutrient StVts (phosphates, silicates and nitrates) in fann areas should be
optimal for primary production. Phytoplankton production depends on these
factors and sun-light (as in the green plants on the land) and this firs 1 link in the
food chain of the sea forms the predominant food of pearl oyster.
Besides the above parameters, the composition of trace elements is considered
important and the colour of pearls is influenced by their quantity and qUality.
Gold-and cream-coloured pearls contain more copper and silver, whereas skinand pink-coloured pearls contain more sodium and zinc. Gold pearls con lain more
metal elements than green pearls (Matsui. 1958).
FOOD SUPPLY
Phytoplankton consists of several groups, of which diatoms and flagellates
are considered to be the ideal tood for the pearl oyster. The amoum and chemical
PEARL OYSTER FARMING
55
composition of phytoplankton determine the quality of pearl. The animal also
seems to derive energy from suspended o~ganic matter. Sudden spurts of overproduction of certain diatoms and dinoflagellates in bloom situations are toxic and
lead to mortality. Areas which often witness blooms of toxic organisms should be
avoided in pearl oyster fanning.
ENEMIES OF PEARL OYSTER
The enemies of pearl oyster can be classified as p)(!.dators. boring organisms
and fouling organisms. By growing oysters in baskets, the predatory problems are
minimized to a certain extent. Boring and fouling Qrganisms are more in oyster
fanns than in natural beds because of intensity of fanning and because shallow
coastal waters have more of these organisms than deeper offshore waters where
natural beds are present
Predators
Coral reef perches such as Balistes, Serranus and Lethrinus, and rays like
Rhinoptera and Ginglymostoma are the common fishes that predate upon pearl
oysters in natural beds. Also starfish and octopus are the avowed enemies. While
these fishes have not posed a problem in pearl culture fanns, some damage on a
minor scale has been caused by fishes like Diodon sp., Arothron nigropunctatus
and Ostraceon spp. (Appukuttan. 1987). Serious damage is caused by predatory
gastropods such as Cymatium cingulatum and Murex virg ineus in farms. as also by
crabs like Charybdis, Atergatis, Leptodius and Thalamita (Dharmaraj el ai.,
1987). These gastropods and crabs get into the baskets through the meshes when
they are small and grow by preying upon the young pearl oysters. Periodic
inspection, and removal and killing of the predators appear to be the only remedy
against these enemies.
Fouling organisms
Several species of marine organisms get a foothold on the shells of live
oysters and thrive thereon. In fact mini-scale biological colonies and assemblages
of one or more species get established on each oyster (Figs 25-26). They settle as
larvae, metamorphose and grow vigorously. The worst of these is the barnacle
Balanus amphitrite. Their number on each shell may run to a hundred virtually
occupying all the space on the shell. The barnacles compete with the oyster for
food, as both are filter feeders. They make the shell heavier, disrupt the hinge
mechanism of shell movement and, in extreme cases, cement the two valves of the
oyster by overgrowth, thereby causing its death. Other serious foulers are the
bryozoans such as Membranipora, Thalanwporella and Lagenipora, simple
ascidians such as Ascidia and Dicarpa, and molluscs such as weaving mussels
A vicula and Modiolus, and oyster Crassostrea (Alagarswarni and Chellam, 1976).
56
PRODUC110N OF CULTURED PEARLS
Fig. 25. Heavy load of fouling on a pearl oyster by sponges, ascidians, bryozoans and
hydroids.
Fig. 26. Heavy fouling of a pearl oyster by barnacles and alge.
PEARL OYSTER FARl>1ING
57
A vicula vexillum, when it strikes, grows profusely on pearl oysters a 3 well as on
the baskets, almost closing the meshes and disrupting waterHow through the
baskets. Several others like seaweeds, hydroids and fouling sponges are also
commonly found. In pearl oyster fanning, biofouling is a major problem necessitating
intensive labour work for periodic cleaning of shells. Biofolliing affects the
growth of oyster and the quality of pearls. Japanese far'll crs employ mechanical
devices and water jets to clean oysters and cages. To some extent the problem can
be minimized by choosing deeper waters outside the coastal belt and choosing the
depth of culture where the occurrence of these organisms is relaLively less.
Boring organisms
Several species of sponges, polychaete worms and molluscs establish their
habitat on pearl oyster by boring through the shell (Figs 27-28). The boring
sponges Cliona celata , C. vastifica and C. margaritiferae, at the extreme stage of
infestation, render the shell fTagile. Polychaete worms of the families Syllinidae,
Nereidac, Spionidae, Terebellidae and Cirrawlidae cause havoc to the shells.
These worms, notably the ubiquitous Polydora ciliata, cut tunnels through the
length and breadth of pearl oyster shell. As these worms try to open the tunnels into
the shell cavity, the oyster fights by secreting excess calcium carbonate substance
to close the entry points. The struggle continues leading to formation of extensive
blisters on the inner aspect of the shells. Oysters become weak and, in extreme
cases, may lose the baLtle to the worms and perish. Relatively, the boring molluscs
such as Martesia and Lilhophaga, and isopod Sphaeroma are of less significance
as they are rarely seen.
The boring organisms can be destroyed by placing pearl oysters in freshwater
for about 6 to 10 hours, depending on size, or by application of a thin film of ] %
Fig. 27. Nwnerous blisters caused by
boring polychaeles.
Fig. 28. Pearl oyster with heavy
infestation by boring sponge.
58
PRODUCTION OF CULTURED PEARLS
formaldehyde solution on the shells and placing them back in seawater after a few
minutes (Velayudhan, 1983). The strength offorrt:lalin and duration of exposure
have to be worked out for every situation so that oysters are nOL killed. However,
oysters once treated will be affected again by the boring organisms and would
need periodic treaUTIent.
Red tide
The discolouration of sea due to blooms of certain noxious planktonic
organisms is referred to as 'red tide' despite the colour variations which may be
caused by the species involved or its intensity. The phenomenon is caused in the
sea by certain dinoflagellates such as Gonyaulax and Gymnodinium. Under certain
abnormal conditions, these organisms multiply very fast and would occupy an
entire area as blooms. Apart from causing oxygen depletion they secrete certain
toxic substances and their decay causes foul odour. Pearl oysters caught in such
environment would face serious problems leading to mortaUty. Although the red
tide is not very frequent, when it occurs, as it happened on several occasions in the
past in the Ago Bay of Japan, the pearl oyster stock can be wiped out. The farmer
should be aware of the consequences of red tide and should remove the stock
elsewhere. Blooms of diatom Trichodesmium thieubautii interfere with culture
operation in the Gulf of Mannar in India, though not leading to mortality.
CHAPTER 7
PRODUCTION OF CULTURED PEARLS
CULTURED pearl is a biological product of the pearl oyster as the natural pearl is.
But in the production of cultured pearl, man aids the oyster in deliberately
providing the two conditions required, viz. the core material or the nucleus and the
mantle tissue. This is done through a skilful surgical operation on the body of the
oyster. Once the initial reaction of the oyster to reject the foreign substance is
suppressed, it learns to live with it and the physiological functions of the oyster
become normalized under ideal conditions of living. The piece of mantle tissue
grows over the nucleus and forms the pearl·sac. The epithelial cells of the pearl.
sac perfow their natural physiological function of secreting nacre or rnother-ofpearl in the same manner as they would if they were a part of the mantle of the
oyster adjoining the shell. The nacre is deposited over the nucleus in hundreds of
micro layers in a concen tric manner. When sufficient numbers of these layers are
formed, colour, lustre and iridescence of pearl appear distinct and it turns in to a
beautiful cultured pearl.
SELECTION OF OYSTERS
Pearl oysters infested with a heavy load of bating arid fouling organisms on
the shells do not produce quality pearls. Bacterial and viral diseases may affect the
gills. The gonads may be heavily parasitized with cestodes and trematodes.
Oysters of above nature are physically and physiologically weak and cannot
produce good pearls. Hence healthy oysters have to be selected for pearl
production. Oysters of desirable size (20 g and above) are brought from the farm
to the surgery and the shells are cleaned of the fouling organism.s and other
encrustations. Initial selection is made at this stage based on size and shell quality
only. Final selection would be possible only when the oysters are opened for
surgery.
NUCLEUSREQurnEMENTS
Raw material specifications
Theoretically, any inert substance can be used as. the core material for the
cultured pearl. The Chinese used small Buddha carvings of ivory; wood, stone, or
metal castings in the freshwater mussel to produce nacre-coated images of Buddha
in the 12th century. Mikimoto, in his early work, used bits of shells, coral pieces,
bits of metal, ground-up scales offish etc. in the Japanese pearl oyster. Over the
years, since pearl culture was commercialized, it has been found by experience
60
PRODUCTION OF CUL11JRED PEARLS
and trade acceptability that beads of freshwater mussel shells are the most suitable
to be used as nuclei for cultured pearls. It is so for the follo,,!,ing main reasons:
1. Shell material has the same general physical properties of nacre.
2. Heat resistance properties of shell material and nacre being the same,
the layers of nacre of cultured pearl do not crack while drilling.
3. The calcium carbonate secreted by the pearl-sac either in the aragonite
or calcite form binds homogeneously and firmly with the calcium
carbor!ate layers of the shell bead with the help of the initial organic
conthiolin layer and, therefore, the pearly component does not get
separated from the nuc.1eus at any time.
4. The density of the shell material is about the same as that of nacre.
It has become well established in commercial pearl production that shell
beads are used as nuclei for cultured pearl production. Any deviation, if tried, will
have to be accepted by the trade and the consumers. The only ex{;eption is for
blister pearls or half-pearls where alabaSter is used as the core substance.
Production of shell-beads
Traditionally, the raw material used for production of shell-bead nuclei has
been the shells of a variety of freshwater mussels, viz. pig-toe, washboard, dove,
tirree-ridgeand butterfly shells, of the family Unionidae. These are available in the
Tennessee and Mississippi rivers in the USA. Some of these shells are abou t 20 cm
long and 30 mm in thickness near the hinge. These mussels were themselves
known for production of natural freshwater pearls once. The shells are imported
into Japan and are cut, ground and processed into spherical shell beads (kaku).
These are made in diameters of2 to 8 mm. The dimensional accuracy of the beads
is about ± 0.25 mm and the spherocity is well acceptable. The shell-bead
manufacturing industry in Japan is a highly specialized one and supplies nuclei to
several countries where pearl culture is practised.
The nucleus for the large baroque or half pearls produced in Pinctada
maxima of Australian waters is a semispb.ere made of alabaster, and these may
range from 10 - 20 mm in diameter.
In India, attempt has been made to use the sacred chank shell (Xancus
pyrum) as raw materialfornuclei (Velu et ai., 1973). Several hundred thousands
of sacred chank are fished annually from the coastal waters of Tam il Nadu, Kerala
and Gujarat. These are sent to West Bengal where the cottage shell industry cuts
them into bangles and rings. More than 70% of the mass of the shells is discarded.
It is often used in making lime. Thick portions of tllese waste shell bits have been
sized, ground into spheres and polished, and used as nuclei for cultured pearls.
Although good cultured pearls have been produced with these shell beads as
nuclei, the technique needs several improvements in dimensional accuracy,
spherocity and large-scale production. Other potential shells are the giant clam
Tridacna spp which occurin Andaman and Nicobar Islands. Freshwater mussel of
large size with thick shells are not readily found ill India. Perhaps P arreysia shells
PRODucnON OF CULTURED PEARLS
61
will offer some possibilities. At present, indigenous production of shell beads is
the weakest link in pearl culture operation in India.
PREPARATION OF OYSTER FOR SURGERY
Preparation of host oysters
For achieving higher rates of pearl production, it is essential that the host
oysters which are to receive the nucleus and graft tissue are in the right condition
to facilitate retention of nuclei and formation of pearl-sac. The requirements are:
(i) the oyster should not react violently at and immediately after the
nudeus implantation, and
(ii) the gonad should be in an empty stage, i.e. inactive! resting reproducti ve
stage, to receive and retain the nucleus and enable pearl-sac formation
without dislocation of graft tissue. Ripe gonad interferes with operation
by the oozing of gametes when incision is made.
The above requirements need manipulation to bring down the metabolic
rate of the oyster and to control the reproductive cycle. In the temperate waters of
:lapan, the metabolic rate of the pearl oyster is brought down by maintaining the
animals in a depth stratum where the seawater temperature is low. Due to thermal
stratification in the bays, the temperature in the depths is lower than at the surface,
except in winter when the reverse may be true. Hanging depth is also chosen where
the food organisms are scarce. Due to the combination of low temperature ahd
scarcity of food, the metabolic rate of oyster comes down. The oyster after a period
of exposure to such condition becomes docile and does not react violently at the
time of nucleus implantation. Recovery to normal level of metabolism is gradual
through step exposure to higher levels of temperature and food availability.
Similarly, temperature is used either to retard gamete formation or to
accelerate spawning. By maintaining the oysters, after ll-teir previous spawning, in
low temperature, the gametogenic actiVIty of the gonad is retarded. If the gonad
is iIi an advanced stage of maturity. the oysters are herded together in higher
density and maintained in depth stratum where warm temperatures prevail. The
gonads quickly reach the ovulation stage and spawn spontaneously in the higher
temperature, a process referred to as 'egg extraction' by the Japanese farmers.
Thus, depending on the time chosen for nucleus implantation, the reproductive
stage is manipulated in advance so that the oysters are in the right condition for
surgery.
The conditioned oysters, when placed in a shalIow tray with the hinge or
dorsal portion of the shell downward and covered w im seawater, would open their
valves in a few minutes. A wooden peg is inserted between the valves. Such
pegged oysters are ready to be taken to the surgical table.
The above process of preparing the oysters using temperature differences at
different depths cannot be applied successfuUy in tropical waters as in India. There
is no thermal stratification in the coastal waters or in the shallow bays. The natural
62
PRODUcnON OF CULTURED PEARLS
reproductive cycle of the pearl oyster has to be studied and the months when the
gonad is in the post - spawning phase or in the early gametogenic phase have to
be chosen for nucleus implantatjon. If extension of the period is required, induced
spawning techniques may bcemployed. Elevation of pH Lo 8.5 by using chemicals
such as tris - buffer with or without hydrogen peroxide is useful (0 make the mature
oysters spawn (Alagarswami el al., ] 983a). So also temperature control and
injection of ammonium hydroxide solution have been effeciive in many instances.
Oysters treated with chemicals should be returned to the farm to enable them to
rccover [rom the effccLS of chemicals before they arc used for nucleus implantation.
Narcotization
Healthy oysters, when taken outside seawater, close their valves lightly by
contraction of adductor muscle. When opened forcibly, the body contracts on
touch of a needle. For surgery, agap of 1.0 - 1.5 cm between the valves is required.
The oyster should not contract when surgery is carried oul. In the Indian pearl
oyster, this is achieved through a process of narcotization using the chemical
menthol.
Pearl oysters arc placed in seawater contained in a tank and the required
amount of menthol crystals is sprinkled on the surface of seawater. The crystals
dissolve slow ly and the oysters become narcotized in the medium. The time taken
for optimum level of narcotization is greater in lower ambient temperature and
less in higher temperature, the range being 60 - 90 minutes. Over _ narcotization
woulcJ lead to excess swelling of tissues, particularly the foot, longer recovery
time and, in extreme cases, death of oysters. Therefore, chemical narcotization on
pearl oyster is done carefully and in batches according to the rate of usage in
surgery. The valves of the conditioned oyster remain open and the soft body does
not contract when the operation is performed. It is important that narcotized
oysters should be returned to normal seawater at the earliest for recovery.
SURGERY
Tools
The surgical kit consists of a special set of tools made of good quality
stainless - steel for the delicate operation on the pearl oyster (Alagarswami and
S ivarajan, 1975). The oyster stand with a top clamp is used to fix the oyster at the
time of operation (Fig_ 29). The specUlum with an adjustable ring is IIsed to keep
the shells open with an appropriate gap. The oyster knife with a bent end is to cut
the adductor muscle and soft body for removal of the mantle. The incising - cum
- grafting needle has a sharp flat oval end for making incision and a bem shirp tip
end to insert the graft tissue. The nucleus insertion needle has a hemispherical cup
of di [ferent di'lmeter at each end to I ifllhe nucleus by surface tension and implant
it in the body of the oyster. A graft- cutting knife, spatula, needle hook, forceps,
PR ODUCTION OF CULTURED PE ARLS
63
Fig. 29. Pearl oyster surgery for implantation of nuclei .
,fig. 30. Surgical tools employed in nucJeus implantation .
a pair of scissors and fine' camel hair brushes form the rest of the tools (Fig. 30).
The tools are maintained properly by cleaning them with freshwater and drying
them in the sun at the end of each surgery session.
64
PRODUCTION OF CULTURED PEARLS
Fig. 31. Removal of part of the mantle for preparation of graft tissues.
'Preparation of graft tissue
An important step in the surgery is the preparation of graft tissues from the
mantle of the pearl oyster (Fig. 31). Healthy oysters are selected as donors of
mantle tissue. The oysters should be in prime condition without blisters formed by
boring polychactes and sponge. Non - narcotized oysters are used for the purpose.
Successful pearl-sac formation is obtained from the mantle of the same species,
aJthough inler-specific graft tissues are occasionally accepted but result in poor.
secretion of nacre. The size of the donor oyster should be the same as that of the
host oyster.
The mantle can be divjded into 3 zones, viz. the marginal zone with lhe
folds. the pallial zone and Lhe central zone (Fig. 32). It is the pallial zone which
is more productive in terms of secretion of shell material and is required for graft
lissue preparation. The mantle should be removed without injury. As stated
earlier. the oyster remains tightly shut when taken out of seawater. A sharp knife
is inserted between the shells up to the adductor muscle and the latter is cut
vertically. The knife is pushed further down to similarly cullhe soft body into two.
Extreme eare is taken to see that the knife docs not touch the mantle on either side.
IfillOuches, the mantle would shrink and cannot be used. The two valves with the
portions of soft body and mantle are separated. The ventral portion of the mantle
is cut sharply with a crescentic cut in situ on the shell and removed on to a
rec t.:'1n gular soft wood block. The dirt and mucus on the mantle are gently removed
with the blunt end of a scalpel and the margins trimmed to yield a long ribbon from
the pallial zone. The ribbon is finally oriented on the block with the outer
65
PRODUCIlON Of CULTURED PEARLS
Pallial
mantle
Periostrocal
groove
Marginal
Inner fold
Fig. 32. Diagrammatic transverse section through the marginal mantle of pearl oyster to
show the mantle folds and pallial zone.
MQr~inal
maritle
1111111110000
Graft tis~ues
Fig.33. Steps in the preparation of graftlissues from mantle.
66
PRODUCTION OF CULTURED PEARLS
epithelium of the mantle facing the technician. Itis then cut inlo piecesof2-3 mm
length and about 2 mm breadth (width of the rib.bon) depending on the requirement
of the graft tissue (Fig. 33). Both the mantles are used for the preparation of graft
tissues. About 20-25 pieces can be cut from each ribbon.
It is important to ensure that the graft tissues remain viable until they are
used up in implantation. The preparation should be done gently and carefully.
Sterilized and filtered seawater should be used during the procedure to keep the
tissues moist Mild solutions of chemicals eosin, mercurochrome or azumin in
seawater may be used to give an antibiotic effect and to impart a gentle colour to
the tissue which is useful to foHow the course of the graft during implantation.
Generally, the tissues should be used up within about 10-15 minutes of
preparation. Prolonged retention on the block might lead to deterioration of the
tissues and failure in pearl-sac formation. Smaller pieces are used for nuclei of24 mm and the larger ones for nuclei of 5-8 mm diameter.
Nucleus implantation
Round pearls. Site: Natural pearls are formed in the muscular region of the
oyster, most frequently in the pallial connective tissue, tissues around the liver and
kidney, levator muscle and in the pulpar region. These pearls are generally small
in size and irregular in shape. The culture technology aims at producing pearls of
large size and round shape. For this purpose, the region of the body to be selected
for nucleus implantation should have adequate space for accommodating the large
nucleus and the organ should not be highly specialized. The gonadal region of the
pearl oyster is the ideal site (Fig. 34). After the nucleus is implanted, the follicles
carrying the gametes and the connective tissue get reorganized without greatly
affecting lhe reproductive function of the oyster. While gonadal region forms the
main site, the peripheral region near the liver or hepatopancreas is also used for
im planti ng n ue lei as the secon dary site. The stomach and in testinalloops traverse
the bepatopancreaLic and gonadal regions. Surgery should take care to see that the
stomach, intestine and other vital organs such as the heart and kidney arc not
damaged.
Nucleus load: In nature, a single oyster may contain from 1 to 200 tiny
pearls and, at the other extreme, a hundred oysters may be opened wi Lhout finding
a single pearl (Herdman, 1906). In culture, a maximum of 5-6 pearls can be
produced in oysters of sufficiently large size. Generally, single nucleus implantation
is practised for nucleus of size larger than 6 mm diameter. Double implantation is
done with a nucleus of 6 mm and another of 5 mm diameter. Triple and higher
levels arc done with nuclei of 4 mm or less diameter. The nucleus load would
depend on size of oyster, condition of gonad, and number and diameter of nucleus.
The choice is made in advance according to the commercial requirements. In all
cases using two or more nuclei, the primary nucleus of larger diameter is
implanted at the venual extremity of the gonad and the secondary nucleus of
smaller diameter at the dorsal side close to the hepatopancreas.
PRODUCTION OF
emTURED
PEARLS
67
h p
f
Fig. 34. Diagrammatic sketch of the anatomy of Pinctadafucata, also showing the position
of primary and secondary nuclei in the gonad. am, Adductor muscle; b, byssal
threads; f, foot; g, gills;" gn, gonad; h, heart; hp, hepatopancreas; i, intestine; Ip,
labial palp; m, mantle; n, nucleus; J, rectum; s, stomach.
The Japanese 'akoya' oyster, the Indian pearl oyster P. juca/a, the silver lip P. maxima and the black - lipP. margaritifera are employed in production of
round pearls. Nuclei of up to 8 mm, diameter are used in P.jucaJa and up to 12mm
diameter in P. maxima and P. margaritifera.
Surgery: The conditioned oyster is mounted on the stand and the tilt of the
oyster is adjusted to suit the convenience of the technician. The speculum inserted
between the two valves of the oyster helps in regulating the gap between the
valves. The man tie, gills and labial palps are smoothly pushed aside to get a clear
view of the gonad region. The foot is gently lifted and held in position. A sharp
incision of length su bequal to the diameter of the primary nucleus is made across
in the pigmented region at the base 0f the foot. The mllscles are gently detached
with the sharp oval end of the needle and a passage is cut lhrough the gonad up [0
68
PRODucnON OF CULTURBD PEARLS
\,
"'~,,::"',",",'"
;,
"", "
'
'
:"
,I
Fig. 35. InseTtion of a piece of mantle into the
gonad of pearl oyster.
_,
,
,
Fig. 36. Implantation of shell-bead nucleus in
the pearl oyster.
Fig. 37. Formation of half-pearls in
Pinetada maxima.
the site of implantation. A mantle piece is picked up atlhe tip of a needle, laken
through the passage and left at the site (Fig. 35). The nucleus is lifted by the needle
with lhe cup end and Laken carefully through the passage. When the nucleus has
reached the site where the mantle tissue had been left, it is discharged there by a
twist of the needle, simultaneously applying a gentle pressure so that the nucleus
remains in contact with the mantle tissue (Fig. 36). Correctly, the outer epithelial
side of the piece should face the nucleus and this orientation is important for
successful formation of the future pearl-sac. In the case of multiple implantation,
the process is repeated for each nucleus through the same incision but cutting the
passage through the gonad in appropriate directions up to the chosen site. Once the
nucleus implantation is over, the two ends of the incision at the base of the fool are
broughL together in contact and smoothed out. The oyster is removed from the
PRODUCTION OF CULTURED PEARLS
69
stand and gently returned to the tank containing fresh seawater for recovery.
Half-round pear). The half-round pearl are produced in P. fn£l.'{imn following
the pearl-Buddha technique of China (Fig. 37). The nuclei in this case are made
of alabaster and may range from 10 to 20 mm in diameter. The technique of haifpearl production (Hancock, 1973) is as follows: The oyster is clamped horizontally
on the stand and the mantle is separated from the upper valve. A spot of special
transparent adhesive 'aron-alfa' (a-cyano acrylate) which cures in water is applied
to the shell. The nucleus is pressed against the adhesive for abollt 2 minutes by a
ring at the end of a special tool. The required number of nuclei are fixed to the
shell. The oyster is now turned over and the opposite shell is treated as above. Care
is taken to see that the nuclei on both shells do not oppose each other. The number
of nuclei attached is in relation to their size, e.g. 3 of 16 - 17 mm diameter and 5
of l3 mm diameter. Similar techniques are employed for prodllction of half-round
pearls in P. margaritlfera and the winged oyster Pteria penguin (Fig. 38).
Fig. 38. Formation of a blister pearl in
the winged oyster Pleria penguin.
Post-operative care
The stress of conditioning and surgery leaves the oyster in a weak and
vulnerabJe state. The oysters are handled very carefully until they recover fully.
They are maintained either in a running seawater system with a mild flow of water
or in a static system with frequent change of seawater. If the location is on a calm
bay or lagoon with clear water, the oysters can be caged and directly suspended
from the rafts. The effect of menthol is got over slowly. The incision would heal
within 2-3 days. This is the period when the oyster would attempt to reject the
nuclei. If the inscision and the passage cut through the gonad arc too wide, the
chances of nucleus rejection are greater. Oysters in which vital organs have been
damaged during the surgery would suffer mortality. The surgical skill of the
technician in treating each oyster on its own meritat nucleus implantation will be
70
PRODUCTION OF CULTURED PEARLS
one of the deciding factors in the successful recovery of the seeded oysters and
retention ,of nuclei. Rough handling and exposure to strong stimuli (cuITent,
waves, tides, light and food supply) would cause greater rate of rejection of
nuclei. The operated oysters are maintained at a low level of metabolism and are
brought to ideal growing conditions step by step over a period of time.
In the oysters which have retained the nuclei, the mantle graft tissue
becomes active and starts growing over the nucleus surface through proliferation
of the epithelial cells. The inner epithelium and connective tissue of the graft
would disintergrate and get absorbed in the gonadal mass. The outer epithelium
alone would grow and spread over the nucleus, ultimately covering the whole
surface and fusing as a complete pearl-sac. This process would take about 4 - 7
days depending on the size of the nucleus and the physiological condition of the
oyster. Once the pearl-sac is formed the epithelial cells start secreting nacre and
depositing it over the nucleus. This sets in motion the formation of cultured pearl.
In the case of implantation oflarge nuclei, one has to be sure that the nucleus
has been retained by the oyster. Otherwise, the farmer would be culturing oysters
which would not contain a pearl at the end of along culture duration. Such oysters
are eX'!ffiined by X-ray to see whether the nucleus has been retained. Hancock
(1973) reports thatP. maxima are kept under post-operative care for 3 to 4 months
and are then X -rayed. About 83 % of these oysters retain the nucleus. Those which
have rejected the nucleus are re-operated or used for half-pearl culture.
POST-OPERATIVE CULTURE
Oysters which have successfully gone through the post-operative care
period are placed in baskets and further reared in the rafts in deeper waters. They
are left undisturbed save for tJte cleaning of the fouling organisms on the shelis
once a quarter or so depending on the fouling load. The number of oysters per
basket is reduced to 50 - 60% of the load of mother oyster culture to provide better
growing conditions. for each oyster. The duration of post-operative culture
depends on the time required for the pearls to attain maturity in terms of thickness
of nacreous layers and lustre. In the Japanese waters, it usually takes 3 - 4 years
for pearls of commercial value to develop in P. fucato (Mizumoto, 1979). Wada
(1973) reported that the period of cultivation differs according to the size of the
nucleus; 6- 24 months for the small sizes and form 36 -48 months forlarger ones.
In the Australian seas, 18 - 20 months are considered sufficient to harvest pearls
in P. maxima using 8 mm nuclei (Hancock, 1973).
Growth of nacre is largely influenced by the temperature of the seawater. In
the temperate waters of Japan, winter temperature of seawater goes down to as low
as lOoC. The oysters enter into a state of hibernation with the lowest metabolic
activity. Hence nacre secretion is practically arrested during this period. Only wi th
the riSing temperature in spring secretion of nacre re-commences. But in the
tropical situation as in India, with prevailing high temperatures throughout the
71
PRODUCTION OF CULTURED PEA..lU1l
year, nacre secretion is uninterrupted and hence the growth of pearl is faster. The
following data on growth of nacre of cultured pearl in the Japanese and Indian
pearl oysters'would illustrate the ilifferences between the temperate and tropic~
waters in this respect:
Nucleus
diameter(mm)
J apm (Calln, 1947)
3.05
4.10
6.10
7.90
India (Alagarswami, 1975)
3.00
4.00
5.81
Thickness of nacre
of cultUred pearl(rnm)
Duration of
culture
0.318
0.363
0.439
0.500
2 years
0.32
0.31
0.26
191 days
161 days
159 days
2'/~ years
3 years
3'/, years
According toWard (1985),the Japanese farmers have progressively red uced
the post-operative culture duration and from 21/2 years in 1960 it has been brought
down to 6-8 months in the recent years due to commercial compulsions. He stated
that a nacre thickness of 0.5 rom is acceptable as pearl and the minimum is 0.35
mm for good lustre and colour, whereas' the thickness obtained in the short culture
of 6-8 months is only 0.2 mm.
Under the Indian tropical conditions acceptable pearls are produced within
3-4 months with nuclei of2-3mm diameter and in 15-18 months with nuclei of
6-7 mm diameter.
PEARL HARVEST
Pearl harvest or 'beaching' of pearls is done during the cooler period of the
year when the lamellae of nacre are thin. Although faster growth of nacre under
higher temperatures is desired for building up an acceptable thickness of nacre,
thin lamellae on the top are considered be·st for colour and lustre. Th.is leads the
Japanese fanner to shift the oysters at the end of post-operative culture to grounds
which favour production of pearls of superior quality, and this phase is popularly
known as 'make-up' culture. Besides low temperature. a body pH of 7.3-7.5 is
known to be favourable. In Japan, pearl harvest commences in October and is
intensified in December.
The oysters are brought ashore and opened individually ta coHect the pearls
(Figs 39, 40) ..The P. fucata oyster is cut open with a sharp knife thereby killing
the oY$tcir: ButP. maxima oysteris carefully opened withoutki11ing it and t}Je pearl
is extracted with instruments. The oyster is then re-used at least far one more crop
by inserting a new nucleus of appropriate size in the already formed pearl-sac
without a fresh mantle piece (Hancock, 1973).
72
PRODUCTION OF CULTURED PEARLS
Fig. 39. Birth of a cultured pearl. TIle oyster has been
open for extracting the pearl.
CUI
Besides cultured pearls, oysters of older age will contajn some nalural
pearls. The flesh, after removal of the cultured pearls, is separated from the shells
and soaked in slack lime. The lot is placed in wooden vats fitled with rotating
wooden blades. The flesh gets pulverised as a slurry and, due Lo the higher density,
the pearls settle at the bottom of the vats. These pearls are collected, washed with
neutral soap water and dried.
The pearls collected at the harvest form the gross production of culture and
their quality ranges from the worthless to the best. From the results of harvest, the
farmer evaluates the entire sequence of culture operations including the source
and quality of oysters used, procedures employed in conditioning and sw'gery.
nucleus load, quality of graft tissues, farming conditions and environmental
parameters, and plans his future operations.
PRODUCTION OF CULTURED l)EARLS
73
Fig. 40. A large cultured pearl in situ in the goand of pearl
oyster
GROSS PRODUCTION
During the post-operative culture period oysters suffer some amount of
mortality due to natural causes as we1l as surgery. In the Japanese farms the total
mortality during a 3-year period is about 30 - 40% (Alagarswami, 1970). Hancock
(1973) stated that 20-30% of operated P. maxima die. Under normal conditions
about 10-12% annual mortality of seeded oysters can be expected. Among those
which survive, some would be found to have rejected the nucleus subsequent to
the post-operative care period. About 10-15% reject jon would be considered
normal even under the most stringent control of surgical procedure and postoperative care.
Shirai (1970) mentioned that pearl yield must be calculated on the basis of
weight of pearls produced from 10,000 inserted nuclei. For example, 10,OOO
numbers of 6-mm nuclei might yield 6.75 kg of pearls for a gross yield of 70%
whereas the same number of 7 -rom nuclei producing 9.38 kg of pearls might gi ve
a gross yield rate of only 40% as the mortalilY rate is much higher in this casco In
74
PRODUCTION OF CULTURED PEARLS
India, gross production of 62.8% in single implantation and 68.3% in multiple
implantation with reference to the number of nuclei used, and 62.8 and 180.6%,
respectively, with reference to the number of oysters used has been achieved
(Alagarswami,1974).
GRADING OF PEA..~S
Gross production of pearls obtained during harvest would comprise the
finest pearls to trash. Some of the pearls may be of perfectly round shape and of
outstanding colour and lustre; many are inferior; some are totally valueless as
gems or jewels. In some cases the oyster would have only the nucleus in round or
eroded fonn without any nacreous layer. Such composition is common to pearl
culture anywhere in the world.
Shirai (1970) classified the gross production of pearls as follows:
Gross production of pearls
I
I
Class A
Flawless,
. Qne flaw, small flaws,
small stain, pink,
silver or light cream
Class B
Fairly large
flaws, stains,
cream colour,
irregularity
ofshpae
1
A-I
Top pearls,
perfectly round,
pink, flawless,
with small
blemishes about
the size of a
pin - point
Class C
Trash pearls,
wild shaped,
badly coated,
heavily pock-marked,
clayey lumps, half gocd
and half bad
A-2
First class pearls,
slightly larger pits
and protuberances (once
treated, will become
indistinguishable from
top pearls)
The economic success of pearl culture enterprise would depend on the
percentage composition of the various classes in the gross production. According
to Shirai (1970), the Class A (A -1 and A - 2) and Class B pearls together usually
account for about 60% of harvested pearls and Class C the remaining 40%. Holl yer
. (1984) gave a further break-up of the percentage composition as follows:
PRODUC110N OF CULTURED PEARLS
75
Qualified pearls
Superior
Fine
Medial
Inferior
10%
10%
30%
10%
60%
Disqualified pearls
Poor
Dust
20%
20%
40%
In India, in the experimental production, the composition was: Class A
37.6%; ClassB 37.6%; and Class C24.8% (Alagarswami,1987a). The percentage
composition would vary from batch to batch depending on several factors.
The pearls are sorted by size, shape, colour, lustre and surface quality.
Internationally sizing is done by 0.5 mm scale from 2 to 10 mm. Stainless-steel
screens with holes of appropriate diameter are used for this purpose. According to
Shirai (1970). pearls of3.5-4.5 mm are designated as extra small, 5.0-6.0 mm as
small, 6.5-8.0 mm as medium, 8.5 and 9.0 mm as large and 9.5 and 10.0 mm as
very large.
Pearls are pink. blue, silver, gold, white, brown, green and black and subtle
combinations of these colours. Shades of pink are the most popular in trade but not
necessarily the most expensive as the cost is generally determined by size and
qUality. Colour is, in certain respects, related to lustre.
Besides size, lustre is considered the most important factor in evaluating
pearls. If lustre and refraction are good it would mean that the nacre is made of
pure aragonite and it is thick and durable. Even mis-shapen pearls and cream
coloured pearls would be considered valuable if the lustre is good.
PROCESSING OF PEARLS
It is rather a common practice of the trade to improve the quality of cultured
pearls through processing (Shirai, 1970; Ward, 1985). The process consists of
bleaching and dyeing for colour adjustment Hydrogen peroxide is used in a fixed
streng~ as a standard bleaching agent. Only the drilled pearls are amenable for
bleaching as hydrogen peroxide works through the drill hole. It liberates molecules
of oxygen which oxidise and remove the stain-caus.ing organic impurities and
lighten the colour. The pearls immersed in solution in tightly closed glass-bottles
are ex.posed to sun light for good effect of bleaching. It has also been reported that
ultraviolet rays and high-frequency radio waves are being used in this process.
76
PRODUCTION OF CULTURED PEARLS
Subsequent to bleaching, colour adjustment is done, ifrequired, according
to needs. Alkali-based, oil-based. acid and straight dyes are used for the purpose
(Shirai, 1970). The dye seeps through the drill hole into the conchiolin layer and
the colour gets stabilized. This colour then shows through the translucen t nacreous
layers. Colour adjustment is a matter of trade ethics which seems to have been
accepted as a practice when a pearl with a good nacreous layer is improved by
chemical treaunent.
Shirai (1970) also reported that costly black pearls were developed by
neutron bombardment, the colour resulting from minute quantities of manganese
in the nacreous layers.
BYPRODUCTS AND THEIR USES
In terms of volume, the byproduct of pearl culture is the total mass of the
oysters after extraction of the cultured pearls. The seed pearls, shell and the flesh
form the byproducts of pearl culture. The tiny seed pearls which are not used as
gems or jewels are used in the preparation of medicine. In the Orient, the pearl
medicine is quite popular. The Indian Systems of medicine use pearl powder and
pearl liquid as important ingredients in several preparations. Mukta-bhasma,
Pittantaka rasa, Vasantakusumakara rasa, Dava-ul-mulk and J avarish-i-lulu are
some such preparations (Nadkarni, 1954). It has been claimed that the pearl
powder is highly 'stimulant, tonic and aphrodisiac'. Other medicinal virtues
ascribed to pearl are . laxative, sedative, emetic and nutritive' . Pearl powder acts
as an antacid and is used in 'heart burn and bilious affections' (Nadkarni, 1954).
Class C category of cultured pearls cannot be used in jewellery. In such
cases, the nacreus layer is ground off the nuclei and the powder is then dissolved
in phosphoric acid, with the final products being separated by additional chemical
processes (Hollyer, 1984). Pearl calcium tablets are marketed in Japan for
'pregnancies, weak bodies, tooth cavities, stomach acid and allergies' (Ward,
1985). Itis also reported thatsomeJapanesecompanies have gained the technology
to extract high quality calcium from the shells which is marketed as pearl shell
medicine.
Large shells are used in shell craft for their mother-of-pearl layer . S mall and
broken shells can be used as ingredients in poultry-feed.
The adductor muscle portion of the flesh of the oyster is edible. Where the
oysters are opened individually for extraction of pearl, the entrails are used for
feeding the fish. Big companies which use the centrifugal process for extraction
of pearls, drain the slurry into the sea and this has been one of the causes of
pollution in the pearl culturing areas of Japan.
CHAPTER 8
STRUCTURE AND COMPOSITION OF PEARL
THE outer epithelial cells of mantle which form the pearl-sac secrete the extrapallial
fluid or the 'mother liquor' which contains mucoprotein, acid mucopolysaccharides,
calcium carbonate and other inorganic ions. The proteinous substance containing
large amounts of aspartic acid, serine, glycine and alanin residues, forms the
organic matrix called conchiolin, on which calcium carbonate crystallizes.
According to Wada (1970), nacre grows by step formation. To begin with,
small crystals precipitate here and there on the matrix formed over the surface of
an inserted shell bead nucleus. The crystals grow larger and larger and join one
another, thereby forming the fIrst mineral lamella. Inter-crystalline matrix substance
is sandwiched between them. The second and subsequent layers are formed, each
followed by the occurrence of a step between two groups of microcrystals of
different orientation at small angles. The lamella grows by advancement of the
step. The growth front of the lamella forms a growth pattern on the nacreous
surface. The mineral lamellae are formed alternatively with the conchiolin layer,
and the organic matrix between the lamellae is tenned interlamellar matrix. Thus
the nacreous substance presents a typical laminar structure, resembling a brick
wall, the bricks representing the crystals and the mortar the organic matrix (Figs
41,42).
The size, shape and nature of aggregation of crystals are influenced by the
secreting activity of the pearl-sac which varies according to the physiological
condition of the oyster and sea~onal changes of environmental parameters.
Generally speaking. pearls with a regular laminar structure will have iridescence
and good lustre, and ~ose with irregular laminar structure will have poor
transparency and lustre (Wada, 1970). The thickness of the min (',ral lamella is in
the'range of 0.29 to 0.60 J.UI1 and that of the interlamellar matrix is O.02I-Lm. Good
lustre is obtained when the layers are thin and numerous. and poor lustre when they
are thick and fewer. Sjnce the secretory activity is influenced by temperature of
the seawater, pearls are harvested in the lower temperature range when thin
lamellae are deposited.
The pearl-sac epithelium is capable of secreting all the organic and
inorganic components that go to the formation of shell. The mineral calcium
carbonate is secreted in two forms, namely aragonite crystals or calcite crystals_
The third form of vaterite crystals has not been reported in the pearl oyster. The
aragonite is the real 'nacre' substance and calcite, the prismatic substance.
Although four types of cultured pearl products are known, viz. organic, prismatic,
nacreous and compound pearls. only the nacreous product is accepted as pearl.
The organic pearl is produced due to dark organic material deposited around the
78
PRODUCTION OF CULTURED PEARLS
Fig. 41. Laminardeposilion of mineral crystals (dark layers)
and !he inter-lamellar organic matrix layers (Simkiss
a.T'ld Wada. 1980).
Fig. 42. The patrem o[fonna ti 011 o[nacreous layers in the shell ofpearl
oyster.
79
STRucrURE AND COMPOSrnON Of PEARL
Imcleus which, when viewed through the nacreous layer, gives the pearl a blue
colour. 'The prisrT)atic pearl is composed largely of layers of calcite crystals
arranged vertically on the plan of the lIucleus surface and are opaque. The
com pound pearl is prod uced with an irregular mix. of organic mallcrial calci te and
aragonite crystals, and is nol of commercial value. The nacreous pearl, which is
of gem quality, is composed of successive layers of aragonite crystals,
The nacreous pearl of Pi)l(.'Jada has the following chemical composition
(Bolman, 1941) :
Calcium carbonate
91.59%
Organic maLLer
3.83%
Water
3.97%
Tot..'l.1
99.39%
(Loss
0.61%)
The hardness, in Mohs scale, of pearls is in the range 3.5 - 4.5. The greater
hardness shows the strong cohesion of the calcium carbonate crystals. Aragonite
pearls are harder than those of calcite pearls.
DISTINGUISHING NATURA.L AND CULTURED PEARLS
The natural pearl is entirely composed of nacreous layers in the organic
matrix except the minute foreign substance that forms the core material. For the
bulk of it, the cultured pearl has a spherical shell bead nucleus inserted by man
around which fewer layers of nacre have been deposited (Fig. 43). While the
nacreous layers are concentric in nature, the shell bead would present parallel
layers of prismatic material in cross-section. Since in both the natural and cultured
pearls, the top-mosllaye.rs are nacreous, it would not be easy to distinguish one
foreign body
shell bead nucleus
Fig. 43. Diagrammalic skelch of sections of a natural pearl and a cultured
pearl.
80
PRODUCITON OF CULTURED PEARLS
type from another. A few genetally helpful features to differentiate them are given
below.
Shape and size
The shape of natural pearl generally follows that of the foreign substance
which has formed its nucleus. Hence the shape of pearl will be irregular-and no two
natural pearls will be alike in shape. Most natural pearls are small in size not more
than 2-3 mm. On the other hand, since the shell bead nucleus is spherical and the
size is large as predetermined, the cultured pearl is also spherical, wilh the
exception of malformations, and is large in size. Hence cultured pearls of identical
shape and size are very common.
Density
The components of pearl, viz. aragonite, calcite and conchiolin, have
different densities. Natural pearls are formed of nacreous layers (predominantly
aragonite) whereas cultured pearls have large nucleus (predominantly calcite).
Hence the densities of natural and cultured pearls are expected to differ. However,
the proportions in which the components occur in either differ considerably from
pearl to pearl depending on several factors and hence density can only be a relati ve
criterion in distinguishing the two varieties. As reported by Bolman (1941), 60%
of the natural pearls have a density of less than 2.70, whereas 85% of the cultured
pearls have a density of 2.70 or more.
Special equipments
X-ray screening, Perlos~ope and Endoscope are some of the methods by
which cultured and natural pearls can be differentiated. The principles based on
which these equipments work have been described by Bolman (1941). Use of
these equipments requires special skill and experience. *
Besides being able to distinguish between natural and cultured pearls, the
imitations which outwardly appear to be no different from the cultured pearl in
terms of shape and sometimes even lustre need to be differentiated. Anon. (1984)
gives the following clues: (i) cultured pearl feels cold when grasped while an
imitation feels warm; (ii) cultured pearl catches when it is scraped against one
•another while an imitation is slippery when scraped; (iii) cultured pearl has a light
from within through layers of nacre while an imitation has only a shiny shallow
surface; and (iv) cultured pearl has a clear, clean 'hole edge' from the drilling of
the pearl while an imitation has a rough hole edge. When examined under a
microscope with a beam of light falling on the object, the surface of a cultured
* The Ihaveri Mahajan
Moti Dhannakanta in Bombay has some of these equiprnents and does a
service by sorting the cultured from the natural pearls for the benefit of the customers for a nominal
fee.
STRUcruRE AND COMPOSmON OF PEARL
81
pearl will show an impression of the growth lines of nacre similar to that of human
thumb lines. An imitation will present a blotched appearance showing the
irregular coating of a natural or artificial iridescent substance. Fake pearls which
are produced by dipping shell beads in a bath of pearl essence (Anon., 1978) are
rio different from the imitations.
CHAPTER 9
FRESHWATER PEARL CULTURE
THE Chinese developed the art of producing nacre-coated images of Buddha in
freshwater mussels in the 12th century A.D. The person responsible for this was
Ye-Jin-Yang. The art was practised in Central China in the area' of Lake Tabu in
Kiangsu. In spring, 8 inch (20 em) long mussels (Cristaria plicata) were collected
from the lake and placed in bamboo cages. With the aid of a forked bamboo stick,
small pellets of hardened clay and outlines of Buddha made of tin were placed
between the mantle and the shell. The cages with mussels were then left in the
canals and pools for about an year. Then the mussels were opened. The tiny pearl
coated images were sawn off the shell and sold in the temple markets. The practice
continued from the 12th century into th~ 20th century without much change.
MODERN TECHNOLOGY
The modem technology of pearl culture in freshwater mussels was developed
by the Japanese in Hirako reservoir of Lake Biwa in Shiga Prefecture. Production
started in Lake Biwa in 1935 and extended to Lake Kasumigaura in 1963. The
species employed was the freshwater pearl-mussel Hyriopsis schlegelii. Until
recently, the technology was confined to the production of non-nucleated irregular'
pearls; but round pearls with nuclei are produced now on an experimental scale.
BIOLOGY OF FRESHWATER MUSSEL
The Unionid mussel H. schlegelii attains a maximum size of235 mm length,
130 mm height and 58 mm width (Kafuku and Ikenoue, 1983). Its life-span
exceeds 40 years. It attains sexual maturity at 100 - 110 mm length when 4 years
old. Fecundity is very high with production of 0.4 -0.5 million eggs by a female.
At ovulation the eggs pass on to the suprabranchial chamber formed by the gills
and are fertilized by sperms brought in by the inhalent siphon. In about 9 days the
fertilized eggs develop into a typical larval form called glochidium and are shed
out through the exhalent siphon. At this stage, the larvae need a fish host for further
development failing which they would perish. Upon attaching to the host in the
gills or fins, the glochidia encyst themselves and further development takes place
within the cysts for about 16 days. Later, the cyst breaks and the young mussel
drops to the lake bottom to start its free life. The life-history of the freshwater
mussel is quite different from that of pearl oyster.
FRESHWATER PEARL CULTURE
83
TECHNIQUE OF PEARL PRODUCTION
The mussels are collected from the lake by dredging. Individuals of 10-13
cm length and more than 4 years old are selected for seeding operations. The
mother·mussels are divided into donor mussels and operation mussels. They are
reared separately by scattering them on the bottom'of the lake at a density of 3 5 mussels/m 2 or by placing them in baskets at 12 - 15 mussels/30 cm 2 (area of
basket) and hanging them from poles at 3 - 5 baskets / m2 area. They are cultured
for about 1 - 3 years in the pre-operation phase until they can be used in surgery.
Freshwater mussels have all along been used for production of nonnucleated cultured pearls. Despite its large size, its anatomy is so complicated
with twisting intestine that there is no space left in the connective tissue of the
gonad region to implant nuclei (Cahn, 1949). In the early experiments with nuclei,
hardly less than 1% of the pearls produced were marketable. Hence the technology
for production of pearls without nuclei and with only the mantle graft tissue was
developed.
The graft tissues are inserted into the mantle of the freshwater mussel unlike
the marine pearl oyster. The donor mussel is opened and the adductor muscle is
cut. Mantle ribbon of about 70 mm long and 5 mm wide is cut from each mantle
andfractioned to 5 mm X 5 mm pieces. Two donor mussels are sacrificed for every
3 operation mussels. The operation mussel is opened with a speculum and pegged
to get a gap of about 1.5 cm. The mantle pieces are implanted into the inner aspect
of the 2 mantles in 2 rows with the help of a sharp needle. The pieces are placed
in the connective tissue of the mantle between the outer and inner epithelium (Fig.
44). About20- 30 pieces are implanted in each operation mussel. The mussels are
then returned to the iake where they remain for the next 3 years.
In the case of non-nucleated pearls the implantation is done in such a way
that the inner epithelium of the graft tissue is the innermost in the curved position
at rest. The inner epithelium and the connective tissue disintegrate and form the
core around which the outer epithelium spreads and forms the pearl-sac. The
pearl-sac epithelial cells secrete nacre and deposit on the organic core, starting the
formation of the pearl. The pearl builds up over a period of3 years when it attains
an irregular shape in the absence of a hard core nucleus to control the shape and
an average size of about 6 mm x3 mm. Almost every graft tissue produces a pearl.
Thepearls produced are solid nacre and lovely salmon pink in colour.
In the recent years, technology has been developed to produce pearls with
round nuclei in the freshwater mussel as in the case of thePinctada pearl (Kafuku
and Ikenoue, 1983) . Ward (1985) reports that regular nucleated pearls of up to 14
- 17 mm diameter are produced in freshwater mussel in Shintone River in Japan,
in addition to the non-nucleated pearls.
84
PRODUCTION OF CULTURED PEARLS
W#d/Rft///U.
.'.1.,.,.1.( .1.1.'.'· , .I.I.! ~I.I.I.I.I.I .j .1
a
liEEI Outer mantle epithelial cells
m;:;I;;l Inner epithelial cells
_
Anomalous oroanic matter
UL.c Shell nacre
XK1""Connective tinue
Fig. 44. Diagrammati.c representation of formation of irregular. non-nucleated cultured
pearls in the mantle of freshwater mussel Hyriopsis schlegelii.
NEW ENTRANTS IN FRESHWATER PEARL PRODUCTION
Japan held the monopoly of freshwater pearls since the thirties although the
production was small (around 7 toones/year) as compared to the marine pearls. In
1970, the first Chinese crop came into the market and expanded fast to reach about
50 tonnes by 1985. The Japanese are reported to buy the Chinese pearls and export
to international markets.
The USA, the home of freshwater mussels has more than 20 species in the
Mississippi - Tennessee river system. This country entered into freshwater pearl
production, and pearls started coming into market by 1987 (Ward, 1985). With a
large number of species, it would be possible to produce nucleated pearls of many
colours in the USA.
Bangladesh has recently started experimental culture of freshwater pearls
with Parreysia corrugata and Lamellidens marginalis (Ahmed, 1982).
CHAPTER 10
CULTURED PEARL INDUSTRY
IN this chapter a description of cultured pearl industry in some countries has been
given.
JAPAN
The cultured pearl industry of Japan has enjoyed monopoly since its
establishment. The production of pearls by Pinctada!ucata was 251 kg in 1926
and reached a pre-War peak of 4,081 kg in 1938. Subsequently, in 1946 ifreached
a very low ebb of 188 kg due to World War II. Thereafter production showed a
steady growth and reached an all-time peak of 127,460 kg in 19&5. Rush in
production resulted in oversupply, supply of sub· standard pearls and fall in prices,
and led to the pearl crash. Production decreased rather abruptly and reached a low
level of 34, 436 kg in 1973. More Government control in production was
introduced to improve quality and stabilize production around 35 lonnes. However,
in 1982 the production increased to 70 tonnes. The number of pearl culture units
which was 33 in 1926 rose to 4,710 in 1966 and came down to 2,526 in 1973
(Mizumoto, 1979).
The Japanese companies are also producing pearls by P. maxima. In the
starting year of 1958 production of round pearls was 18 kg and of half pearls
26,184 numbers. It rose to 437 kg rounds and 118,000 numbers of halves by 1972.
The number of farms was 2 in 1958, a maximum of 8 in 1965 and came down to
5 in 1972 (Mizumoto, 1979).
Freshwater cultured pearl production using Hyriopsis schlegelii started with
112 kg by 6 units in 1955 and rose to 7,218 kg by 61 units in 1972 (Mizumoto,
1979). The trend was declining thereafter and in 1977, the production was 5.6
tonnes (Kafuku and Ikenoue, 1983).
About 65% of all pearls, marine and freshwater, are exported mainly to the
USA and Federal Republic of Germany. In 1982, the exports amounted to 46.2
tonnes, worth some US $ 208 million (HoUyer, 1984). In 1984 the exports to the
USA amounted to US $ 348 million. The freshwater pearls are exported largely to
India where there is a local market as well as re-export market. A good amount of
round cultured pearls is also exported to India.
The problems of the Japanese pearl culture industry have been coastal
pollution, decline in quality Of the pearl culture grounds due to repeated culturing
in the same areas over a period ono -- 80 years, deterioration of the quality of pearl
oyster due to mass production and temptation for short culture practices reducing
the duration of culture by more than half.
86
PRODUCTION OF CULTURED PEARLS
In the late fifties Japan wanted to extend pearl culture to other parts of the
world. Their natural stock.was P.Jucata which had limitations of size. Openings
were sought to be made on species of larger size and better qUality such as P.
maxima andP. margaritifera. Japan attempted this without losing its monopoly on
technology and trade under a joint-venture package. Under this, the Japanese
technicians do the operations and tend the oysters; they harvest and sort the crop
of pearls; and they control the value of pearls as they are shipped off to Japan for
processing and marketing (Ward, 1985). Joint venture pearl culture was started in
Australia in 1956 and in the Philippines in 1958 (Alagarswami, 1970). It also
spread to other countries in the Indo-Australian Archipelago - Burma, Thailand
and Indonesia, and to Pacific Islands of Micronesia, Melanesia and Polynesia.
AUSTRALIA
The first pearl culture farm was established at Brecknock Harbour in Kuri
Bay in Western Australia in 1956. In the seventies, 7 companies operated 11
culture frums, 4 in Western Australia, 6 in Queensland and 1 in Northern Territory.
Pearl culture is entirely P. maxima-based. In 1971, the production was 107,777
numbers of round pearl, 62, 179 numbers of baroques and 413,964 numbers of
half-rounds pearl. The shells traded as byproduct of pearl culture amounted to
161.7 lonnes. The total value of all pearls was Australian $ 3.5 million and that of
shells Australian $ 89,000. The number of oysters employed in pearl culture was .
839,000 in 1968. It dropped to 333,000 in 1971.
The industry faced serious problems of shortage oflive oysters for operation
in their natural areas and high levels of mortality of oysters in both the natural.
populations and culture farms. Shortage of labour became an added problem. The
labour employed in 1966 was 322 hands which came down to 142 by 1971.
PAPUA - NEW GUINEA
A pearl culture farm was established by the joint Australian - Japanese
Company in 1965 in Fairfax Harbour near Port Moresby in Papua - New Guinea.
As the local supply of oysters was not adequate, mother-shells were transhipped
from Torres Strait of Australia. Produc tion was about 40,000 pieces per year from
P. maxima. High mortality among the stocks due possibly to pollution ih the
harbour caused the closure of the farm in 1975. Another farm was started in 1966
in Dagadagalsland (laterrenamed as Pearl Island). In 1975, 15 village-Ievelfarms
were operating in 4 islands under the Milne Bay Pearl Farmers' Association and
a school for training local personnel in pearl farming was established. Production
was entirely half-pearls. Because of financial and other problems the activities of
the pearl farmers have virtually ceased (Lock, 1982).
CULTIJRED PEARL INDUSTRY
87
THE PHILIPPINES
Pearl culture farms were established in Guiwan, Davao. Zamboanga,
BusuangaandCullionislands.P. maxima.P.margaritifera and Pter ia macroptera
were the main species used for pearl culture. Blister pearls were harvested after 6
months and spherical pearls after 10 - 12 months. A raft of 6.7 m x 6.7 m yielded
700 -1,000 blister pearls or 150 - 200 spherical pearls (Blanco, 1972).
MALAYSIA
Pearl culture began in Sabah in 1963. Approximately 870 ha of coastal
waters were occupied by the farm. P. maxima and P. margaritifera are the local
species. The yield ranged from 30,000 to 50,000 half-round pearls per annum in
the late sixties. The main problems were mortality of pearl oysters in the natural
beds and in the farm due to illegal use of explosives (Fisheries Division, Malaysia,
1972).
THAILAND
Three companies were engaged in pearl culture in Phuket region on the
Andaman Sea coast. P. margaritifera. P. maxima and Pteria perguin are the
species used in pearl culture (Saraya, 1982).
INDONESIA
South Sea pearl production technology was perfected by the Japanese in
Butung Island at the southern' end of Sulawesi. The.activity was attempted to be
revived after the War, but due to lack bf oyster (P. maxima) population, the proj ect
failed (Shirai, 1970)..
UNION OF MYANMAR (BURMA)
Pearl culture farm is located in Sir Malcolm Island and Owen Island in
Mergui Archipelago of Andaman Sea. Japanese technicians w~re managing
production, but in 1963 the farm was taken over by the Burmese. P. maxima is
collected from 20 m depth by divers engaged by a co-operative society which gets
the boats and equipment from the government. The oysters are sold to the
Government. The pearl culture farm produces both round pearls of 10 mm
diameter and half-round pearls oH6 mm diameter usirtg nuclei produced locally
auctioned by the government
from Tridacna shetland opercula ofTurbo. Pearls
during January - February every year and pearl merchants from many parts of the
world participate in the auction. In the 21st Burma Gems, Jade and Pearl
Emporium held in Rangoon in 1984, Burma offered 153 lots of pearls for sale
are
88
PRODUCTION OF CULTURED PEARLS
(Anon., 1984 b). Experimental work on hlack pearl production in P. margaritlfera
was being attempted.
FRENCH POLYNESIA
Pearl culture plays a significant role in French Polynesia. The lagoons of
Tuamotu-Gambier Archipelago shelter natural populations of P. margaritifera.
Natural resources which are limited to some atolls and islands have been
overfishcd and are dwindling. Spat collection with polyethylene sheets has been
successfu1. Nucleus implantation is done on 3-year-old oysters which are reared
further in underwater platforms for 2 years - the time required to obtain nacre
deposit of about 1.5 mm. Black pearls of 9 - 12 mm diameter are produced.
Fourteen co-operative societies and 8 private companies, employing about 200
persons, are involved in pearl culture. Exports of pearls yielded US $ 1.0 million
in 1980 and was expected to have doubled by 1981 (AQUACOP, 1982). One of
the private farms in Marutea lagoon, employing 35 persons, produced 22,000
black pearls in 1984. The farm aims at 10-16 mm diameter pearls with 1.5-2.5
mm nacre (Ward, 1985). Black pearl cultivation is the most valuable industry in
Tahiti. The pearls earn US $ 4.98 million a year. The annual production by Tahiti
Perles is 80,000 - 100,000 pieces, by the 69 co-operatives 40,000 pieces, and by
a small group of private farmers 20,000 pieces (Anon., 1986).
CHINA
Culture of pearl oysters was started only recently in Guangdong and
Guangxi provinces. The pearl farms are run by the State and collectives. P.
martensii is the most abundant species. In Hainan Island pearl culture with P.
maxima has been started (Zhong-Qing, 1982).
China revived pearl cultivation in freshwater mussels in 1960s. The first
crop came into market in 1970 and production by 1984 reached 50 tonnes, may be
even 80 tonnes, far surpassing the Japanese 5 tonnes (Ward, 1985). Japan buys part
of China's production for the international market. Low-tech labour-intensive
opera6ons characterize China's pearl production. To improve quality over quantity,
the government-controlled industry has built an artificial lake for research 60 km
south - west of Shanghai (Ward, 1985).
USA
With 24 species of freshwater mussels in the Tennessee and Mississippi
River VaUeys, the USA is gelling into pearl production. An American pearl farm
is scheduled to start marketing large, round pearls in 1987 (Ward, 1985). The USA
has been the major market for the pearls exported by Japan accounting for more
than 50 per cent of the Japanese exports.
89
CULTURED PEARL INDUSTRY
., ,
.,..,~
...
J
'w
,
•
,
.
......
•
.
.j
.. . 'r
,
.
'.
..
.: .
. t'
;(
')"'-
.
1.
... ""
:.
.
, "\.
....
,./
~
.....
.... . j</' .....,.
,,''.
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i
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.
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.Ii.,. '"# ,.
"
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Fig. 45. A collection of cultured pearls produced inPinctadafucata (Pearls: Courtesy Shrr
V. Chidambaram, Managing Director, Tamil Nadu Pearls Pvt. Ltd).
INDIA
The first pearl culture company in India was established in 1983 to produce
cultured pearls in P.fucata. It has produced about 12 kg of pearls (Fig. 45).
However, India has a pearl trade of considerable national and international
importance through import and export. There is a great domestic demand for
cultured pearls which is met entirely by imports. India imports raw pearls
(cultured marine pearls and cultured freshwater pearls) mainly from Japan. In the
recent years Chinese freshwater pearls are also imported. Besides, Japan pearls
also come via other countries such as Hong Kong, Singapore, the USA and the UK.
In 1982-83, the pearl imports from all sources amounted to Rs 80.4 million. India
has a traditional processing industry. although not using modem techniques.
Value-added items in the fonn of processed pearls and pearl jewellery are
exported from India. The values of exports during the last 10 years has been as
follows:
90
PRODUCITON OF CULTURED PEARLS
Export value
Year
(Rs million)
20.4
23.4
1976-771977 -78
1978 -79
1979- 80
1980- 81
1981- 82
1982- 83
1983- 84
1984-85
1985 -86
19.9
36.4
44.8
63.5
47.4
71.1
71.8
84.1
In the order of importance, the exports are to Japan, the USA, UAE, Hong
Kong, Kuwait, Switzerland, Qatar, FRG, and Saudi Arabia. There is a great
turnover of pearl business in India, with Bombay as the trade centre with satellite
units of processing, Hyderabad as tourist centre for retail marketing of pearls,
established pearl jewellery markets in several cities and mobile sale emporia
which move from place to place selling pearls. Although the freshwater pearls are
called in trade as 'natural pearls' , these are the non-nucleated pearls cultured in the
freshwater mussels in Japan.
PRICING OF CULTURED PEARLS
Cultured pearls are priced according to size, shape, weight and qUality.
Unlike the bullion market where quality is precisely defined and prices fluctuate
according to international market, the price of pearls eludes any standardization
because of infinite differences in quality and preference variations of customers.
However, some idea on pricing is worth having.
The approximate size - weight - number relationship of Pinctada fucata
cultured pearls is given below:
Size - range (rom)
Average weight (g)
No. of pearJs/g
-
0.0578
0.0870
0.1314
0.1715
0.2122
0.3175
0.3633
0.4713
0.5956
0.7690
17.30
11.49
7.61
5.83
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
-
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
4.71
3.15
2.75
2.12
1.68
1.30
91
CULTURED PEARL INDUSTRY
The weight of a 9-mm pearl would be around 1.075 g and that of IO-mm
pearl around 1.493 g. These size ranges are grouped as extra small, small, medium,
large and very large, and for each group the prices are different. TheJ apanese pe~l
market goes by price per momme (1 rnomme = 3.75 g), while the Indian market
goes by tola (1 to1a = 11.62 g). Further down, the prices are by carat weight (1 g
= 5 carats). Natural pearls are further scaled down to the unit of grain (1 carat
4 grains),
The pricing is different for pearls of different origin, viz. freshwater
nucleus-less pearls, freshwater nucleated (round) pearls, marine P .fucata pearls,
South Sea white pearls, South Sea black pearls, and the blisters and baroques of
P. maxima. While the freshwater nucleus-less pearls fetch the lowest, the South
Sea pearls fetch the highest price.
S orne of the reported prices of cultured pearls with reference to the years of
l'eporting are given below for a general appreciation of the prices of pearls of
different kinds:
=
Description
Freshwater, nucleus·
less pearls, Japan
Freshwater, nucleated,
10 mm round, Japan
F~eshwater, nucleusless pearls, China
Price
Reference
US $ 2,OOO/kg
Kafuku and Ihnoue (1983)
US $ l,OOO/pearl
Ward (1985)
¥ 12,OOO/kg for I
clas~;
Anon. (1986b)
¥ 70/kg for VI class
Marine P.fucata
pearls, China, expon
Marine P.fucata pearls,
Japan
¥ 25,OOO/kg for I class;
¥ 2,800lkg for IV class
Anon. (1986b)
US $ 18/pearl
US $ 1,OOO/necklace
of 56 pearls
Ward (1985)
South Sea P. maxima
pearls, 13 rom or larger,
round
US $ lO,OOO/pearl
Ward (1985)
P. margaritifera
black: pearl, Tahiti
US $ 6OO/pearl ;
US $ 6,OOO/necJc1ace
Anon. (1986a)
A South Sea pearl of 4.0 mm x 33.4 mm size weighing31 g cultured in a farm
off Samui Island in Thailand and extracted in January 1987, is considered ()ne of
the largest in the world (fide Indian Express, Cochin, 23 February 1987).
92
PRODUCTION OF CULTIJRED PEARLS
SOME UNIQUE NATURAL PEARLS
Some very large and unique natural pearls have fantastic prices on them.
The 'Pelegrina' pearl weighing 133.2 carats, which once belonged to the Youssoupoffs,
one of the wealthiest families under the Tsar, was recently sold for US $ 467,123
(/ide Indian Express, Madras, 17 May 1987). The 'La Peregrina' pearl, 1 inch
(2.54 cm) long was sold in 1969 forUS $ 37,000 (Ward, 1985). The 'La Peregrina'
is originally from Panama and weighed 250 carats (Abbott, 1972). A pearl of 450
carats in the form of sleeping lion was sold in India in 1779 for £ 4,500 (AbbOtt,
1972). The 'Pearl of Asia', 7.5 em x 5 cm (3 inches x 2 inches) size, found in
Persian Gulf in 1628, had a pre-war estimated value ofRs 0.2 million. The 'Bird
Pearl' , in the shape of a flying bird, from Tennessee River Valley was valued at
US $ 500,000 (Anon., 1984a). The 'TridaenaPearl', 24.13 em x 13.97 em (91/2
inches x 5 1/2 inches) and weighing 14 Ib 1 oz (6.37 kg), resembling the shape of
human brain, was auctioned for US $ 200,000 (Anon., 1980).
CHAPTER 11
RECENT DEVELOPMENTS IN PEARL CULTURE
JAPAN has held monopoly of technology, production and trade of pearl culture for
a long time and to a large extent] apan holds the sway still. In the recent years some
countries have been abl~. to- fun the business alone as in Myanmar and some
companies in Australia. Japanese production slided down with the pearl crash
after 1966, but is climbing back, although she may not again reach the peak 1966
production of 127 lonnes of marine pearls. Her freshwater production has also
declined. Australia, Papua - New Guinea, the Philippines. Indonesia. Thailand
and Myanmar are all facing shortage of pearl oyster stocks and production from
this region has also come down.
In contrast, Chinahas entered pearl culture in a big way with 50 - 80 tannes/
annum of freshwater pearls. far exceeding Japan's production, and also has
programmes on marine pearls using P. jucaJa and P. maxima. The USA was
expected to put the first crop of freshwater pearls into the market in 1987 (Ward,
1985). If she succeeds, with all her .technological capabilities, 24 varieties of
mussels and a big market, she should get into the top very soon. Bermudas is
currently showing interest in marine pearls with the local species of P. imbricata.
With the spread of technology in that region, marine pearl culture is a possibility
in Venezuela, Panama and Mexico. While Bahrain is interested in improving
production of natural pearls inP. radiata (=P.jucata) in terms of yield and size,
Iran appears to have an interest in technology of cultured pearls. Sudan had
initially failed in her attempts on black pearls from P. margarilijera due to
repeated mass mortalities of oysters in the Dongonab Bay in 1969, 1973 and 1975.
She has a pearl shell trade by production through spat collection and rearing.
French Polynesia has already established a lead in black pearl production.
Micronesia, particularly Fiji. has been interested in pearl culture.
In the Indian subcontinent, India is experiencing the travails of establishing
a new marine pearl culture industry and would perhaps steady herself sooner or
later. Bangladesh has been working on freshwater pearls.
It would then seem that the face of pearl culture is perceptibly changing from
a monopolistic industry to a trend of diversification in several parts of the world.
The success of this trend would depend on development of appropriate technologies
for producing pearls. of quality in different species in different regions, economic
viability of the new ventures and the future trends in cultured pearl prices in the
world market.
94
PRODUCTION OB CULTIJRED PEARLS
SCIENCE AND TECHNOLOGY 1RENDS IN PEARL CULTURE
The future of pearl culture would seem to depend on quality of the pearls
rather than on quan tity of production. Supply and demand will have to be balanced
so that the post· 1966 situation would not repeat itself. This has to be taken special
note of in the context of several new entrants interested in pearl production as
indicated earlier. Cost of production will go up in any part of the world as time
passes and quality alone can meet this challenge to make profits in this industry.
A lot would depend on advancements in science and technology of pearl culture.
This is a biology based industry and what further controls can be exercised in this
biological process would be the moot question which science should address itself
now and in the future.
Resource management
The pearl oyster is a sedentary organism having restricted distribution in
some areas and can thrive only under certain ecological conditions. Many of these
resources have been 'fished out' with excessive pressure and others appear to be
on their way out if they are not managed judiciously in time. Pinctada maxima of
the Indo-Australian Archipelago has dwindled in many pans of the region. Same
is the case with P. margaritifera in French Polynesia (AQUACOP, 1982). P.
jucata of India is a classica'l example .of absence of management resulting in
several nonproductive seasons with a sprinkling of few productive ones here and
there. Apart from fishing pressure, pollution is taking its own toll resulting in
mortality or degeneration of stocks (Anon., 1975). Natural causes such as
predation and changes in bottom topography have also contributed to decline in
populations as in the Indian example. With the current emphasis on pearl culture,
the danger to the wild populations of the different species of pearl oysters is often
not realized. It is necessary to revive the pre-culture interest on the natural
populations and strengthen scientific investigations leading to development and
management of these resources.
More than a quarter century has passed since the last pearl fishery was
conducted in the Gulf of Mannar by India and Sri Lanka. When the population of
pearl oyster starts building up by chance next, it is necessary not to fish the stocks
but to launch an intensive investigation to understand the factors that have led to
their build-up. There is a greater need to study the causes and incidence of
formation of natutal pearls. Such detailed studies would help in proper management
of the resource to derive greater benefits of natural pearls and to supply a part of
the stocks to the pearl culture industry.
In the recent years sea-ranching has been adopted as a technique of
improving the natural resource of finfish, crustaceans and molluscs. Hatchery produced seed are ranched in the sea providing appropriate protection to the
juveniles by laying special structures wherever necessary. Such a programme has
recently been started f.or the pearl oyster in the Gulf of Mannar and this needs
RECENT DEVELOPMENTS IN PEARL CULTURE
95
strengthening with appropriate inputs.
Mother-oyster stock improvement
The Japanese pearl culture depended on the wild stock of pearl oysters
collected by the women divers in the pre-War phase. Subsequently as demand for
mother·oysters increased severalfold, techniques for spat collection in the subsurface waters using cedar sprigs were developed. Until the seventies these
supplies were plentiful and the industry could use as much as 12,000 tonnes of
pearl oysters per annum from this source. As this source began to show signs of
depletion, the farmers resorted to hatchery production of pearl oyster. Since there
has been quite a mix-up of wild populations over a period of time, the genetic
qualities of the stocks were not ascertained. It is feared that there has been a
degeneration of wild stocks, in terms of pearl quality. The attempt now is to
identify the genetic characteristics of the few isolated wild stocks and build a
breeding programme on this material. By selective breeding, Wada (1975, 1984.
1986) confinued that pearls without yellow pigments can be produced more
effectively. Genetic work on pearl oyster attempts to produce stocks yielding
pearls of desirable quality, resistant to microbial diseases, adaptable to environment3I
stress and having high growth potential. In the case of Pinctada maxima and P.
margaritifera. the two species which are in short supply, hatchery technology is
yet to be applied on a commercial scale although experimental production has
been achieved (Tanaka and Kumeta, 1981; Alagarswami et al.,' 1989). The
attempts to breed the blaCk-lip oyster in French Polynesia have not been successful
so far (CoeroJi et aI., 1984).
In India, mass production of P. fucata in hatchery has been established.
Selective breeding programme has already been initiated for P.fucata with regard
to colour and quality of nacre. In P.fucata more than 60% of growth is obtained
in the flrst year itself and this growth potential with high survival rate during the
flrst year of rearing should be achieved to make the hatchery technology
economically viable in tenns of cost of production of operable size oysters. P.
margaritifera spat has also been produced but juvenile rearing has problems
(Alagarswamietal., 1989). Ideally,betterresultscan be achieved in Andaman and '
Nicobar Islands where this species has its natural distribution.
Pathological problems
Mass mortality of animals occurs frequently in culture systems. Since the
oysters are reared in high density in a limited area and they are in the same water
medium. diseases spread fast. Frequent mortality has been reported for P.
margaritijera in Dongonab Bay of Sudan. Mortality of this species due to disease
has also been reported from French Polynesia. The natural stocks of P. maxima in
the Australian waterf> have dwindled due to disease problem which has received
attention (Pass et at .• 1987). According to these authors an excessive mortality of
oysters has had a serious impact upon the industry since 1974 and losses amounted
96
PRODUCTION OF CULTURED PEARLS
to about 80% of the harvested shell. Marine Vibrio ba_cteria have been held
responsible. In the sea it will not be possible to control disease outbreaks once they
start. However, it is necessary to identify the pathogens and take prophylactic
measures. This area of research is fairly new. Even in recurring mortalities of
edible oyster CrassoSlrea and Ostrea in the US~, Europe and Japan, the diseases
could not be controlled. Intensive research is called for in this field to safeguard
the farm stock since raising the resource itself is done at high cost.
Pearl culture environment
In pearl oyster farming, the oyster is controlled totally by the environment
in which it lives. It draws from available natural nutrition and depends on the
quality of seawater for its entire metabolic functions. The quality of pearls is
influenced by the environmental factors. A good deal of base-line studies on pearl
culture grounds has been made in Japan. These results have led to decisions on
establishment of farms and shifting culture grounds fcSr improvement of quality of
pearls. While the basic aspects have been fairly well understood, the critical
aspects of environment that influence the physiological function of secretion of
organic and inorganic components of the pearl and its inclusions have to be
investigated further. The am oun t of trace elements presen t infl uence the colour of
pearls. Depth and light penetration contribute to pearl colours. Availability and
quality of food phytoplankton influence pearl quality via its role of energy supply
(Matsui, 1960). Since the pearl-sac derives its energy from the surrounding
connective tissue of gonad, energy sharing between somatic growth and reproductive
growth at different times will have a role to play in influencing the growth of
pearls. These will be areas for future research for controlling production and
quality of cultured pearls.
Techniques of surgery
The basic techniqu~s of surgery have not changed much in respect of
Pinctadafucata and P. maxima. Great improvements have been seen in producing
black pearls inP. margaritifera. While pearls of9 - 12 mm are normally produced
in this species, success seems to have been achieved to increase the size up to 16
mm in French Polynesia (Ward, 1985). A major breakthrough has been production
of round nucleated pearls of up to 17 mm in diameter in the freshwater mussels
(Kafuku and Ikenoue, 1983; Ward, 1985). The future challenge will be to control
the mortality of oysters in the post-operative phase, reduce the rate of rejection of
nuclei and improve production rate of quality pearls. Presently, the average
production of good quality pearls is only about 30% irrespective of the species and
region and this would need improvement. This can be achieved only through a
greater understanding of the physiology of oyster and the quality of pearl-sac
epithelium.
RECENT DEVELOPMENTS IN PEARL CULTURE.
Bio~minera1i1.ation
97
of nacre
A great deal of research has been carried out on mineralization and spec tral
characteristics of pearls to understand the formation of organic matrix and
crystalline microlayers (Wada, 1972, 1983). In the shell nacre of bivalve molluscs,
aragonite crystallizes in the extrapallial fluid secreted by the outer epithelium of
the mantle. The fluid is characterized by protein and polysaccharides synthesized
in the outer mantle epithelial cells and mucous gland cells. It contains calcium
carbOnate and other inorganic ions (Wada, 1972). The formation of organic matrix
and growth of nacreous layer in alternate fashion has been studied in detail (Wada,
1970). The crystal form (aragonite or calcite) and size vary in close relation with
the variation of the secreting activity of nacreous matters in the outer mantle
epithelial cells. The activity differs in species, in environments or in the physiological
condition of animal (Wada, 1972). A sound knowledge on these aspects would
greatly help in controlling the quality of pearls when controls on the causative
factors would be possible in the future.
Tissue cu]ture
Tissue culture of pearl oyster mantle has been pursued for many y~ars with
the object of isolating and culturing the outer evithelial cells responsible- for the
secretion of fine aragonite crystals. In vitro culture of mantle epithelium of P_
jucata carried out by Machii (1974) resulted in accumulation of a large number
of migrated cells derived from the explant consisting of roundish epithelial cells,
pigmented epithelial cells, spindle-shaped muscle cells and depOsition of organic
su bstances. Cell colonies deri ved from epi thelia! -like cells ha ve been establ ished
for P.fucata (Machii et al., 1985). Arising from the tissue culture experiments, it
has now been found possible to produce pearls by injecting around the implanted
nucleus a fraction of the cell suspending liquid resulting from mantle epithelial
cell culture (Anon., 1985). The cells in suspension would form the pearl - sac
which would secrete nacre leading to pearl formation. It is perhaps a short step
from here to isolate and culture the type of epithelial cells that would predictably
secrete the aragonite crystalline matter which would form the top qualify pearls.
Ithas been hoped by the scientists of pearl culture that in future it might be possib Ie
to culture the finest pearls in vitro outside the pearl oyster.
CHAPTER 12
TRANSFER OF TECHNOLOGY AND STRATEGY FOR
PEARL CULTURE IN INDIA
THE rust cultured pearl of India was produced on 25 July 1973 in a pearl oyster
which had been operated on 12 June 1973. Confirmatory results came up in the
succeeding batches of oysters. In the background of India's interest in pearl
culture as evidenced by the past experimental programmes of the Department of
Fisheries, Governments of Tamil Nadu (Devanesen and Chacko, 1958) and
Gujarat (pandya, 1974), and failures ofnuwral pearl fisheries in both the regions,
an important recommendation was made at the 'Group Discussion on Pearl
CulLure' on 24 January 1974 to commercially exploit the new technology
(Swaminathan, 1974). It was also decided that the Central Marine Fisheries
Research Institute, Cochin, should organize training courses in pearl cullure for
!.he benefit of the intended development programmes in the country.
TRANSFER OF TECHNOLOGY
Training courses
As a result of the above decision, the CMFRl, developed a curriculum for
a long-term training course of 6 m.onths and another for a short-term technicians
trail).ing course of 4 - 6 weeks (fide Anon., 1977). The programme was made
demand-oriented for the target group of fisheries development officials of the
governments of the maritime States and Union Territories. A Manual on Pearl
Culture Techniques was later published as a practical guide to the training courses
(Alagarswami and Dhannaraj, 1984). The long-term course is a comprehensive
one aimed at the managerial and supervisory personnel, comprising the subjects
of pearl oyster resources, biology, ecology, farming, surgery, pearl production and
management (Alagarswami, 1987 d). The short-term course has a restricted scope
offering training at the technicians level in mother-oyster culture, surgery and
pearl production. The training courses are heavily oriented towards field work and
practical training keeping the class-room lectures to the essential minimum (Fig.
46).
With the development of hatchery technology for pearl oyster production,
a shan-term training course of 4 weeks has also been introduced since 1986 in
pearl oyster hatchery technology. The course curriculum includes shellfish
hatchery, breeding of pearl oyster, induced maturation and spawning, larval
rearing, water quality management, microalgal production, spat settlement and
juvenile rearing (Alagarswarni, 1987d).
The only component in the total technology of pearl culture which has been
TRANSFER OF TECHNOLOGY AND STRATEGY FOR PEARL CULTURE l i''l lNDlA
99
Fig. 46. Trainees at nucleus implantation operation in the Trainin& Course at the
CMFRI.
lackingis the production ofnuclei. The experimental and commercial programmes
are dependent on shell beads imported from Japan. This is an engineering problem
which will have to be ~olved with some urgency (James, 1987).
Beneficiaries
The firsl long-term training COlise in pearl culture was organized from
S eptem ber 1976 to Marc h 1977. The subsequent courses were of short-term nature
and4 such courses were organized in 1977, 1979, 1984 and 1986. The firsLtraining
course in pearl oyster hatchery technology was conducted in 1986.
The beneficiaries of these programmes were predominantly, the fisheries
development personnel from the states of Gujarat, Karnataka, Kerala, Tamil Nadu
and Union Territory of Lakshadweep. The Fisheries Departments of the Union
Territory of Andaman and Nicobar Islands, and Tamil Nadu and West Bengal had
also sponsored qualified private candidates. A few scientists and technicians of
research institutions such as the Konkan Krishi Vidyapreth, the Central Agricultural
Research Institute for An dam an and Nicobar Islands, and the Cenrral Marine
Fisheries Research Institute have also undergone training. A fisheries technician
from the South - East Asian Fisheries Development Centre of the Philippines,
participated in one of the short-term courses in 1979. Officials of the joint venture
pearl culture industry were also given lIaining.
Besides regular training courses, the Institute has included pearl culture and
hatchery technologies in the curriculum of post-graduate education programmes
100
PRODUcnON OF CULTURED PEARLS
leading to Master's and Doctoral degree. A component on pearl culture has been
included in the Summer Institutes on sul?jects relating to molluscan shellfish
culture organized by the Institute.
In the transfer of technology programmes, the Central Marine Fisheries
Research Institute has adopted an open policy to extend the technology to the
Indian nationals as well as foreigners subject to the arrangements falling within
the policy framework of the Charter of the Indian Council of Agricultural
Research.
STRATEGY FOR PEARL CULTURE
India has gained some practical experience in commercial production of
cultured pearls and this has given an insight into the travails of the new industry.
Any biology-based industry will have some problems in control of production and
the maritime base of pearl culture adds another dimension to it. A -new venture in
the above context is bound to show some unpredictability due to variability of
parameters which were not known previously or not taken seriously, but the
experience gained is invaluable in filling the loopholes, bridging the gaps and
considering more appropriate strategies suitable to the Indian context. Some of
these aspects are examined here in general tenns.
Environment
The basic tenet of any aquaCUlture programme is the soundness of the
environment most appropriate to the candidate species and the technology. This
should not be compromised under any circumstances. Detailed topographical and
site survey should precede project preparation. Although data of a general nature
for the Indian coastline and island territories are available, these are not adequate
for making decisions on sites for establishing pearl culture farms. Specific surveys
should be taken up to look on all these aspects. While dealing with the mariculture
potential of Andaman and Nicobar Islands, Silas and Alagarswami (1983)
indicated the potential areas for pearl culture but emphasized the need for further
detailed survey. In Lakshadweep, although the islands are situated in the same
generic ecosystem, the lagoon of Bangaram has been found to be different from
that of Agathi (Alagarswami et ai., 198~) in supporting pearl oyster fanning. The
gulfs of Mannar and Kutch, the natural abode of pearl oyster, similarly show
differences within and between the ecosystems. The mainland coastline is bereft
of bays as found in Japan or the Philippines and is subject to the effects of the
south-west and north-east monsoons as well as cyclones in certain areas.
Considering these limitations, ideal sites for pearl culture may be a few and these
have to be chosen after a careful study of all relevant parameters.
Species
The second aspect to be taken note of is the species of pearl oyster.
TRANSFER OF TECHNOLOGY AND STRATEGY FOR PEARL CULTURE IN INDlA
101
Undoubtedly Pinctadafucata is the major species on which work has been carried
outin India andis the species on which the Japanese pearl culture industry is based.
This should be complemented with P. margaritifera for its special quality of
producing the black pearls. The resource position in Andaman and Nicobar
Islands and initial success achieved in hatchery production of black-lip pearl
oyster have already been referred to (Alagarswami, 1983; Alagarswami et al.,
1989). Technology for production of pearls in this species remains yet to be
developed in India. This work may be taken up in Andaman and Nicobar Islands.
This possibility of occurrence of a third species P. maxima in the Andaman and
Nicobar Islands, based on parallels with the Mergui Archipelago of Myanmar and
Phuket region of Thailand, has been indicated (Alagarswarni, 1983). An appropriate
survey of the deeper waters of the shelf is required to explore its occurrence and
distribution.
Shell beads
The third and important gap in the total technology of pearl culture is the
shell bead. The early attempt of Velu et aI. (1973) has not been followed up
vigorously. It has been felt by the industry that the cost of imported shell beads is
even higher than that of imported raw pearls. Hence, this technological gap should
be filled with extreme care on the choice of indigenous shell material from among
Xancus pyrum, Tridacna spp., Trochus nitotieus, Turbo marmoracus etc. which
are some of the larger species. The operculum of some of the gastropod shells may
also have to be examined. Occurrence of large shells of freshwater mussel
Parreysia corrugata requires investigation. Cultured pearls are largely sold by
weight and, hence, the density of shell bead should be close to acceptable
international standard.
Farming
Certain engineering problems remain to be solved with reference to fann
structures as suitable for the sites. Floatation and mooring devices for rafts,
longlines or under-water platfonns are to be made operationally easy, logistically
sound, economically viable and durable. To make pearl oyster farming costeffective and less fatiguable for people working in the fanns, it is necessary to
modify and improve the system, design and materials offarming. A separate R&D
programme on open-sea mariculture structures will go a long way in helping the
development of not only pearl culture but also other shellfish and finfish culture.
Options (or organizational set-up
Pearl culture is a composite industry ,like textiles. with different components.
These include raising of mother-oystets, pearl production, processing and marketing.
Each is a field specialization requiring separate technology, skill and equipment.
Puttogelher, it becomes a composite industry raising the capital, manpower and
t~hnology requirements to a higher level. Th~ advantage will be that a composite
102
PRODUCTION OF CULTURED PEARLS
enterprise can mobilize resources, manage problems with compet~nce and can
have greater control over situations. The disadvantage will be that any miscalculation
in a single area can upset the entire system.
Japan's pearl culture industry has been of a decentralised nature. Motheroyster culture and pearl culture are practised mutually exclusively. Pearl trade
looks after processing and marketing. The 1966 production of 127 tonnes of P.
jucata pearls came from 4,710 management units which were independent
(Mizumoto, 1979). Of them, 48.7% of the units were very small operating only 114 rafts and very few units operated over 1,000 rafts (Furukawa, 1972). There were
8,633 units engaged exclusively in mother-oyster culture in the same year
(Furukawa, 1972). The data would show that more small units contribute to pearl
culture in Japan. In French polynesia a number of small units and a few big
companies, besides co-operatives, are engaged in pearl culture. In Australia, the
companies are big in view of heavy investments required for collection of oysters
from far-off grounds. In Papua - New Guinea the Pearl Fanners Association
operates village level units. In Myanmar too, the co-operative society is engaged
in oyster collection. Thus, a wide range of options is exercised in other pearl
culturing countries in the world.
Pearl farmers' co-operative
In the background of India's experience in pearl culture, a second option is
perhaps worth contemplating. A co-operative structure of smaller units with State
support in critical areas in the early stage of development may be considered.
Young fishermen with aptitude for pearl culture may form themselves into
a Pearl Farmers' Co-operative Society with financial support from the Cooperative Sector. The society may have, besides its executive, a technical advisory
body represented by fisheries, co-operative and trade interests to plan and guide
the functioning of the society. The society will look after both input supply ann
output management.
Input supply
Acti vities under this may include: (a) facilitation of leasing of sea area and
shore facility; (b) supply of oysters; (c) supply of farm materials; (d) supply of
nuclei, chemicals and equipments; (e) arrangements of security; and (f) arrangements
for training of the members. While the society should have its own hatchery in
course of time, spat supplies may be arranged with Government organizations in
the early stages. Collection of oysters from the natural beds may be kept as
secondary option in seasons of abundance. While import of shell beads may be
unavoidable in the beginning, the society may set up its own unit for their
production without much loss of time.
Output management
The society will (a) purchase the pearls produced by the individual units; (b)
TRANSFER OF TECHNOLOGY AND STRATEGY FOR PEARL CULTURE IN INDIA
103
attend to sorting, grading and processing; (c) sell the pearls to the domestic market
and/or export them; and (d) dispose of byproducts in value added k>rm.
The above is a very generalized picture of the suggested set-up, but details
will have to be worked out.
Policy support
Pearl culture has some potential for generating employment for the skilled
and semi-skilled persons in the coastal rural areas, particu1arly among the
fishermen families. It also gives employment opportunities to managerial and
technical personnel. It will add to the GNP and can also earn foreign exchange. It
can cut down imports of raw pearls. It is a new industry and would need policy
support, flnancial assistance, subsidy and economic incentives from the Government
in the early stages until pearl culture becomes a sound economy on its own merit.
To repeat the earlier quotes for the sake of emphasis: "the only economically
sound way of making the Indian ....... Pearl Fisheries permanently and regularly
remunerative is to concentrate upon the inducement of pearls by artificial means
in comparatively limited number of cultivated pearl oysters" (Hornell, 1916);
"pearls give the highest profit return of all marine products cultivated in coastal
waters" (ofJapan) (Wada, 1973); and, according to Hollyer (1984), pearl culture
is a long-term investment and big profits can be made in a successful culture
operation as there is still a great demand for pearls.
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10.8
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APPENDIX I
ECONOMICS OF PEARL CULTURE ~ A PROJECTION
IN working out the economics of pearl culture, the experience gained in the first
ever commercial venture in India has also been considered. Pearl production
activity is a continuing one with simultaneous rearing of pearl oysters for seeding
(nucleus implantation) as also rearing of seeded stock for pearl production.
Depending on the size of oyster and size of nucleus , the culture period also varies.
Hence, for a projection on the economics, one standard crop of 6 months duration
using 100,000 oysters has been considered. The unit is assumed to be engaged only
in pearl production activity. receiving supplies of pearl oysters of the required size
(12~ 15 g weight) either from the natural source or from a hatchery at a fixed cost.
The species is Pinetada Jucata and single implantation with 4 mm diameter
nucleus has been considered. The cost of capital assets as well as rafts and cages
has been shown proportionate to one crop duration. A small-scale project has been
suggested and several such individual units may be organized on a co-operative
basis involving local fishermen so that security of rafts and materials could be
ensured. The project is assumed to be located in an ideal site.
With the above assumptions, the projection of economics of one crop of 6
months duration would be as follows:
COST OF PRODUCTION
A.
Capital assets
1. Building (semi-permanent)
B.
1.
2. Boat and outboard engine
3. Furniture and fixtures
Rs
Rs
Rs
250,000
50,000
50,000
Total
Rs
350.000
Recurring expenditure
Rafts
Cost of 10 units of raft each of 6m x 6m
with all accessories required for rearing
100,000 oysters
2.
Rs 85,000
Cages
Cost of 1 ,000 ca~s with ropes etc. required for
rearing 100,000 oysters
Rs 65,000
110
PRODUCTION OF CULTURED PEARLS
3.
4.
5.
6.
Pearl oysters
Cost of 100,000 oysters @ Rs l.SO/oyster
Cost of additiona110% oysters
for graft preparation
-
Rs
150,000
-
Rs
15,000
Total
-
Rs
165,000
Cost of 100,000 shell-bead nuclei of
4 mm diameter at 35 paise/piece
.
Rs
35,000
Cost of chemicals, glassware, insuuments,
fuel, energy and labour (one crop)
-
Rs
25,000
Estabishment charges
Designation
Technical Manager
Technicians
Farm hands
Security staff
No.
1
8
6
3
Salaries per year (Rs)
30,000
96,000
54,000
18,000
198,000
Total
Salaries for 6 months
99,000
Total ofB. 1 to 6
C.
Total capital investment required
Total of A
Total orB
Total
D.
E.
Interest on above capital
@ 12.5% per annum for one
crop duration of 6 months
474,000
Rs
Rs
350,000
474,000
Rs
824,000
Rs
51,500
Actual cost of production of one crop of 6 months duration
Cost of capital assets @ 1120 of A
Cost of rafts @ 1/6 ofB. 1
Cost of cages @ 1/2 of B. 2
Cost of oysters B. 3
Rs
Rs
Rs
Rs
17,500
14,167
32,500
·165,000
111
APPENDIX I
Cost of nuclei B. 4
Cost of chemicals etc. B. 5
Establishment charges B. 6
Interest on capital D
Rs
Rs
Rs
Rs
35,000
25,000
99,000
51,500
Total cost
Rs
439,667
Say Rs 440.000
PRODUCTION OF PEARLS AND REVENUE
Basic stock of oysters
Survival to harvest@ 80%
Gross production of pearls @ 60%
100,000
80,000
48,000
Grading
A-I Grade@ 12-1/2%
A - 2 Grade @ 12- 1/2%
B Grade@ 35%
CGrade@40%
6,000
6,000
16,800
19,200
Note: Discard C grade for calculation; These will have some value, however.
Weight
Mean weight of cultured pearl on 4 mm
diameter nucleus in 6 months
Weight of A-I grade pearls
Weight of A - 2 grade pearls
Weight of B grade pearls
Value o/production.
Sale value of A-I grade @ Rs 45/ ct
Sale value of A - 2 grade @ Rs 40/ ct
Sale value of B grade @ Rs 35/ct
Total anticipated revenue
Note:
carat
0.5
3,000 (:t
3,000 ct
8,400 ct
Rs
135,000
120,000
294,000
,Rs
549,000
Rs
Rs
Value of byproducts has not been considered; the pearl oyster shells will have some
value, however.
112
PRODUCTION OF CULTURED PEARLS
PROFITABILITY
Total sale value of cultured pearls
Total cost of production of one crop
Profit
Note:
.-
Rs
Rs
549,000
440,000
Rs
109,000
Factors of high sensitivity are the unit cost of oyster and sale value of different
grades of pearls. Marketing cost will have to be adjusted in the profits.