2. What is pearl?
Pearl is a shining , variously tinted nacreous concretion
secreted around a foreign body by various molluscs.
Pearl is the oldest known gem being used in ornaments.
It is also used widely in religious ceremonies . It is also
beingused inmanyayurvedic medicines.
3. HISTORY
Fishing of pearl oyster in order to obtain pearl is
known to Indians since ancient days. The chief
sources of pearls are marine pearl oysters, however
the fresh-water molluscs are also known to produce
pearls but they are of poor quality and almost
worthless. Pearl is known to human beings since
ancient times. A pearl due to its delicate appearance
and shine has retained its position as a costly
ornamental object. Due to its properties, it occupied
important place in the crown of great emperors and
queens. The origin of pearl is not known to us
however Chinese records show that pearl was known
to them as far back as 2300 B.C.
4. Pearl producing oysters
a. Pinctada maxima
b. Pinctada chemnitzi
c. Pinctada margaritifera
d. Pinctada vulgaris
e. Pinctada atrapurpuria
5. Kingdom Animalia
Phylum Mollusca
Class Bivalvia
Order Filibranchia
Family Pteridae
Genus Pinctada
Species vulgaris/margaritifera/
maxima/chemnitzi.
Systemic position
7. Structureof mantleand shell
Shell of pearl oyster is composed
of three distinct layers. They are
as follows:
1.Periostracum
2.Prismatic layer
3.Nacreous layer
8.
9. Prismatic Layer: It is the middle layer
secreted by mantle. This layer is made
up of minute crystals of calcium
carbonate, It gives strength and
rigidity to the shell.
10. Periostracum: It is the outermost, greenish
brown, thin, translucent layer made up of
an organic substance “Conchiolin”. It is
secreted by mantle. It serves to protect the
underlying layers from harmful effects of
weak carbonic acid in water.
11. Nacreous Layer: It is the inner most layer of the shell and is
better known as mother of pearl”, because this layer is
responsible for the formation of pearl. It consists of
alternate layers of calcium carbonate and conchiolin. This
layer is also secreted by mantle and its function is to protect
the delicate surface from harmful effects of the foreign
particles.
12. Natural Pearl formation
Pearl formation is an abnormal response. In fact ,
formation of pearl occurs as a result of defensive
response of the oyster .whenever any foreign object
such as a sand grain or an egg or a micro-organism
finds entry into the body of oyster and reaches between
the shell and the mantle , the mantle epithelium gets
stimulated and surrounds the intruder completely. Now
the mantle epithelium starts secreting concentric layers
of nacre around the intruder. In due course of time
several layers of nacre are secreted resulting into the
formation of pearl.
13.
14. Harvesting of pearls
Rearing of oysters
Insertion of nucleus
Preparation of nucleus
Preparation of graft tissue
Collection of pearl oysters
Themain steps in pearl culture are:
15. Collectionof Oysters
After the construction of pearl farm, the
divers set out to the bottom of the sea, to
collect the oysters. Oysters are generally
located on a flat rock bottom . The shells
collected, are cleaned, sized, and placed
into baskets for storage until they are
transferred to the pearl farm. The larvae
of the oysters can also be collected. That
process is called spat collection.
16. Preparationof the graft tissue
piece of tissue inserted into the body of
oyster is called graft tissue . A strip is cut
from the edge of the mantle of a healthy
oyster . The piece is cleaned and washed
. Now from this piece of mantle square of
2 x 2 mm size are cut and used as graft
tissue for transplantation .
17. Preparation of nucleus
Although any foreign object can act as
nucleus for the formation of pearl but it
has been observed that a calcareous
nucleus results into better deposition of
nacre . Hence molluscan shell is most
commonly used as nucleus .for the
production of round cultured pearls
spherical shell-beads are used as nuclei.
18. Insertion of nucleus
Nucleus is inserted through surgery hence
oysters are to be anaesthetized. For this
purpose crystals of methanol are sprinkled
over the sea water in the tanks in which the
oysters are placed. They get anaesthetized
under the effect of methanol in about 60-90
minutes.. Their adductor muscle relaxes and
the valves can be opened easily. Now the
nucleus is placed in the graft tissue and it is
implanted in the gonad.
19. Rearing of oysters
The operated oysters are kept in cages
and the cages are hanged from raft in
seawater at a depth of 6-10 ft. in about a
week oysters get themselves recovered.
Now oysters are again inspected so that
dead ones may be removed . After
removal of dead oysters cages are again
hanged in sea water at the same depth.
20. Harvesting of pearls
It is done during periods of low temperature
and pH. The oysters are taken out from cages
three years after the implantation of nucleus
and pearls are obtained. When the same
oysters are to be used for second crop ,pearls
alone are carefully removed by opening the
pearl sacs through the gonad and oysters are
returned to the farm.
21.
22. Name – Christina Mathew
Class – C-067
Subject – Zoology
Submitted to- Prof. Deepa
Rathore
