There is limited domestic demand for oyster meat as
it is not conventionally eaten. However, there is great
demand for oyster meat in international market and can
be exported especially to South East Asian Countries.
The product can be exported in frozen, canned or in
smoked form. A marketing tie up with the processing
plant will have to be done for marketing of the product.
10. Interest rate for ultimate
Banks are free to decide the rate of interest within
the overall RBI guidelines. However, for working out the
financial viability and bankability of the model project
we have assumed the rate of interest as 12% per annum.
11. Interest rate for refinance from
As per the policy circulars of NABARD issued from
time to time.
Refinance to the banks is available from NABARD for
such activities which are technically feasible and
financially viable and the rate of refinance will be as
prescribed by NABARD from time to time.
As can be seen from Annexure IV the borrower will be
able to repay the bank loan in five years with a
moratorium of one year for repayment of principal.
Banks may take a decision as per RBI guidelines.
Annexure - I
BIOLOGY, TECHNICAL PARAMETERS AND FARMING
PRACTICES OF C.madrasensis
(I) Biology of C.madrasensis
The edible oyster is a sedentary animal. The soft
body of the animal is encased by two shell valves out of
which the upper valve acts as a lid to open and close by
contraction and relaxation of adductor muscle.
The food of oyster mainly consists of organic
detritus and phytoplanktonic organisms like diatom and
nanoplanktons. It is reported that spores and
particulate matter of sea-weeds were also found in the
stomach. They are also capable of absorbing dissolved
organic matter in the water through the surface of
gills, palps and mantle.
Oysters are generally dioecious but hermaphrodites
are not uncommon. Young oysters of
C.madrasensis, primarily function as males
(60-75 per cent) and later become females. In zero age
group upto 78 mm. in length, 75 per cent are males and
in one year and above with 80 - 115.5 mm. length,
females represents 72 per cent. The peak spawning period
is reported to be during March-April and July-September.
(II) Technology of oyster culture
The technology of oyster culture consists of two
important phases namely oyster seed production and
farming to grow oyster seeds to marketable size.
(A) Oyster seed
The seed requirement for culture of oyster is met
either from natural spat collection or through hatchery
system. For collection of spat from natural grounds,
suitable spat collectors or cultch materials are
provided at appropriate time which may be oyster shells,
coconut shells, asbestos sheets, mussel shells or other
materials. These are arranged on Nylon rope or G.I. wire
as strings and suspended from racks in the water at
suitable spots. The larval period of
C.madrasensis is 15 to 20 days and as such
exposure of collectors will be ideal just after a week
or 10 days of spawning activity.
Mass production of oyster seed is also possible in
hatchery system for which technology is available.
(B) Culture of Oyster seed
For selecting suitable site for farming, several
factors like water depth, bottom characteristics,
protection from wave action, tidal flow and height,
turbidity, water quality including chemical parameters,
predation, fouling, pollution and accessibility are
considered. Optimum requirements for several factors are
not worked out for C.madrasensis, however,
based on the distribution of species and performance at
Tuticorin the following generalities are made. Selected
areas should be sheltered from strong wave action,
should be from 22 to 35 ppt and temperature range should
be from 210 to 310 C.
Farming methods are normally grouped as bottom
culture and off bottom culture. Raft, rack, long-life
and stake are used in various off-bottom culture
practices. The off bottom culture methods are
advantageous over the bottom culture in the following
(i) The growth and meat yield is relatively better.
(ii) It facilitates three dimensional utilization of
the culture area.
(iii) Biological functions like filtration, feeding
etc. become independent of tidal flow.
(iv) Silting and predatory problems are minimum.
The bottom culture method is yet to be experimented
in India. Various off bottom culture methods are as
a. Rack and string method
It is also called ren method. The racks are
constructed at 1 to 1.25 m. depth. Rack is a fixed
structure, comprising several wooden poles vertically
driven into the substratum over which a wooden frame is
made at a height of 0.5 m, above the water level. The
shell rings are suspended from racks. A rack covering 80
sq.m. area holds 90 strings and 125 racks in a ha. At
the end of 12 months, each string may weigh 7 to 7.5 kg.
and the production of oyster is estimated at 80 t / ha.
The mortality is about 45 per cent.
b. Rack and tray method
The nursery reared single spat (cultch-free)
measuring about 25 mm. are transferred to trays of size
40 x 40 x 10 cm. at a density of 150 to 200 oysterlings
/ tray. The tray is knitted with 2 mm. synthetic twine
of appropriate mesh and is suspended from rack. Once the
oyster reaches 50 mm. length they are segregated and
transferred to rectangular tray of size 90 x 60 x 15 cm.
and these trays are placed on the rack which occupies 25
sq.m. area and holds 150-200 oysters. The average growth
rate of oyster is 7 mm/ month and at the end of 12
months, the oyster attains an average length of 85 mm.
The production estimated is 120 t/ ha/ year which
compared to string method is higher, but the production
cost is high.
c. Stake culture
In this culture, a stake is driven into the
substratum and one nail on the top end and two nails on
the sides are fixed, which hold a shell with spat
attached. The stakes are placed 60 cm. apart. In this
method, the nursery rearing of spat is carried on the
same stake. Initially for 2 months, the spat is covered
with velon screen till a size of 25-30 mm. is attained
and in another 10 months they reach marketable size. The
production is estimated to be 20/ t/ ha/ year.
d. Raft culture
Raft is the most suitable farm structure in sheltered
bays where the depth is 5 m. and above. It is made of
wooden poles placed parallelly and tied across with coir
rope to make a rigid frame. Four empty airtight barrels
of about 200 litre capacity are tied to the underside of
the raft at corners. It is moored by two anchors and a
chain. The size of the raft varies and the rafts of 6 x
5 m. size are found to be quite suitable. PVC pipes
instead of wooden poles and styrofoam floats in place of
barrels may be used. However, this method has not been
tried in India so far.
e. Long line culture
In this system long ropes or cables are anchored at
each end and are supported at intervals by floats. Long
lines of 50-100 m. length are easy to manage. Double
long lines comprising of one line on either side of the
floats are also used.