About NABARD I Role and Functions I Subsidiaries
I Associates
I Rural Economy I Model Bankable Projects
 Minor Irrigation  
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Model Bankable Projects



Edible Oyster Culture


The oysters are highly esteemed sea food and considered a delicacy in USA, Europe, Japan etc. In India there is a growing demand for oyster meat in some parts of the country. It is said that 'oyster ' is scientifically the best known marine animal. It is one of the most widely cultivated species. As early as the first century BC the Romans were the first to develop simple methods of collecting oyster seeds and growing them for food. the Japanese developed 'Habitat culture technique' i.e., culture in nets fixed to bamboo poles during the seventeenth century and at the turn of the 20 th century they evolved off bottom culture, especially hanging methods.These methods yielded good results and were adopted by majority of oyster farmers of Japan as the environmental conditions of the coastal areas were highly favourable for practicing these methods. Until recently, oyster farming has been considered as a traditional practice followed only in the temperate countries.The awareness about the vast potentialities for development of oyster farming in tropics is recent. Serious efforts are now being directed in its development under tropical conditions.

2. Scope for oyster farming in India

In India pioneering attempts were made by James Hornell in 1910 in developing Oyster Culture in erstwhile Madras state. Central Marine Fisheries Research Institute undertook scientific investigations at Tuticorin from early 70's and as a result, complete package of the technology is now available in the country. Vast stretches of backwaters, estuaries and bays spread over several lakh ha. are present along Indian coast harbouring natural population of the oyster suggesting suitability of the habitat for oyster culture. Being filter feeders, the oyster converts primary production in the water into nutritious sea food. Permission from State Governments will have to be taken for establishing the unit in the suitable area. The site selection criteria is indicated in the annexure - I.

Six species of oysters namely the Indian backwater oyster Crassostrea madrasensis (Preston), Chinese oyster, C.rivularis (Could), West coast oyster, C.gryphoides (schlothim), Indian rock oyster, Saccostrea cucullata (Born), Bombay Oyster, Saxostrea cucullata (Await and Rai), and giant oyster Hyostissa hyotis (Linnaeus) are found in India. The first four species mentioned above are of commercial value.

C.madrasensis is more widely distributed, is euryhaline and inhabits backwaters, creeks, bays and lagoons and occurs in the coastal areas of the States of Orissa, Andhra Pradesh, Tamil Nadu, Kerala, Karnataka and Andamans. C.gryphoides is also euryhaline and occurs along north Karnataka, Goa and Maharashtra coast. C.rivularis is found along Gujarat and Maharashtra coast while Saccostrea cucullata is found all along the main land coast and Andamans and Lakshadweep islands. Culture of these species is possible at places where the seed is easily available.

3. Technical Parameters

The biology of C.madrasenis, technical parameters required for the culture of the species and farming methods are described in detail in annexure-I.

4. Borrower's Profile

The Borrower should have experience in Oyster farming and should be able to manage culture, marketing and other related aspects.

5. Financial Outlay

Details of the financial outlay have been indicated in Annexure II. It can be seen from that the capital cost for 0.4 ha. unit has been estimated as Rs.55,000/- while the operational cost for one crop works out to Rs.46,000/-. The unit cost indicated is, however, illustrative and actual cost will have to be worked out based on actual field conditions while submitting the project to the Bank.

6. Margin Money and Bank Loan

The entrepreneur is expected to meet 25% of the project cost out of his own resources and the balance of 75% will be available as bank loan.

7. Rate of refinance

NABARD refinance is available for such of these projects that are technically feasible and financially viable.

8. Financial viability

The following assumptions have been made for working out the financial viability of the project as per the experiments conducted at Tuticorin.

(i) Unit area 0.4 ha.
(ii) Culture period One year
(iii) Survival rate


(iv) Expected production 70 tonnes/ ha/ year
(v) Sale price for meat Rs.30/- per kg
(vi) Sale price of oyster shell Rs.300/-kg

The financial analysis has been shown in Annexure III. The results of the analysis are

(i) NPW at 15% DF : Rs.1.247 lakh
(ii) BCR at 15% DF : 1:62:1

IRR is more than 50%


9. Marketing

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 borrowers

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 NABARD

As per the policy circulars of NABARD issued from time to time.

12. Refinance

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.

13.Repayment period

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.

14. Security

Banks may take a decision as per RBI guidelines.

Annexure - I


(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 production/collection

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

Site Selection

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

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 respects :

(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 follows :

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.


Farm management and Harvesting

Farm management practices involve periodic cleaning of the oyster, oyster rearing trays, farm structure like racks and manual removal of predators and foulers. Oysters are harvested when the condition of the meat reaches high value which in case of C.madrasensis is found to be good during March-April and August-September. Harvesting is done manually and oysters are transported to shore in dinghies.


FOR CULTURE OF C.madrasensis

By rack and string method in 0.4 ha. unit area (illustrative)

  Unit Rs
A Capital Cost    


Construction of pond for nursery  



FRP dinghy 1 No



Outboard motor (8 HP) 1 No.



Pump set (3.5 HP) 1 N0.



Farm accessories  




B Operational Cost    


Cost of seed  



Cost of stakes 50 No.



Nylon rope  



Other farm materials, repairs etc.  






Harvesting Charges  




C Production    


Total harvest of meat 3.00 tonne  


Oyster shell 25 tonne  


Income from sale of meat Rs. 30 per Kg



Income from sale of Oyster shells Rs 0.30 per Kg




Annexure III

Financial Analysis

(Amt. in Rs.)

Items Years
  1 2 3 4 5
Capital cost 55000        
Recurring cost 46000 46000 46000 46000 46000
Total cost 101000 46000 46000 46000 46000
Income 97500 97500 97500 97500 97500
Net Benefits -3500 51500 51500 51500 51500
PW of costs @ 15% DF 87826 34783 30246 26301 22870
PW of benefits @ 15% DF 84783 73724 64108 55746 48475
NPW 124810        
BCR 1.62:1        
IRR >50%        

Annexure - IV


Total Outlay 101000
Margin ( 25 % ) 25250
Bank Loan 76000

(Amt. in Rs.)

Year Bank Loan Net Income Repayment Net surplus

@ 12% pa

Principal Total
1 2 3 4 5 6 8
1 76000 97500 9120 - 9120 88380
2 76000 51500 9120 19000 28120 23380
3 57000 51500 6840 19000 25840 25660
4 38000 51500 4560 19000 23560 27940
5 19000 51500 2280 19000 21280 30220

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