|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 present along Indian coast harbour 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. The site selection criteria is indicated in the annexure - I.
3. Candidate species
Six species of oysters namely the Indian backwater oyster Crassostrea madrasensis, Chinese oyster, C.rivularis, West coast oyster, C.gryphoides, Indian rock oyster, Saccostrea cucullata, Bombay Oyster, Saxostrea cucullata, and giant oyster Hyostissa hyotis are found in India. The first four species mentioned above are of commercial value.
Of the six species of oysters, the Indian backwater oyster C. madrasensis is the dominant species, 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 cucullatais 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.
4. 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.
5. Borrower's Profile
The Borrower should have experience in Oyster farming and should be able to manage culture, marketing and other related aspects. Self Help Groups can also take up this activity in clusters. Interested borrowers may be trained in oyster farming.
6. 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 .120000/- while the operational cost for one crop works out to Rs 78000/-. 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.
7. 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.
8. Rate of refinance
NABARD provide refinance to the banks for their financing edile oyster farming activities. The rate of refinance is decided from time to time.
9. Financial viability
The following assumptions have been made for working out the financial viability of the project as per the experiments conducted at Tuticorin.
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.
11. 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.
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 Crassostrea madrasensis
(I) Biology of C.madrasensis
The edible oyster is a sedentary animal. The soft body of the animal is encased in two shell valves out of which the upper valve acts as a lid to open and close by contraction and relaxation of the adductor muscle.
Oysters mainly feed on organic detritus and phytoplanktonic organisms like diatoms and nanoplanktons. They are also capable of absorbing dissolved organic matter in the water through the surface of gills, palps and the 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 represent 72 per cent. The peak spawning period is reported to be during March-April and July-September.
Oysters, like other bivalve molluscs, spend the first few weeks of their lives as small, drifting larvae. When the larva is about one-third millimetre long, it attaches to a substrate (sets)undergoes a change in its internal organs, eventually reaches sexual maturity and spawns, thus completing its life cycle.
(II) Technology of oyster culture
The technology of oyster culture consists of two important phases namely (A) Oyster seed production/ Spat collection and (B) Grow- out.
(A) Oyster seed production/ spat collection
The seed requirement for culture of oyster is met either from natural spat collection or through hatchery rearing. For collection of spat from natural grounds, suitable spat collectors or cultch materials are provided at appropriate time which may be oyster shells, coconut shells, asbestos sheets, mussel shells or other materials. 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.
A reliable source offering sufficient quantities of spat of the desired species is critical to successful oyster culture. Natural collection is the most important source of spat and will continue to be so until commercial hatcheries are established.Mass production of oyster seed is also possible in hatchery system for which technology is available, though no commercial hatcheries are available yet.
For efficient spat collection the farmer should know the (a) spat setting season and (b) the sites to collect sufficient spat for stocking in the grow-out ponds.
(B) Grow out
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. Selected areas should be sheltered from strong wave action, salinity should be from 22 to 35 ppt and temperature range should be from 21 to 31 degree Celsius.
Farming methods are normally grouped as (a) bottom culture and (b) off bottom culture. Raft, rack, long-line and stakes are used in various off-bottom culture practices. The bottom culture method is yet to be experimented in India. The off bottom culture methods are advantageous over the bottom culture due to the following reasons :
(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.
Various off bottom culture methods are as follows.
a. Rack and string (ren) method
It is also called ren method. This is the most common method advocated for Indian conditions for which the oyster shell ren is used as spat collector. This method is ideal for shallow estuaries, bays and backwaters. 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 strings are suspended from these racks. A rack covering 80 sq.m. area holds 90 strings and 125 racks in a ha. At the end of 7-10 months, each string may weigh 7 to 7.5 kg. and the production of oyster is estimated at 80 tonne / ha. The mortality is about 45 per cent. The meat yield is about 10%.
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 spat / tray. The tray is knitted with 2 mm synthetic twine of appropriate mesh size and is suspended from the rack. Once the oyster reaches 50 mm length they are segregated and transferred to rectangular tray of size 90 x 60 x 15 cm 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 tonne/ ha/ year which when compared to string method is higher,however the production cost is quite high.
c. Stake culture
In this culture method, stakes with one nail on the top end and two nails on the sides are driven into the substratum . These nails hold the shells with spat. The stakes are placed 60 cm. apart. In this method, the nursery rearing of spat is carried on the same stake. Initially for 2 months, the spat is covered with velon screen till a size of 25-30 mm. is attained and in another 10 months they reach marketable size. The production is estimated to be 20tonnes/ ha/ year.
d. Raft culture
Raft is the most suitable farm structure in sheltered bays where the depth is 5m and more. 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 however rafts of size 6m x 5 m. are found to be quite suitable. PVC pipes instead of wooden poles and styrofoam floats in place of barrels may be used. 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, thinning, sorting or grading and manual removal of predators and foulers. ‘Fouling’ includes mud, ascidians, coral, sponges and other encrusting organisms. These agents attach themselves to trays and oysters and interfere with the feeding and respiration of the oysters. If not attended to on time, a thick blanket of fouling organisms and silt develops and the growth of oysters is hampered. Mortality also increases due to the restriction of water circulation over the animals.
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. After landing, the harvested oysters should be brushed and any fouling organisms removed. Oysters should be depurated to ensure they are free of bacterial contamination. Depuration should be carried out for 36 hours. Undepurated oysters are unsafe for consumption and may cause gastroenteritis and related diseases. Reservoir water in the depuration unit should be replaced for each run. Oysters are marketed after depuration. Some oysters may be sold as shucked meat. A special ‘shucking’ knife should be used to open the oysters and remove the meat. Care must be taken not to damage the oyster meat during shucking. The meat should be weighed and then kept on ice until sale.
Training and Extension
The Central Marine Fisheries Research Institute (CMFRI), ICAR provides technology, training and extension services to the interested farmers to take up culture.
ESTIMATED FINANCIAL OUTLAY AND PRODUCTION
FOR CULTURE OF C.madrasensis
By rack and string method in 0.4 ha. unit area (illustrative)
Financial Analysis (Amt. in Rs.)
Annexure - IV
ESTIMATED BANK LOAN AND REPAYMENT PERIOD (ILLUSTRATIVE)
Total Project Cost 198000
Margin (25%) 49500
Bank Loan 148500
(Amt. in Rs.)