Annex VI
STATUS OF MOLLUSCAN FISHERY RESOURCES IN INDIA AND THEIR SANITATION AND MARKETING

V. V. Sugunan
Central Inland Capture Fisheries Research Institute

I. INTRODUCTION

Although in India the majority of the population is meat-eating by tradition, the intake of animal protein is markedly low. Protein consumption in India is estimated at 52 g per person per day of which animal protein constitutes a meager 6 g, compared to 92 g and 65 g in USA and 92 g and 61 g in Australia. If population growth projections are of any guide, India should, in addition to conventional sources of animal protein (fish, beef, pork, chicken, etc.) explore unconventional areas to increase the present protein level intake as well as to ensure alternative foods at reasonable prices. Among the unconventional sources of animal proteins, molluscs as a group have great prospects. India has a rich variety of edible marine and freshwater molluscs such as oysters, mussels, clams, squid, cuttle fish, octopuses and land snails, apart from the commercially harvested species such as the pearl oysters and sacred conchs.

Despite the rich variety of commercially valuable molluscs in India, their contribution to the yearly catch is insignificant. Various estimates show that the contribution of marine molluscs to the overall annual fishery output varies from 0.85 to 1.0% (Nair and Mahadevan, 1983). At present there is no reliable production data of edible inland molluscs such as the freshwater mussels and other gastropods known to be consumed in various parts of the country. Apart from the tremendous potential to mitigate the protein deficiency in the country, some of the molluscan resources command a lucrative overseas market.

The status of the major molluscan resources of economic importance in India are detailed below.

II. OYSTERS

Although edible oysters are considered as prized delicacies in the west and other advanced countries, they still remain more or less alien to the Indian palates. Despite the wide distribution of this mollusc species, there is very little demand in the domestic market except in Bombay. The local demand in Bombay is satisfied by oysters collected from the wild. The present fishery of edible oysters is highly localized and it caters mainly to the western style hotels. The oyster capture fishery from wild stocks is under-exploited and, there are no commercial oyster culture ventures to supply domestic and export markets.

Resource distribution

Thirteen species of edible oysters have been reported from India (Awati and Rai, 1931; Rao, 1974) among which, four species viz., Crassostrea gryphoides, C. discoides, C. madrasensis and Saccostrea cucullata are of commercial value. C. gryphoides and C. discoides are mostly found in the North-Western coast of India; the former being more important and occurring in the coastal areas of North Canara and Maharashtra (Nair and Mahadevan, 1983). According to Alagarswamy and Narasimhan (1973), C. discoides is distributed in the muddy creeks of Kutch, the Arama creek and off Poshetra point, Port Okha, Dwaraka and Porbunder. Along the Maharashtra coast, C. gryphoides is the prevalent species although the other species also occur at a few places. Crassostrea madrasensis enjoys a wider distribution along the South-West and East coasts of India and it is found in almost all the estuaries and backwaters.

Malad, Boiser, Satpuri, Palghar, Kelva, Navapur, Utsali, Dahisar and Mahim creeks are all important fishing grounds around Bombay, Palghar being the most important one. Oyster spats are collected from the natural beds and reared to the market size for almost 12 months in suitable fattening sites.

In the State of Maharashtra, oyster fishing is practiced in Alibag, Ratnagiri, Jayatpur and Malwan. Oyster beds are often 4 to 5 fathoms deep and the divers use chisels and hammers to detach the molluscs from the substrate. In Goa, oysters are exploited at Ribander, Siolim and Curca. The oyster beds of Karkal Island, Karwar Acad and Ladies Beach near Karwar are not exploited to any appreciable extent. Along the coast of Cochin, in Mulki, Udayavara, Coondapur and along the Kali river, oysters are collected for domestic consumption.

In the East coast of India, C. madrasensis fishery used to be a lucrative activity, particularly during the 1920's. This species is also abundant in Sonapur backwaters of the Bahudi river and lake Chilka. In Pulicat Lake small-sized oysters were traditionally collected and then reared in shallow waters for the market in Madras City. This practice no longer exists and the sporadic local demand is now met by collecting the oysters from the wild.

The oyster beds of Kovalam-Muthukadu backwaters in Madras cover an area of about 2.6 hectares carrying a biomass of an estimated 417 MT. Every three years the rural communities in the area indulge in large scale removal of the oysters to supply the lime kilns at Palavakkam, Kovalam and Tambaran. In 1987 almost 364 MT of oysters were harvested and sent to the lime industry.

The rock oyster, S. cucullata, is extensively distributed in both the East and West coasts of India. Unlike the other species mentioned above, they require high salinities and thrive under marine conditions. Although they are known to have a rich flavour, their small size makes exploitation difficult.

At present, the exploitation of wild oyster stocks is mainly carried out to cater to the needs of western-style hotels in major Indian cities. In coastal villages and communities, this edible mollusc forms a supplementary food for the poor who consume the shellfish with very little concern regarding the quality and hygiene of the product.

There is vast potential for culturing edible oysters in India, especially the large C. madrasensis and C. gryphoides. Techniques for their spat collection and culture have been developed and demonstrated feasible in various parts of the country (CMFRI, 1980; Joseph and Joseph, 1983; Nair and Mahadevan, 1983; Reuben et al., 1983). Oyster seed production through hatchery techniques have also been developed at the Central Marine Fisheries Research Institute (CMFRI) in Cochin (Anon, 1982).

Oyster culture technology

The Central Marine Fisheries Research Institute in Cochin has developed a technique for culturing the large Indian oyster C. madrasensis at Tuticorin Station in the East coast of India. A rack system was developed on which the oysters are placed on a wooden platform above the sea bottom. The oysters are maintained below the water surface in order to enable optimum water filtration and feeding thus promoting faster growth and fattening.

Spat collection. Using the technology developed by the CMFRI, oyster spats are collected by suspending lime-coated semi-cylindrical country tiles from a wooden platform at different water depths. Oyster spat are collected during the spawning seasons which vary according to the species and locality, however a peak period for the major species occurs during April-May. Spat settled on the artificial substrata are allowed to grow on them until they reach 3.0-3.5 cm. The young oysters are eventually scrapped off the cultches and transferred into a nylon-meshed cage of 12 mm mesh size and made of a 6 mm iron rod frame. Each cage measures 40×40×10 cm and holds about 200 juvenile oysters. After a culture period of two months, they are transferred to larger rectangular cages of 22 mm meshed nylon netting measuring 90×60×15 cm.

Oyster rack culture. Wooden poles are erected in mid-water by staking teak wood poles in such a way that the cages fastened to the wooden platform are only exposed to air during the lowest low tide periods. A rack of about 26 sq m can accommodate 20 rectangular cages containing each 150–200 oysters for fattening. With this culture system the oysters attain a size of 8.5–9 cm in 12 months with a total weight of 120 g (shell-on) and a meat weight of about 10 g (8–10 % of total weight). In one hectare area it is possible to erect at least 280 racks and stock nearly one million oysters with an expected annual production rate of 135 MT of shell-on oysters yielding 13.5 MT of oyster meat.

Fouling organisms and parasites. A large number of fouling organisms settle on the spat collectors and cultured spat. The most common fouling organisms are several species of barnacles (Balanus amphitrite communis, B. amphitrite denticulata and B. amphitrite cocqiensis). Tube-dwelling polychaetes, Hydroides norweqica, Pomatoceros triquetor, Spirobis sp. and Polydora ciliata are also found to compete with the oysters for space. Heavy fouling by barnacles and polychaetes impairs the growth of oyster spats. The problem is compounded by the fact that the breeding seasons of all these unwanted associates coincide (Joseph and Joseph, 1983). Oysters cultured by the CMFRI along the Tuticorin coast also suffered mortalities up to 15% by the predatory gastropod Cymatium cingulatum.

Studies on the control of biological competitors, parasites and predators need attention in India. This would stimulate the development of oyster farming as an industry.

Purification of cultured oysters

Adequate techniques for purifying farm-grown and naturally occurring oysters for safe human consumption is an essential prerequisite to the development of trade in edible oysters in India. The depuration technique developed by the CMFRI is highly efficient and ensures the oysters, are safe for human consumption. Under this system (Nair et al., 1983), seawater is pumped in from the open sea and stored in underground sumps 80 cm away from the beach. From the sump, water is pumped into the cleaning tanks via four sedimentation tanks and one filtration tank. Oysters are initially cleaned with a jet of water and then placed in the tanks where they are left for 12 hours to get rid of bacteria by natural physiological processes. After a second cleaning by water jet, they are kept in the cleaning tanks for another 12 hours. At the end of the cleaning phase, the oysters are treated in 3 ppm chlorine followed immediately by dechlorination. The dechlorination process can be replaced by ultraviolet sterilization in order to achieve higher hygienic results.

Canning of edible oysters

Successful experiments have been conducted in India to can oyster meat (Balachandran et al., 1984). The canning yield of oyster was 15% higher from farmed oysters than from wild specimens.

According to the CMFRI, an area that demands immediate attention is the marketing of oysters in the domestic and overseas markets. Extension work on market development, product marketing on relatively low rates, and ascertaining the consumer preferences of quality of flesh are needed in the domestic front. Proper technology for oyster meat processing and preservation to satisfy the consumer taste need to be developed to foster the overseas markets.

III. MUSSELS

Two species of edible mussels, Perna viridis and Perna indica are widely distributed along the entire coast of India. They are found on hard substrata to a depth of 10 m and are usually chiselled out by the fishermen at low tide. The green mussel, P. viridis enjoys a wide distribution along the west coast (Nair and Rao, 1985). In the west coast thick beds exist at Quilon, Alleppey, Cochin, Malabar, Karwar, Goa, Malvan, Ratnagiri and Gulf of Kutch, where they are regularly exploited for their meat. This mussel is particularly abundant on the rocky coasts from Calicut to Tellicherry, where there is an active fishery. In the Coromandel coast, P. viridis occurs at very few places such as Visakhapatnam, Kakinada and Madras. It attains a length of 92 mm at the end of one year at Kakinada and its breeding period is prolonged, extending from December to July (Narasimhan, 1980). The brown mussel has a limited distribution from Varkalai near Quilon on the southwest coast to Cape Comorin with rich beds at Varkalai, Kovalam, Vizhinjam, Poovar, Muttom and Colachel. The brown mussel grows to a size of 35–36 mm in a year at Vizhinjam coast and breeds from May to September (Appukuttam and Nair, 1980). The existing sustenance fishery of brown mussel at Vizhinjam is estimated to be 50–150 MT a year (CMFRI).

The CMFRI has developed a technique for rope culture of mussels. The green mussels are cultured on 5–10 m long ropes suspended from wooden rafts of 36 to 100 sq. m. in area. The ropes are seeded by embedding the spat on the rope with the help of cloth firmly stitched to it. Mussel seeds in the size range of 20–35 mm are considered suitable for rearing. They reach the marketable size of 55–60 mm during a culture period of about 5 months. The average production is 10–12 kg of mussels per metre of rope in the bay in 7 months and 15 kg in the open sea in 5 months. On a raft of 30 sq. m. in area, 50 ropes (each 6 m in length) can be suspended for culturing mussels.

Uncertainties in the availability of mussel spat and the seasonal nature of their availability are major constraints in developing mussel culture as a viable industry. It appears necessary to develop a technology to artificially induce mussels to spawn and techniques to rear larvae indoors up to the transplantable stage (young mussels). Green mussels have been successfully spawned at the Kovalam field laboratory of the CMFRI and over 20,000 juvenile spat have been produced (Sreenivasan et al., 1988). Structure of the rafts need to be suitably designed to withstand the rough weather allowing year round operation in the open sea.

Muraleedharan et al. (1982) have developed processing methods for dried and pickled mussels, fried and pickled mussels and smoked and pickled mussels. India has exported 2 MT of canned mussels worth Rs. 0.48 million in 1979. More work on processing and preservation of mussel meat is needed.

IV. CLAMS

Clams contribute substantially to the total production of molluscs for human consumption as well as for raw material for the cement and lime industry. Clams are abundantly found along the entire coast of India, however the richer resources are found along the west coast of the country. Meretrix casta, Katelysia opima and Paphia laterisulca are commonly caught in the backwaters of Maharashtra, while M. meretrix and Villorita cyprinoides support fisheries at the Goan estuaries. In Kali river of North Karnataka the production of M. meretrix, Paphia malabarica and V. cyprinoides amount to about 2,000 MT per year. In South Karnataka M. casta dominates. In Nethravati estuary at Mangalore 79–128 MT of clams are caught annually dominated by V. cyprinoides.

The extensive sub-fossil clam deposits in Vembanad Lake are well known. An estimated 1,988,090 MT of clam shells are collected from the lake of which 26,859 MT are live (Rasalam and Sebastian, 1976). The clam shell constitutes the raw material for the Travancore-Cochin Cements Ltd. and the Travancore Electro-Chemical Industries Ltd., for the manufacture of cement and calcium carbide, respectively. Large quantities of sub-fossil deposits are exploited from the Kodungallore, Ashtamudi, Kadalundi and Veli lakes in Kerala State. Vittorita spp. form 90% of the clam resources of Vembanad lakes and their meat is widely consumed in Alleppey District. There is a good fishery for K. opima in Ashtamudi lake which supports an export trade of clam meat.

In the east coast of India, Meretrix sp. occur in Bahundi River (Orissa), Chilka Lake and Kakinada Bay. In Kakinada Bay about 400 MT of clams are landed annually compared to 210 MT in the Vellar Estuary (Natarajan et al., 1979). Pulicat Lake contains rich deposits of sub-fossil clams.

Clam culture

Experimental culture of Meretrix casta var. ovum and M. meretrix attempted in the Mulky Estuary (Karnataka) produced encouraging results (Rao and Rao, 1983). The experiments, conducted in pens of about 23 to 43 sq m, showed an average meat increase of 1.79 g in four months in the case of M. casta and 1.36 g in M. meretrix. Survival rates were 89.5% and 72.5%, respectively.

Clams support a regular export trade and the annual export amounts to 407 MT valued at about Rs. 8.45 lakhs equivalent in foreign exchange (1982). At present, the clam species that contributes substantially to this export market is K. opima. In 1981 about 16 MT of frozen clams were exported worth Rs. 0.11 million; the corresponding figures for 1983 were 478 MT and Rs. 5.87 Million (see Table 1 for additional information).

At present there is a large scope for developing commercial scale clam culture in order to sustain and increase the export trade, however suitable culture technologies are yet to be developed.

The blood cockle Anadara granosa forms a fishery of some magnitude in Kakinada Bay where an estimated 1,000 MT are landed annually. Some experiments have been conducted in India to culture blood cockles in pens, cages and boxes (Naramsinhan, 1983). The pen culture yielded production rates ranging from 84 to 357 kg/sq.m.

A depuration technology which starves the clams has been developed to render the clams within the safety standards for human consumption. Clams are allowed to starve for 24 hrs in clean lake water for depuration followed by keeping them in chlorinated (5 ppm) water for 2 hrs. Bacteriological quality of raw clam meat, depurated clam meat and shucked clam meat are given in Tables 2, 3 and 4 (Balachandran and Surendran, 1984). Technologies for canning, freezing and pickling clam meat have been developed and these three items have become a regular foreign exchange earner.

Table 1. Total export of processed clams from India in 1981 and 1982. Q: Quantity in MT; V: Value in Rs. (From: Sarvaiya, 1989).

Table 2. Sand content and bacteria levels in clam meat, water and mud samples. (From: Balachandran and Surendran, 1984).

Table 3. Effect of starvation for 24 hrs in natural and chlorinated waters on the sand content and bacteria levels in clam meat. (Balachandran and Surendran, 1984).

Table 4. Bacterial level of clam meat after a 24-hr depuration in water, and 24-hr depuration in water followed by 2 hours chlorination. (Balachandran and Surendran, 1984).

V. OTHER BIVALVES

There are other bivalve species such as Solen sp., Donax cuneatus, D. faba and D. incarnatus found in the intertidal zones in various parts of the country which are fished for their meat. Species like Mesodesma globratum, Gafrarium sp., Pinna bicolor and Atrina pectinata merit some attention as their meat is edible.

VI. CEPHALOPODS

Squid and cuttlefish have already entered the export market and octopods are fast becoming an important marine export item. About 60% of squid and cuttlefish are obtained as by-catch in trawlers nets, shore seines, boat seines, and hook and line. Annual cephalopod production increased from 1,696 MT in 1977 to 14,292 MT in 1986. Squid export which stood at 46.1 MT in 1975 increased to 1,240 MT in 1982 with a value hike of Rs. 0.3 million to Rs. 1.5 million. Table 5 shows more details of frozen squid export from India. Frozen cuttlefish and fillets have now found a place among the exported Indian seafood items.

Table 5. Export of frozen squid from India to major European markets. Q: Quantity in MT; V: Value in hundred thousand Rs. (From: Sarvaiya, 1989).

Frozen cuttlefish and fillets have now found a place among the exported Indian seafood items. Fourteen MT of cuttlefish valued Japan is the biggest customer of India in respect of cuttlefish followed by Spain, France, Singapore, Thailand and Hong Kong (Sarvaiya, 1989). The economically important cephalopods in India are squid, mainly Loliqo duvancelli, Sepioteuthis lessoniana, Doryteuthis sp., Loliolus investigatoris, and cuttlefish, mainly Sepia pharaonis, S. aculeata, S. breviamana, S. elliptica, S. prashadi and S. inermis. Ramanathapuram is well known for its fishery of squid using a special shore seine. known as Ola valai (Rao, 1954). Octopods are regularly fished in Lakshadweep Islands by spearing and annual production ranges between 13–20 MT. There is considerable scope for enhancing the production of cephalopods from Indian waters as Flippova (1968) and Silas (1969) have pointed out. The oceanic squid is common at depths beyond 180 m off the South coast of India.

Table 6. Export of frozen cuttlefish and fillets from India. Q: Quantity in MT; V: Value in millions of Rs.

VI. INLAND MOLLUSCS

Several species of aquatic gastropods and bivalves are consumed by villagers all over the country, especially species such as Pila globosa, Bellamya benqalensis, Lamellidens marginalis etc. These molluscs constitute a source of cheap food for the rural poor; they have not yet appealed to the palates of the well to do and middle class. The Science and Technology Committee of the Government of West Bengal conducted a survey and found the details as given in Table 7.

Land snails

Epicurean value of land snails like Helix aspersa and Achatina fulica in western Europe, particularly in France is well known. Although both species are non-endemic to India, the latter established itself in India after an accidental introduction in 1847. The population of A. fulica, the giant African snail has increased at an alarming rate and it has become a serious agricultural pest. Despite being an agricultural pest, there is sufficient scope to collect the giant African snail from the wild for export purposes. There is a persistent demand for edible land snails in the western European countries. The annual demand in France alone is estimated by the Marine Products Export Development Authority of India at 20,000 MT. In addition to the prospects of collecting the land snails from the wild, they can be cultured in controlled and semi-controlled conditions. The Central Inland Capture Fisheries Research Institute (CICFRI) has developed a technology for breeding the snail in terraria and field snail-farms (Vinci et al., 1988). In the snail houses of the CICFRI, A. fulica grew from 5 mm to 74 mm in 150 days with practically no mortality.

Table 7. Consumption of inland snails in different Indian States.

Wild and farm-grown snails are processed in a simple method developed at the Institute. Under this process, the snails are repeatedly washed under a water jet followed by dipping in chlorinated water. Snails are then treated in warm water to enable easy shucking of meat. The foot portion is chopped off without disturbing the viscera. Processed meat is packed in polythene and quick frozen in two-kg blocks. Processed snail meat at the CICFRI was exhibited in the Anuga Fair in Cologne in October 1987. Many buyers are keen to import Indian snails. Hemiplecta basileus and Ariophanta beddomei are close relatives of the prized Helix spp. which are available in India meriting attention of the culturists.

VII. VALUABLE MOLLUSCS AS ORNAMENTS AND OTHER USE

Pearl oysters

Pearl oysters, Pinctada fucata and P. margaritifera are the most important among the commercial species other than the edible ones. Pearl collection is a traditional vocation in India and oysters have been fished for pearls from time immemorial. Large scale pearl fishing is conducted by the Government of Tamil Nadu in the pearl beds of Mannar Gulf from time to time. Pearl oysters in the Gulf of Kutch yield an annual production of 30– 70,000 pearl oysters (Mahadevan and Nair, 1973). The Central Marine Fisheries Research Institute has developed a technology for producing spherical cultured pearls in the pearl oyster, P. fucata (Alagaerswamy and Qasim, 1974).

Sacred conch

The sacred conch, Xancus pyrum, due to religious reasons, is an important species of mollusc in India. About 90% of the conch are obtained through diving. In the east coast, about one million conch are collected annually, whereas in Ramanathapuram, the annual production is about 0.3 million. About 40,000 conchs are fished in Chinglepet. In Thanjavur and South Arcot district in Tamil Nadu, in the west coast, nearly 35,000 conchs are caught in trawl nets and hook & lines. Capture of conch less than 57 mm in size is prohibited by law as a conservation measure. Sacred conchs with sinistral shells are very rare and highly valued.

Seashells and oyster shell powder

Indian exports of seashells and cuttlefish bones to countries such as Saudi Arabia, USA, Malaysia, UAE, France, Australia, FR Germany, and Switzerland from 1973 and 1985 are shown in Table 8. The cowries and cuttlefish bones are collected by departmental lessees in the State of Gujarat. During 1981, India exported 200 kg of oyster shell powder worth Rs. 12,000; the corresponding figures for the year 1982 being 10,000 kg and Rs. 81,000, respectively.

Table B. Export of seashells and cuttlefish from India. Q: Quantity in MT; V: Value in hundred thousand of Rs. (From: Sarvaiya, 1989).

ACKNOWLEDGEMENT

The author acknowledges the guidance and encouragement received from Dr. P.V. Dehadrai, Deputy Director General (Fisheries), Dr. M.Y. Kamal, Assistant Director General (Fisheries) Indian Council of Agricultural Research, New Delhi and Dr. Arun G. Jhingran, Director, Central Inland Capture Fisheries Research Institute (CICFRI), Barrackpore, India for the preparation of this document. Thanks are also due to Mrs. G.K. Vinci and Dr. V.K. Unnithan, Senior Scientists of the CICFRI for their valuable contribution to the paper.

REFERENCES

Alagarswamy K. and K.A. Narasimhan, 1973. Clams, cockle and oyster resources of Indian costs. Proc. Symp. Living Resources of the Seas around India. CMFRI. Special Publication: 648–658.

Alagarswamy K. and S.Z. Qasim, 1974. Indian J. Fish., 20 (2): 533–550.

Anon, 1982. Mar. Fish. Infor. Serv. T&E Ser., 44: 14–17.

Appukkuttan K.K. and T. Prabhakaran Nair, 1983. Culture of brown mussel, Perna indica at Vizhinjam, southwest coast of India. Proc. Symp. Coastal Aquaculture, Cochin, India 12–18 1980.

Awati P.R. and H.S. Rai, 1931. Ostrea cucullata (The Bombay oyster). Indian Zool. Mem., 3: 1–104.

Balachandran K.K. and P.K. Surendran, 1984. Studies on the depuration of live clams. Fish. Technol., 21 (1): 65–69.

Balachandran K.K. and Vijayan P.K. and P.V. Prabhu, 1984. Canning of oysters. Ibid., 21: 47–50.

CMFRI, 1980. Culture of brown mussels. Mar. Fish. Infor. Serv. T&E Ser. of the Central Marine Fisheries Research Institute, Cochin, 16: 11–13.

Flippova J.A., 1968. Proc. Symp. Mollusca Mar. Biol. Ass. India, 1: 257–264.

Joseph M.M. and J. Shanta, 1983. Some aspects of the experimental culture of the oyster, Crassostrea madrasensis (Preston). Proc. Symp. Coastal Aquaculture, Cochin, India 12–18 Jan. 1980.

Mahadevan S. and K. Nagappan Nir, 1973. In: Proc. Symp. Living Resources of the Seas around India, CMFRI, Cochin. Special Publication: 659–671.

Muraleedharan V.K., George Joseph and K. Devadasan, 1982. Pickled products from green mussel. Fish. Technol., 19: 41–43.

Nagappan Nair K. and S. Mahadevan, 1983. Oyster culture in Tuticorin. Proc. Symp. Coastal Aquaculture, Cochin-India 12–18 Jan. 1980.

Nagappan Nair K., Rajapandian M.V. and D.C.V. Easterson, 1983. Purification of farm grown oysters. Ibid. 505–508.

Nagappan Nair K. and K.S. Rao, 1985. Mar. Fish. Infor. Serv. T&E Ser., CMFRI, 61: 1–7.

Narasimhan K.A., 1980. Chapter III. Bull. Cent. Mar. Fish. Res. Inst., 29: 10–16.

Narasimhan K.A., 1983. Experimental culture of blood clam Anadara granosa (Linnaeus) in Kakinada Bay. Proc. Symp. Coastal Aquaculture, Cochin-India 12–18 Jan. 1980.

Natarajan P., Devadoss P. and K. Muniyandi, 1976. J. Mar. Biol. Ass. India, 18 (2): 323–355.

Rao K.V., 1954. Indian J. Fish., 1: 37–66.

Rao K.S., 1974. Edible bivalves: mussels and oysters. In: The commercial molluscs of India. Bull. Cent. Mar. Fish. Res. Inst., 25: 4–39.

Satyanarayana Rao K. and G. Syda Rao, 1983. Experimental clam culture at Mulki, Dakshina Kannada. Proc. Symp. Coastal Aquaculture, Cochin-India 12–18 Jan. 1980.

Rasalam E.J. and M.J. Sebastian, 1976. J. Mar. Biol. Ass. India, 18 (2): 323–355.

Reuben S., Appa Rao T. and P.E.S. Manickam, 1983. Proc. Symp. Coastal Aquaculture, Cochin-India 12–18 Jan. 1980.

Sarvaiya R.T., 1989. Molluscan export from India with reference to the Gujarat State. Fishing chimes, 6: 43–46.

Silas E.G., 1969. Bull. Cent. Mar. Fish. Res. Inst., 12: 86 pp.

Sreenivasan P.V.K., Satyanarayana Rao K., Poovannan P. and R. Thangavelu, 1988. Growth of larvae and spat of the green mussel, P. viridis in hatchery. Mar. Fish. Res. Infor. Ser. T&E Ser., 79: 23–26.

Vinci G.K., Unnithan V.K. and V.V. Sugunan. Farming of the giant African snail, Achatina fulica: a manual. Cent. Inland Fish. Inst., Barrackpore-India, Bull. 56, 28 pp.