The Indian backwater oyster is an irregularly shaped oyster with straight shells. The shell has a deep left valve and concave right valve. The hinge which joins the shells is narrow and long. The animal has a right and left mantle lobe which encloses the mantle cavity which in turn encloses the rest of the organs

Xavier, Biji

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161Crassostrea madrasensis (Preston, 1916)*Biji XavierI D E N T I F I C A T I O NSource of image : CMFRI, Kochi                                *Crassostrea bilineata (Roding, 1798) as per Huber,M. (2010)Local names: Kadal muringa, Muringa, Muru (Malayalam); Ali, Kalungu, Patti (Tamil);Muri (Kannada)MORPHOLOGICAL DESCRIPTIONThe Indian backwater oyster is an irregularly shaped oyster with straight shells. The shell has adeep left valve and concave right valve. The hinge which joins the shells is narrow and long. Theanimal has a right and left mantle lobe which encloses the mantle cavity which in turn encloses therest of the organs.Order : OstreidaFamily : OstreidaeCommon/FAO : Indian backwaterName (English) oyster162Prioritized species for Mariculture in IndiaP R O F I L EGEOGRAPHICAL DISTRIBUTIONCrassostrea madrasensis is widely distributed along both the east and west coasts of India. Alongeast coast, it is available in Bahuda estuary, Visakhapatnam; Sarada estuary, Kakinada; deltas ofGodavari and Krishna rivers; Pulikat Lake; Ennore; Guggalore and Mandapam. Along west coast,it is distributed in Anchengo back water; Ashtamudi and Vembanad lakes; Kochin harbour andbackwaters; Azhikode; Beypore; Thellicherry; Elathur; Chauyar estuary; Pavanji; Sambhavi; Sitanadhi;Coondapur; Venkatapur; Sharavathi and Kalinadhi estuaries and Pirotan Islands, Gujarat. It alsooccurs along Pakistan coast.HABITAT AND BIOLOGYIt is a euryhaline brackish water oyster, inhabiting backwaters, estuaries, ports and harbours. Italso occurs occasionally in open sea as thick bed. It is found in intertidal zones at depths of around4 m. It grows to a maximum size of 212 mm and larger ones are available in estuaries.163Oysters have separate sexes generally but hermaphrodites are also present. In one spawning, afemale of length 80-90 mm size releases 10-15 million eggs. The eggs and sperm are dischargeddirectly into the water, where fertilization and development takes place. Larvae drift for few weeksand attach to substrate, when they are one-third millimeter long.BREEDING IN CAPTIVE CONDITIONSThe induced breeding, larval rearing and spat production of C. madrasensis has been successfullyachieved at Tuticorin R. C. of CMFRI. Oysters (1 yr old) with uniform gonadal state were used forbroodstock development. The stocking density used for broodstock development was 25 individuals/100 l of water. They were fed a mixture of Chaetoceros affinis, Skeletonema costatum, Thalassiosirasubtilis, Nitzschia closterium, Isochrysis galbana, Pavlova sp. and Chlorella salina.  Food was providedtwice daily and a cell concentration of 0.8-1.0 x 106 cells/ml was maintained. Water was exchangedevery day morning prior to feeding. The matured individual was induced to spawn with a temperatureincrease of 2-4 °C above the ambient. Males spawned first, which induced the females to spawn.The fertilized eggs settled at the bottom and reached morula stage within 4 h.LARVAL REARINGThe 'straight hinge' or 'D' shell larval stage was observed after 20 h of fertilization and the larvaemeasured 66 µm in length on first day. It was reared in rectangular FRP tank and fed withphytoflagellates. Early umbo stage (100 µm) was obtained on 3rd day and late umbo stage (260-270 µm) between 12-15 days. Eyed and pediveliger stages were observed on 13-17 and 14-18days, respectively. At pediveliger stage, the larvae developed functional foot, sank to the bottomand started crawling (swimming creeping stage). The pediveliger larvae settled down, losing thevelum totally. The shell edges grew hexagonally and the larvae developed the characteristic adultfeatures and metamorphosed into spat of 450 µm in length. The mixture of Isochrysis spp. andPavlova spp. were used as feed during different larval stages. However the concentration of algaewas increased based on the larvae's nutritional requirements, viz., 'D' shape: 3,000-4,000 cells/ml/larvae; early umbo: 4,000-5,000 cells/ml/larvae; umbo: 5,000-8,000 cells/ml/larvae; late umbo:8,000-10,000 cells/ml/larvae and eyed, pediveliger and spat: 10,000-12,000 cells/ml/larvae.NURSERY REARINGNursery rearing of spat can be carried out either in tank or in wild in natural water. In tank, spatwere fed with Chaetoceros spp., Skeletonema costatum, Thalassiosira, Nitzschia spp. and otherphytoflagellates. In wild, the spat were stocked in netlon net cages in natural water, where noadditional feed was supplemented. Spat cultured in natural waters exhibited rapid growth of 62.5mm in 6 months with a growth rate of 10.2 mm/month.P R O D U C T I O N  S Y S T E M S164Prioritized species for Mariculture in IndiaGROW OUTBottom culture and off bottom culture are the two culture practices followed for the oyster culture.Off bottom culture methods include rack and string or ren culture, where oyster shell is used as renfor spat collection. This method is suitable for shallow estuaries, bays and back waters of 1-1.25 mdepth. Rack is a fixed structure from which shell strings are suspended for the collection of spat. Theestimated production is 80 t/ha/yr for a period of 7-10 months of culture. In rack and tray method,cultch free nursery reared spat of 25 mm size are transferred to trays (40 x 40 x 10 cm) @ 150to 200 spat/tray. The tray is knitted with synthetic twine of suitable mesh size and suspended fromrack. Once the shell grows to a size of 50 mm, it can be transferred to bigger rectangular trays andagain suspended from racks. The estimated production is 120 t/ha/yr. In stake culture, stakes holdthe shells with spat. In this system, nursery rearing is carried out for 2 months and grow out iscontinued for 10 months. The estimated production is 20 t/ha. Raft culture is an oyster farmingmethod suitable for sheltered bays with depth more than 5 m. So far this method has not been triedin India. In long line culture, long ropes or cables are anchored at each end and are supported atintervals by floats. This farming method is practiced in deeper waters.FOOD AND FEEDINGThis oyster feeds on organic detritus and phytoplankton (mainly diatom and dinoflagellates) byfiltering sea water with the ciliary action of its gills.GROWTH RATEGrowth depends on food availability and environmental factors like temperature and salinity. Fastgrowth of spat occurs during the first three months. An average size of 87 mm is reached at the endof one year with a growth rate of 12.6 mm/month.DISEASES AND CONTROL MEASURESMultinucleated Sphere Unknown (MSX) disease caused by single-celled parasite, Haplosporidiumnelson; Oyster trematode disease caused by Gymnophallid metacercariae; Metacercaria infectioncaused by sporocyst; Bucephalosis infection caused by cercariae of Bucephalus has been reportedin C. madrasensis. In addition, Vibrio alginolyticus, V. parahaemolyticus and V. harveyi are thedominant bacterial flora infecting the backwater oyster. Reports are available on the presence ofprotozoan parasite Perkinsus beihaiensis in Crassostrea madrasensis from the Indian subcontinent,which caused mass mortalities in wild and farmed bivalve populations.165PRODUCTIONEstimated world production of oyster is one million tonnes per annum. USA, Japan and Koreaare largest producers of oyster through culture.MARKET AND TRADEMajor oyster market in the world is represented by four countries namely, South Korea, Japan,USA and France. Global trade in oyster products are in the form of fresh, chilled, frozen, cannedin brine, smoked, salted and dried oysters to the tune of 3,00,000 mt. Small scale farming of edibleoyster is practiced to meet the domestic demand in India. However oyster shell powder is exportedto the Arab countries. Edible oysters are usually marketed as live oysters with shell, shucked oystermeat, frozen oyster meat and canned oyster meat. Value added products suitable for the Indiandomestic market viz., oyster pickle, dried oyster, smoked oyster in oil, canned oyster in brine,minced meat products, battered and breaded IQF meat, soups, oyster chowder, and oyster extractsetc. have also been developed.Though mass scale production has been achieved successfully in the hatchery, heavy mortalitydue to bacterial, fungal or viral diseases are common. Hence studies on larval diseases and theircontrol measures need to be undertaken to ensure higher survival in production systems. In addition,consumer preference, market structure and marketing channel needs to be studied. Oyster cultureis labour intensive. In order to ameliorate the non availability of skilled labour and increasing labourcost there is an urgent need for mechanization of the post harvesting process. Environmental monitoringof shellfish culture areas need to be strictly followed since these areas are mostly exposed to bacterial,industrial and domestic sewage pollution.India is blessed with good oyster resources which have small pockets of good demand. Howeverthe future of edible oyster mariculture depends on the successful development of its market throughoutthe country as well as exploring its export potential.C H A L L E N G E S  T O  M A R I C U L T U R EF U T U R E  P R O S P E C T SP R O D U C T I O N ,  M A R K E T  A N D  T R A D E166Prioritized species for Mariculture in IndiaBaheerathi, C. G. and Revathi, K. 2013. Bacterial contaminants in Crassostrea madrasensis harvestedfrom Muttukadu Backwaters. Indian J. Applied & Pure Bio., 28(1): 91-94.CMFRI. 1993.  Overseas market prospect for oyster meat and oyster products. Mar. Fish. Info. Serv.Tech. Ext. Ser. (125): 17-21.Ford, S. E. and Haskin, H. H. 1988. Management strategies for MSX (Haplosporidium nelsoni)disease in eastern oysters Amer. Fish. Soc. Spec. Publ., 18: 67-78.Ford, S. E. and Tripp, M. R. 1993. Diseases and disease mechanisms. J. Shellfish. Dis., 18: 52-68.Huber, M. 2010. Compendium of bivalves. A full-color guide to 3300 of the world's marine bivalves.A status on Bivalvia after 250 years of research. ConchBooks Publishers, Hackenheim, 901 pp.Joseph, M. M. 1978. Observations on the larval trematode Bucephalus sp. parasite in the oysterCrassostrea madrasensis. J. Invertebr. Pathol., 32(3): 381-383.Kripa, V. and Appukuttan, K. K. 2003. Marine Bivalves. In: Modayil, M. J. and Jayaprakash, A. A.(Eds.), Status of exploited marine fishery resources of India. CMFRI, Cochin, p.211-220.Laxmilatha, P., Surendranathan, V. G., Sivadasan, M. P. and Ramachandran, N. P.  2011. Productionand growth of cultchless oyster spat of Crassostrea madrasensis (Preston) for single oyster culture.Mar. Fish. Info. Serv. Tech. Ext. Ser. (207): 8-11.Mahadevan, S., Nayar, K. N. and Muthiah, P. 1980. Oyster farming. Mar. Fish. Info. Serv. Tech. Ext. Ser. (26): 1-3.Mahalinga and Kripa, V. 2007. The impact of suspended culture of the edible oyster Crassostreamadrasensis (Preston) on benthic faunal assemblages. J. Mar. Biol. Ass. India, 49 (1): 47-50.Manmadhan Nair, K. R. and Girija, S. 1993. Edible oysters-Present status of product developmentand domestic market potential in India. Mar. Fish. Info. Serv. Tech. Ext. Ser. (125): 10-17.Muthiah, P., Rajapandian, M. E., Ramadoss, K., Appukuttan, K. K. and Velayudhan, T. S. 2000. Theedible oyster culture. Marine Fisheries Research and Management. CMFRI; Kochi, Kochi, p. 786-801.Nayar, K. N., Satyanarayana Rao, K., Rajapandian, M. E., Gopinathan, C. P. and Gandhi, A. D.1987. Production of Oyster seed in a hatchery system. CMFRI Bulletin, p. 52-58.Nayar, K. N., Rajapandian, M. E., Gandhi, D. and Gopinathan, P. 1984. Larval rearing and productionof spat of the oyster Crassostrea madrasensis (Preston) in an experimental hatchery. Indian J. Fish.,31(2): 233- 243.Rajapandian, M. E. and Rajan, C. T. 1989. Biological aspects of oysters.  Bull. Cent. Mar. Fish. Res.Inst., 38: 30-39.Rao, K. S. 1987. Taxonomy of Indian Oysters.  In: Nayar, K. N. and Mahadevan, S. (Eds.), Oysterculture-status and prospects. CMFRI Special Publication, 88: 1-6.Rao, K. V. 1983. Induced spawning of the adults and laboratory rearing of the larvae of the edibleoyster Crassostrea madrasensis (Preston). Proc. Symp. Coastal Aquaculture, 2: 479-482.Sanil N. K., Suja, G., Lijo, J. and Vijayan K. K. 2012. First report of Perkinsus beihaiensis in Crassostreamadrasensis from the Indian subcontinent. Dis. Aquat. Org., 98: 209-220.S U G G E S T E D  R E A D I N G

Crassostrea madrasensis (Preston, 1916)*

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Crassostrea madrasensis (Preston, 1916)*

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