Molluscs contribute 18.1% to the total world

aquaculture production, in which clams form 21.9%. China,

Republic of Korea and Malaysia are the leading clam

producing countries. In India, clams are the most important

among the bivalve resources. They are distributed in the

backwaters and estuaries along the Indian coast 

Muthiah, P

CMFRI Digital Repository

MOLLUSCAN CULTURE CLAMIC A RP. M u th ia hTuticorin Research Centre of Central Marine Fisheries Research Institute,TuticorinPublished by :Tamilnadu Veterinary and Animal Sciences University, Chennai Manonmaniam Sundaranar University, Tirunelveli University of Madras, Chennai Annamalai University, Chidambaram Aquaculture Foundation of India, ChennaiIntroductionM o l lu s c s  c o n t r ib u te  1 8 .1%  to  th e  to ta l  w o r ld  aquaculture production, in which clams form 21.9%. China, Repub lic  o f  Korea and Malaysia are the leading c lam producing countries. In India, clams are the most important among the b ivalve resources. They are distributed in the b a c k w a te rs  a n d  e s tu a r ie s  a lo n g  the  In d ia n  c o a s t .  Commercia lly exploited and cultivable clams are M ete tr ix  casta. M. m eretrix , Paphia malabarica, Anadara granosa  and V il lo h ta  c y p r in o id e s  a long  th e  m a in land . G ood resources of g ian t c lams are ex is t ing  in Andaman and Nicobar Islands and Lakshadweep.Species of clamsM e re tr ix  cas ta (Chemnitz)Shell th ick ,  sm ooth , devo id  o f  any scu ltu re  and triangularly ovate. Outer surface pale yellowish brown tinted with dark grey posteriorly and very faintly rayed with grayish radial lines.It occurs in great abundance in all estuar ies and backwaters along the west coast. Rich beds of this species exist in Puiicate lake, Vellar, Athankara i and Pinnakayal estuaries along east coast. Fishing is done throughout the year and sum m er month during low tide is the best period. A fisher woman collects 300-400 c lams per day and even 2000 -  3000 if the  bed is dense.The major spawning season is from September to March. The size at f irs t maturity is 17 mm and the clam grows to 35-40 mm in length. Studies on age and growth indicated that it a tta ins 36.5 mm in s ix months, 46.6 mm in one year and 56.5 mm in three years. A long east coast, s p a w n in g  ta k e s  p la c e  tw ic e  a ye a r ,  A p r i i -M a y  and  S e p te m b e r .  N a tu ra l  spa t s e t t le m e n t  o c c u rs  d u r in g  Septem ber-Decem ber and April-May.The meat contains good amount of protein (7.98 to 12.29%) and minerals. The fat content varied from 0.57 -  1.07%. The in jection o f insulin led to  increase o f  glycogen in d ig e s t iv e  d iv e r t ic u la  and  fo o t ,  s to re h o u s e s  o f carbohydrates. The saponification value of male clam was higher whereas iodine number was higher in the fa t  of females.It is one of potential clams fo r  culture. Good seed resources (197 t) are availab le in Kalinadi, M ulky and Gurpur estuaries. The CMFR Institute has standardized the technique for seed production through hatchery system. On day 9, settlement occurred at 181 pm size and in one month, a maximum length o f 1.2 mm was attained. During 1996-98, 3,03 million seeds o f M. cas/a were produced with settlement percentage of 2.3 -16.3% from 15 spawnings in the hatchery.Field culture experiments conducted in Mulky estuary showed that the clams had grown from 17.9 to 31.5 mm in4 months w ith survival percentage of 48.2%. At Ve lla r  estuary, 7.33 mm weighing 0.25 g had grown to 41.5 mm with 31.34 g in one year.M e re tr ix  m e re t r ix  ( Linnaeus) (Great clam)The shell is triangularly ovate, thick, usually smooth sometimes weakly concentrically sculptured. The lunule is not well defined and the ligament is usually short. The hinge area is th ick bearing 3 cardinal teeth.This 'great clam' is d istr ibuted in large quantities in Kalleadevi and Bhatea creek in Maharashtra; Chaporal, Sal. Mandovi and Zuari estuaries in Goa; Kalinadi, Tadri and coondapur in Karnataka and in Tellicherry coastal area and Ash tam udi lake in Kerala. A long the east coast, it occurs in major estuaries o f Tamil Nadu, Pulicat lake and Chilka lake on the seaward side.Though the clams are fished throughout the year, they are indiscrim inately exploited during August and April. The flesh is mainly used for local consumption. Since they  are exploited before spawning, the meat is tastier.The spawning period o f the clam is September and May along the eas t coast. At Ve lla r estuary, the spawning extends from February -  September, whereas at Tuticorin, two peak o f spawnings are during January-February and September. The life span is estimated as 7-8 years with size range o f 14.6 - 91 mm. The growth of tagged c lams of size 14.6 to 88 mm registered a growth rate of 0,15 mm to2.2 mm. Seeds o f M. meretrix  could not be collected from estuaries.C M FR In s t i tu te  succeeded in 1988 in evo lv ing  hatchery techn iques for seed production. Spat settlement at 184 fim occurred in the hatchery between S'” to 12*'’ day a fte r fertil ization. Average size o f 2.9 mm was attained on day 75 with surv iva l rate ranging from 7.4 to 15.6% from initial larval stage. During 1996-97, 0.254 million seed were produced with percentage of seed production varying from 2.8 to 18.8%. The hatchery produced young clams of 7.8 mm had grown to  14.5 mm in 5 months.The growth of 2 mm seed exposed to salinities 6.7 to 33.5 ppt indicated that high growth rate (189.65%) was obtained in 20 ppt.M arc ia  o p im a  Gmelln ( Baby clam )The shell is m ore or less elongately ovate with the umbone inclined forwards. The surface is e ither smooth or finely concentrically striated. The lunue and the area are clearly defined. The hinge margin bears three thick diverging teeth. The outer surface o f shell polished pale yellowish brown or straw coloured and rayed with purplish grey markings. The photograph is given in cover pageIt occurs in great abundance along the estuaries and backwaters of South India. It prefers r iver-mouth and is found burrowing in mudflats of Gulf  o f  Mannar, Ashtam udi Lake, Ratnagiri, North Kanara, Bombay and Chennai coasts. The estimated resource in Ashtamudi Lake was 6000-6500 t. Clam fishing is done throughout the year with peak in February-March. The methods of f ish ing are handpicking, scoop net and dredging. A canoe with 2 f ishermen takes about 200-300 kg of clams per day. Good fishery also exists in Batya creek and Kalbadevi creek in Ratnagiri. The size of the clams ranged from 5-44 mm. It grows to 26-33.8 mm in one year and the life span is about 3 years. Sexual maturity is observed in the size 11-12 mm o f 3 months old. Spawning season is December to February.Five percent of the total clam production is consumed locally and the rest are exported. The shells are util ized for calcium carbide industry. Considering the vast resources and its export value, the seed production through hatchery system was evolved by CMFR Institute. Spat settlem ent occurred on day 9 at 273 pm. On day 29. the mean size was 2 mm which increased to 2.38 mm on 45"’ day. The clam seed reared further in nursery atta ined a size o f 11.5 mm in 4 months. Through 7 spawnings, tota lly 5.4 lakhs spat were produced and the percentage o f settlement varied from 13.9 to 56.2.Paphia m a la b a r ica  ChemnitzThe shell is more or less elongate, smooth o r concentrica lly sculptured with narrow and elongated lunule. The hingearea is short with narrowly diverging teeth. The pallial sinus is moderately deep and ‘U’ shaped.Good f ishe ry  ex is ts  in Karwar, north Kanara and Ashtamudi lake in Kerala. It usually occurs in depths upto 4 metres in sandy mud. The fishery extends throughout the year w ith a peak between January and July. During lowtide fishermen take small scoop nets in one hand against the current and the clams are pushed into the net with the other hand. Good quantities are collected during full and new moon days. Each individual collects 40 kg/day and about 1000 kg are landed in a centre daily.The size at first maturity is 20 mm. The peak spawning period is from October to February. This species attains a length of 36.3 mm in 6 months and 48.1 mm in one year. Seeds of this clam could not be collected in natural beds. Hence seeds were successfully produced in the hatchery. Settlement occurred on day 9 and completed on day12 at 286 (im. In 3 months, the seed had grown to a mean length of 2.9 mm with a maximum length o f 4.2 mm. The higher growth rate (305%) of this clam was observed in 28 ppt salinity.V illo rita  c y p r in o id s  ( Gray) ( Black-clam )Shell thick, ovately triangular with strong concentric ridges, umbones prominent, well elevated, hinge margin short and thick with three oblique cardinal teeth. Pallial sinus small, lunule narrow and ligament large. Periostracum dark olive brown to blackish brown.In the northern region it occurs in Siridavo, Savoi, Amonen and Naibag in Goa. Majority o f  the stock is from Kalinadi, Aghnashiri and Gurupur estuaries in Karnataka, Vembanad, Ashtamudi and Kodungathiore lakes in Kerala, In Vembanad lake, the resource was estimated as 21,490 -  27,0001. At Ashtamudi, Kumbalattu kayal Is very rich with this clam. The annual production is estimated as 6000 t and the present stock in Kayal is 12,000 t in a bed covering 50 ha. The fishing season is from February to April, 75-90 canoes are employed every day. Further 82.1 t of seed resources is available in Kalinadi, Mulky and Gurpur estuaries in Karnataka.5In Cochin, the spawning occurs twice a year i.e. May- September and January -  March. It attains sexual maturity at 11-15 mm size. In nature, it grows to 30 mm length in one year. In Nethravathi estuary, the spawning season is from October to May. Vast beds occur in the farthest ends of backwaters where salinity is below 15 ppt. Young clams of 15-20 mm to lerate 0.87 to 29.8 ppt whereas 40-50 mm clams to lerate 4.73 to 27.1 ppt. However it survives in freshwater in Kerala and Karnataka estuaries.The protein content of the meat is 10.09%, fa t 2.52% and glycogen 6.68%. V. cyprinoides  was also induced to spawn in the laboratory and spat settlement occurred on 11 day in experimental rearing. This observation indicated tha t la rge  sca le  seed p roduc t ion  is poss ib le  th rough  hatchery system like in other clams.Anadara  g ra n o sa {  Linnaeus) Blood clamShell of th is species thick and attains large size. The shell is strongly ridged. It occurs in abundance in Kakinada bay, at 4 m depth. The beds exist on a bottom o f muddy sand and also sandy backwaters o f the east coast. A t Kakinada, heavy catches were reported in March -  April and August -  September. The catch per unit effort varied from 14.7 to 40.4 kg. The length o f the clams varied from 15 -  71.2 mm. The total catch varied from 104 to 222 t, in the natural bed covering an area of 44 km^ in Andhra coast. Total annual production was estimated as 2000 t of which 10 % is used fo r  human food. Fishing is by handpicking.It breeds throughout the year with peak spawning from January to April. It grows to a length o f 31,5 mm in 1" year and 49.5 mm in 2"" year.Field culture experiments were carried out with 24.3 mm size seed collected from nature. The production rate ranged from 38 to 42 t/ha. The survival rate was 88.6% with flesh weighing 20%,In 1988, th rough  hatchery sys tem , 8090 seed of b lood c lam  w e re  s u c c e s s fu l ly  p ro d u ce d .  S e t t le m e n toccurred on IB"* day. The 2.4 mm young clams (2 months old) reared in cages grew to 20 mm in 5 months with 72% survival. H igher growth rate of 419.2% was observed in the juveniles reared in 25 ppt salinity.Clam fisheryTotally 45 ,412 t o f  clams are landed annually and only5 -10% is util ized fo r  human consumption. The shells ,a by-product of c lam fishery are sold to carbide, cement and lime industries. Apart from shells o f  live clams, subfossil deposits o f  c lam shells to the tune o f 41,445 to 69,306 tons are being regu larly  exploited in Vembanad lake. The shells are also used in paper, leather, tiles and rayon industries and as shellgr it  fo r  poultry.From 1981, clam meat is exported as frozen, canned and as pickles to Japan, Oman and UAE. The quantity of export o f  clam meat varied from 371 to 1396 t.Three incidences of paralytic shellf ish poisoning has been reported due to consumption of clams collected from polluted areas. Hence proper monitoring of the clam beds and sanitary measures have to be implemented for arresting the pollution o f the clam beds. This will make the clams safe for human consumption.Clams, being f i l te r feeders, harbour pathogenic and faecal co l ifo rm s. The in testine conta ins  mud and sand imparting m uddy f lavour and gr it t iness to the meat . In depura tion process, the harvested clam is c leaned in f iltered seaw ater fo r  18- 24 hours followed by chlorination (5 ppm ) and and mainta ined fo r  2hrs. This led to the removal of pathogenic bacteria and sand to negligible levels. Hence depuration has to be made a mandatory requirement before marketing.Proper Indian standards have to be also evolved for processing and canning the clam meat since there is no Indian standard fo r  canning of clams.7The exp lo ited size group o f these clams is be low 20 mm. Due to  the  e x p o r t  o f  c lam  m eat, th e re  is indiscriminate f ishing for small clams. Over 1000 numbers of small clams o f 25-30 mm are required for 1 l<g of meat whereas the same could be obtained from 460 numbers of 35 - 40 mm clams. Thus the exploitation of small size clams adversely affects the future resources and production. So mesh size o f hand dredge to 30 mm has to be regulated to prevent the exploitation of smaller clams. In the pretext of mining the sub-fossil deposits, nearly live clam beds are also dredged. Hence the beds o f live clam have to be excluded from mining. Licensing system for clam fishing has to be adopted along the maritime states, as fo llowed in Vembanad lake, so as to have sustainable yield. For each area fishing season has to be adhered to rather than fishing throughout the year.Clam c u l tu reSeed is one of the prime requisites for culture. In India, seed resource of 1 9 7 1 and 82.1 t has been estimated for Meretrix casta  and Villoritta cyprino ides  respectively. But seed o f  M. m e re tr ix ,  M a rc ia  op im a  and P a p h ia  m a la b a r ic a  c o u ld  no t be re c o rd e d  in n a tu ra l  beds . Considering this, the CMFR institute has developed suitable techniques fo r  mass seed production  through she llf ish  hatchery at Tuticorin, with annual production capacity o f  2 to 3 million clam seeds. Many of the European countries are mainly depending on the seed supply from hatcheries. In the Southeast Asian countries, seed required for culture is met from natural resources. Recently, because of raising demand in Taiwan, 15 hatcheries have been established to supply seed o f M eretrix  lusoria.In Malaysia, Thailand and China wild seeds of blood clams are used fo r  farming in pens erected in intertidal mud flats with average production o f 40t/ha. The production rate8of A. granosa  in the Kakinada bay compares well with those reported from Malaysia and Thailand. The Venerid clams are amenable candidate species fo r  farming. In France, culture o f Manila clam {Ruditapes philippinarum) is being carried out in in tertidal enclosures. The annual production is 300 t. O f recen t Meretrix lusoria  is intensively cultured in ponds used fo r  shrim p cu ltu re . Thus the techn ica l feasibility o f  culture of M. casta has been established through experimental tr ia ls. In India, vast intertidal areas as well as ponds used fo r  shrimp farming could be effectively used for clam culture. Pilot projects have to be undertaken by th e  F is h e r ie s  D e p a r tm e n ts  o f  m a r i t im e  s ta te s  to  demonstrate the economic feasib ility  of clam culture.There is g rea t demand for dried adductor muscle of giant clams apart from the edibility of the meat. In Papua New Guinea and Austra lia  a ttem pts are being made to produce seed and culture of giant clam. Having the potential resources and area for culture, major thrust has to be given for the seed production and culture of giant clam in India.

Molluscan Culture: Clam

http://eprints.cmfri.org.in/9788/1/Molluscan_Culture_Muthiah.pdf

Molluscan Culture: Clam

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