Molluscan Aquaculture Submitted to Submitted byProf. (Dr.) B Madhusoodana Kurup Judine John ChackoDirector, 4th SemeseterSchool of Industrial Fisheries (SIF), MSc. Industrial Fisheries,CUSAT S.I.F
Introduction Mariculture is the rearing of aquatic organisms under controlled or semi controlled condition in coastal and offshore waters where salinity is maximal and not subject to significant daily or seasonal variation. Mollusk farming is a type of mariculture done in open sea water on racks, rafts or longlines. Oysters, calms, mussels ,scallops and abalones are the major group of mollusks farmed.
The commercial imporstance of mollusc culture is food security, pearl production, lime manufacture etc.. In 1984, molluscs accounted for approximately 35% of the total production of coastal aquaculture in terms of gross weight in the region (Shang, 1986).
Global status In 2006, molluscs accounted for the second- largest share, 14.1 million tonnes (27 percent of total production), worth US$11.9 billion. (SOFIA 2008). Major countries farming mollusk are China, Indonesia, Malaysia, Philippines, Singapore, South Korea, Sri lanka, Taiwan and Thailand.
Site Selection Success of farming depends on proper site selection. Area location- Cockles, Clams culture ground should be located in areas where strong winds do not prevail. Culture systems such as poles, racks are placed in low tide area. Water depth – Water depth range from 1- 15 m as mean tide level. Water movement – Water current of 0.02 -0.1 m/sec suitable for bottom culture and stronger for hanging methods. Turbidity – Minimum sechhi disc reading 15cm.
Salinity – 24-31 ppt Bottom slope – 5-15 ˚ seaward slope is preferred for bottom culture.Muddy bottom for mussels and rocky or coralline substrate for oyester. Food availability – Phytoplankton availability. Pollution – Toxic waste can contaminate mollusk meat so pollution free areas should be selected.
Cultured Species Perna viridis Crassostrea madrasensis
Species description Oysters Oysters are one of the most valued seafoods and are farmed extensively.Nearly 12 species are commercially popular. In India , Crassostrea madrasensis , C gryphoides, C, rivularis and Saccostrea cucullata are the main species and C .madrasensis is the most preffered for farming. Racks and rens are used for farming and culture period is 7- 10 months C.gryphoides- 17cm ; Saccostrea cucculata -20cm Estimated average production 2.5 tonnes from 500 rens. (BFFDA)
Mussels Mussel farming is the one of the popular mariculture operation in the temperate countries. Cultured 9 different species belonging to genus Perna and Mytilus. In India 2 species Perna viridis and P. indica are extensively farmed. Culture practice – Pole culture, Rack culture and raft culture Farming up to 4-8 months. P. indica and P . viridis reach about 63cm and 54cm length in one year. Estimated average production is 15kg/m rope/5 months.
Pearl Oyster The pearl oyster belong to the genus Pinctada. Six species are found in India; Pinctada margeritifera, P.chenanitzii, P.sugillata, P.anomioides and P.atropurpurea. The pearl oyster are reared for production of cultured pearls. The nucleues implanted oysters grow in the farm and secrete the mother of pearl around the nucleus. Prevailing culture methods are Raft culture and on bottom culture and cages are used to protect oyster.
Pearl implantation1. Selection and conditioning 1.5 to 2 yr old oyster with not less than 25gm are selected for implantation. Oysters are arranged in a container with its hinge point downwards. Narcotization of selected oyster by sprinkling menthol in the seawater. Insertion of a small wooden peg between the 2 valves to facilitate nucleus implantation.2. Preparation of graft tissue Select healthy non narcotizd oyster and cut the mantle strip into 5 cm length and 0.5cm width. Remove mucous and mussel from the mantle and cut the mantle strip into 20 – 25 pieces of 2-3 mm squares Keep cell live by adding azumin/eosin solution in sterilised sea water
Implantation3. Implantation The graft mantle piece is placed in th gonad near the intestinal loop through an incision and placing the sterilized nucleus on the graft mantl piece.4. Convalescence Placing the implanted oyster in fresh seawater with mild circulation for 2-3days. Maintaining water quality by water exchange. Removing dead oysters and shifting the healthy implanted oysters to the natural environment.
Clams Clams or cockles for a valued item of food in many countries. Clams under commercial production are Venerupsis sp., Meretrix sp. , Mercentrica sp. and Anadra sp. And in India the important species are Villorita cyprinoids, Paphia malabarica, Meritrix casta and Anadra granosa. Simplest system of culture is the transplantation of seed growing beds with sandy bottom in the shallow intertidal areas.Pens are also used. Experimental culture of Anadara granosa , Villorita cyprinoids and Meretrix meritrix were done in Kakinada, Karnataka and Kerala respectively. Average production rate is 39-41.6 tonnes/ ha/ 5.5months for the blood clam culture.
Scallops Commercial scale production is limited mainly to China and Japan. The major species cultured are Chlamys barrei, C.nobills, Placopecten magellanicus and Argopecten irradians. Grow out is by planting in suitable beds and spats are released during summer months. Stocking density – 5-6nos./m2. In longline and raft system stocking density is 20 nos./compartment. Thy reach marketable size in 1.5-2 yrs.
Abalones (Gastropod) Abalones have soft meat and are capable of producing good quality rainbow colour pearls. USA , Mexico , South Africa, Australia , China, Taiwan, Ireland etc are the major abalone farming countries. India has not yet started farming abalones commercially. Babylonia spirata(whelk) is a common species cultured. Bottom culture with cages are used for farming. Stocking density is 150 larvae /litre and growth of juvniles is 0.06mm/day Culture period is 18 months were the organism attain 1010g weight.
Farming methods Basic method Bottom culture or broadcast technique Off bottom culture technique Stake or pole method Rack Raft Longline
Bottom culture Mainly done in Phillipines, USA, Holland and France. Simplest way of farming Oyster and Clam. Oyster shells and bamboo splits are used as spat collectors or clutches. Clams are protected from the predators through the use of screned boxes and trays with net coverings.
Pole or Stake culture France and Philippines are the major countries doing pole or stake culture. Oak or bamboo poles are used for stake culture. Poles with 3 m length and 20cm diameter are driven into the sea bed with 1-2 m exposed above the ground and spaced 1 m apart. Seed or spats are wrapped around the poles. Harvesting is done after 5-7months by pulling up the pole and the mussels are striped off using an iron rod.
Rack or Ren methodRack and string method The racks are constructed at 1-1.25m 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 0.5m above the water level. Nylon ropes or strings with cocofibres or empty oyster shells attached at 10 cm interval. The spat will attach the substrate and grows.Rack and tray Cultch free spat are transferred to 40x40x10cm size trays at a density of 150-200 seed /tray. The tray is suspended from rack.
Raft method In raft mthod, frames are floated using any floating structures or rafts and are held in a tray or stringed. Raft can be of any shape or material , usually oil drums are used as floats. Rafts are anchored to the bottom and each raft carries 200-300 hanged ropes. Harvesting is done by pulling up the ropes and giving a vigorous shake to remove the oysters.
Long line method Long line culture is an alternative to raft culture where areas less protected from wave action. A long line is supported by a series of small floats joined by a cable or chain and anchored at the bottom on both end is employed. Spats collected are suspended on ropes or strings on the line.
Depuration The process of purification by which the mussels are rendered free of harmful materials or to remove toxic metals is called depuration. Depuration can be done simply by starving the bivalves in clean and filtered sea water for a certain period of time.
References Agarval, V.P, 2000. Aquaculture Science, S.R Scientific Publication, Agra , 321-341 p. Narasimham, K.A, Molluscan fisheries of India, B.R Publishing Corporation, Delhi, 56- 98 p. John, S.L, 1998. Aquaculture, Farming aquatic plants and animals, Blacwell publishing ,USA, 443-465 p. Handbook of fisheries and aquaculture , 2006 ,ICAR, New Delhi, 406-422 p. www.fao.org Molluscan aquaculture practices.