Pearl Culture

April 4, 2018 | Author: morisrav23 | Category: Pearl, Oyster, Atrium (Heart), Heart, Anatomical Terms Of Location


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PEARL AND PEARL CULTUREOYSTER FARMING TABLE OF CONTENTS Prepared for the Pearl Oyster Farming and Pearl Culture Training Course conducted by the Central Marine Fisheries Research Institute at Tuticorin, India and organized by the Regional Seafarming Development and Demonstration Project (RAS/90/002) February 1991 Training Manual 8 PREFACE Pearls, one of the highly esteemed gems, are very valuable due to the high demand and prices for them. Several countries bordering the Indian and Pacific Oceans and some countries along the Eastern Atlantic Ocean have pearl oyster resources. Many of these countries, particularly those in Asia, are very much interested in pearl oyster farming and pearl culture. Japan stands foremost in the two fields having developed technologies and innovations in the field. The techniques of pearl oyster farming and pearl culture are not widely known. There is a need to promote more widely the techniques and relevant information on the bionomics of pearl oysters. In India, interest in pearl culture began at the start of this century. Several studies have been conducted by the Madras Fisheries Department in the 1930s. In 1972, the Central Marine Fisheries Research Institute (CMFRI) took up intensive research on pearl culture at Tuticorin achieving a breakthrough in July 1973 when it produced free spherical cultured pearls by employing the mantle graft implementation technique. Since then intensive research has been carried out by the Institute on pearl formation, pearl oyster biology and ecology, and hatchery techniques for production of pearl oyster seed. Considerable information of applied value has been obtained. The development of the pearl oyster hatchery technology in India in 1981 opened the way for large and commercial scale culture of this bivalve species. Based on the technical know-how provided by the CMFRI, a company has been established at Tuticorin to produce cultured pearls. In view of the keen-interest shown by countries in the region, the FAO/UNDP Regional Seafarming Development and Demonstration Project (RAS/90/002) requested the Indian Council of Agricultural Research (ICAR), New Delhi to conduct a training programme on "Pearl Oyster Farming and Pearl Culture" at the Central Marine Fisheries Research Institute in Tuticorin, to train personnel from different countries. In line with this training course, this training manual was prepared. This manual deals with various aspects of pearl oysters, pearl oyster farming, pearl production technology, etc. The Manual is designed for technicians as well as entrepreneurs. The effort by Mr. A. Chellam, Dr. A.C.C. Victor, Mr. S. Dharmaraj, Mr. T.S. Velayudhan and Dr. K. Satyanaryana Rao in preparing and editing the manual is acknowledged. I would like to thank Mr. Chen Foo Yan, Coordinator of the Seafarming Development and Demonstration Project, and his staff, particularly Mr. Pedro Bueno, Mr. Alessandro Lovatelli and Prof. H.P.C. Shetty for further editing and publishing the manual. Dr. P.S.B.R. James Director Central Marine Fisheries Research Institute, Cochin, India National Coordinator Regional Seafarming Development and Demonstration Project (RAS/90/002) Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics. This electronic document has been scanned using optical character recognition (OCR) software. FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version. TABLE OF CONTENTS PREFACE LIST OF FIGURES LIST OF PLATES CHAPTER I Pearl culture in India 1.1 Introduction CHAPTER II Taxonomy and distribution 2.1 2.2 Distribution CHAPTER III Morphology and anatomy 3.1 Morphology 3.1.1 3.1.2 Shell structure 3.2 Anatomy 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 3.2.8 3.2.9 3.2.10 Reproductive system CHAPTER IV Biology and ecology 4.1 Biology Mantle Foot gland system system system system system system Shell features Taxonomy Byssal Muscular Digestive Respiratory Circulatory Excretory Nervous 1.1.2 Ecology CHAPTER V and Age and feeding habits growth Hatchery techniques for seed production 5.2 Environmental conditions 6.3.2.1 6.1 Broodstock 5.3.4.1 Phytoplankton 5.4.2 Live food production 5.2.2 5.4.2 5.3 Aeration 5.3 5.3.1.5 6.4.1 Food 4.2 5.2.6 6.4.1.1 5.3 Reproduction 4.3 6.2.3 Broodstock handling and spawning 5.2 6.2.2.2.1 Selection of culture sites 6.4 Larvae and spat handling 5.2 4.4 6.2.7 Primary productivity Temperature Salinity Bottom Depth load current Larval Spat rearing conditions production Feeding Transplantation maintenance Spawning Fertilization Hatchery Seawater building management Silt Water .1.3 5.1 5.3.1.5 Survival CHAPTER VI Pearl oyster farming 6.4 5.1 Artificially reared spat 5.4 Early development and larval rearing 5.4. 2 7.1.1.6 Other organisms 7.5.4.2 7.2 Juvenile rearing CHAPTER VII Biofouling and predation 7.1 Biofouling organisms 7.1 9.1.1.4 Control measures 7.1 Culture operations CHAPTER IX The mantle 9.1.3 Predation CHAPTER VIII Culture system 8.4 Rearing methods 6.2 On-bottom culture 6.3 Supply of oysters 6.1.5 7.1 7.1 Culture 6.2 Boring organisms 7.2 Marginal Mantle mantle isthmus Fouling Boring Barnacles Ascidians Bryozoans Molluscs Sponges of mother oysters Raft culture .1 Mantle structure 9.4.4 7.6.3 Predator organisms 7.1.5.1.4.1 6.5 Rearing containers 6.3 7.1 7.4.4. 2 Cultured pearl formation CHAPTER XII Post-operation culture 12.3 9.1.3 Pearl harvesting CHAPTER XIV Improvement of pearl quality 14.1 14.9.1.1.6 Surgery CHAPTER XI Pearl formation 11.1 Development of implantation technique 13.1 Natural 11.1.4 Central mantle CHAPTER X The surgery 10.1 Measures for enhancing pearl quality 14.2 Nucleus retention and pearl production 13.3 10.4 10.5 14.1.2 14.1 10.1.2 10.6 Tool maintenance Oyster Narcotization Graft Oyster of tissue selection oyster preparation Implantation convalescence .5 10.4 14.3 14.1 Culture conditions CHAPTER XIII Production of cultured pearls Pallial mantle Surgical Selection Graft Conditioning of tissue for instruments Nucleus oysters preparation surgery pearl formation 13.1.1. Cont'd.= middle fold. 6. II. 2) oesophagus. III.= marginal mantle). 5. (A) Pinctada fucata and (B) Pinctada margaritifera. 14) nucleus implanted in the gonad. I. 4) left labial palp. Process of pearl formation. (A) mantle tissue when removed from an oyster (p. (B) half cultured pearl. (A) round and half natural pearls.F. (B) A FRP styrofoam buoy. 6) crystalline style.= nacreous layer.m. pearl oyster hatchery in Tuticorin.S. and P.= pallial mantle and m.2 Colour of pearls APPENDIX I REFERENCES LIST OF FIGURES Figure No. (B) Eye-spot larvae and (C) Transitional stage.F. C.14.= periostracal secretion. 7) liver.M. (1) Central mantle. Section of the shell of Pinctada fucata. 8) digestive diverticula. I. P.F. (E) Pinctada anomioides and (F) Pinctada atropurpurea.G. P. 7.I. Cont'd. (E) Early cleavage and (F) Morula stage.= periostracal groove. 3.L.= prismatic layer. LIST OF PLATES Plate No. (B) Male oyster while spawning and (C) Pyriform oocytes. (G) Trochophore larvae and (H) Straight-hinge larvae. World distribution of pearl oysters. Steps in graft tissue preparation. M. 2. (C) Pinctada chemnitzii and (D) Pinctada sugillata. Cont'd. 12) anal papilla.= conchiolin layer. 10) ascending intestine.L. (C) A mild steel buoy. and (C) round cultured pearl with an artificially implanted nucleus. 9) descending intestine. 5) left inner labial palp. 3) stomach. Anatomy of Pinctada fucata. (D) Fertilized oocytes. 11) rectum. 1) Mouth. (B) trimming of the margins to remove marginal mantle and inner muscular tissue. (A) Inside view of the C. Section of oyster mantle. . and (D) Oyster long-line culture system. Cont'd. (2) Pallial mantle.= shell fold.m.L. and N. 1. 4. S.F. (A) Umbo larvae. and (D) cutting of the ribbon into small sections. (3) Marginal mantle. 13) byssal gland.R. (A) Culture raft constructed with teak poles. (C) further trimming to obtain ribbons of pallial mantle.= inner fold. VIII. (A) A scuba diver diving to collect pearl oysters and (B) A culture raft floated with mild steel barrels. IV. Cont'd. Implantation of a pearl oyster. (A) A box-cage containing pearl oysters and (B) A frame netcage with oysters. Cont'd. (E) Plantigrade larvae and (F) spat. Cont'd. (C) Implantation of the nucleus. (D) Pediveliger larvae. Implantation of a pearl oyster.Cont'd. (C) A netcage for rearing oyster spat of 3–10 mm in size and (D) Rearing netcage covered with velon screen. a major pearl oyster predator. Cont'd. V. (A) Opening of the oyster valves and (B) Insertion of the graft tissue. (C) A culture raft with FRP styrofoam buoys and (D) Oyster long-line culture. VI. (C) Damage caused by a boring sponge and (D) Cymatium cingulatum. VII. Pearl oyster surgical instruments. and (D) General view o . (A) Fouling organisms on adult oysters and rearing cage and (B) Oysters heavily encrusted with barnacles. The pearl oyster resources in the two areas have been fished for pearls until the early 1960's. The oysters were reared in cages and induced to form pearls. Government of Tamil Nadu. production of cultured pearls by multiple implantation was successfully achieved. The Japanese grafted a piece of mantle with a small bead in a pearl oyster and reared the oyster in protected coastal waters with favourable environmental conditions..highly important for successful pearl culture -. Following this success an Ad-hoc Research Scheme on pearl culture under the Indian Council of Agricultural Research (ICAR) was implemented (from 1973–78) by the CMFRI in association with the Department of Fisheries. while they are sparsely distributed in the Gulf of Kutch. In October 1972 the Central Marine Fisheries Research Institute started a pearl culture research project at Tuticorin. These bivalves form large beds on hard substrata in the Gulf of Mannar. The pearl oyster fisheries are located in two main areas: 1) in the Gulf of Mannar off Tuticorin coast and 2) in the Gulf of Kutch on the northwest coast of the country. Hornell (1916) recommended that in order to maintain pearl fisheries profitably it was necessary to develop techniques to induce the Indian pearl oysters to form pearls by artificial means. Efforts in Gujarat did not meet success either. This is a delicate operation. That work managed to produce only two poorly shaped pearls and a half-pearl attached to the shell. Many attempts have been made to culture pearls in freshwater mussels.CHAPTER PEARL CULTURE IN INDIA 1.were investigated. These structures are secreted by the mantle (i. detritus. parasites. in the intertidal zone in the Gulf of Kutch. the skin) of pearl oysters in response to irritations caused by external or internal stimuli such as sand grains. success was achieved early in this century in Japan on the production of spherical cultured pearls. After considerable perseverance and study on the mode of pearl formation. The pearl oysters are found in two different environments in the two localities. India has one of the highest demand for pearls for setting in jewellry. This breakthrough was achieved by introducing a graft of the oyster mantle in the gonad of an adult specimen together with a shell bead nucleus. at depths up to 23 meters in the Gulf of Mannar. and is particularly famous for its pearl oyster resources which yield superb pearls. Research focused mainly on the biology and ecology of several species. the then Madras Government Fisheries Department carried out preliminary research at the Marine Biological Station in Krusdai Island. In response. Gulf of Mannar. During this Research Scheme.e.1 Introduction I Pearls have been known to mankind since the beginning of civilization. After surveying the pearl oyster resources and fisheries in the two Gulfs at the beginning of the century. molluscs eggs. Several aspects of pearl formation and pearl oyster biology and ecology -. . They are highly esteemed as gems for their beauty and splendour. and other foreign particles. In the 13th century the Chinese fixed small Buddha figures inside freshwater mussels which became covered with a pearly layer. Success came in July 1973 when a perfectly spherical pearl was produced. The CMFRI is making efforts to promote the pearl culture technology by conducting shortand long-term training programmes.The CMFRI also succeeded in artificially spawning Pinctada fucata. ecology and pearl oyster seed production through hatchery techniques. Scientific and technical personnel from fisheries institutes in all of the maritime states as well as from the Fisheries Faculties of Agricultural Universities are given the opportunity to be trained in these programmes. Since then other companies have became interested in taking up pearl culture on a commercial scale. such as taxonomy. and pearl oyster framing. Recently the CMFRI also produced seed of the black-lip pearl oyster. This manual covers various aspects of pearl oysters. To follow-up on the development of pearl culture technology. the Tamil Nadu Fisheries Development Corporation and the Southern Petro-chemical Industries Corporation Ltd. and producing seed in the laboratory by hatchery techniques. . rearing of larvae. anatomy. morphology. established in 1983 a company to produce cultured pearls. with the farm at Krusadai and the nucleus implantation centre at nearby Mandapam. Pinctada margaritifera which produces the highly valuable black pearl. This breakthrough is very important in light of the difficulty in obtaining sustained supplies of oysters from natural banks for culture purposes. P. sugillata (Reeve). anomioides (Reeve) and P. The posterior ear is fairly well developed. This pearl oyster is also known as the Black-lip pearl oyster due to the dark marginal colouration of the shell. a cavity below the anterior angle for the byssus. Pinctada chemnitzii (Philippi) . P. and usually a scaly surface of the outer shell valves. The width of the nacreous region at the hinge is about 2/3 that of the broadest part of the valves (Plate I B). Shell valves are moderately convex. margaritifera (Linnaeus). the long axis of the shell is at a right angle to the hinge. The anterior ear is larger than in the other species. the shell width is much longer than the height and the hinge angle is prominent and pronounced. The left valve is deeper than the right. and the byssal notch. In Pinctada spp.76. Members belonging to the Pteriidae family are characterized by a straight hinge with 1–2 small tooth-like thickening.1 Taxonomy II The true pearl oyster belongs to the genus Pinctada (Roding) under the family Pteriidae. P. Six species of pearl oysters. Externally. The byssal notch is broad. Pinctada margaritifera (Linnaeus) The hinge is shorter than the width of the shell and has no teeth. at the junction of the body of the shell and the ear. The anterior border of the shell extends in front of the anterior lobe. order Dysodonta. The nacreous layer is thick and has a bright golden-yellow metallic lustre (Plate I A). The anterior ear is well developed while the posterior ear and sinus are absent.CHAPTER TAXONOMY AND DISTRIBUTION 2. The family includes the pearl oysters belonging to the genus Pinctada and the winged oyster shells of the Pteria genus. the hinge is rather long and straight. one each at the anterior and posterior ends of the ligament. P. The outer surface of the shell valves is reddish or yellowishbrown with radiating rays of lighter colour. the left valve is slightly deeper than the right and there is a byssal notch on each valve at the base of the anterior ear. the shell is dark grayish-brown with radially disposed white spots. The nacreous layer is iridescent with a silvery lustre except distally where it is black. In Pteria spp. Their morphological characteristics are as follows: Pinctada fucata (Gould) The hinge is fairly long and its ratio to the broadest width of the shell is about 0.85 and that to the dorsoventral measurement is about 0. The posterior end of the shell meets the hinge almost at a right angle. Pinctada fucata (Gould). atropurpurea (Dunker) occur along the Indian coasts. Hinge teeth are present in both valves. chemnitzii (Philippi). is slit-like. . Pinctada sugillata (Reeve) The hinge is considerably shorter than the antero-posterior axis of the shell with a ratio of 1:1. The anteroposterior measurement is almost equal to the dorso-ventral measurement. The anterior ears are slightly bent towards the right. The anterior ear in both valves is small and the byssal notch is a moderately wide slit. The anterior and posterior hinge teeth are present. The nacreous layer is thin and bright.2–1. The hinge and dorso-ventral axis have a ratio of 1:1. The posterior ear is well developed and the convexity of the valves is less than in P. the former is small and rounded and the latter prominent and ridge-like. The convexity of the valves is not prominent. The posterior ear and the posterior sinus are well developed. Pinctada anomioides (Reeve) The hinge is shorter than the width of the broadest region of the antero-posterior axis of the shell with a ratio of 1:1.4. The posterior ear and sinus are absent. while the non-nacreous layer is yellowish-brown (Plate I C). The shell valves are translucent and externally yellowish or grayish. fucata.The hinge is almost as long as the antero-posterior measurement of the valves. The posterior ear and sinus are poorly developed. Hinge teeth are absent or poorly developed. The nacreous layer is slightly iridescent (Plate I E). especially that of the right valve. Some shells have faint radial markings. The shell valves are yellowish externally with about four or more light brownish radial markings from the umbo to the margin of the shell. The growth lines of the shell are broad. The anterior ear is moderately developed and the byssal notch at its base is deep.5.3. The shell valves are reddish-brown with six yellowish radial markings (Plate I D). The hinge teeth are small and the posterior one is slightly elongated. PLATE I. (A) Pinctada fucata and (B) Pinctada margaritifera. . The gold/silver-lip pearl oyster P. Although a number of species of pearl oysters have been identified. Burma. The black-lip pearl oyster. 2. translucent and moderately convex. P. They occur in several seas of the tropical belt and in the sub-tropical region. Pinctada atropurpurea (Dunker) The shell is roundish and its hinge narrow.PLATE I. Indonesia. Cont'd. only a few have been found to produce pearls of good quality and commercial value. Philippines and Papua New Guinea at depths ranging from low tide level to 80 m. fucata stand out. (C) Pinctada chemnitzii and (D) Pinctada sugillata. maxima. Of these. margaritifera is widely distributed in the Persian . The valves are thin. P. margaritifera and P. P. Thailand. maxima occurs along the north coast of Australia. The shell valves are copper coloured (Plate I F). A poorly developed anterior hinge tooth is present in some oysters.2 Distribution Pearl oysters of the genus Pinctada are widely distributed in the world. Venezuela and Western Pacific Ocean (Fig. P. Persian Gulf. Sudan. fucata occurs sporadically on loose sandy substratum attached to submerged objects in littoral waters. fucata has contributed to the pearl fisheries in the Gulf of Mannar and Gulf of Kutch. Southwestern part of the Indian Ocean. In the Gulf of Mannar. settlement of spat of P. French Polynesia. Andaman and Nicobar Islands. Indonesia.Gulf. anomioides has been observed on the ridges of rocks and corals. 1). In the Indian waters six species of pearl oysters occur but only P. fucata is distributed in the Red Sea. Australia. Japan. Red Sea. the pearl oysters occur in large numbers on the submerged rocky or hard substrata known as paars. Kerala coast. India. From Lakshadweep. Korea. large numbers of spat of P. China. margaritifera is confined mostly to the Andaman Islands where it is common in some places. . P. Papua New Guinea. fucata have been collected from mussel culture ropes. The blacklip pearl oyster. the pearl oysters are found as stray individuals on the intertidal reefs known as khaddas. The paars lie at depths of 12 to 25 m off the Tuticorin coast along a stretch of 70 km. The occurrence of this species is sporadic along the coasts of mainland India. In the Palk Bay. In the southwest coast of India at Vizhinjam. The pearl oyster P. Japan and the Pacific Ocean. In the Gulf of Kutch. World distribution of pearl oysters. (E) Pinctada anomioides and (F) Pinctada atropurpurea. . Cont'd.PLATE I. FIGURE 1. The adductor scar is elongated and sub-central. Its scar merges with that of the adductor scar. There are 12–15 insertion scars between the umbo and antero-ventral border. Besides these distinct scars.1 Morphology 3. The growth edge or projecting lamellae are laid down by the oyster at successive intervals on the distal border. The innermost nacreous or mother-of-pearl layer is composed of numerous fine lamellae of aragonite crystals (Fig. The pallial line and scars are caused by the insertion of the pallial muscles in fan-shaped bundles of fibres radiating outwards. It is reflected to join the surface of the ectoderm cells of the mantle edge in the longitudinal groove where it is secreted. transparent and extends beyond the calcareous matter. Elongated ridge-like teeth are present at the anterior and posterior ends of the ligament. The prismatic layer is deposited by the mantle epithelium near the free edge just behind the margin which forms the periostracum and many such layers on fusion are formed successively. 3.5 mm thick over the greater part.1. 2). The hinge is narrow and runs along the greater part of the straight dorsal edge. The non-nacreous border of the inner surface of the valves are characterized by brownish or reddish patches which coincide with the external rays. The very thin outer layer is uncalcified cuticular conchiolin layer or periostracum.2 Shell structure The shell is composed of three layers. This is an extremely delicate horny layer which allows the colour of the layer below to show through and usually becomes worn off in old shells.CHAPTER MORPHOLOGY AND ANATOMY 3. At the free margin of the shell the periostracum is very thin.1. each new one beneath the last.1 Shell features III The shell of Pinctada fucata is about 1. there is a narrow continuous insertion band confluent with the posterior and ventral edges of the adductor scars. as the shell grows. . The middle or prismatic layer shows a cellular structure formed of calcareous prisms or columns running vertically to the surface and appearing polygonal in section. 3).2 Foot The foot is highly mobile. It arises from the anterior region of the visceral mass nearly midway between the mouth and the intestinal lobe and the anterior branchiae flanking it on either side.2 Anatomy 3. The dorsal portion has more chromatopores while the ventral portion has the pedal groove.2.3 Byssal gland The byssus gland organ (Fig. .2. 3.L.1 Mantle The free edge of the mantle lobe is thick.= conchiolin layer.L. the central.= nacreous layer.2. 3) extending along the whole of the remaining length of the ventral surface of the foot. 3. The byssal gland lodges the common root of a bundle of stout. The major part of the foot is composed of a network of fibres running in various directions. It is extensively penetrated by blood spaces and the organ is highly contractible. a little away from the margin. C. Each pallial lobe may be divided into three parts. Each fibre of the byssus anchors the pearl oyster to rocks and other hard objects by means of a discoid attachment at the distal extremity. pigmented and fringed with branched tentacles. Section of the shell of Pinctada fucata. P.L. The anterior edge of the mouth of the byssal gland passes into the pedal groove (Fig.FIGURE 2. thus ensuring a wide range of movement. tongue-shaped organ capable of considerable elongation and contraction (Fig. 3. laterally compressed bronze-green fibres: the byssal threads. 3) is located ventrally at the proximal end of the foot.= prismatic layer. and N. distal or muscular and marginal mantle. The pallial edge of the mantle is attached to the shell. The mouth is a large. There are also muscle bundles running longitudinally down on each side of the principal filaments. the other composed of broad and massive semitranslucent fibres occupying the remainder of the mass. slit-like depression placed transversely between the anterior levator muscles of the foot (Fig.5 Digestive system The oesophagus. occupies a subcentral position anterior to where the posteroventral fold disappears midway along the floor. The head of the crystalline style projects out of the sac where it is formed and across the cavity of the stomach where it bears against an irregular area of cuticle known as the gastric shield (Fig. passing through the visceral mass to be attached to the valves behind the anterior levator scar. 3). It has two distinct regions. and grooved on the opposite side close to the mouth aperture. the descending and ascending portions and the rectum (Fig. 3. namely. 3). With the exception of heart and indistinct striations on larger portion of the adductor muscle. The posterior levators are short and insignificant. 3). flattened and oblique. They run within each ctenidial axis from end to end. It is a massive wedge-shaped bundle of muscle fibres. 3). the crystalline style. conceal the aperture of the mouth. The retractors of the foot are a pair of symmetrically disposed muscles lying in the horizontal plane of the body. one a narrow tendonous strip made up of white glistening fibres forming the posterior border. The contraction of the anterior levator causes the foot to be retracted and raised dorsally. The pallial muscles are retractable and together they constitute the orbicular muscle of the mantle. the labial palps. Two horizontal lips. close to the dorsal edge. the ascending intestine turns sharply upwards. The narrow end points upwards and lies immediately behind the ventricle of the heart. The rectum runs posteriorly through the upper part of the pericardium (Fig. The folds and depressions diversify the walls and floors of the stomach and break them into definite areas. the largest and the most important muscle in its body. The mouth leads into a straight. The tissues consist largely of greenish-brown masses often termed as liver or digestive diverticula (Fig. running parallel and closely adjacent to the upper part of the descending portion (Fig. The valvular folding of the intestinal ridge gives way to the ascending portion and curves backwards along the base of the visceral mass to the left of the descending intestine. The branchial muscles cause the shortening of the gills and withdrawal of their posterior extremities. Their ends are attached to the right and left valves without making a separate scar in the nacre. 3). The terminal part of the rectum runs in the middle line along the posterior surface.2. From the point of intersection. 3). The adductor muscle stretches transversely across the body from valve to valve. A peculiar (gelatinous) rod.3. They are smooth on the surface. The muscles are V-shaped and originate from the byssal gland. Beyond this it curves vertically and passes around the posterior part of the adductor muscle in . 3). originating at level with the mouth. and the greater portion of the intestine lie within the viscero-pedal mass. The intestine may be divided into three sections. two anterior and two posterior. possessing only the posterior adductor (Fig. dorso-ventrally compressed and ciliated oesophagus. stomach.4 Muscular system The pearl oyster is monomyarian. the muscle fibres throughout the oyster's body are non-striped. The foot has four levators.2. The power exerted by the adductor in bringing the valves together by its contraction is considerable with rapid action resembling a ratchet mechanism. the mantle lobes of the two sides are slightly united by the inner mantle folds thus dividing the mantle cavity into a large inhalant chamber containing the gills and a much smaller exhalant chamber. They serve to purify the blood flowing in the filaments and to convey the food particles to the mouth. The deoxygenated blood is collected in veins which carry it either into the gills or excretory organs. 3. Its convexity extends first forwards and then downwards. returns to the heart through efferent branchial vein by way of auricles. The external renal aperture is a minute oval opening with a sphincter muscle. flows outwards to the free margin. Each nephridium opens into the pericardium by a wide duct and to the exterior by a minute pore. The latter is short and supplies blood to the adductor muscle. convey blood from the axial trunk to the base of reflected lamellae. the inter-lamellar junctions.the median line and ends by the anus in an erectile ear-like process. two halfgills on each side which hang down from the roof of the mantle cavity like book leaves. containing branches from the afferent vessels. passing over to the direct filaments. together with that from the gills. The common base of each ctenidium is a vascular ridge reaching from the anterior end of the gills. where it joins the efferent vessel by openings along each side. returning inward to the branchial or ctenidial axis. The normal function of the ordinary cilia on the branchiae is to create a current of water which enters the pallial chamber and passes over and through the branchial lamellae. Hollow outgrowths.6 Respiratory system The gills consist of four crescent-shaped plates. Where they terminate. It opens immediately below the genital aperture .7 Circulatory system This system consists of a heart and a series of arteries which lie above the adductor. The nephridia are two large symmetrical pouch-like sacs located on either side in the hinder half of the viscero-pedal mass.8 Excretory system The excretory system consists of a pair of nephridia and numerous small pericardial glands projecting from the walls of the auricles. They receive blood from the body by way of the gills and mantle. Two rows of long delicate branchial filaments are inserted at right angles along the whole length of the axis or vascular base which extends from the ventral border of the palps anteriorly curving round ventrally and posteriorly to a point opposite the anus.2. They represent a series of ciliated sieves. These open into the sinuses or blood spaces in which blood circulates slowly. The heart consists of a single ventricle and a pair of contractile thin walled auricles. Blood is driven by contractions into the anterior and posterior aorta. and pass it to the ventricle. The nephridia inter-communicate by a wide channel beneath the auricles. 3.2. Water enters by one and leaves by the other. The anal papilla is comparatively large and slightly curved. The filaments are joined chiefly by the inter-locking stiff cilia of the large ciliated discs which occur at intervals throughout their length.2. rectum and anus. Back-flow of blood is prevented by valves. The aorta communicates with a pair of large blood vessels that run around the margin of each mantle lobe. The blood of the pearl oyster is colourless. providing an efficient feeding surface. and contained in a pericardium. Blood is supplied to the rest of the body by the anterior aorta through a series of minor arteries. From the kidney it is pumped into the marginal vessel of the mantle by a pair of accessory hearts. 3. The blood from the mantle. The blood enters the individual filaments. one on each side. No portion of the reproductive glands extends into the foot or into the mantle. Both are creamy yellow in colour. connecting a greater part of the outside of the proximal portion of the viscero-pedal mass (Fig. The latter is situated dorsal to the renal aperture of the same side. while a pair of cerebro pedal connectives join the cerebral ganglia with the pedal nerve mass. a little anterior to the anus. The gonads of the two sexes consist of branched tubules with myriads of succate caecae. 3. 3). From the base of each. membranous and directed forwards. The cerebral ganglia are supra-oesophageal in position and a nerve cord or commissure forms the two parietosplanchnic ganglia (Visceral ganglia).9 Nervous system The nervous system is laterally symmetrical and has three pairs of ganglia. (2) the pedals joined to form a single ganglion at the base of the foot and (3) a pair of large visceral or parieto-splanchnic ganglia lying upon the anterior surface of the adductor. (1) the cerebral ganglia at the sides of the oesophagus. The ramification of the pallial nerves in the muscular marginal region of the mantle and their anastomosing forms a complex network of nerves. turns down into the base of the gills and then backwards to the posterior tips following the afferent vessels.within an inconspicuous lipped slit at the junction of the inner plate of the inner gill with the visceral mass at a point about midway between the ventral border of the latter and the base of the foot.2. It has thin membranous walls and is bounded behind by the lower part of the pericardium and in front below with the body wall and forms part of the root of the adductor embayment of the suprabranchial chamber. . the alveoli. a stout nerve passes straight back and reaches the pigmented pallial sense organs of its respective side. The cerebro-pedal connectives arise from the posterior and outer sides of the cerebral ganglia and run downwards within the visceral mass just behind the levator muscles of the foot to the pedal ganglion. The accessory pericardial glands on the walls of auricles have excretory function.10 Reproductive system The sexes are separate except in occasional cases. and the first two sections of the intestine.” 3. with the concavity ventrally. The reno-pericardial tubules are a pair of wide lateral prolongations of the pre-cardiac part of the pericardium. The stout paired cerebro-visceral connectives link the cerebral ganglia with the parieto-splanchnic ganglia. The posterior pallial nerves emerge from the posterior end of the visceral ganglion. the male gonad is pale creamy and the female gonad yellowish creamy. The passage connecting the right and left nephridia is wide and lies beneath the auricles. Each branchial nerve leaves the ganglion at the anterior lateral corner. The aperture is a curved slit. In the mature stage. Each of the visceral ganglia receives from above the stout cerebro-visceral connective. The gonads are paired but asymmetrical.2. They form a thick envelop covering the stomach. the “pallial plexus. They are thin walled. the two ganglia themselves being united by a single transverse visceral commissure. The spermatozoa and ova develop in these. The accumulated ripe gametes fill these alveoli and tubules and later pass into three trunks which converge into one which leads to the external genital aperture. liver and the stomach. Three principal nerves arise from the pedal ganglion and innervate the foot and the byssal gland. The male and female gonads are indistinguishable from external appearance in the initial stages. 10) ascending intestine.FIGURE 3. 9) descending intestine. 12) anal papilla. 13) byssal gland. 2) oesophagus. 8) digestive diverticula. 1) Mouth. 7) liver. 3) stomach. Anatomy of Pinctada fucata. . 5) left inner labial palp. 6) crystalline style. 11) rectum. 4) left labial palp. 14) nucleus implanted in the gonad. heteropods.CHAPTER BIOLOGY AND ECOLOGY 4. larvae of lamellibranchs. 50–55 mm at the end of the second year.0 mm at the end of the third year. fucata produced in the hatchery and grown in the farm at Tuticorin Harbour during 1983 revealed that the species attains a modal size of 47.1 Food and feeding habits IV Like other bivalves. the pearl oyster is a filter feeder. 30. algal filaments. The food particles collected thus are carried by the cilia to the crest of the branchial lamellae and from there they are directed by the labial palps into the mouth.3. flagellates. 60–65 mm at the end of the fourth year and 65–70 mm at the end of the fifth year.1. third. The weight of the oysters was 10. Minute food organisms in the water.6 and 45. appendages and frustules of copepods.1. fucata collected off the coast of Tuticorin. The labial palps have the ability to reject unwanted materials like mud particles. fourth and fifth years. crustacean nauplii. detritus and sand particles were also noted in the stomachs and intestines of cultured P. 4.0 mm at the end of first year. second. 45.5 mm at the end of the second year and 75. microscopic examination of smears and histological studies. five developmental stages have been distinguished in the gonads of P. The pearl oysters have been estimated to have a longevity of 5–5. Based on the external appearance. Minute embryos and larvae of various organisms. respectively. The corresponding weights at ages 1 to 3 years were 8. gastropods. algal filaments. Oysters from natural beds were also found to contain the same organisms in their stomach and intestine. 55–60 mm at the end of the third year. respectively.5 years in natural beds.3 Reproduction In pearl oysters. . 31. 64. Observations made on cultured pearl oysters collected near Krusadai Island and at Tuticorin show that the oysters can grow to a height of about 35–45 mm at the end of one year. 60 and 70 g at the end of the first. Unicellular organisms including infusorians.4 g. spicules of alcyonarians and sponges were also observed. but have been observed to live up to seven years when reared in the farm. Tracing the growth history of P.1 Biology 4. 4. spicules of sponges and unidentified spores. These are carried towards the branchiae which act as fine strainers arresting every particle in the water current. the sexes are separate although hermaphrodite conditions have been observed in some individuals.1.2 Age and growth The age and growth of pearl oysters in the Gulf of Mannar have been studied in detail. foraminifers and radiolarians have been found in the stomach of pearl oyster. enter inside the mantle cavity along with water current passing though the narrow slit formed by the inwardly directed edges of the pallial lobes. The presence of diatoms. Change of sex takes place in some oyster towards the end of spawning. The description of the spent stages applies to the oysters which have recently undergone oogenesis. As the stage advances. . In some cases it is pale orange in colour. the inter-follicular spaces become reduced and the lumen of the follicle may contain some free oocytes.Stage 4: Partially spawned The gonads become loose in consistency and the visceral epithelium becomes dull. In advanced stages.0 x 50 µm with a well defined germinal vesicle.4 µm. The average size of the oocytes is 60.fucata off Tuticorin coast. if present. It is mostly yellowish cream.Stage 2: Developing/maturing The transparent nature of the resting gonad is lost and it becomes distinguished from other visceral masses. Pinctada fucata from the Gulf of Mannar has two peak spawning seasons in a year: JuneSeptember and November-December. In other stages of gametogenesis. Most of the oocytes are spherical and nucleated. The lumen of the follicle is filled with free oocytes.Stage 1: Inactive/spent/resting The gonad is completely shrunken and translucent. the gonad begins to branch along the posterior side of the retractor muscle and advances to the anterio-dorsal region.0 × 47. Large vacuolated yellow (fat) cells are seen in the interfollicular spaces. the gonads of males and females appear similar when observed externally. The majority of the oocytes are pyriform in shape. if present are few and spherical. The majority of the oocytes are irregular in shape and the germinal vesicle (nucleus) is not distinctly seen.Stage 3: Mature The gonad spreads on to most of the visceral tissues. Gametogenic materials begin to appear in the gonad. is 20. Ruptured follicles are seen in some cases and the lumen sometimes contains ruptured cells. The mean diameter of the nucleus is 25 µm. the colour of the gonad is pale cream. The average size of the oocyte is 51. Oocytes. Otherwise they transform to the spent resting stage quickly.7 µm. Some of them are attached to the follicular wall by means of slender stalks. The five stages of sexual maturity described below are based on the gonad development in female oysters. The average size of the oocytes is 54. Males show the same pattern of reproductive activity. However. . The gametes begin to proliferate along the follicle wall. The average size of the oocyte is 68. . The sex at this stage can hardly be distinguished.0 µm. coinciding with the southwest and northeast monsoons. in stages 2 and 3. .5 µm and the germinal vesicle. . The oocytes are free and found along the follicular wall. .Stage 5: Spent The gonads shrink further with a few left over gametes in the lumen of the follicles. The follicles shrink with the reduction of gametes in the lumen. . but the quality of pearls is inferior.5 ‰. In farming the pearl oysters. Individual oysters spawn more than once in the same spawning season as the gonads are not emptied at one stretch. A high amount of silt in the farm water may affect the filtration efficiency of pearl oysters. are usually associated with pearl oyster beds. It is well known that the benthic ecology of the pearl culture grounds plays a vital role in the rate of production as well as quality of pearls. salinity in the natural beds fluctuates between 27. the preferred depth of culture is about 10 m where silting should be minimal.0–32. The salinity values in the oyster culture site at Veppalodai. This may happen during unusual heavy rain and heavy discharge of fresh water from rivers in the vicinity. are good but there should not be noxious blooms. salinity. Rocky or gravelly bottoms are more suitable. growth and reproductive pattern of oysters. echinoderms. the formation of the nacreous layer is faster. The oysters obtained from the beds are successfully reared in shallow coastal waters with depths ranging from 4–8 m. current. hydroids. polychaetes. it may lead to mortality. therefore they can adapt and live in varying environmental conditions within this range. temperature. Some grounds yielded pink or white pearls while others produced only yellow and golden pearls. oyster growth will be affected. nutrient salts. where the sea does not become rough. The rich nutrients discharged by the rivers into the sea increase the productivity of the water. the variation in temperature and salinity is not much pronounced in the Gulf of Mannar. comprising members of various groups like sponges.5 °C (May) whereas in the oyster farm at Tuticorin. both in the natural beds and farms.15 ‰ and 33. Areas rich in phytoplankton which is consumed by oyster. 4.90 ‰ with an annual range of 8. Repeated culture on the same ground sometimes affects the quality of pearls. and faecal matter. In Japan it has been observed that some culture grounds yielded pearls of good quality. waves.50 ‰ during 1974–76. An unusual dilution of seawater to 15. it fluctuates between 24. decapods. which is often exposed to prolonged dilution of seawater due to flooding. ranged between 32. A slight rise in water temperature may be considered as the stimulating factor for the onset of the gametogenic cycle and a slight reduction in water temperature stimulates the oysters to spawn. and primary production play a crucial role in the settlement.4 ‰ and 35. while others did not.2 Ecology Pearl oysters are found from the low tide level to depths of about 75 m. In the Gulf of Mannar. and if such condition is prolonged. maturing and ripe gonads are present in almost all of the months of the year. but also to bring in fresh plankton as well as for the removal of metabolic products. pH. If salinity level falls below 15 ‰. The temperature of seawater in the natural beds varies from 27. the pearl oysters live on rocky or other hard substrata which lie roughly in a line parallel with and at a distance of 10–16 km from the coast. Unlike in Japan.respectively.5 °C. The oysters can also directly remove the organic matter and calcium dissolved in the water. dissolved oxygen. However a few inactive. A rich fauna. wind. Environmental factors such as bottom topography. lamellibranchs. water movement. Similarly. If oyster culture farms are located in places such as the vicinity of a river mouth. If the water current is strong. fishes etc. A mild current of two knots per hour is necessary not only as a source of oxygen-rich seawater.0 °C (January) to 32.69 ‰ for short durations at the Veppalodai farm in November 1977 did not affect the oysters. amphipods. light. 5.CHAPTER V HATCHERY TECHNIQUES FOR SEED PRODUCTION 5. The suitability of the technology has been proved by producing seed during most of the year. Air is drawn at the required places from these pipes running the entire length of the hatchery through nozzles. The technology developed is helpful in overcoming the problem of insufficient supply of mother oysters for cultured pearl production.2 Live food production 5.2 Seawater management The seawater is usually drawn from the sea beyond the low water mark into a well through PVC pipes. The concrete floor has sufficient gradient facilities for easy drainage. 5. Glass panelled large windows and ventilators are provided for free passage of light and air. The seawater sterilized by ultraviolet irradiation is used only in specific cases.1 Phytoplankton Flagellates measuring less than 10 µm form the main food for pearl oyster larvae. fibreglass and stainless steel materials are used in the hatchery. The seawater is pumped to sedimentation tanks and passed onto the biological filter which contains coarse river sand at the top. pebbles below it and charcoal at the bottom. 5. The air is supplied to the tanks through diffuser stones.1.1 Artificially reared spat Seed of P. Part of the roof of the wet laboratory has translucent fibreglass sheets to allow sufficient light for indoor phytoplankton culture. fucata.3 Aeration Air compressors with storage tank are used to aerate seawater in the rearing tanks.1. The hatchery is one of the most important sources of sustained supply of pearl oysters. The hatchery methods developed are simple to adopt and inexpensive. 5. Periodic cleaning of the filter bed keeps the seawater uncontaminated. The filtered seawater is stored in a water sump and lifted to an overhead tank for supply to the hatchery. maturation and spawning. Isochrysis galbana is an important algal food for the larvae. as well as larval and spat rearing (Plate II A). . The compressed air is passed through a series of filters to remove oil and moisture and is supplied to the various culture vessels through PVC pipes.1 Hatchery building The pearl oyster hatchery of the CMFRI at Tuticorin has facilities for oyster conditioning.1. PVC.2. were produced in 1981 in the laboratory through hatchery techniques at the Central Marine Fisheries Research Institute at Tuticorin. Other microalgal cells such as Pavlova. The roof of the hatchery building is sufficiently high to avoid high temperature. 5. In the absence of natural spawning the technique of induce spawning is employed.0 °C).532. 9.3 Broodstock handling and spawning 5. The growth and spatfall timing varies with the different algal foods. Different pH media (8. the maximum cell concentration is reached within 5–6 days. while spawning of these oysters can be stimulated by raising the water temperature by few degrees. They enter the stationery phase of growth in about 15 days in Haufkin flasks and are maintained for two months without aeration.2 g : 30.2 Spawning Spawning of natural oysters with mature gonads occurs when there is a simple change in the seawater environment or a mechanical shock by shell cleaning or a change in water pressure. They are fed with a mixed algal diet at a ration of 4 l per oyster/day. 9.2 g : 0.128 millimolars) of hydrogen peroxide in combination either with normal seawater or alkaline seawater (pH 9. Conway or Walne's medium is used for the culture of these flagellates.5 °C to 35.0. The algal food is supplemented by raw corn flour at 30 mg per oyster/day.1) is used in inducing spawning. Different concentrations (1. The matured oysters can be kept for a prolonged period at 25–28 °C.0) are prepared either using Tris buffer or Sodium hydroxide pellets (NaOH) and the pearl .5 and 10.3. 3. The composition of the medium used for mass culture as well as mixed algal culture is as follows: Potassium nitrate Potassium dihydrogen Orthophosphate Sodium silicate Sodium EDTA Filtered seawater : 0.4 g 5. Pearl oysters with maturing gonad fed with the above food for 45 days will spawn with a 30 % response.3.2 g : 0. Spawning of pearl oysters can also be effected by chemical stimulation.064 and 6. In mass culture. 5. Chromulina promotes faster growth while Dicrateria gives better spatfall.Chromulina and Dicrateria are also suitable for the larvae. In this technique thermal stimulation is adopted predominantly by gradually increasing the water temperature by several degrees (from 28. In all cases males spawn first (Plate II B) and this induces the females to spawn within 30 minutes. The flagellates are grown in 4-1 Haufkin flasks as stock culture and in 20-1 glass carbuoys and 100-1 perspex tanks in mass culture.0 l : 0.1 Broodstock maintenance Oyster broodstock are maintained at a water temperature ranging from 25–28 °C in a controlled room. 3. The polar body is placed at the cleavage furrow (Plate II E). they are pyriform in shape measuring 73. Fertilization takes place externally in the water medium.9 µm along the long axis and 45. The stage with three micromeres and a macromere is called Trefoil stage. During fertilization the polar body appears and persists on the embryo up to blastula stage. the pyriform eggs assume a spherical shape with the breakdown of the germinal vesicle (Plate II D).3.5 in NaOH gives 78.2 ml of N/10 ammonium hydroxide (NH4OH) solution into the adductor muscle of the pearl oyster results in 48 % spawning. The egg is enclosed in a vitelline membrane and a large germinal vesicle is seen at the centre (Plate II C). 5.oysters are induced to spawn. 5. and so on until the morula stage (Plate II F). Injection of 0.4 % of spawning. .4 Early development and larval rearing Cleavage The first cell division is seen 45 minutes after fertilization resulting in the formation of a micromere and a macromere. 16-cell. respectively. The yolk cytoplasm is heavily granulated and opaque. Each micromere develops a small cilium which helps in the movement of the embryo. During the second cleavage the micromere divides into two and the macromere divides unequally into a micromere and macromere. A pH value of 9.3 Fertilization When the eggs are released in the medium.2 µm in width. Micromeres divide repeatedly thus becoming smaller and smaller and passing through 8-cell.6 % and 68. The macromere does not take part in further divisions. Following fertilization.0 in the case of Tris buffer and 9. pearl oyster hatchery in Tuticorin. I. (B) Male oyster while spawning and (C) Pyriform oocytes. Blastula The embryo is ball-like with transparent cells and a blastocoel. are discarded. The embryos lift themselves in the water column and congregate at the surface. The blastula stage is reached 5 hours after fertilization. R. etc. Reorientation of cells starts and the blastocoel and blastopore are formed. containing broken tissues. M. Gastrula . sperm.PLATE II. The floating embryos are siphoned out to clean containers and the residues at the bottom. unfertilized eggs. (A) Inside view of the C. undeveloped embroys. F. mantle and rearrangement of the pre-oral tuft of cilia into a velum. The dorsal ectodermal cells secrete the embryonic shell. The gastrula exhibits negative photrophism.Gastrulation takes place by epiboly. The archenteron is formed. A single apical flagellum is developed at the anterior side. known as the prodissoconch I. The cells convolute and differentiate into different dermal layers. The single flagellum. . thus marking antero-posterior differentiation of the embryo. The movement of the larva is affected by the propulsive movement of the flagellum (Plate II G). The embryo is bean-shaped as there is convolution of cells. This stage is reached in 20 hours. preoral and post-oral tufts of cilia disappear.5 µm along the antero-posterior axis and 52. The anterior portion of the larva is broader while the posterior end is tapering like an inverted triangle. Trochophore larva The minute cilia present in the gastrula stage disappear and the pre-oral and post-oral tufts of cilia develop. The veliger larva measures 67.5 µm along the dorso-ventral axis (Plate II H). Veliger A definite ‘D’ shape is obtained by the secretion of the prodissoconch I having a hinge line. This stage is reached in 7 hours. (D) Fertilized oocytes. (E) Early cleavage and (F) Morula stage.PLATE II. . Cont'd. the larvae develop an eye spot at the base of the foot primordium.PLATE II. The typical clam shaped umbo stage is reached between 10–12 days and it measures 135 × 130 µm (Plate III A). Cont'd. prodissoconch II. Eye spot stage After attaining the full umbo stage. The shell valves are equal and the mantle folds are prominent. (G) Trochophore larvae and (H) Straight-hinge larvae. A well developed velum effects the movement of the larvae. Umbo stage Further development of the veliger to the umbo stage is gradual with the development of the shell. The ctenidial . Spat By the repeated addition of dissoconch. The stage is reached in 20 days at the size of 220 × 200 µm (Plate III E). The minimum size at which the larva develops the eye spot is 180 x 170 µm (Plate III B) usually in 15 days. A healthy spat measures 300 µm in 24 days.ridges develop at this stage. The left valve is slightly more convex than the right one. Plantigrade When the pediveliger larva selects a substratum for settlement. additional shell growth is seen along the globular shell margin except at the vertex of the umbo region. Later the foot becomes functional while the velum disappears. in the form of a very thin. The transitional stage from the swimming to the crawling phase has both velum and foot (Plate III C). It resembles an adult with the hinge line. In the meantime the byssal gland secretes byssal threads for attachment. Labial palps and gill filaments develop. Gill filaments are now visible (Plate III D). The sizes and days given for the different larval and post-larval stages vary from batch to batch according to the environmental conditions. Pediveliger stage The foot is developed on the 18th day when the larvae measures 200 × 190 µm. anterior and posterior auricles and the byssal notch (Plate III F). uniform conchiolin film. transparent. the plantigrade transforms into a spat. The spat attaches itself to the substratum with the aid of the byssal threads. . PLATE III. (A) Umbo larvae. . (B) Eye-spot larvae and (C) Transitional stage. At higher densities the growth and spatfall are poor.1 Larval rearing conditions Larval density plays a significant role in the growth of pearl oyster larvae. Cont'd. Under identical conditions the larvae show differential growth rate at different larval densities. . (E) Plantigrade larvae and (F) spat.4 Larvae and spat handling 5. Spatfall is much higher in FRP black tanks than white and blue tanks. A culture density of two larvae per ml produces optimum growth and spatfall rates.4. 5. (D) Pediveliger larvae.PLATE III. The colour of the culture tanks also influences the setting of larvae. Aeration during larval rearing affects growth and spatfall. The effect of aeration is more pronounced in smaller volumes of water. However, aeration is required after the setting of the pearl oyster larvae. 5.4.2 Spat production Spat production is carried out in the molluscan hatchery at Tuticorin throughout the entire year. However, during May-August the spatfall is less due to high salinity, dustfall and warm landward wind. Sudden spurt of ciliates in the culture medium is common during this period. Such problems can be overcome by good management. 5.4.3 Feeding The microalgal cell Isochrysis galbana is provided to the larva from the veliger stage onwards. The optimum ration for a larvae is 5,000 cells/day up to umbo stage. The dose is doubled from the umbo to the pediveliger stage and tripled afterwards up to settlement. For about 15 days after settlement each spat is fed with I. galbana at 50,000 cells/day. Mixed algal diet containing mostly Chaetoceros and I. galbana is given in a ratio of 1:1 in the following 15 days. Later the spat is supplied with a mixed algal diet. 5.4.4 Transplantation The spat are reared in the hatchery for about two months. By then they shall have grown to 3 mm or more. They are then transferred to the farm in velon screen netcages with a mesh size of 400 µm. Mortality may occur if spat measuring less than 3 mm are transplanted. Spat growth is monitored carefully and the netcages are changed whenever necessary. The size of mesh of the rearing cages is also monitored. The oyster spat attain an average size of 40–45 mm in 12 months. 5.4.5 Survival In the hatchery about 20 % production of spat is achieved in tanks of 500-1 capacity and 40– 50 % production in 50-1 tanks. The survival of transplanted spat in the farm is about 30 % at the end of one year. CHAPTER PEARL OYSTER FARMING 6.1 Selection of culture sites VI In any farming activity, culture site selection is of paramount importance. Technological and economic considerations play a major role in the selection process. A careful appraisal of the habits of the organism to be cultured would give a resonable level of confidence on the tolerance limits within which the various environmental parameters can vary. Due consideration has to be given to possible effects of fluctuating water flow, primary production, siltation, etc. in order to obtain the optimum level of growth and production of high quality pearls. Unsuitable levels of environmental factors such as salinity, water temperature, cold water currents and other factors such as red tides, hydrogen sulphide and pollution by industrial and domestic effluents are serious hazards to pearl culture. Sheltered bays are ideal locations for pearl oyster farms. They offer good protection to the culture structures such as rafts and cages. Shallow coastal waters where the sea is calm most of the year can also be considered as a suitable site. 6.2 Environmental conditions 6.2.1 Temperature In temperate regions, the water temperature plays an important role in the biological activities of pearl oysters. In Japan, the optimum temperature for oyster growth has been found to be between 20–25 °C. A temperature below 13 °C causes hybernation. Below 6 °C, the oysters die. At temperatures above 28 °C, the oysters show exhaustion. The thickness of the pearl layers are affected by the minute changes in water temperature during the day and also vary considerably according to the season of the year. The deposition of calcium stops at a water temperature of 13 °C. In the Gulf of Kutch, the oysters grow vigorously in winter months when the seawater temperature ranges between 23–27 °C. A slight decrease in temperature triggers spawning in oysters in the Gulf of Mannar. The growth-temperature relationship is presumably valid only up to a certain temperature for optimum growth. 6.2.2 Salinity Pearl oysters tolerate a wide range of salinity from 24–50 ‰ for a short duration of 2–3 days. Salinities of 14 ‰ and 55 ‰ may cause a 100 % mortality among the oysters. The effect of salinity on the growth of pearl oyster has not been clearly investigated. However, it appears that pearl oysters tend to prefer high salinities. Oysters raised in such salinities produce pearls with a golden tint. 6.2.3 Bottom Gravelly bottoms are suitable for pearl oyster farming, while sandy or muddy bottoms should be avoided. Oyster growth is affected by water temperature and nutritional condition of the ground. Repeated culture on the same ground leads to some extent the deterioration of pearl quality. The chemical and physical state of the sea bottom is affected by the organic substances discharged from the oysters and fouling organisms. Periodic removal of such accumulated substances from the bottom of the culture grounds often increase production as well as quality. 6.2.4 Depth The optimum depth for farming pearl oysters is around 15 m. At greater depths, even if the rate of nacre deposition is slower, pearls of high quality with a pinkish colouration are obtained. 6.2.5 Silt load Pearl oysters generally prefer clear waters as high turbidity levels will affect their filtration efficiency. A decline in oyster condition was noted at Veppalodai farm due to the high silt content in the farm area throughout most of the year. 6.2.6 Water current Culture sites should be naturally sheltered against strong winds and waves. Tidal amplitude and currents must be sufficient in order to allow replenishment of oxygenated water and fresh plankton and flush away waste materials. In strong water currents the formation of the pearl layers is usually fast, but the quality of pearls produced is affected. 6.2.7 Primary productivity The condition of a specific culture ground depends primarily on the chemical constitution of the seawater and on the species and amount of plankton present. Rich nutrients discharged by rivers into the sea are responsible for high primary productivity. The oysters probably derive their chief source of conchiolin from the nitrogen substance of the plankton. The organic matter and calcium dissolved in the seawater are directly absorbed by the food consumption cells. The calcium passes through the mantle to be deposited on the surface of the shell or pearl in the process of their formation. The presence of trace metals in small quantities influences the colour of the nacre. 6.3 Supply of oysters In pearl oyster farming, oysters collected from the natural beds or reared from naturally collected or cultured spat are used. In the Gulf of Mannar, several pearl banks are distributed off Tuticorn at a distance of 12–15 km and at depths of 12–25 m. Pearl oysters from these beds are collected by skin and SCUBA diving (Plate IV A). Wide fluctuations in terms of pearl oysters availability have been noted in different pearl banks in this area during the last few centuries as also during the most recent years. In the Gulf of Kutch, the pearl oysters are found on the intertidal flats and the population is sparse. Collection is done by hand. In Japan, oyster spat are collected by submerging bundles of cedar twigs near the water surface during the peak larval settlement season. Hyzez films and old fish nets are also commonly used as spat collectors. Almost the entire requirement of oyster supply to the pearl culture industry is met by this type of spat collection. Spat collection attempts in India have not been successful, and this may be due to the distance of the pearl oyster beds from coastal waters. However, India has recently succeeded in producing pearl oyster seed under hatchery conditions, therby providing the industry with a more dependable source of oysters. 6.4 Rearing methods 6.4.1 Raft culture Raft culture is considered to be one of the most suitable farming methods in sheltered bays. The size of the rafts can be altered according to the convenience of the situation. A raft of 6×5 m in size can be easily constructed and floated with 4 buoys. Rafts are usually constructed with logs of teak, venteak or casuarina wood, of chosen length with the bottom of about 10 cm diameter tapering to 6 cm diameter at the tip. These logs are arranged as per the requirement and lashed with coir ropes. Floats are attached to the raft to give buoyancy. The floats can be sealed empty diesel drums of 200 l capacity with fibreglass coating, mild steel barrels painted with antisaline/anticorrosive paints or FRP styrofoam floats (Plate IV B and C). Unit raft system is found to be convenient and well suited to the Indian sea conditions. Rafts are moored with anchors at opposite sides with tested quality chains and their direction is decided according to the prevalent wind direction at the specific site (Fig. 4 A-C). In the long-line culture method, spherical or cylindrical floats which are connected by horizontal synthetic rope or chain are used (Plate IV D; Fig. 4 D). The oyster cages are suspended from the ropes. This system is good for open sea conditions. In another method of hanging, a hole is drilled near the hinge of the pearl oyster. A small thread is put through the hole, which is then tied to a straw rope coated with tar. The straw ropes are hung from a raft. 6.4.2 On-bottom culture Sea bottoms with a granite or coral stones composition can be used for on-bottom culture. In the Tuticorin Harbour Basin where the breakwater has been constructed with granite stones, the protected portion of the breakwater is used for culturing mother oysters. 1 m of water is available below the low water mark. Due to constant circulation of seawater, settlement of fouling organisms is poor and inconsistent. However, it has been noted that the growth of the mother oyster is slower in on-bottom culture compared to the growth of oysters cultured in raft. 6.5 Rearing containers 6.5.1 Culture of mother oysters Box cages, measuring 40×40×15 cm, are used to rear mother pearl oysters. The size of the mesh varies with the size of the oysters to be reared. The frames of the cages are made up of 6 mm mild steel rods, coated with anticorrosive paints or coal tar. Box-cages are useful in general mother oyster culture (Plate V A). measuring 60×40 cm each with five compartments. The oysters are arranged in rows and held in the compartments when closed. The frames. open as a book. frame nets are used. PLATE IV. The space available in between the two frames is about 10 mm which is sufficient for the oysters to open their valves for feeding and respiration (Plate V B). .To trace the history and performance of individual oysters. meshed and hinged at one end. (A) A scuba diver diving to collect pearl oysters and (B) A culture raft floated with mild steel barrels. The mouth of the bag is tied with a synthetic twine which facilitates opening or closing when required.PLATE IV. Cont'd. (A) Culture raft constructed with teak poles.2 Juvenile rearing Juvenile pearl oysters are reared in netcages (Plate V C-D). The mesh size of the screen depends on the size of juveniles to be reared. Synthetic fabric of velon screen bags whose sides are stretched with a steel rod in the form of a prism are used for rearing of juveniles. To provide further protection from predators the bags are placed in old nylon fish . (B) A FRP styrofoam buoy. (C) A mild steel buoy. FIGURE 4. and (D) Oyster long-line culture system. 6. (C) A culture raft with FRP styrofoam buoys and (D) Oyster long-line culture.5. sun-dried and reused.net bags. . PLATE V. Spat of up to 2 cm in size are reared in these small netcages. (A) A box-cage containing pearl oysters and (B) A frame netcage with oysters. Box-cages which are used for rearing mother oysters can also be used for juvenile rearing by providing an additional velon screen cover inside the cage. Clogging by silt and by the growth of fouling organisms can be prevented by periodical replacement of the velon screen bag which can be cleaned. (C) A netcage for rearing oyster spat of 3–10 mm in size and (D) Rearing netcage covered with velon screen. Cont'd.PLATE V. . When the barnacles were dense they completely cover the entire surface of shell valves (Plate VI A and B).290 (September) to 2. Ascidians are particularly found in large numbers during the period from October to December. 7. such as Watersipora and Bugula are more commonly found during February and June.1. The settlement was considerably less from January to May. Singly or in combination. these organisms can cause heavy mortality to the farm stock through physiological stress and diseases. borers and predators is a labour intensive activity. 7. compound ascidians belonging to the genus Diplosoma and.1.500 barnacles (July) to a maximum of 3.1 Biofouling organisms 7. while 1. The removal of foulers.3 Bryozoans Species of Membranipora. the shell margins were also damaged resulting in the recession of shell growth.700 (November) in the second peak. during the removal of barnacles. .CHAPTER BIOFOULING AND PREDATION VII Major problems in pearl oysters farming are caused by biofouling organisms which settle and grow on the oyster shells. Other species. Thalamoporella and Lagenipora represent the group almost throughout the year. In the farm at Veppalodai a minimum of 2. particularly in the culture sites. species of Botrilloides have been recorded throughout the year.1 Barnacles The cirriped Balanus amphitrite variegatus is one of the major fouling organism. In addition to this.460 barnacles (June) have been recorded on an area of 25 square cm during the first peak. and by predators which feed on the oysters. The seasonal variations of the dominant fouling organisms and predators have to be carefully investigated. by boring organisms which riddle through the shells making them weak and friable..2 Ascidians Ascidia depressiuscula. Two peaks of heavy settlement of these organism.1. PLATE VI. The peak period of occurrence is usually between November and December. Dicarpa sp. 7. have been recorded in India: one from mid-June to August and the other from September to November. Heavy settlement of barnacles cause physical obstruction to the opening and closing of the oyster valves. (A) Fouling organisms on adult ovsters and rearing cage and (B) Oysters heavily encrusted with barnacles. and suitable techniques for their control should be adopted on a periodical basis. Major hydroids belong to genera such as Campanularia. In several Indian farms over 20 % of the oysters have been found to be infected by such sponge. polyclad worms. mostly near the adductor impression. the blisters erupted as tumour-like protrusions. Sertularia. Abeitinaria. Boergesenia and Ceramium. The spatfall of Avicula vexillum can be so numerous in the rearing cages. These borers initially attach themselves near the umbo region of the shell and later spread over the surface of the two valves. molluscs and isopods may cause considerable damage to the pearl oyster shell. Diphasia and Thuiaria. Nereidae. Blister formation by boring polychaetes in oysters of 40 mm in length and less is usually less than in large oyster specimens. October and December. Avicula vexillum and spat of Crassostrea sp. 7. Spionidae.1.7. Other organisms such as anthozoans. are numerous on the farm during April to June. flava and the cirratulid Cirratulus cirratus are the most common borers. Major boring sponges are Cliona celata. hydroids and algae typically occurring in June.2 Boring organisms Boring organisms comprising polychaetes. typically caused simple and compound blisters on the inner side of the oyster shells. juveniles of Panulirus sp. C. Oysters affected by these sponges have to secrete more nacre in order to . Codium. Terebellidae and Cerratulidae have been found to bore pearl oyster shells.6 Other organisms Besides the above mentioned groups. Among them the spionids Polydora ciliata and P. 7. margaritifera.5 Sponges The profuse growth of sponges such as Callyspongia fibrosa and Haliclona exigua may result in the complete covering of an individual oyster or a cluster of oysters. the furrow eventually becomes deeper and wider causing the peeling of the periostracal layer thus weakening the shell. Commonly occurring algae are Gracilaria. that the pearl oyster spat cannot be easily separated without causing damage to or killing the spat.1. tubicolous polychaetes. has been recorded in the farm during May-July and November-January. 7. alcyonarians. opisthobranchs. The settlement of these organisms can significantly affect the culture of the mother oysters as well as the production of the cultured pearls. usually occurring in July. The occurrence frequency of these sponges is usually low at the present Indian farm site and the damage caused to the oysters is negligible.4 Molluscs Among the fouling molluscs. vastifica and C. blennid fishes and Pinna spat may occur on the oysters and rearing facilities in certain months of the year. Polydora spp. the fouling community may be composed of a large number of other organisms such as amphipods..1. Pycnogonids. crinoids. Polychaetes belonging to the families Sillinidae. sponges. As a result. The cirratulid Cirratulus cirratus is found in furrows between the layers of periostracum of the pearl oyster shell. Modiolus metcalfei is another common fouling mollusc. The spatfall of Pinctada sp. In a few cases. crabs. Lytocarpus. With heavy infestation the oyster shell usually becomes extremely fragile and susceptible to further infestation and damage (Plate VI C). PLATE VI.4. they crush and feed on the pearl oyster spat. 7.. Predators in wild beds are mainly benthic fish which feed on young oysters below one year of age. virgeneus. brine and chemical treatment are also found to be effective. and Thalamita spp.1 Fouling The most effective method of controlling fouling growth is by cleaning the oysters. liver and gonads of pearl oysters. octopods and starfish feed on adult oysters.seal off the perforations. The pholadid bivalve Martesia sp. periodical exposure of the oysters to sun light for a few hours results in the killing of the larvae of most undesirable settlers. as they grow. 7. cages and farm materials regularly. has been found to make a significant number of holes on the oyster shells. Suspending the oyster cages at depths below 5 m during the peak barnacle settlement period usually reduces the degree of settlement of this organism. Martesia sp. Neptunus spp. Leptodius exaratus. (C) Damage caused by a boring sponge and (D) Cymatium cingulatum.5 mm and 20 oysters in 19 days by two Cymatium of 61. . Charybdis lucifera. Cont'd.0 mm in size within a period of 37 days. Finally.4 Control measures 7.3 Predator organisms Besides fouling and boring. the peak spawning and settlement season of major fouling organisms can be also avoided by timing the introduction of the new spat stocks in the farms. Fresh water. the isopod Sphaeroma sp. Three species of parasitic trematodes have been isolated from the foot. and. Their monthly percentage of infection has been recorded to vary from 3–20 % in a single farm site. 20 oysters in 20 days by two Cymatium of 40. A study on the feeding rate of Cymatium cingulatum in the laboratory showed that 20 oysters were consumed by two Cymatium 26. gill.0 mm in size consumed 20 oysters in 49 days in a laboratory experiment. are some of the crabs commonly found inside the pearl oyster cages in the Indian oyster farms. Recently. mantle. Atergatis integerrisimus. Cymatium cingulatum (Plate VI D) and Murex virgeneus have been found to be serious predators in natural oyster beds. a major pearl oyster predator. Usually in the culture sites crabs are the worst predators.8 mm. while rays. the mytilid Lithophaga sp. Two specimens of M. 54. are occasionally found in the culture farms. These gastropods have been shown to survive starvation for 57 to 125 days. In addition. These crustaceans enter the spat rearing cages during their larval phase and. predation is another menace encountered in pearl culture farms as well as in natural pearl oyster beds. 2 Boring The boring polychaetes are easily killed by immersing the oysters in freshwater for about 6 hours. The oyster shell valves infested with boring organisms can also be brushed with 1 % formalin. brine has been shown to kill all polychaete species within 8 hours. At a concentration of 78 %. Oyster spat can be additionally protected from fish by covering the rearing cages with old fish net. 7.7. The above treatment is found to be effective against sponges and Martesia sp.3 Predation Periodic monitoring of the culture facilities and manual removal of the predators is the only way of containing predation on the oysters.. and partly against Polydora sp. dipped in freshwater and returned to the sea.4.4. . larval rearing. major inventory and manpower of a pearl culture establishment is summarised briefly to provide an overview for an easy understanding of the nature of this industry. U. Major work is in the sea involving pearl oyster collection and farming.710 co-operatives half of which were operating 1–14 rafts. · Oysters cultured from hatchery spat Activity: Induced spawning. The Japanese pearl culturist has the advantage of being able to buy the mother oysters for his farm from those who are solely engaged in seed collection and mother oyster culture. glassware.500 in 1973. · · Oysters cultured from wild spat Activity: Collection of pearl oyster spat by suspending spat collectors from rafts at suitable sites. glass carbuoys. In the peak period of production (1966).1 Culture operations VIII Pearl culture in Japan is carried out mostly by small cooperatives or family enterprises. there were 4. snorkel. · Manpower: Same as above and farm labour. · B) Pearl oyster farm .V. depth-gauge. · Manpower: Boat crew. while only a few large-scale operations exist. The total number of co-operatives came down to about 2. chain and spat collectors. sterilizing unit. The activities.CHAPTER CULTURE SYSTEM 8. culture of larval food. · Inventory: Hatchery building. compressed air units (main and portable compressors). This shows that small-scale operations are the mainstay in pearl culture. collection kit and oyster bins. 12. A) Raw material: Pearl oyster (Pinctada fucata) Oysters from natural beds Activity: Seasonal survey of beds and collection by diving. one fifth operating 15–29 rafts. plasticware. technical assistants. · Manpower: Biologist. lighted buoys. diving assistants. FRP tanks 50 l and 1 ton capacity. seawater flow-through system.0 %. chemicals. Inventory: Boats. anchors. masks. In India also such small-scale operations at family level is possible if the production of oyster seed is done by hatcheries and supplied to the pearl culturist. navigator. A/C larval food production room. laboratory technicians. belt. · Inventory: Rafts. 30–49 rafts and the rest more than 50 rafts. divers. spat production. knife. self-contained underwater breathing apparatus (SCUBA) and diving accessories such as fins. Manpower needs and inventory items vary according to the scale of the operation. transplantation. chain rope. and colour improvements. technical assistants. long line. floats. · Manpower: Pearl processing expert and technical assistant. · Manpower: Same as for pearl oyster farm and on-shore establishment. oyster knife. · Inventory: Log rafts. · Manpower: Electrical supervisor and assistant. plasticware. floats. sterilized water for larval food production and larval rearing. etc. Inventory: Surgical tools and accessories. sorting and grading of pearls. over-head tank. long lines. treatment of pearls for removal of minor blemishes. · Manpower: Farm superintendent. anchors.Activity: Juvenile rearing. post-operation care. bleaching. glassware. chain. flow-through system and other tanks. · Air supply . miscellaneous tools. · C) On-shore establishment Surgical unit Activity: Pearl oyster surgery and convalescence. shell bead nuclei of different sizes. furniture. farm labour. Inventory: Plasticware. lighted buoys. out-board motor. · Inventory: Sorting trays. · Manpower: Chief technician and technicians. floating sheds and miscellaneous tools. chemicals. supply channel with regulators. anchors. cages. farm structure maintenance requirements (repairs and maintenance of raft. vats. chemicals and glassware. farm maintenance and farm stock maintenance. filter bed. juvenile rearing cages. Inventory: Oyster cleaning tools. sump. Manpower: Technical assistant E) Pearl processing centre Activity: Cleaning. chemicals. dyeing. · F) General services Seawater supply Activity: Supply of quality filtered seawater to pearl oyster hatchery and surgery. dinghy. cages. ultraviolet lamps and raceway. · · D) Pearl collection centre · · · Activity: Collection of cultured pearls and incidental natural pearls. · · Farm house Activity: Shore support for maintenance of farm and farm stock. raceway. · Inventory: Pump house.) and oyster tanks. frame nets. mother oyster culture. otherwise linked to other items. · Manpower: Specific manpower to handle by-products processing work. · Manpower: Same as above. · Power and fresh water supply G) Laboratory Activity: Monitoring of oyster health and condition. collection. administration. accountants and stores staff. and pearl oyster surgical room. otherwise. Inventory: If the unit is self-contained. maturity. . all items required for utilization of shell and meat. · · I) Management and administration · · Activity: Planning. bacterial analysis of seawater. laboratory technicians. · Manpower: Biologist. unit sale to outside agencies. · Inventory: General biological laboratory equipment and analytical equipment for seawater analysis. seawater analysis. · Inventory: Air blowers with air supply tubes and regulators. · H) By-product unit Activity: Conversion of by-products of pearl culture to value-added items. preservation and storage of materials. Manpower: General manager. feed-back to research system. advice to farm superintendent and chief technician. chemist. if selfcontained. execution and administration of project.Activity: To supply oil-free air to hatchery. larval food production laboratory. 45 µm in size. pigmented and fringed with branched tentacles. while the central mantle is dorsal to the pallial mantle. .1 Marginal mantle The marginal mantle consists of three folds: the inner.1. pallial and central mantle (Fig. The fold is lined with ciliated columnar epithelium cells 5–50 µm thick. middle and outer fold. is responsible for the secretion of the shell. the marginal mantles of the two lobes fuse to form the mantle isthmus. the arrangement of the columnar epithelial cells. and the outer (shell) fold is secretory in function. 9.CHAPTER THE MANTLE 9. which have a distinct basal nucleus. Further towards the tip. Outer (shell) fold Close to the shell margin is the outer mantle fold. The pallial mantle is attached to the shell. Even though the mantle folds look similar morphologically.1 Mantle structure IX The mantle. is similar in nature. are found below the epithelial layer. functionally they are quite different. 5). Longitudinal and transverse muscle cells. which are not ciliated or pigmented. which is an important part of the molluscan body. each consisting of three regions: the marginal. The outer margin of the middle fold has ciliated cells. The margin of the fold shows a conspicuous pigmentation. The free edge of the marginal mantle is thick. The outer surface of the fold is lined with specialized cells. and also with a distinct pigmentation. a little away from the shell margin. throughout the inner surface from the groove to the tip of the mantle fold. Middle fold The inner margin of the middle fold is similar to the inner margin of the inner fold. In the pearl oyster the mantle is bilobed. which are also pigmented. The inner fold is muscular in activity. columnar in shape. Elongated (15–30 µm) stratified columnar epithelial cells occur near the periostracal groove on the inner surface of the fold. Along the hinge line. these cells become smaller in size (10–20 um). However. Inner fold The inner fold is relatively large compared to the other two folds. the middle sensory. and P. (2) Pallial mantle.2 Mantle isthmus The dorsal marginal mantle or the mantle isthmus consists of non-ciliated columnar epithelial cells.4 Central mantle Below the shell and dorsal to the pallial mantle is the central mantle. Histologically. Section of oyster mantle.1. the outer epithelium cells are non-ciliated and smaller (20–30 µm) than those of the ciliated inner epithelium. S. and are highly vacuolated.FIGURE 5. I.= shell fold.3 Pallial mantle The portion of the mantle just dorsal to the marginal mantle is known as the pallial mantle. M. 9. (1) Central mantle.= middle fold. 9.G.= inner fold.1. Here. .= periostracal groove. the secretory cells of the inner epithelium of the central mantle look similar to those of the epithelial cells of the inner pallial mantle. Sub-epithelial or epithelial secretory cells are totally absent in this region. The outer surface of the central mantle is lined with small columnar epithelial cells (10–15 um).F.1. and the sub-epithelium layer. which covers the body of the animal.F.S. (3) Marginal mantle. P. Secretory cells are found in both the epithelium. 9.= periostracal secretion.F. 5 cm near the tip. The blade is made by hand forging and finished by filing and grinding. along with a spherical shell bead nucleus. (2) preparation of graft tissue.CHAPTER THE SURGERY X The two items needed to induce the formation of a cultured pearl are a piece of mantle and a nucleus. . 10. (4) pearl oyster surgery and (5) post-operation care. Scissors This is a pair of straight surgical scissors of 10 cm length. The different steps followed in the operation are: (1) selection of oysters. It is used for cutting a long and narrow strip of mantle from its edge. The anterior portion of the blade is slightly curved corresponding to the curve of the oyster shell.1 Surgical instruments A set of specially made surgical tools is used in the surgery (Plate VII). (3) conditioning of oysters. Knife The knife has a blade 9 cm long and a wooden handle 11 cm long. The cutting edges are sharp and the tips are finely ground so as to enable quick cutting of a strip before the mantle withdraws under the stimulus of contact. is grafted into the gonad of the recipient oyster. The width of the blade is 1. The knife is used to open the unconditioned oysters by sharply cutting the adductor muscle without touching the mantle lobes. to hold it while cleaning and trimming and to reverse the strip on the wooden block. It is used to lift the mantle strip from the shell. The material near the joint is ground to proper size to get required mild tension after due hardness is imparted. taken from a donor oyster. Forceps The forceps is usually 14 cm long. The mantle piece. so that the blade can be easily inserted between the two shells in closed condition. The two components are filed and ground and are provided with serrations and finely ground points at the tips. These instruments can be made to specification by any surgical instrument manufacturing company.2 cm at the base and 1. 5 cm in length and 8 cm in width.5 cm long.PLATE VII. with a round handle of 13 cm length and 4 mm diameter and a blade 4. The required springiness is given to the blade by grinding and the edges are smoothened out. labial palps and gills of the oyster during surgery so that the foot and the main body are exposed. Scalpel . The spatula is used to remove dirt on the mantle strip and to smoothen the folds on it. Pearl oyster surgical instruments. It is also used to gently lift back the mantle. Spatula The spatula is 17. 5 cm high.0 cm.5 cm long and its diameter is slightly less than 1 cm.3 cm and a height of 7. The top of the straight portion is flat and rectangular with rounded corners. which passes through a hole in the shaft. helps regulate the distance between the flat ends as desired. the collar is slipped down to maintain the gap. They are described below: Oyster stand The stand is used to hold the oyster in a stable position. 4. to remove unwanted tissue and to sharply cut the tissue into small bits of the required size. They are then assembled to form the oyster stand.5 cm wide. The components are individually made to size and shape and are heat treated to sufficient hardness. the flat ends open and along with them also the shell valves. When the oyster partially opens its shells. The clamp consists of two plates. The instrument is 14. A vertical tube of 15 cm in length and 1 cm inner diameter is welded to the basal plate. Each component has a long straight portion and an arc. The maximum possible opening between the shell valves differs from oyster to oyster. The plate assembly can be tilted from a vertical to a horizontal position according to the convenience of the operator. It consists of two parts. The instrument is then heat treated to get high hardness. The second group of tools used in the actual operation are designed for the pearl culture industry operators. the head-plate and a movable jaw. The spring between the two arcs keeps the instrument in a closed position normally.The scalpel is flat and 17 cm long. which tend to follow the curve of the oyster shell and prevent lateral movement of the oyster. When the desired gap is obtained. The tube has a collar at the top provided with a threaded hole for fixing a bolt to hold the shaft of the clamp tightly in position. By gently closing the two arcs. This is about the distance between the two valves of the operable size oyster when the adductor muscle is in a fully relaxed condition under narcotisation. so that the operator's hands are free to perform the surgery. A maximum opening of 1.5 cm broad and 8. The two arms are fitted together by a male-female joint at about 5 cm from the tip. Shell speculum The shell speculum is used to keep the oyster open for the duration of the operation. The scalpel is used for trimming the mantle strip on both edges. A threaded hole and bolt are provided at this point to fix the rod in position. which are made by forging from round bar stock to proper size and shape. the length of the blade portion being 3. the movable jaw is opened by applying finger pressure at the bottom of the plate and after the oyster is placed in position the pressure is released. . It is also used in place of scissors to cut strips from the mantle. The jaw holds the oyster firmly against the head-plate. The shaft is 11.5 cm. The scalpel is produced by forging from bar stock or blanked from sheet metal and the actual size and shape are obtained by filing and grinding. The front edges of the two plates form short. For fixing the oyster. The head-plate has a breadth of 5. The head-plate is mounted on an adjustable tilting head supported by a shaft. The movable jaw is held against the head-plate by a spring. The base consists of a wooden board. A metal collar. To the head-plate is fixed a curved rod. slightly curved lugs. which is provided around the straight arms. the base and the clamp.5 cm is obtained between the flat ends with the collar pushed to the bottom.5 cm long and consists of two components. The 2 cm broad cutting edge provided at the end has a delicate curve and is smooth and sharp. The movable jaw is 5. to which is screwed a metal square plate. the flat end of the speculum is inserted between the two valves. While withdrawing the needle. can be used after studying the specific gravity of the material and other characteristics. provided with a sharp bent hook at the tapered end.5 cm long). Each needle consists of an elongated spindle-shaped aluminium handle in the middle (6. as for example the shell of the chank Xancus pyrum. Molluscan shell material is preferred due to phylogenic affinity. but the tip is provided with a sharp. through cutting. Then the hemispherical cup is cut to the required size of slightly less than the diameter of the sphere and imparted a vacuum finish. The cups are of different dimensions to enable lifting of nuclei (spherical shell beads) of 2–8 mm diameter range. The lancet is a thin (2 mm) stainless steel tapered shank with its tip slightly curved and flattened to form an elliptical blade. These beads are prepared out of thick shells of other molluscs. usually freshwater mussels. 10. The shells are processed into spherical beads of different diameters. The cup end is inserted into the channel through the incision cut on the body of the oyster and the nucleus is placed in contact with the tissue graft. locally available thick molluscan shells which have a composition akin to pearl oyster. pointed spur. shaping . but are provided with hemispherical cups at both ends of the shanks. These shells are imported into Japan from USA. The retractor is used to hold the foot of the oyster in a stretched position during the operation.Retractor It is a slender. They are polished to the required extent and fitted to the handle. with a lancet and a graft lifter. Nucleus-lifting needles These are similar in construction to the needles described above. The spurred tip of the needle is used to pick out the small graft tissue from the wooden block and to insert it into the site of implantation through the channel. popularly called pig-toe shell (Tritogonia). The lancet is used to make a sharp incision at the base of the oyster foot and to cut a channel through the tissues of the gonad up to the site chosen for nucleus implantation. There are three such needles. The edge of the blade is rendered smooth and sharp. where the freshwater mussels. occur in the tributaries of the Tennessee River. The graft lifter is similar to the lancet. three-ridge shell (Pleurobema) and washboard shell (Megalonais). themselves known to produce pearls. grinding. each with two cups at the ends. flat rod 15 cm in length. the nucleus is made to drop from the cup by a slight turn of the needle. Alternatively. The sizes of the cutting blade of the lancet and the spur are a graded series according to the size of the graft tissue to be lifted. The lancets and graft lifters are made to the desired shape and size by hand forging and finished by filing and grinding with abrasive wheels.2 Nucleus Spherical shell beads are used as nuclei to produce round pearls. at the two ends. chemical composition. Lancet-cum-graft lifting needles There are three such needles.5 cm long. binding strength and heat resistance properties which are similar to those of the nacre. generally 2–7 mm for Pinctada fucata. each 5. The cup is moistened by dipping in seawater and made to touch the dry surface of the nucleus which immediately adheres to it. The cup shoe is initially drawn by hand forging and finished to dimensions by pressing with iron balls of proper size in the cold condition. with the adhering body tissue. i. at a time.3 Selection of oysters The factors to be considered in the selection of oysters are their weight. 6 A). . the oyster should not suffer from polychaete blisters. Dimensional accuracy. smooth finish and high polish are important factors. Small pieces of the pallial mantle taken from the donor oysters are used as grafts for implantation (Fig. lift the mantle gently and place the tissue on a soft. since during surgery the gametes tend to flow out and block the visibility of the implantation site so that proper orientation of the mantle piece and nucleus cannot be ensured. oysters in the immediate postspawning recovery phase or those in the early phase of gametogenesis should only be selected. The donor oyster is cut open as follows: · · · · · Hold the oyster dorsal side down and the posterior end facing the technician. while 20 g oysters can be considered for implantation of smaller size nuclei. The selected oysters should be cleaned and all the fouling organisms carefully removed. This factor in turn decides the annual surgery period. Separate the two valves by tearing the hinge. The beads should be cleaned and dried before use. Press the knife straight downwards to cut through the adductor muscle.and polishing using appropriate machines and tools. A weight of 25 g or more is the ideal size for implantation. Insert the curved end of oyster knife between the two valves at the posterior side. sponge borings and trematode infection. At this stage the inner epithelium of the mantle is facing the technician. · With the aid of the knife. The steps involved in the removal of the mantle (marginal and pallial region) are given below: Deal with one valve. If disturbed. clean. cut the mantle tracing a curve up to the anterior margin (Fig. Push the knife straight through the oyster until the knife tip reaches the anterior end. Expose the mantle lobes by gently brushing aside the gills with the tip of spatula. Therefore. With a wet sponge. 10.e. moist wooden block without changing the side. Use the graft knife to cut away the marginal mantle (this mantle is characterized by numerous folds and it is highly pigmented). gently wipe out all the mucus and dirt. · Using the forceps. 10. In addition. reproductive stage of development and overall health. · · Further steps in the preparation of graft tissues are as follows: · · · Gently stretch the tissue end to end. Fully matured oysters are not suitable. starting from the posterior margin.4 Graft tissue preparation The donor oysters do not have to be subjected to any conditioning process. the lobes will shrink and cannot be used. Care should be taken for the mantle not to shrink. 6). 2–3 mm in diameter. which the recipient oysters have to undergo. without disturbing the two mantle lobes. Where such techniques do not work. copious secretion of mucus and mortality. With the use of a soft brush smear the mantle pieces with a highly diluted solution of water-soluble eosin. however it can be practised only in regions where there is stratification of seawater temperature. due to spawning. In about 60–90 minutes. smooth and moist all the time.· · · · · · · · · In the same manner cut away the inner muscular portion of the mantle on the opposite side. Use only clean. Wooden blocks must be clean. however once narcotised the oysters become almost non-responsive to touch. 10. Such conditioned oysters can be readily used in surgery. such as in Indian waters. sterilised. All instruments must be washed and sun dried before their use. . Remove all the dirt and mucus from the wooden block. Using the thermal differences. Wipe the mucus and dirt softly without causing damage to the outer epithelial layer. reverse the side (top to bottom) and place it on the block. The size of each piece has to be in proportion to the size of the nucleus (Fig 6 D). A duration of about 30–40 minutes after response is the safe limit. the oysters become narcotised and relax their adductor muscles and open the valves.5 Conditioning for surgery Natural conditioning is ideal and inexpensive. Precautions · · · · · · Care should be taken to ensure that the knife does not injure the palm of the technician while inserting it between the valves of the oyster. the oysters are spawned in the upper water layers which have a relatively high temperature. Trim the margins on either side until a mantle ribbon of about 3 mm width is obtained (Fig 6 B and C). Holding one end. as well as sharp difference in food availability. Different sections of the sponges must be used for each wiping operation. Keep the tissues moist until they are used within about 30 minutes. lift the mantle ribbon. The conditioned oysters are usually operated within the next 10 to 15 minutes as prolonged exposure causes swelling of tissues. Shrunken mantles should not be used due to difficulty in handling them. The time of response varies with the water temperature. Use the graft knife to cut the ribbon into small pieces (2–3 mm). With the loss of the stored energy. in order to reduce their metabolic rate. the weakened oysters are further subjected to starvation by placing them at depths where phytoplankton production is low. This method works well in the sea conditions in Japan. chemical conditioning is resorted to. transfer the mantle ribbon to a new block without changing sides. filtered seawater throughout the operation. Sponges must be clean and moist. and therefore the pearl oysters should be treated in batches. Now the outer epithelium is facing the technician. Menthol crystals are sprinkled over the seawater in the tanks in which the oysters are placed. Again wipe the mucus and dirt with a wet sponge. If necessary. (A) mantle tissue when removed from an oyster (p. (C) further trimming to obtain ribbons of pallial mantle.m. Steps in graft tissue preparation. Nuclei with diameters ranging from 4–6 mm are used for double implantation. Single and double implantations are common while multiple implantations are usually carried out when large numbers of small pearls of about 2–3 mm are required. 10. in the range of 6–7 mm. are generally used in single implantation.FIGURE 6. (B) trimming of the margins to remove marginal mantle and inner muscular tissue.m. a large and a . Large diameter nuclei.= marginal mantle).= pallial mantle and m.6 Surgery The number of nuclei to be implanted in one oyster is usually decided before the operation. one nucleus in each oyster. and (D) cutting of the ribbon into small sections. deflect the needle gently so that the nucleus drops. Nuclei with diameters of 2–3 mm are generally used in multiple implantations. Remove the oyster from the clamp. The speculum is now towards the left-hand side of the technician. Mount the oyster with the speculum on the clamp. If there is too much tear of tissues. With the oval knife end of the incision-cum-grafting needle in the right hand. The steps involved in pearl oyster surgery are as follows: · · · · · · · · Insert the end of the speculum through the posteroventral corner of the oyster and open it by sliding backward the gap-regulator ring (Plate VIII A). At this stage the nucleus must be in contact with the outer epithelium of the mantle tissue which was grafted into the gonad by the preceding step. · · . On reaching the site. withdraw the speculum by slipping the gapregulator ring forwards and place the oyster in clean seawater. The best site for nucleus implantation is the gonad. Withdraw the needle. If the incision is too large the nucleus may slip out. make a sharp incision at the base of the foot. wash the instruments in clean seawater. Withdraw the needle gently through the passage. do not proceed. Through this opening. Pick a piece of graft tissue. five or more nuclei in one oyster. Gently withdraw the needle. particularly in its ventral portion. Precautions Before and after use. · The incision should be a sharp cut and of the required length for the size of nucleus to be inserted. The nucleus implantation operation is now over. Hold the needle in position until the operation is completed. Adjust the pressure on the foot in a way that the foot does not get torn while pulling it with the needle hook. In double implantation. Attention should be paid not to open the oyster too much as the adductor muscle may snap and kill the oyster. Hook the tip of the foot with the needle with the left hand and gently pull it so that the base of foot is slightly elevated. Single implantation is always done at this site. is used for the smaller nucleus. close to the hepato-pancreas.small one in each oyster. Lift a nucleus with the moistened cup end of the appropriate nucleus-implanting needle and gently insert the nucleus through the gonad (Plate VIII C and D). gently deflect the needle and allow the graft tissue to drop. Place the oyster back in fresh seawater and return to the farm for future use. On reaching the site. The oyster should be placed correctly between the two plates of the clamp so that it does not slip. with the tip of the needle (same needle as above but reversed) and gently insert it through the passage cut in the gonad. the above site is used for the larger nucleus while a site in the dorsal region of the gonad. steadily and gently cut a passage through the gonad connective tissue up to the site of implantation. passing the needle below the outer skin. Now the outer epithelium of the graft tissue is facing the passage (Plate VIII B). already on the block. Smoothen the incision with the cup end and let the two margins of the incision come in contact. intestine and heart during the surgery. Implantation of a pearl oyster. if there is copious flow of gametes.While cutting the passage through the gonad. (A) Opening of the oyster valves and (B) Insertion of the graft tissue. . · Skill and patience are the key factors for a successful operation. do not proceed but return the oyster to the farm. · Do not cause damage to the vital organs such as stomach. · PLATE VIII. · The orientation of graft tissue (outer epithelium) and nucleus should be correct. Cont'd.PLATE VIII. . Implantation of a pearl oyster. and (D) General view of oyster surgery. (C) Implantation of the nucleus. forming a pearl in due course of time. The conchiolin is organic in nature and consists of mucopolysaccarides. In any pearl formation. In response to this stimulus. only the exposed portion becomes covered by the pearl-sac resulting in a blister pearl. The inner epithelium and connective tissue of the mantle disintegrate and become absorbed by the surrounding tissue. The outer epithelium of the mantle forms the pearl-sac on the free surface of the nucleus and the halfpearl is formed. the mantle piece graft tissue and the shell bead nucleus are implanted together.2 Cultured pearl formation Cultured pearls are formed in a pearl oyster. decaying parts of plants. into the gonad of the oyster. thanks to human interference. two things are required. Through careful surgery. or between the mantle. the foreign body is invaginated by the outer epithelium of the mantle and a pearl-sac is formed around it (Fig. 7 B) are produced by affixing many nuclei on the inner surface of the shell valves. In cultured pearls the nacre quality and the process of pearl formation are the same as in the formation of natural pearls. the outer epithelium of the mantle lobe and core substance or nucleus. These pearls are produced either within the mantle. such as parasites adults or larvae. epithelium or blood cells of the same animal. . Large and spherical pearls are still rarer to find.1 Natural pearl formation XI The principal causative factor in pearl formation in a pearl oyster is the presence of a nucleus. They are generally small and irregular. The epithelial cells of the pearl-sac secrets the nacre which becomes deposited over the foreign body. sand grains.60 mm thick and are made of calcium carbonate in the form of highly laminated crystals. side by side.CHAPTER PEARL FORMATION 11. The pearl-sac is derived from the internal or external layer of the apithelium of the mantle or of the gill plates. It was found that cut pieces of the mantle epithelium would provide the pearl secreting cells and that processed shell beads would be accepted by the oyster as the foreign body. etc. and the interior surface of the shell. These foreign bodies may become embedded between the shell and mantle. Cultured half-pearls (Fig. The cells of the pearl-sac derive their nourishment from the surrounding tissues and soon reassume their function of nacre (mother-of-pearl) secretion which is deposited over the nucleus in the form of concentric micro-layers (Fig. It can be of organic or inorganic origin. Pearls are not produced without the formation of the pearl-sac. The aragonite layers are 0. When the extraneous matter becomes fixed to the shell. molluscan eggs. Such pearl production is accidental and occurs very rarely. It forms the binding layer for the aragonite crystals. The outer epithelial cells of the graft tissue proliferate and rearrange themselves over the shell bead nucleus. The nacreous matter consists of thin alternate layers of aragonite and conchiolin deposited around the nucleus. 11. in other soft tissues of the oyster. These tiny particles or organisms enter the oyster when the shell valves are open for feeding and respiration. 7 C). forming a pearl-sac.29–0. 7 A). The oysters are then returned to sea for further growth. Process of pearl formation. and (C) round cultured pearl with an artificially implanted nucleus. (B) half-cultured pearl.FIGURE 7. (A) round and half-natural pearls. . The Culture period ranges between 3–24 months for 2–7 mm diameter nuclei under tropical conditions. The length of the culture period following the operation phase depends on the size of the nuclei inserted and the desired size of the pearls to be obtained. it is desirable to rear the operated oysters under laboratory conditions till the wound heals completely. If the sea is not calm. The quality of the pearl to be formed is influenced by several hydro-biological factors. the rafts are towed to warmer water bodies to allow the pearl oysters to over-winter. In Japan. Settlement of undesirable organisms and silt on the oysters is responsible for the formation of poor quality pearls. newly operated oysters are hung in deep and calm waters for a period of 2–3 weeks. Over-crowding may cause adverse effects such as production of low quality pearls. However. the nucleus could slip out of the oyster. as in India. In Japan.Some Japanese pearl culturists examine the pearl oysters individually after recuperation by fluoroscopy. if cultured in rough waters. The normal duration of wound healing is only a day or two. by which time they recuperate fully. The oysters must be suspended in areas of high phytoplankton production and also at greater depths than the mother oysters.CHAPTER XII POST-OPERATION CULTURE 12. Only those with the nucleus in the proper position are further cultured for pearl production. in areas where the inshore waters are not calm. However. If no flow-through system is available. When normalcy is resumed. slow formation of the nacre layer. shell damage and physical stress. trace metals content. such as primary production. During the post-operation rearing period. Periodic sampling of each oyster batch will give the basis for deciding on when to harvest. it is always advisable to keep the operated oysters for 3–4 days in the laboratory under observation and then transfer to the farm. etc. Afterwards they are hung as in normal culture practices. when the seawater temperature drops below 10 °C during winter. they will be subjected to undue stress. and therefore command a lower market price. the oyster density in the culture cages and culture grounds should be kept at a minimum. they should be placed in plastic troughs or FRP tanks. as well as oyster mortality from diseases and parasites. If the oysters are suspended in rough sea immediately after the operation. in order to check the condition of the inserted nucleus. temperature. Hence the oysters should be monitored periodically and fouling organisms thoroughly eliminated. the oysters slowly re-open their valves and commence their pumping and filtering activity. current. the seawater has to be changed frequently to overcome the narcotizing effect of menthol. . the culture site and depth at which the hanging culture structures should be fixed must be carefully chosen to have the most favourable conditions for the culture of the pearl oysters. slow formation of the pearl layer and oyster mortality. if the surgery is rough or the incision is large. Coastal waters deeper than 5 m are usually favourable for the formation of high quality pearls. Pearls with a thin nacreous layer usually will not have good lustre and iridescence. which may lead to the dislodging of the nuclei. If kept in the laboratory.1 Culture conditions Freshly operated oysters should be reared undisturbed for a few days. while the rejected ones will be retained as mother oyster for future use. However. where seawater is allowed to flow gently. the shell bead nuclei were wrapped in mantle tissue and implanted into the visceral mass of the pearl oyster. 13. Water soluble eosin and mercurochrome are some of the chemicals used as sterilising and colouring agents to enable the operator to place correctly the graft tissue. particularly in the case of large ones. is sufficient for nuclei of 2–6 mm in diameter. However. this miss-happening can be kept to the minimum by improved surgical methods. A small piece of mantle section measuring 2×3 mm in size. biofouling. Later it was found that a small piece of the mantle epithelium would suffice for the formation of the pearl-sac.A. the nucleus may either remain as it is or become eroded. However. shell boring and pollution may also be responsible for oyster mortality. probably due to the non-formation of the pearl-sac. in terms of its orientation. . These beads are manufactured from the shell of a freshwater mussel species found in the Tennessee and Mississippi Rivers in the U. The thickness of the epithelium layer plays an important part in the formation and quality of the pearls. but also by the inherited capabilities of individual oysters.1 Development of implantation technique Free spherical cultured pearls are produced with the help of spherical shell beads.2 Nucleus retention and pearl production Nuclei ejection does not commonly occur. Defects in surgery and incorrect orientation of the nucleus and graft are two of the reasons for this defect. The inner epithelium and the connective tissue rapidly disintegrate. Proper farm management procedures usually keeps the oyster mortality rate below 10 %. The quality of pearls with regard to their shape and colour. at the time of insertion. These shells are collected and exported to Japan. In the initial phase of the development of the implantation technique. However. which is responsible for the secretion and deposition of the mother of pearl on the nucleus itself. in some cases they are retained for re-implantation as no nacre has been deposited over them. diseases. which are important factors in terms of their market value.S. known as nuclei. The actual pearl formation. 13.CHAPTER XIII PRODUCTION OF CULTURED PEARLS Cultured pearls are produced by pearl oysters as a result of delicate techniques developed by scientists over many years. leaving only the outer epithelium layer to proliferate and form the pearlsac. Discharged nuclei are usually thrown away. are not only influenced by external environmental factors. However. In cases of non-formation of pearls. the human role in the pearl production process stops with the successful completion of surgery for nucleus implantation and in providing suitable environmental conditions through careful selection of the culture sites. A common cause of death is serious infection of the wounds inflicted at the time of the implantation operation. which results due to an internal biological process. where they are cut and processed into precisely spherical beads of different diameter. is left entirely to the pearl oyster itself. Oysters may die in the culture farm due to a variety of reasons. As in the case of natural pearls. the quality and the rate of cultured pearl production are only partly controlled by the activities of the pearl culturists. while in multiple implantation. pink.3 Pearl harvesting Harvesting of the cultured pearls is usually carried out manually.with slightly larger pits and protuberances. in a commercial pearl culture farm the combination of class A and class B pearls should account for at least 60 % of the gross production of cultured pearls for it to run economically. flawless and lustrous. half good and half bad. their nuclei can be often salvaged and reprocessed. First class pearls . stain marks. The production rate can be improved by adopting appropriate technology and care during surgery and subsequent culture. from the finest quality to trash. These pearls are usually referred to as ‘trash pearls’. Class C Features: wild shaped. Shirai (1970) has categorised the cultured pearls as follows: Class A Features: flawless. a rate up to 180% has been obtained. This is a common feature in all pearl culture centres around the world. while a large proportion are inferior and some totally valueless as gems. small stain marks. Class B Features: fairly large flaws. the process can be automated with the use of simple machines. Generally the success of a pearl culture industry depends greatly on a high production of good quality pearls as a percentage of the total numbers produced. pink. creamy in colouration. one flaw. This class may also include pearls with small blemishes of the size of a pin point. These pearls are further classified into: A1: A2: Top pearls-perfectly round. Generally. The remaining 40 % of class C pearls are usually rejected. heavily marked. by cutting the adductor muscle. and irregularities in the shape. Usually a small percentage of the pearls produced have an outstanding colouration and perfectly round shape. the production of cultured pearls is also a result of a biological process within the pearl oyster itself. When treated these pearls become indistinguishable from the pearls categorized as A-1. making . However. badly coated. small flaws. This rate can definitely be improved by professional technicians with considerable knowledge and practical experience. In India. clayey lumps. The gross production of pearls includes all kinds of pearls. Therefore. In the case of manual extraction the pearls are collected by initially separating the two shell valves. the highest recorded production rate achieved in single implantation was about 65%. However. silver or light cream in colouration. ‘Gross production’ usually refers to the number of cultured pearls produced by oysters which have survived the implementation of the shell bead. 13. and after a certain length of time they can be operated for a second time to produce additional pearls. polished with refined salt and sorted for sale according to size. the pearls are carefully removed by opening the pearl-sac through the gonad taking care not to damage nor stress the oyster. harvesting is done during periods of low temperature and pH as the pearls tend to be of higher quality due to a thick and compact outer nacreous layer. lustre and other external characteristics. the harvested pearls are washed in distilled water. colour. shape. The machines used for pearl extraction usually work by dissolving the oyster soft body parts with the use of chemicals while the pearls remain as they are and become easily extractable. In case the oysters need to be reused for a second time. Finally. The oysters are then returned to the culture site for recovery.an incision on the gonad and squeezing the pearl out. . In Japan. size. To achieve a high rate of production of quality pearls. or a combination of both. However. The value of a pearl is decided by its quality. Therefore. Good water quality and correct level of the chemical agents should be used in maintaining the tissue pieces. They must be free from a heavy fouling load and blisters caused by sponges and polychaetes.4 Implantation The nucleus implantation is one of the most important factors in cultured pearl production. Its success greatly depends on the selection of the correct site and skill of the technician.CHAPTER XIV IMPROVEMENT OF PEARL QUALITY 14. individual variations are bound to occur in each and every pearl.1 Measures for enhancing pearl quality Quality commands a premium price in pearls. trimming and cutting of the donor mantle tissue.1.1. but can be considerably improved through appropriate care in surgery and during farming. cleaning. The donor oyster should be of the desirable size with a well developed and healthy mantle. with unpredictable and subtle variations in structure and composition. the quality of cultured pearls cannot be controlled absolutely. Exceptional pearls command special premium price. in terms of size and weight should be selected. the colour and lustre. The success of the pearl culture industry depends on the high rate of production of quality pearls.1 Oyster selection Large oysters. the following factors are required to be taken care of: 14.Even under the highest possible human control. The final product may range from the finest to the trash due to such variations. 14. Extreme care should be taken in selecting. may be organic or inorganic in origin. Only the size and shape of the cultured pearls are under the control of the pearl culturist. which depend on the secretion of the pearlsac. which influence the formation of pearls.Being a product of biological origin. considerable attention is paid to this aspect. which leads to the formation of the pearl. 14. The secretion of the mantle or the pearl-sac. can also be improved to some extent by proper understanding of individual biological and physiological factors as well as the environmental conditions of the culture farms.1.3 Graft tissue preparation The graft tissue is one of the most critical factors in controlling the rate of pearl production.2 Narcotization of oyster The amount of menthol required to narcotize. and the duration of narcotization should be carefully adjusted depending on the volume and weight of the oysters. colour and lustre.1. The oysters should be healthy as can be judged from the colour of the visceral mass and gills. shape. The . stretching. 14. Higher temperature leads to faster growth in oysters and higher rate of nacre deposition. pearl oysters are shifted to places of potential quality pearl yielding grounds. Periodic removal of these deposits increases the production of pearls with desirable quality.positioning and orientation of graft tissue in contact with nucleus is also critical and should be carried out with great skill and patience. However. Fouling and boring problems and siltation are considerably less at depths of 10 m or more. This is very clearly shown by Pinctada margaritifera (black or steel grey). and repeated culture on the same ground has been shown to affect the quality of pearls.5 Oyster convalescence Oysters can be made to recover from the effect of narcotization through periodic changes of water or gentle flow-through. the colour of the pearls produced may be golden yellow. fucata. Organic substances discharged by the pearl oysters and fouling organisms are deposited on the sea bottom and their build-up eventually affects the chemical and physical state of the water. 14. 14. such as liver. depending on slight differences in the site of nuclei implantation. The colour of a pearl is usually similar to the colour of the shell nacre of the mollusc which produces it. The thickness of the epithelium of the graft tissue is also considered to be responsible in determining the quality of pearls.1. in proximity to the hepato-pancreas. P. A thin graft (2–10 µm) usually produces pearls with a good surface. abalones (green) and freshwater mussels (pink). while those produced in the dorsal region of the gonad. maxima (silvery white). Pearls produced close to the retractor muscle tend to be baroque in shape with irregular protrusions and with a distinct black colouration. are usually grey or white. The pearl culture grounds also play a significant role in determining pearl quality. Multiple nucleus implantation requires still greater care and patience. Sufficient time must be allowed for the incision wound to heal before taking the oysters to the sea for further farming. Thinner laminar nacreous layers. this character is genetically controlled.6 Tool maintenance The tools must be sharp. But this affects the quality of pearls. Temperature controls the metabolic rate of the molluscs. A number of environmental factors plays a predominant role in determining the colour and lustre of the pearl nacre. byssal gland and intestine. During the final “make-up culture” period. Flawless pearls of regular form are frequently seen among the pearls developed in contact with internal organs. 14. while thicker ones (>20 µm) tend to produce dull and badly coloured pearls. are desirable at . Water depth is one of the most important factors. rust-free and should have been either sterilized or suitably cleaned and sun-dried. as quality pearls tend to be produced in waters below 10 m.1. pink. The pearls produced in the ventral region of the gonad are white or golden. in the case of P. white or cream. which result from low temperature and pH.2 Colour of pearls Different molluscs produce pearls of different colours. 22 0.26 Duration of culture (days) 94–108 161 191 161 159 The rate of pearl growth in relation to the size of oysters. Pearls with 0. Good quality blue pearls are of this origin. Minerals and trace elements in the seawater are important. Pearls should be allowed to reach maturity in proper time. It has been found that the golden and cream coloured pearls contain more copper and silver. which influences the colour of pearls.least in the later phase of the culture period. as obtained at Tuticorin.Short duration culture practice is another cause for inferior quality of pearls. The chief source of conchiolin are the nitrogenous substances of the plankton.5 mm nacre are accepted in the market. The rate of nacre growth is dependent on the size of the nucleus.692 0.732 0. since the thinner mineral laminae in the upper layers of the pearl give a better lustre to the pearls. is as follows: Oyster (mm) 40–50 40–50 50–60 50–60 60–70 size Nucleus (mm) 3 4 3 4 5 diameter Thickness (mm) 0.32 0. Iron-bound peptide in the nacre favours the formation of yellow pearls. This depends principally on differences in chemical composition of the seawater. The physiological state of the pearl oyster and the condition of the culture ground have bearing on oyster growth and the size and colour of pearl.26 0.8 Thickness of nacre (mm) 0.609 0. while skin coloured and pink pearls contain more sodium and zinc. as these also influence the colour of pearls. The organic substances deposited at the beginning of the pearl formation also would influence the colour. The pearl colour varies according to the amount of porphyrins and metalloporphyrins present in them. as well as the kind and amount of plankton in the area where the pearl oysters are reared.31 0. The pearl growth rate obtained at Tuticorin is as follows: Nucleus diameter (mm) 3 3 3 4 5. The golden coloured pearls have been found to contain more metallic elements than green pearls.929 0.590 of nacre Duration (days) 388 402 395 404 318 of culture . It is managed by the pearl processing technicians according to the market needs of various trading centres. presenting a regular laminar brick wall-like structure with micro-layers of elemental mineral lamellae alternating with homogeneously deposited organic matrix in concentric layers around the inserted nucleus. The lustre of the pearl is due to the play of light on the laminated aragonite layers of the nacre due to absorption and reflection of the waves of incident light. and 3. The prismatic layer pearls are formed by calcite crystals and the organic ones by proteinous layers of conchiolin. Nacreous layer pearls are composed of aragonite crystals of calcium carbonate and they alone are valued as gems. would qualify as gems. The rest of the formations will have less or no commercial value. organic layer pearls These are determined by the quality of secretion of the pearlsac. Homogeneity.The quality of mantle of the donor oyster also influences the quality of the pearls. . The structure and composition of pearls reveal that several formations are possible during the development of cultured pearls. Therefore. Processing of cultured pearls through bleaching and dyeing is a highly specialised technique for value addition. prismatic layer pearls. It is believed that most of the cultured pearls in the market go through some kind of processing to remove minor defects and improve colour. it is very important that the final phase of post-operation culture of every batch of oysters should be done under ideal conditions. thinness and smoothness of these layers are responsible for the great play of lustre. nacreous layer pearls 2. Cultured pearls are broadly classified into: 1. Only those formed by aragonite crystals in tabular form. Utmost care should be taken in the selection of donor oysters and in the process of graft tissue preparation. 1. pearl oyster surgery and pearl collection. in which 25 personnel were trained. In accordance with the policy of the Indian Council of Agricultural Research on transfer of technology.1 Training programmes in pearl culture The technology of pearl culture was originally developed in Japan.Appendix References Publications and Documents. Malaysia.2 Short-term training course The above long-term course has been replaced by a shortterm course of 4–6 weeks duration. Since fisheries development in India is the responsibility of the States/Union Territories. 15. Four such programmes were conducted between 1977 and 1986. universities and other agencies. not only to Indian citizens but also to foreign technicians who are sponsored by their respective Governments. The scientists of the Fisheries Colleges of Agricultural Universities and other Research Institutes are also given training.1 Long-term training course A long-term training course of six months duration was conducted once in 1976–77 by the CMFRI for managerial and supervisory personnel. Myanmar. oyster biology. mother oyster culture. Indonesia. Details of the curriculum are given below: Introduction . 15. Japan has helped some other countries. The course is more popular among the interested organizations. This was a comprehensive course which dealt with pearl oyster resources. like Australia. in developing pearl culture practices. Nine trainees from maritime states of India participated in that programme. pearl collection and farm management. the above technologies developed by the Central Marine Fisheries Research Institute have been disseminated through training courses offered to candidates sponsored by different governments.1. which naturally captured the world market for cultured pearls. The Central Marine Fisheries Research Institute. Philippines and Thailand. The aim of the training programmes has been to extend the technical know-how to end-users. The content was developed for technicians. after developing the technology indigenously. RAS/90/002 APPENDIX I TRAINING PROGRAMMES The Central Marine Fisheries Research Institute is the nerve centre of pearl culture technology in India. 15. the target group for training consists of technical officers of fisheries departments of the maritime States and Union Territories. The course curriculum is confined to mothe-oyster culture. has adopted an open policy of imparting the technology through training courses. Mother oyster culture Practical: oyster raft culture. collection of pearls.3 Training programme in pearl oyster hatchery This is a 4-week course. larval rearing.4 Training for mariculture students An intensive one-week training on the techniques of pearl culture and pearl oyster hatchery is given to each batch of students of M. a batch of 16 participants of a Summer Institute in Culture of Edible Molluscs. larval feeding. were also trained on the techniques of pearl culture and pearl oyster surgery. microalgal food production. short-term and refresher courses in pearl culture. The first training course was conducted during 1986. spat settlement. The course curriculum includes infrastructure facilities needed for a hatchery. Refresher training courses have also been conducted as and when requests were received. 15. cleaning of pearls.Theory: Morphology and anatomy of pearl oyster. construction of rafts and holding baskets. graft tissue preparation. nucleus implantation. Apart from the above nominees who underwent training in the long-term. pearl oyster collection and farming. selection and conditioning of oysters. functions of mantle.1. 15. and Ph.1. This is useful not only to those concerned with pearl culture. care of oysters. water quality management. disease control. Pearl oyster surgery Practical: Handling of surgical instruments. Pearl collection Practical: Bleaching. . controlled maturation and spawning. spat collection and juvenile rearing.D. mechanism of production of cultured pearls. but also to the molluscan aquaculturists who wish to raise marine bivalve stocks in hatchery. pearl-sac formation. post-operation care of oysters. biology of pearl oyster.Sc. courses in mariculture under the postgraduate teaching programme in mariculture of CMFRI every year. farm maintenance. sorting of pearls. Pt. C.F. 1975. 1975. 1983. K. 34: 72–78. K. Spl. . Biol. 4(2): 192–205. Development of cultured pearls in India. Bull.ALAGARSWAMI.ALAGARSWAMI. M. Ass. 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