Saltwater Pearl Fisheries And Pearl Culture In India: An Update

By P.S.B.R. James and K.A. Narasimham

Recently. C. Ricbard Fassler (199 1 a, 1991 b, 1992) gave an overview of pearl culture in the world and discussed both "opportunities and obstacles" for the development of pearl culture. While Japan still bolds the monopoly, China is fast catching up and several countries are producing pearls on commercial lines, mostly with Japanese collaboration, the notable being Australia, Frencb Polynesia, Indonesia, New Caledonia and Cook Islands, Fassler (1991 a) stated that thougb the Indians bave developed their own pearl industry, there is little publisbed information.

The natural pearls from the Gulf of Mannar in India and the Persian Gulf are famous througbout the world as "Orient pearls" and beld in esteem in the world trade from time immemorial. Unfortunately, the pearl fisberiesofindia came to a grinding bait in the 60's, with no bope of revival in the near future. Working at the Central Marine Fisberies Re­searcb Institute (CMFRI), India, Alagarswami (1974)

Production Proven Rainbow Eggs

Mt. lassen Trout Farm REO · BLUFF. CALIFORNIA

For more information please call, write or FAX

achieved a breakthrougb in 1973 in the production of spberi­cal cultured pearls in the pearl oyster Pinctadajucata (Gould). Since then, with considerable thrust given to R&D programs on pearl culture by CMFRJ, significant advances bave been made in the batcbery production of pearl oyster seed, mother oyster fanning, production of cultured pearls, training in all aspects of pearl culture both at national and international level and transfer of technology. In the past two decades more than 70 scientific papers bave been publisbed mainly based on the work done at CMFRI, and except for 4 papers, they all appeared in Indian journals. Imponant general accounts on pearl culture in India are by Alagarswarni (1987 b, 1991), Anonymous (1991), James et al (1991) and James and Narasimbam (1993).

Pearl Oyster Resources and Flsbery Resources and distribution: In Indian waters six species

of pearl oysters, namely Pinetada Jueata (Gould), P.

Why do MAJOR trout producers throughout the world buy from

Mt. Lassen Trout Farms, Inc. QUALITY: Excellent Hatchability and Survivability.

PERFORMANCE: Over two decades of progeny tested production fish resulting in PROVEN GENETIC GAIN for FASTER GROWTH AND BETTER CONVERSION.

AVAILABILITY: Production of trout eggs YEAR AROUND.

DISEASE FREE CERTIFICATION: Done by impartial government agencies, available on request.

TECHNOLOGY: Mixed Sex, Females, Mt. Lassen Trout Farms, Inc. Female Triploids', live unfertilized eggs and

sperm (Bioassay), Customized Orders; All 28125 Hwy 36 East availale Year Around .

Red Bluff, CA USA 96080 COMMITMENT: Our goal is to provide the Phone (916) 597-2222 best egg possible thru RESEARCH and Fax 916-597-2068 GENETIC SELECTION evaluated by Kleth Brown Mary Mackey Phil Mackey PRODUCTION TESTED PERFORMANCE,

"WE AREN'T RESTING ON OUR REPUTATION, WE'RE BUILDING IT"

R.S. No. 318 • Available in limited quantities.

AQUACULTURE MAGAZINE JULY I AUGUST 1994 41

A collection of cultured pearls.

margaritifera (Linnaeus), P. chemnitzii (Philippi), P. sugil/ata (Reeve), P. anomicides (Reeve) and P. atropurpurea (Dunker) have been recorded. Among these, the fIrst two are of commercial value in pearl production aud the remaining four species are broadly called as "flat" oysters.

P. jucata is the most dominant aud occurs in large numbers in the pearl banks, made of hard ground, called 'paars' in the Gulf of Maunar. There are about 65 paars located at a distance of 12 - 20 Ian away from the coast at 15 - 25 m depth. The extent of these paars varies from a few

TM

OCTOPUS The Next Generation Controller

hundred square meters to a few square kilometers. In the Gulf of Kutch, P.jucala is found in small numbers in the intertidal coral reefs known as "Kbaddas." There are about 42 reefs covering 24,000 ha.

The black-lip pearl oyster, P. margaritifera is confined to . the Andarnan & Nicobar group of islands. Recently few specimens were collected from the Gulf of Mannar. .

Fishery: The documented history of pearl fisheries in the Gulf of Mannar indicates that so far 38 pearl fisheries have taken place between 1663 to 1961. The pearl fisheries were irregular and inter-spaced with long gaps of unproductive periods due to the decline of the oyster population. The Tamil Nadu government exercises a monopoly and organizes the fishery after ascertaining the abundance of pearl oysters in the paars. Plank-built canoes are towed by a motorized boat to the predetermined pearl bank and the divers work without any diving aids. Each dive lasts for a maximum of 90 seconds. The 1955-61 series, the last conducted till date, is considered as the best held so far and the average annual yield was 12,322, 116 oysters; the average annual revenue was Rs. 316,065.

The Gulf of Kutch pearl fishery is controlled by the Gujarat government The fIshermen wade through the inter­tidal beds and hand-pick the oysters. During 1913 to 1967 twenty five pearl fisheries were held and fewer number of oysters were collected when compared to the Gulf of Mannar fishery. From 1950 to 1967, the average number of oysters

AQUADYNEn

,

(Juality Used MicnJSCIDpE!S

Unit [ompl..tely 5,,!rvilo::e!dI With Warranty

• pH, ORP, and Temp. Management • Infrared Datalogger Option • Computer Networkable • Plus many more options

The Octopus represents the latest in microprocessor based controllers for the aquaculture market. With 5 channels supporting pH, ORP, and Temperature monitoring and control, the Octopus can be configured to meet a wide range of needs. With the optional datalogger the controller can record up to 7 days of data, and graph it on a low cost portable infrared printer without the need of a separate computer. An optional computer link is available which includes the ability to network the Octopus in both local and wide area configurations. Give us a call and we will send you our 1994 Octopus Configuration Guide to see how you can bring this exciting technology to your application.

R.S. No. 543 Aquadyne Computer Corporation

7343 Ronson Rd. Suite p. San Diego, CA 92111 TEL (619) 569-2082 • FAX (619) 495-3119 • Cserve 73377,3007

WE ALSD SELL NEW MICROSI:OPES

, 'Buy' • • Sell· .

• Refurbish •

42 AQUACUL TORE MAGAZINE JULY I AUGUST 1994

fished per year was about 17,000; t1fe highest value of pearls realized from the fishery was Rs. 619693 during 1943-44.

P. margarilijera occurs in low densities and does not form a fishery.

Current Status of Resources

- ---;:.----

A view of the pearl oySler farm made of racks.

Scuba diving was introduced in India in 1958 for the survey of pearl banks under the auspices of FAO. The surveys conducted by CMFRI during 1975 to 1986 in the Gulf of Mannar showed revival of pearl oyster population in some paars but the yield was inconsistent except for 3 or 4 paars. During this period, for a total diving effon of 595 hours in various paars, 239,000 oysters were fished. Pearl oysters other than P. jucala (flat oysters) formed 10.36% of the population. Predation of the oysters by the gastropods Cymatium cingulatum and Murex virgineus led to heavy monality. In successive years the population was composed almost entirely ofless than one-year old pearl oysters. These oysters are too young to be of use for the production of natural pearls. Experience showed that oysters above three years of age give satisfactory pearl yield.

There was no improvement in the Gulf of Kutch pearl oyster population since 1968.

box-type cages covered with synthetic net webbing, have been ranched on 17 occasions. Due to practical difficulties in locating the cages, the ranched stock could not be moni­tored.

Spat Collection From Nature Sea Ranching of Hatchery Produced Spat

With the objective of enhancing the natural stocks of P. jucala CMFRl has embarked upon a sea ranching program of the hatchery produced spat in the Gulf of Mannar. During 1985-1990, a total of 1,025,300 spat of P. jucata placed in

Many attempts to collect pearl oyster spat by laying collectors such as empty pearl oyster shells, ropes, synthetic filamentous spindles, split bamboo and coconut shells made at Veppalodai and Tuticorin harbor farms of CMFRI during 1975-81 were futile either with no spat or very few spat. At

MASTER SYSTEMS

1 Record Production" 2 Record Feed Conversion" 3 Improved Water Quality" 4 More water movement than

paddle wheel type aerators" 5 Lower total and unionized

ammonia concentrations" 6 Decreased off-flavor" 7 Less disease problems"

• For copies of documentation of above claims:

1-800-533-6748 D-S Inc., dBA Master Systems

Highway 49 West Belzoni, MS 39035

R.S. No. 237

AQUACULTURE MAGAZINE JULY I AUGUST 1994

27 - 36 H:P.

1.000 Lb.

43

World Class Producers of Grass Carp and Bass, Fry and Fingerlings

We're major producers of: • Hybrid Striped Bass • Triploid Grass Carp • Rosy Red Fat Head Minnows • Big Head Carp • Black Fat Head Minnows

KEO FISH FARMS, INC. ~ P.O. Box 123, Highway 165 N, Keo, AR 72083

(501) 842-2872, FAX 842-2156

. ;, ' . " ',", .':.

.. , ' ,', .' ...

INTERNET PROTECfION ABOVE and

·Water ' ~"' .. ' " _. - ,~.

. . .. '. . . . . . .' . .

Choose from our huge selection of square, rectangu lar and Vexa!'" diamond mesh plastic nets and grids.

m~~ • Cages, Traps, Trays, Screens, Feeders in heavy grids

from ~ to lY. " hole openings • Up to 17' wide rolls of lightweight net

z

. .' . .

• Sleeve bags for Lobster bait, Culturing and Grow Out

Order only what you need! Immediate, Reliable Service!

Call , or send, for FREE samples and color brochure.

fElnterNet, INCORPORATED

44

2730 Nevada Ave. No. Minneapolis, MN 55427 Phone (612) 541·9690

1-800-328-8456 R.S. No. 211

Graft implantation.

Vizhinjam. nylon ropes. hapa. or fish cages proved to be useful but profuse seulement of fouling organisms affected pearl oyster seulement.

Hatchery Production of Spat Success was achieved in the breeding and production of

spat of P. Jucota at the Shellfish Hatchery Laboratory of CMFRI at Tuticorin in 1982 (Alagarswami et al 1983 b). The techniques are basically the same developed in the U.S.A. for several bivalves (Loosanoff and Davis 1963). Ripe pearl oysters are held in groups of 25 in tlle conditioning room around 25' C and fed with mixed micro-algae grown in outdoors tanks. Spawning is induced by slowly raising the water temperature to about :noc. Spawning has also heen induced by chemical methods (Alagarswami et al 1983 a) such as transfening the oysters to seawater containing hydrogen peroxide (62.5% success). tris buffer (7&% suc­cess) and injecting hydrogen peroxide at the base of the foot (48% success).

The larvae are reared in I t FRP tanks and the seawater (sand filtered) is changed on altemate days. Isochrysis golbana. cultured in 100 liter perspex tanks at 25' C under axenic conditions is given as food. Spat settlement occurs in about 20 days with 20-30% survival from the initial larval stock. The spat are fed with mixed microalgae and reach 3 mm size in about 2 months from spawning. The hatchery has the capacity to produce one million spat per spawning run under favorable conditions.

Success was also achieved in the breeding and spat production of P. morgoritifera (Alagarswami et al 1989).

Pearl Oyster Farming This involves two aspects namely mother oyster culture

and post-operative cultures. The former comprises growing the spat collected from the pearl banks/hatchery until the oysters reach nucleus implantation size. The farming tech­niques are broadly the same for these two phases of culture except that additional care is taken on the implanted oysters.

Wooden rafts measuring 6 x 5 m. moored in 5 m and above depth and also racks of 6 x 6 m size erected in I to 2.5 m for suspending the pearl oy~ter cages. Box-type cages of 40 x 40 x 10 cm or prism-shaped cages with 35 cm sides made of 6

AQUACULTURE MAGAZINE JULY/AUGUST 1994

myt steel rod and covered with 2 mm mesh velon screen are used for rearing spat. These cages are insened into a bag made of IO-mrn nylon fish net for protection against crabs and predatory fishes. As the oysters grow, the velon screen net is dispensed and the box-type cages are covered with nylon fish net of appropriate mesh. During the grow-out the predatory gastropods such as Cymatium cingula tum and Murex virgineus and crabs Charybdis sp, Atergatis sp, Leptodius sp and Thalamitta sp enter the cages in young stages and cause serious damage. Biofouling by barnacles, bryozoans, simple ascidians and bivalve molluscs is COll­

mono Boring sponges and polychaetes drill their way and form blisters in the pearl oyster shell. The cages and the oysters are periodically cleaned to remove the predators, foulers and borers; other remedial measures include immer­sion of oysters in freshwater for 3 - 10 hr depending upon size, exposure to air for 2 -3 hr and immersion in I % formalin for a few seconds. Hatchery produced P.Jucata, grown in the Tuticorin Harbour farm attained 47.0, 64.5 and 75.0 mrn at the end of I - 3 years respectively. The survival of both implanted and mother oysters in the grow-out of 10 - 12 months is about 80%.

Nucleus Implantation and Post-operative Culture P. Jucata measuring 45 mrn and above and in inactive or

resting reproductive phase are used in pearl production. Sprinkling of a small quantity of menthol powder into the seawater containing the oysters make them slowly open their

Growth of Nacre: India VS. Japan

Country Nucleus Thickness of Duration of diameter nacre of culture

(mm) cultured pellrl (mm)

Japan 3.05 0.318 2 years (Cahn 1947)

4.10 0.363 2.5 years

6.10 0.439 3 years

7.90 0.500 3.5 years.

India 3.00 0.32 191 days (Algarswami

1975) 4.00 0.31 161

5.81 0.26 159 days

valves in 60-90 minutes. Immediately a wooden plug is inserted in between the valves and thus the oysters are conditioned. The ventral pan of the mantle of a donor oyster is cut into 2 to 3 mrn long and 2 mrn broad pieces for grafting. Mild solutions of eosin, mercurochrom.e or.a.?:!l:min in seawa­ter are used in graft tissue preparation. The surgical instru­ments are indigenously fabricated and consist of oyster knifes incision-cum-grafting needles, nucleus insertion needles,

Hot or Cold

TITANIUM CHILLI!R & HEAT PUMP

+ Skld mounted + Cool only or with Heating + DigItal Temperature Control

+/- 1 F or C

ACRY-TEe OFFERS: TIrANIUM CHILLERS HEATERS & PUMPS

ULTRAVIOLET STERILIZERS SYSTEM PACKS

HEAT EXCHANGERS

SYSTEM PACK

••

TITANIUM INUNE HEATI!R

+ Slcid mounted + Vertical or Horizontal Hook-up + Digital Temperature Control

+/-IForC

R.S. No. 779

3351 National Ave., San Diego, CA 92113 (619) 696-6655 1-800-422-7983 FAX (619) 696-6675

AQUACULTURE MAGAZINE JULY/AUGUST 1994 45

spatulas needle hook, graft knifes, forceps, speculum and oyster clamp. The conditioned oyster is mounted on oyster stands speculum inserted between the two valves, a passage is cut through the gonad up to the spot selected for nucleus implantation and the mantle piece is placed at the selected site. The shell bead nucleus is placed in contact with the outer epithelium of the mantle piece. In multiple implantation the process is repeated for each nucleus through the same incision by cutting the passage, through the gonad in suitable directions up to the selected site. After implantation, the two ends of the incision at the base of the foot are brought in contact and smoothed out. In P. Jucata 2-8 mm diameter nuclei, imported from Japan are used. Indigenously made nuclei from the chank, Xancus pyrum appear promising.

Mterimplantation, on transfer to slowly moving seawater the oyster recovers in about 30 minutes. For 2-3 days the oysters are kept under observation in FRP tanks having mild flow of seawater. Then they are placed in box-type cages of 40 x 40 x 10 cm and transferred to the farm. The skill of the technician is an important factor in the surgery. A technician implants about 100 oysters per day. The common reasons for the rejection of nucleus are too wide incision and passage cut through the gonad, damage to vital organs, rough handling and exposure to strong stimuli such as currents, waves, tides etc. Good quality pearls are produced when oysters are cultured in 5 - 10 m depth. Strong sun light on oysters results in poor quality pearls. The duration of the post-operative

culture for the production of pearls depends upon the size of the nucleus implanted, water temperature, food supply etc. In Indian waters due to favorable watertemperature the pearl grows fast and reaches marketable size in 3 - 4 months with 2 - 3 mm nucleus and 15 - 18 months with nuclei of6 -7 mm diameter. The following table on the growth of nacre illustrates the advantage of pearl culture in India when compared to the temperate waters of Japan.

The pearls are harvested by cutting open the oysters with a sharp knife, thereby killing the oysters. During the post­operation culture some oysters die due to natural causes and surgery while some reject the nucleus.

Production of Cultured Pearls . Considerable variations in the production rate are discern­

ible. In the Veppalodai (Tamil Nadu southeast coast) farm ofCMFRI, gross pearl production of62.8% in single implan­tation and 68.3% in multiple implantation with reference to the number of nuclei used has been reported (A1agarswami 1974). In a recent sIDdy (A.C.C. Victor, Personal communi­cation conducted by CMFRI at Valinokkam (Tamil Nadu, southeast coast) by scaling up the operations, out of a total of 9414 oysters implanted (single implantation with 3-5 mm nuclei) mortality during one year post-operative cultnre was 2108 oysters (22.39%). On harvest, the remaining 7306 oysters have yielded 1849 pearls (25:31 %). A total of 5457 oysters (74.69%) did not contain pearls due to rejection of nuclei or non-deposition of nacre. This variation in the

CAGES FROMINQUA DOUBLE-Q" SOFT-TOP and TOPLESS CAGES

NET PENS and OUR CLASSIC HARD-TOPS

N°ft!!ls~ • ALL GUARANTEED FOR FIVE YEARS •

EVERY CAGE WE MAKE IS AVAILABLE WITH

SOFT-TOP OR TOPLESS.

SOFT-TOP -FASNAP"" NETTING TOP SNAPS ON AND OFF

OUR STANDARD HARD-TOP

-SINCE 1975 4' x 4' x 4' DEEP

TOPLESS -COMMERCIAL SIZE" 8' x 8' x 4' DEEP

ALL CAGES USE STRONG PLASTIC NETIING AND

ALUMINUM PIPE CONSTRUCTION

Send b'" ~ cage ClJlture" bookIel Send $4 for delivery in U.S., Canada or Mexico. $5 eIIewhere. 'M"M or eal. R.S. No. 344

INQUA CORPORATION Box 86, Dobbs Ferry, NY 10522 (212) 840-3333 FAX (212) 840-0712

BLUEGILL

* PERCH

** CATFISH

*** PANFISH

HATCHERY

~ •. ~WAl~EYE

BASS .. ** .' NORTHERN

" PIKE

*** CRAPPIE

'We Specialize in Walleyes/"

Fingerlings and Larger Fish Available

Live Delivery Guaranteed

Anywhere in the Central United States

~ NORTHSTAR -FISH HATCHERY

Montour, Iowa 50173 (515) 492-6159

-"One of the Country's Oldest ,., ~ Private Hatcheries"

In BusinesS Since 1940

46 AQUACULTURE MAGAZINEJULY/AUGUST 1994

production of the pearls in these two studies is indicative of the range of production under variable conditions.

Grading and Processing oC Pearls Grading: The quality of the cultured pearls depends upon

the thickness of the nacre; iridescence, lustre, color, size, shape and flaws. They are graded into the following three main categories (Shirai 1970).

A-grade: Flawless, one flaw, small flaws, small stain, pink, silver or light cream.

B-grade: Fairly large flaws, stains. cream color, irregular shape.

C-grade: Trash pearls, wild shaped, badly coated, heavily pock-marked, clayey lumps, half good and half bad.

In the earlier studies by CMFRI at Veppalodai, A-grade formed 37.6%, B-grade 37.6% and C-grade 24.8% (Alagarswami 1987). In the recent study at Valinokkam (A.C.C, Victor# personal communication) A-grade formed 36.15%, B-grade 54.03% and C-grade 9.82%.

Processing: In surface processing the pearls are mixed with salt in equal volume and placed in a tub with little water. The residual mucus on the surface of the pearl is removed by rubbing with salt to obtain good lustre. To improve the quality the drilled pearls are bleached with hydrogen perox­ide.

Technology TransCer Concurrent with the development of pearl culture technol­

ogy, CMFRI has given priority to train the man power for

operating the pearl culture ventures, Beginning from 1976 officials sponsored by foreign countries and the fisheries departments of Tamil Nadu, Kerala, Karnataka, Gujarat, West Bengal, Andaman & Nicobar Islands andLakshadweep and also pearl farmers, numbering 72 have been trained in eight training programs organized by CMFRI. The training course is 4-6 weeks long, specially designed for technicians, and covers all aspects of pearl culture. CMFRI adopted an open policy in dissemination of technology and subject to the Indian Council of Agricultural Research guidelines foreign­ers had the benefit of these programs. In 1979 a technician from the South East Asian Fisheries Development Center, Philippines participated in a training course. The Regional Seafarming Development and Demonstration Project of the Network of Aquaculture Centers of Asia (NACA), Bangkok has recognized CMFRI as a Lead Center to train the Aquac­u1turists of southeast Asian Countries on pearl culture. Under this program an International Training Course was organized by CMFRI at Tuticorin from February I, 1991 to February 28, 1991 and 26 candidates from 10 countries have been trained.

Tamil Nadu Pearls Ltd., a joint sector company was the first to commercialize the technology developed by CMFRI and produced over 13 kg of cultured pearls and marketed. With the same technology Gujarat State Fisheries Depart­ment at Okha and Sikka and the Lakshadweep Fisheries Department at Bangaram have produced cultured pearls in small quantities.

"Big John" Water Movers

PTO PADDLEWHEEL

AERATORS

R.S.No 200

ELECTRIC PADDLEWHEEL AERATORS

PTO PUMPS

AQUACULTURE MAGAZINE JULY/AUGUST 1994

SAVE $$$'s with Top of the line, High Quality,

Low Maintenance Aerators

Call "Big John" Toll Free (800) 257-4743

"BIG JOHN" Water Movers 7013 West Jefferson Quinton. AL 35130

Phone (205) 674-9086 Fax (205) 674-9091

S +,-e_ Manufactured by:

G ~",:r...",,--_ 47

Current status Based on the technology developed by CMFRI the Tamil

Nadu Fisheries Development Corporation (TNFDC) is operating a pearl culture project at Krusadai since 1990 and has produced more than 3 kg of pearls and marketed them. Since the revival of the natural stock of pearl oysters in the Gulf of Mannar pearl banks is uncertain, to meet the requirements of the commercial venture, 1NFDC has set up a hatchery in 1992 with technical assistance from CMFRI_ The TNFDC pearl farms are located atKrusadai and Tuticorin.

Cnrrently the R&D programs of CMFRI on pearl culture are carried on at the Institute's farms located at Tuticorin and Valinokkam. Local fishermen are actively participating in the farm work at Valinokkam and recently they have been trained in nucleus implantation also. As a result they have developed the necessary skills to take up pearl culture on their own.

India has the advantage of possessing a complete package of tested technology (except for the import of nuclei), solely developed by indigenous efforts. Another advantage is the presence of strong R&D base and also well trained manpower to operate pearl culture ventures. However, entrepreneurs and farmers are yet to take up pearl culture in the country for reasons such as the nced to locate suitable culture sites along the mainland coast, lack of awareness, hesitancy due to risk­prone nature, absence onaws forthe usageofbodies of water, governmental monopoly over resources, constraints by way of input supply etc. Suitable sites for pearl culture are indicated in the Gulf ofMannars, Bangaram in Lakshadweep and Andaman and Nicobar group of Islands.

Future Outlook In recent times, with the Indian cultured pearls available

in the market, there is increasing awareness among the people about the technology and product. It will not be long before the message "pearls give the highest profit return of all marine products cultivated in coastal waters" (Wada 1973)

reaches the entrepreneurs and farmers, venturing into pearl culture.

At CMFRI, priority is given for short range projects on location testing of pearl culture at several places along the Indian coast. R&D efforts, already directed to take the technology to the grass root level as is being done at Valinokkam, will be strengthened. While the program on the . upgradation of the technology in P. jucata would continue, pearl production in P. margaritifera would receive attention. Also plans are underway to iuitiate a project on P. jucata mantle epithelium culture, leading to in vitro production of pearls of desired color.

References Alagarswami. K. 1974. Development of cultured pearls in India. Current Science. 43: 205-207. Alagarswami, K. 1975. Preliminary study on the growth

of cultured pearls. Indian Journal of Fisheries. 22 (1 &2): 300-302.

Alagarswami. K. (Ed.) 1987. Pearl culture. Bulletin of the Central Marine Fisheries Research Institute. Cochin. 39: 1-136.

Alagarswami, K., S. Dharmaraj, T.S. Velayudhan. A. Chellam, and A.e.C. Victor. 1983 a. On control/ed spawn­ing of Indian pearl oyster Pinctadajucata (Gould). Proceed­ings of the Symposium on Coastal Aquaculture, 2: 590-597. Marine Biological Association of India. Cochin.

Alagarswami, K., Dharmaraj, S .• Velayudhan, T.S., Chel/am. A .. Victor. A. e. e. and Gandhi. A.D. 1983 b. Larval rearing and production of spat of pearl oyster Pinctada jucata. (Gould). Aquaculture. 34: 287-301.

Alagarswami. K. Dharmaraj. S.. Chel/am. A. and Velayudhan. T.S. 1989. LArvalandjuvenile rearing of black­lip pearl oyster Pinctada margaritifera (Unnaeus). Aquac­ulture, 76: 43-56. .

Alagarswami. K. 1991. Production of cultured pearls. Indian Council of Agricultural Research, New Delhi: 1-112.

ONLY FRESH-FLO FORCES A MIXTURE OF AIR AND WATER WITH UNIOUE, ENLARGED SLOTS.

Widest selection of aerators available anywhere Speeds nature's own way of adding oxygen to water Motor operates trouble-free above the water surface

If you have a problem with production , the best solution may be the simplest ... Fresh-Flo aerators . Fresh-Flo's patented aeration process expels water (drawn up in the tube) through enlarged slots forcing a mixture of air and water that provides for the most positive, efficient addition of oxygen. Fish farmers have depended on Fresh-Flo for trouble-free aeration since 1959. Float models are available. Also 12-volt unit for fish transport. And dip nets.

~ FOR INFORMATION, CALL 800-493-3040

~ ;f?@{Ylbllllev R.S. No. 209 FRESH-FLO CORP. Phone: <Y4-528-8236, Fax: 414-528-8139 W6915 Stat. Hwy. 28, Cascade, WI 53011

48 AQUACULTURE MAGAZINE JULY/AUGUST 1994

Anonymous. 1991. Pearloysierfanningandpearlculture Training Manual 8: 1-104. Regional Sea Fanning Develop­ment and Demonstration Project Bangkok.

Cahn. A.R. 1949. Pearl culture in Japan. Fishery Leaflet 357: 1-99. United States Department of the Interior Fish and Wildlife Service.

Fassler. C.R. 1991 a. Fanning Jewels. The Aquaculture of pear Is. Aquaculture magazine. 17(5): 34-51.

Fassler. C.R. 1991 b. The return oftheAmerican Pearl. Aquaculture Magazine. 17(6): 63-78.

Fassler. C.R. 1992. Pearls: An Update. Aquaculture Magazine. 18(3): 66-70.

James. P.S.B.R. and Narasimham. K.A .. Victor. A. C. C .. Dharmaraj. S. Velayudhan. T.S. and Chelklm. A.1991. The Indian Marine Pearls. A culture technique for their produc­tion. 1-23. Central Marine Fisheries Research Institute. Cochin.

- POND LINERS - TANK LINERS

-TANK COVERS - RACEWAY COVERS

Woven Reinforced Polyolefin Fabric • Lightweight and flexible for easy handling

and installation • Rip. puncture and tear resistant • Ultra-Violet stabilized for lonller life • Reduces ground contamination in ponds • Low cost. affordable in most applications • Non-laminated

James. P.S.B.R. and Narasimham. K.A. 1993. Handbook on Aquafarming - Molluscs. Pearl Oyster Fanning And Pearl Culture. 1-32. The Marine Products Export Develop­ment Authority. Cochin. India.

Loosanoff, V.LandDavis.H.C.1963. Rearingofbivalve molluscs. Advances in Marine Biology. I: 1-36.

Shirai. S. 1970. The story of pearls. 1-32. Japan Publications.Inc .. Tokyo.

Wada. K. 1973. Modern and traditional methods of pearl culture. Underwater Journal. 5(1): 28-33.

10-TIMES STRONGER THAN STEEL AQUA-GRID is a fiberglass reinforced geosynthetic concept designed to cushion. protect and reinforce pond liners. The product is a composite of a high modulus. high tensile fiberglass grid laminated to a synthetic non-woven felt.

AQUA-WEVE LMER

~.~ .. .-: .. :.:;~ AQUA-GRID UNDERLAYMENT • ~ • COIW. • UM

• AQUA-GRID is an underlayment to increase the life of your liner from hostile terrain such as coral. rock or marshy conditions.

~_"-.r~ ji. ;:T~ AQUJi."WEV£

~:~:m~:ANR~ • AQUA-GRID is an underlayment to keep road

beds from collapsing or shoring up marshy sink holes.

Call us ... 1-800-236-3328

FREE SAMPLES!

R.s. No. 176

YUNKER PLASTICS Division of Yunker Industries

200 Sheridan Springs Road· Lake Geneva. WI 53147 414·249-5233 or Fax 414-249-5239

AQUACULTURE MAGAZINE JULY/AUGUST 1994 49