Pearl Oyster Hatchery.pptx

Pearl Oyster Hatchery

1. An Assignment On Pearl Oyster Hatchery T echniques Presented By : Rajesh V. Chudasama

2. Pearl Oyster Hatchery Techniques Pearl oysters are of immense value as they yield natural pearls . They are sedentary bivalves found in the ocean, at a depth of 18-22 meters and found attached to rocky ridges, usually 19 kms off shore. A remarkable natural pearl oyster fisheries is found in the area between Capekomerin and Killakarai , Gulf of Mannar , Palk bay and Gulf of Kutch in India.

3. Taxonomic Classification Kingdom Animalia Phylum Mollusca Class Bivalvia Order Pterioida Family Pteriidae Genus Pinctada Species Fucata Pinctada Fucata

4. Reproductive Biology of P. fucata There is no sexual dimorphism. Hence, male and female can't be distinguished externally. There is a pair of gonads (testis in male and ovary in female) placed over the intestine and hepatopancreas . Sperm from the testis and ova from ovary are released into the surrounding water where fertilization takes place.

5. Life Cycle The oyster life cycle very much dictates the growing schedule on a farm. It takes 18 to 24 months for oysters to become adults or grow to market size, approximately 3 inches. Since growers only have a finite amount of land, they also only have a finite amount of oysters they can grow on their farm. Some of that area has to be devoted to oysters that are maturing to market size. Very much like agricultural farming, growers have to plan their farming schedule to allot enough time for growout .

6. Selection of culture sites Technological and economic considerations play a major role in the selection process . E ffects 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.

7. Environmental conditions for culture Temperature (20 – 25°C) Salinity (above 30 ppt ) Bottom (Gravelly) Depth (Optimum depth at – 15m) Good phytoplankton production Moderate water currents

8. Hatchery Technology Brood Stock Development Unit In order to develop the brood stock pearl oyster farming is undertaken. Pollutant free coastal waters where salinity and temperature do not fluctuate widely and having sufficient depth are suitable for pearl oyster farming. Three types of culture techniques such as raft culture, rack culture and onshore tank culture are practised .

9. 1. Raft culture Raft culture is under-taken where water depth is 5 meter and more. A raft is prepared with wooden logs and kept floating on the surface of water with 4 buoys of 200 litre capacity. About 100 culture cages can be hung from this raft. Raft culture

10. 2. Rack culture If water depth is less (<5 m) wooden poles are driven to the sea bottom at intervals of 1 meter and horizontal wooden poles are tied to the vertical ones above the sea level. Culture cages are suspended into the sea water from the horizontal ones. Rack culture

11. 3. Onshore tanks culture large concrete tanks of 75 to 150 tons capacity and of 3 meters depth and used for rearing the oyster sea water is pumped into the tank. Culture cages consist of box cage of 40 cm x 40 cm x 10 cm with synthetic fabric . At the end of 1St year it grows to 41 mm (8. 3 g), at the end of second year it reaches 64 mm (31. 6 g) size and at the end of of 3rd year it grows to 75m m (45 g).

12. B. Induced Spawning Unit Fully ripe oysters spawn by thermal stimulation or chemical stimulation . Thermal Stimulation The spawning tanks (76 x 46 x 46 cm) is filled with freshly filtered sea water. It is provided with an immersion heater which is thermostatically controlled and a thermometer. Water temperature is gradually increased to 35°C by switching on the immersion heater. This gradual rise in temperature induces ripe oysters to release the gametes in to the medium . Usually , the male releases the sperms followed by the female. About 50 to 100 numbers of ripe oysters from conditioning unit are released into the tank.

13. 2. Chemical Stimulation Spawning tank is provided with sea water and pH of the sea water is raised to 99. 5 using either Tris buffer solution or NaOH buffer solution. Oysters are released In to the spawning tank. They usually spawn in about 1-2 hours. After the osyters release the eggs and sperms fully, parents are separated from the tank. Soon after the gametes are released into the water, fertilization takes place and fertilized eggs settle down. The newly fertilized eggs are collected in 30 pm sieve and released into freshly filtered sea water in FRP tanks of 1 ton capacity.

14. C. Larval Rearing Unit

15. Larval stages of pearl oyster

16. About 20 hours after fertilization, the trochophore larva that hatches out developes in to veliger larva. It is a free swimming larva. The veliger larva is to be stocked at the rate of two numbers per ml of water in the FRP tanks. On day one, no feeding is required. The rearing tanks are usually covered with thick black cloth to avoid dust and light. On day two, micro algae, Isochrysis galbana @ 5000 cells/ larva/ day is fed to the larvaeS . Water is exchanged once in two days using 45 um sieve. This is continued till 10th day. At this time water exchange can be with 100 um sieve. On day 18, when pediveliger stage is reached feeding has to be 15000 cells / larva / day. On day 20, plantigrade stage is reached when water exchange is done using 140 um sieve.

17. On day 24 plantgrade transforms into spat when isochrysis @ 20, 000 cells / spat/ day is given upto 30th day. Water exchange is done using 180 um sieve. Spat will settle to the sides and bottom of the rearing tank. Feeding is increased to 30000 cells/ spat/ day and aeration is also done. At this time mixed algae cultured out doors containing chaetoceros is mixed with isochrysis is given at the ratio 50 : 50. Chaetoceras is considered good for the spat. It grows to 2-3 mm size and at this stage isochrysis feeding is stopped and only mixed algae is given. By 90th day spat becomes 3-5 mm.

18. D. Algal Culture Unit Isochrysis is the microalgae required for feeding the larval stage up to 60th day of rearing. Hence, facilities are to be made for its mass culture and also for mixed algal culture as mixed algae is given as feed during the later stages . Preparation of stock culture to be used as inoculum for mass culture is the first step in algal culture.

19. Preparation of nutrient solution A. Potassium nitrate 100 g Sodium orthophosphate 20 g Sodium EDTA 45 g Boric acid 33. 4 g Ferric chloride 13 g Manganese chloride 0-36g Distilled water 1000 ml B. Trace metal solution Zinc chloride 4.2 g Cobalt chloride 4 g Copper sulphate 4 g Ammonium molybate 1.8 g Distilled water 1000 ml

20. C. Vitamin 1 . Dissolve 200 mg vitamin B1 (Thiamine) in 100 ml dist . 2. Dissolve 10 mg Vitamin B12 ( Cyanocobalamin ) in 100 ml distilled water and refrigerate Composition of nutrient to be added to 1000 ml of filtered, sterilized seawater for growth of isochysis is one ml. Of ’A ’+ 0.5 ml. of ’B’ +0.1 ml of C (1) and 0.1 ml of C (2)

21. Mixed Algal Culture Filtered sea water is stored in 1 ton FRP tanks kept in sunlight. The water is fertilized with the following chemicals. Potassium nitrate - 13. 2 g EDTA - 6. 6 g Sodium orthophosphate - 6. 6 g Sodium silicate - 6. 6 g (in 1000 litre of sea water) Algae for indoor mass culture is used as inoculum . The mixed algae shall bloom in 3-4 days.

22. Dr. P. C. Thomas, Dr. Suresh Ch. Rath , Dr. Kanta Das Mohapatra , (2016), Daya publishing house, Breeding and Seed Production of Fin Fish and shell Fish, Pearl Oyster, pp 258 to 264 References

23. Thank You