Saturday, February 28, 2009


Hatchery Technology of Giant Freshwater Prawn
Macrobrachium rosenbergii is the giant freshwater prawn usually cultured in India. It is euryhaline and eurythermal in habit, so it is a suitable candidate species for culture. Macrobrachium rosenbergii matures when they are months old. The female after a premating moult mates with a hard shelled male. The fertilized eggs are carried by the female in a brood pouch in the ventral side of the abdominal region. The fertilized eggs hatch out in 18 to 23 days. The newly hatched larvae require estuarine water but it can survive in fresh water for three to five days. The larvae after passing through many stages in estuarine region become postlarvae which then migrate to freshwater.

Brood stock collection and hatching:
Female prawn carrying fertilized eggs in the abdominal pouch is called berried female. It can be collected either from rivers or culture ponds. While collecting, care should be taken to see that the eggs are not lost due to rough handling. The berried females are transported with oxygen packing. Hatching can be done either in larval tanks or in a separate hatching tank using freshwater or 12 ppt saline water. Usually hatching of egg takes place during night hours. The hatching period lasts for 3 or 4 days. Major quantity of larvae is released on the second day of the hatching. The newly hatched-out larvae can survive for about 5 days in fresh water. After hatching the mother prawn should be removed from the hatching tank. The larvae pass through 11 stages to become post larvae. For collecting the larvae they can be concentrated at one portion of the tank by putting a light at the collection point after covering other parts with a black cloth or black sheet as they are very much attracted by light.

Feed and feeding:
Feeding of larvae starts from second day onwards. Artemia is the most ideal and widely used feed for larval rearing. Artemia is a small crustacean seen in hyper saline water. Its eggs are collected, packed and supplied by several companies. The cysts are hatched in separate tanks and the hatched out naupli are fed to larvae.
Giant Freshwater Prawn Farming

Farming of giant freshwater prawn, Macrobrachium rosenbergii is a growing industry in India. Generally prawn ponds are shallow having depth of 1.5 to 2.00 meters.

Preparation of Pond:
Pond preparation includes checking and repair of sluice gates and eradication of unwanted species, liming, placing of hide outs, manuring and filling of water. In older ponds, pumping out the water and drying helps in elimination of unwanted species. Drying helps mineralization of bottom soil and improves the productivity of the bottom sole. Disease spreading micro organisms and parasites also can be eliminated by drying. Ploughing of bottom soil after drying helps removal of obnoxious gases. In undrainable ponds, eradication can be done by poisoning. Poisons of plant origin, like mahua oil cake, tea seed cake derris root powder are advisable. After eradication, liming and ploughing can be done. Liming helps in disinfection of pond bottom and improves the fertility of the bottom soil. The quantity of lime could be around 200 kg to 1000 kg based on the pH of the soil. After drying, liming and ploughing, the pond bottom should be kept in a moist condition for a week to facilitate bacterial action. Then manure can be applied. Manuring helps the development of worms like tubifex, zooplankton, algae, etc.

Laying of shelters: Freshwater prawn are cannibalistic. They grow by moulting. Moulting is a process by which the old exoskeleton is shed and new exoskeleton is formed over the body. It takes nearly 24 hours for hardening of the new exoskeleton. During that period moulted prawns require protection from other prawns. Tile, bricks, etc., can be provided in the pond as hide outs. Discarded PVC pipes, earthern pipes can also be used as hide outs. Apart from hide outs, it is advisable to keep some floating weeds like Eichornia, Pistia and duck weed.

Stocking the pond: 7 to 10 days old (PL 7 to 10) post larvae is the ideal age group for transportation and stocking the pond. Before stocking the PLs are to acclimatized to freshwater, preferably with the pond water itself. The density of stocking depends on the intensith of management. For semi-intensive culture with a targeted production of 3 to 3.5 tonnes per year per hectatre, 75000 PLs or 60000 juveniles can be stocked.

During the rearing period, artificial diet is given to the growing prawns. Water quality parameters are to be checked regularly. Disease control measures are to be followed by maintaining a healthy environment, avoiding over stocking, etc. Harvesting should be done by netting the pond, after removing the hide outs. Harvesting should be done during early hours when the temperature is less. After harvesting the prawns are cleaned in freshwater and are iced and transported.

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