Guide for FRESHWATER PRAWN CULTURE

Marine industry has a huge export potential and hence gives back good profit ratios. Farmers in the coastal areas are taking up this activity and successfully augmenting their income. The investemnt involved is decent when compared to profit margins and hence has a profitable business opportunities. Giant freshwater prawn Macrobrachium rosenbergii is commonly known as “SCAMPI”. It is widely distributed in Southeast Asia and found in most river systems in India. It is highly valued due to its high price, large size, rapid growth, good taste and high export demand. These prawns inhabit rivers, canals, estuaries and coastal waters in nature. It can also be cultured in freshwater as well as slightly brackish water. ICAR-CIFA has developed a package of practices for the scientific culture of Macrobrachium rosenbergii. It involves a nursery phase and grow out phase.

Nursery phase

During nursery phase, delicate post-larvae (PL) (15-20 mm) procured from prawn hatcheries are raised to juveniles (2-5g) in the small earthen ponds/tanks. The size of nursery pond may range from 0.02-0.1 Ha, the recommended stocking density of seed (post-larvae) range from 20-50/m². Provision of floating weeds inside a PVC frame covering 10% of pond surface is recommended to provide shade and shelter to PL. Commercially available prawn/shrimp feeds (starter feeds in crumble form) is recommended for good growth and survival. It should be fed @ 100% of the biomass/ day for first two weeks and reduced to 20% of biomass towards the end. If the farmer does not have access to commercial feed then powdered groundnut oil cake and rice bran can also be used. Nursery period may range from 45-60 days during which the PLgrow to juveniles of 2-5g size.

Juvenile prawns (2-5g) are harvested from nursery ponds and stocked in larger grow out ponds (0.2 to 1 ha) @3-4/m². Prawns are fed with commercial prawn/shrimp feed @10% of their biomass which is gradually reduced to 2% towards the end of the culture period. During culture period of 6-8 months, water quality need to be maintained at optimum levels (dissolved oxygen >3ppm; pH-7-8; alkalinity-60-100 ppm; transparency-30-35 cm). Culture period including nursery may range from 8 to 10 months. Partial harvesting to remove larger prawns can start from 4months of culture and final harvesting is done by netting followed by complete draining of the pond. Survival is expected to be 70%; final average size -50g.

Site selection for pond :

Proper site selection is an important factor for successful freshwater prawn culture. Culture sites where water temperature remains above 20° C for 6-8 months are suitable. The water pH should be above 7. The pond bottom soil should be clayey-loam or sandy-loam.

Pond construction:

The pond should be preferably rectangular in shape with a size of 0.2-1 ha. Provision of inlet and out let and water control structures are recommended. Pond bottom should have suitable slope towards the outlet. Depth of water should be 1.0-1.5 m.

Pond Preparation

For pond preparation pond is dried and pond bottom is exposed to sunlight for one week. If it is not possible to dry the pond then mahua oil cake or urea and bleaching powder are added for removal of predatory fishes. Liming is done @200 kg/ha or as per requirement based on soil pH. Cow dung @200 kg/acre or urea @10 Kg and SSP @15 Kg is added in the pond for plankton development at weekly interval. Then water is properly filtered and filled in the pond up to a level of 4ft. As prawns grow by moulting (shedding of outer shell) and are very soft and are easy prey to other prawns, earthen tiles, small tree branches and tyres are provided in the pond as hideouts to save them from predators during moulting. The pond is covered with nylon net or threads to save them from predatory birds. For monoculture practice, they are stocked @3-4 juveniles/m² and for polyculture, 1-1.5 prawn juveniles/m² along with 3000-5000/ha Rohu and Catla fingerlings.

Food and feeding

Prawns feeds on small animals like worms, crustaceans, bottom detritus, and plant material available on the pond bottom. When there is lack of feed they feed on the soft shelled weak prawns that result in low production. It is recommended to feed prawns twice daily with commercial prawn/shrimp feed (2-3mm pellets)@10% of their biomass which is gradually reduced to 2% towards the end of the culture period. The feed is broadcasted to the pond from the dykes. Feed can also be given in check trays placed 2-3 m away from the dyke for better feed management. Feed management should be done properly to ensure better growth and environment management

Water quality management

Visibility and colour of the pond is an important indicator of the health of pond ecosystem. In unproductive ponds the visibility can be up to the bottom which will lead to growth of bottom algae that adversely affect the growth and survival of prawns. Ideally, the visibility should be maintained in the range of 30-40 cm to avoid water quality deterioration. Provision of aerators (paddle wheel or any other such devices) is recommended especially during the final 2-3 months when the biomass in the pond is high. When the oxygen level in the pond is critically low, the prawns come to the surface along the periphery which indicates the need for taking immediate remedial actions such as water exchange or operation of aerators to avoid mortality of stock.