Nursery Phase
The nursery can be either indoor or outdoor. The selection of sites for indoor nurseries should follow the same pattern as for hatcheries. Site selection for outdoor nursery facilities should be similar to that for grow-out ponds.
Holding Tanks
After rearing freshwater prawns in hatchery, hold them until ready for stocking in ponds. Concrete tanks of 50 m3 are convenient for holding postlarvae (PL) prior to transport for stocking in ponds. Use nets suspended from floats in the tanks to increase the surface area available to the PL but this may make the normal operations of feeding, cleaning etc. more difficult.
Indoor Nursery Facilities
Tanks for indoor freshwater prawn nurseries can be constructed from concrete or fibreglass. The use of asbestos cement tanks is not recommended. The shape of nursery tanks is not important and their size, usually from 10 to 50 m2 with a water depth of 1 m. The best stocking density for indoor nursery tanks depends on the length of time the animals will remain in the tanks before transfer to an outdoor nursery or grow-out facility. It is recommended not to exceed a stocking density of 1000 PL/m3 in tanks without substrates.
Artificial substrates of various designs and materials can be used to increase surface area; these provide shelter and increase survival rates. Layers of mesh can therefore be used to increase the amount of surface edges available to the prawns in both vertical and horizontal planes. The water supplies for indoor nurseries can be flow-through or recirculating. For flow-through, water is allowed to continuously enter from above the tank and exit from the lowest part of the tank through a vertical standpipe. Standpipes are covered with a 1.0 mm mesh screen to prevent PL and juveniles from escaping. This drainage system draws water from the tank bottom where food waste and detritus settle.
Outdoor Nursery Facilities
Nursery ponds are similar to grow-out ponds in design and facility requirements. They usually vary in area from 300 to 2000 m2 . Artificial substrates can be used to increase the surface area available to the prawns. PL is retained in holding tanks for more than a week or two prior to stocking in nursery facilities, grow-out ponds. Whilst the PL are in the holding tanks water is exchanged at a rate of 40-50% every 2-3 days and provide aeration. PL is at densities of up to 5000 PL/m2 for one week, or up to 1500-2000 PL/m2 for one month under these conditions. If you need to hold them for one month, you could improve survival if you reduce the density to 1000/m2. Using substrates can help you maximize the stocking density, thus reducing other equipment and labour costs.
