Farming freshwater prawns

5CHAPTERPostlarval holdingand nursery phases5.1 Basic requirements and facilitiesThe 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 TANKSAfter rearing your freshwater prawns in your hatchery, you need to be able to hold themuntil you stock them in your ponds or sell them to other people. 50 m 3 concrete tanks areconvenient for holding postlarvae (PL) prior to transport for stocking in ponds. However,you can also use other sizes and types of tanks, similar to hatchery tanks. There are no specialrequirements, except that they must have supplies for freshwater and air. You can usebranches and nets suspended from floats in the tanks (both referred to as ‘substrates’ inthis manual) to increase the surface area available to the PL but this may make the normaloperations of feeding, cleaning etc. (similar to hatchery operation) more difficult.Figure 37 shows PL utilising a nylon screen inside a holding tank.INDOOR (PRIMARY) NURSERY FACILITIESTanks for indoor freshwater prawn nurseries (Figure 38) can be constructed from concreteor fibreglass. The use of asbestos cement tanks is not recommended. The shape of nurserytanks is not important and their size, usually from 10 to 50 m2 with a water depth of 1 m,depends on the area of the outdoor ponds which you (or those you sell juveniles to) areeventually going to stock with your product. You can use artificial substrates of variousdesigns and materials to increase surface area; these provide shelter and increase survivalrates.Prawns tend to use the edges of substrates, whether they be natural (e.g. leaves,branches) or artificial. Layers of mesh can therefore be used to increase the amount of surfaceedges available to the prawns in both vertical and horizontal planes (Figure 39). PlasticCHAPTER 575