The quantity of freshwater and seawater required for a freshwater prawn hatchery depends not only on the proposed scale of operation but also on the type of management utilized (flow-through, recirculation, use of brine).
Flow-through systems obviously require the maximum quantities of water. All other systems will either require less seawater or, in the case of those which utilize brine or artificial seawater, none.
It is therefore not possible in this manual to define the exact quantities of water needed, as these are scale, site and management system dependent.
An example of the water requirements for a flow-through system using seawater that includes ten 5 m 3 larval tanks, each capable of producing 50 000 postlarval prawns (total 500 000 per larval cycle) within a maximum of 35 days, is provided in Box 2.
Other Requirements For Hatchery Sites:
In addition to having sufficient supplies of good quality water, a good hatchery site should also:
- have a secure power supply which is not subject to lengthy power failures. An on-site emergency generator is essential for any hatchery - this should be sized so that it has the output necessary to ensure that the most critical components of the hatchery (e.g. aeration, water flow), can continue to function;
- have good all-weather road access for incoming materials and outgoing PL;
- be on a plot of land with an area appropriate to the scale of the hatchery, that has access to the quantity of seawater and freshwater supplies required without excessive pumping. The cost of pumping water to a site elevated high above sea level, for example, may be an important factor in the economics of the project;
- not be close to cities, harbours, mines and industrial centres, or to other activities that may pollute the water supply;
- be situated in a climate which will maintain water in the optimum range of 28-31°C, without costly environmental manipulation;
- have access to food supplies for larvae;
- employ a high level of technical and managerial skills;
- have access to professional biological assistance from government or other sources;
- have its own indoor/outdoor nursery facilities, or be close to other nursery facilities; and
- be as close as possible to the market for its PL. In the extreme case, it should not more than 16 hours total transport time from the furthest farm it will be supplying.
Author:
Michael B. New
