Water Management
Water quality and supply
Freshwater is normally used for rearing freshwater prawns from postlarvae to market size. Water of 3-4 ppt salinity may be acceptable for the culture of M. rosenbergii. The reliability of the quality and quantity of the water available at the site is a critical factor in site choice. However, as in the case of hatchery water supplies, the absolute ‘ideal' for rearing sites may be difficult to define; a range of water qualities may be generally suitable. As for hatchery water, the level of calcium in the freshwater seems to be important. Growth rate has been reported to be lower in hard than in soft water. It is recommended that freshwater prawn farming should not be attempted where the water supply has a total hardness of more than 150 mg/l (CaCO3).
Water quality requirements for prawn nursery and grow out
| Variables | Recommended range |
|---|---|
| Temperature (oC) |
28-31
|
| pH |
7.0-8.5
|
| Dissolved oxygen (ppm) |
3-7
|
| Salinity (ppt) |
<10
|
| Transparency (cm) |
25-40
|
| Alkalinity (ppm) |
25-60
|
| Total hardness (ppm) |
30-150
|
| Ammonia (ppm) |
<0.3
|
| Nitrite (ppm) |
<2.0
|
| Nitrate (ppm) |
<10
|
| Boron (ppm) |
<0.75
|
| Iron (ppm) |
<1.0
|
| Copper (ppm) |
<0.02
|
| Manganese (ppm) |
<0.10
|
| Zinc (ppm) |
<0.20
|
| Hydrogen sulfide (ppm) |
Nil
|