Water quality at the intake point is a vital consideration in successful shrimp farming. The site should have access to an unpolluted estuarine or marine water supply, with an optimum salinity range of 15 to 25ppt. Seasonal effects of rainfall and evaporation can cause fluctuations, but salinity should not be less than 1 ppt o r greater than 35 ppt (average salinity level for sea water). Areas of tropical coasts that experience extended dry seasons will be particularly prone to high salinity in ponds, which can slow growth rates and subsequently increase production costs. The optimum range for pH of water source is 7.5 to 8.5. The pH of estuarine waters can be affected by acid sulfate soils and other local soil factors. Water sources affected by significant coastal pollution from industry, urban areas, and agriculture and water treatment facilities should be avoided. A very important aspect of the intake requirements for a successful shrimp farm is access to sufficient quantities of seawater. Before choosing a location as a pump station site, one may need to determine whether sufficient daily volumes will be available for the design and size of the farm considered. A good water quality monitoring program will give additional tools to manage growth, survival, health and productivity of the crop. The monitoring should be:
- It is done at the same place, same time each day or month
- It is conducted repeatedly and consistently
- Information is available at any time
- It is user-friendly so that others can understand it
- It gives feedback on crop progress
- It enables analysis of disease problems caused by previous events
- It can provide ability for rapid response to situations
- It can be used for future planning and decision making.
Key instructions for Water Quality Management:
- Screen the intake water as it is important t keep the disease carriers away. Use water reservoir is in the 3:1 ratio (pond area: reservoir area). Start water pumping not more than 20 days before stocking date. Pond should be filled with water within 4days. At the time of water pumping, screen the water with 3 levels of twin screens.
Foot valve should be placed in bamboo basket or metal cage and it should be covered with 20 size mesh to prevent large animals getting into inlet mesh. Use double layer of 60 size filter mesh at water inlet point. Tie filter nets properly to the delivery pipe. Provide additional two layers of 80size mesh hapa below the inlet.
Depending on the pumping capacity increases, the surface area of the filter nets. Every day the meshes should be properly washed away from pond, and the waste should be disposed properly. Meshes should not be washed in the rearing pond. After washing, dry the filter nets and they should be checked thoroughly for any damage, if damages are found, better to to replace it with new meshes. Always keep extra filter nets ready at farm. Keep the feeder canal clean. After filling the pond, hold water for 7 to 110 days before stocking the seeds. The filter nets must be maintained throughout the crop.
- Do not use pesticides to disinfect or kill fish, shrimp and crabs in the pond. Pesticides will enter and remain in the body of shrimps and when consumed cause health problems in humans. Pesticide-contaminated shrimp are BANNED in the international market due to serious health hazards. If necessary use Tea seed cake@ 10ppm (50 kg/ha at 0.5 m water depth) to kill unwanted fish in the pond.
- Fertilize the pond water to produce good plankton bloom which is essential for successful shrimp culture. Plankton bloom shades the pond bottom and prevents the growth of benthic algae. It provides the darker environment which is less stressful for shrimp. Make sure pond is filled to minimum 1.2 m water level at the centre prior to stocking of seed. One week after the water is filled; bloom normally develops in vermicompost/compost manure applied ponds.
If the colour of the pond water is clear, carry out chain dragging once a week to stabilize the plankton bloom. Add 200kg of Dolomite per hectare during sunny period. Apply 2 days fermented mixture of rice bran, jiggery and quality brewer’s yeast @ 25kg +10kg +0.25kg/ha in doses for three days during the morning period. Spread the fermented mixture across the pond using a floating device.
When the colour of the water is green the pond is ready for stocking. If there are benthic or floating algae in the pond, remove them. The best approach is manual removal.
Do not heavily fertilize the water to get dark green water. It will reduce the oxygen in water during night time thus suffocating the shrimp. It is one of the reasons for lower survival rate of shrimp seed. During the first month of culture, whenever the water colour intensity reduces (Secchi disc reading of more than 50cm), add fermented mixture of rice bran, jiggery and yeast @ 25kg +10kg+0.25kg/ha.
Do not carry out chain dragging from the day of seed stocking until 45 DOC. After 45DOC, follow chain dragging of entire pond phased over 3 to 4 days at least once a week.
- Water quality parameters that are known to be important in the health of aquatic animals are temperature, dissolved oxygen, pH, salinity, ammonia, nitrate, nitrite, hardness, alkalinity, turbidity and he levels of toxic agents such as heavy metals, herbicides and pesticides. For the maintenance of good health and growth rate of shrimp. The generally accepted ranges of the critical water quality parameters are provided below:
Water Parameter Optimal Range Dissolved Oxygen