Liming and Watering in Stocking Ponds

Liming

• Lime is frequently applied in aquaculture practices to improve water quality. After the pond is ploughed, cleared and smoothed, it should be conditioned with lime. Liming increases the productivity of a pond and improves sanitation. It is both prophylactic and theuraptic.
• New ponds can be limed before they are filled with water.
• The limestone should be evenly spread over the dry pond bottom.
• In ponds with water, it is better to spread evenly on surface of water.
• Whether the pond is new or old, a layer of lime should be placed on the bottom of the pond. The lime should be added to the pond two weeks before the water is pumped into the pond.
• The best time for lime application is during the period when fertilization has been stopped. Lime should not be applied while the pond is being fertilized

The main uses of lime are:

• Liming is most essential to maintain the pH of water.
• The water should be slightly alakaline as it is useful for the eradication of microorganisms in the pond and also to help maintain the hygienic condition of water.
• Lime is useful to neutralise the acidic condition which will result while manuring. Lime is applied at the rate of 250 kg/ ha. Its dose has to be increased upto 1000 kg/ha in highly acidic soils.
• To raise the pH of acidic water to a neutral or slightly alkaline value.
• To increase the alkaline reserve in the water and mud which prevent extreme change in pH.
• To promote biological productivity, since it enhances the breakdown of organic substances by bacteria, creating increased oxygen and carbon reserves.
• To precipitate suspended or soluble organic materials.
• To decrease biological oxygen demand (BOD).
• To increase light penetration.
• To enhance nitrification due to the requirement of calcium by nitrifying organisms.
• To neutralize the harmful action of certain substances like sulfide and acid.
• To indirectly improve fine textured bottom soil in the presence of organic matter.
• Liming increases the alkalinity of water thereby increasing the availability of carbon dioxide for photosynthesis.
• Liming raises the total hardness by adding alkaline earths (calcium and magnesium)
• By lime treatment, waters may be cleared of humic stains of vegetative origin, which restrict light penetration.
• The net effect of changes in water quality following liming is to increase phytoplankton productivity, which in turn, leads to increased fish/shrimp/prawn production.

Types of Liming Material

A number of different substances are used as liming materials, the chemical used for the liming of soil and water are the oxides, hydroxides and silicates of calcium or magnesium.

Typical liming substances include the following:

1. Calcium (CaCO3) and dolomite (calcium-magnesium carbonate) [CaMg(CO3)2]
2. Calcium oxide (CaO)
3. Calcium hydroxide (Ca(OH)2)

Guidelines for liming during culture period

Status	Activities
During the first month of culture when there is no water exchange and if the pH value is normal 7.5-7.8 in the morning.	Dolomite should be done every 2-3 days at the rate of 150-200 kg/ha.
The pH value is normal 7.5-8.0 in the morning and does not increase more than 0.5 in the afternoon, but there is blooming phytoplankton.	Using dolomite at the rate of 200-250 kg/ha every 2-3 days during the daytime.
The pH value in the morning is lower than 7.5	Using dolomite broadcast at the rate of 150 kg/ha/day then measure water pH the next morning; repeat the liming once a day until the pH value increase to 7.5.
Water pH in the morning is about 8, but increases more than 0.5 in the afternoon (such as 8.8 or 9) and the watercolour is normal.	Using dolomite 200 kg/ha/day in the morning, repeat the application daily until pH during the day does not vary and water pH is not so high in the morning
Large sized shrimp 1 or 2 months before harvest. Water is a dark colour or during no water exchange, the water might have bubbles. Morning water pH value varies greatly during the day.	Using dolomite at the rate of 200 kg/ha/time at night or early morning. The frequency of liming depends on watercolour and water exchange. It is recommended that liming should be done every other day. However, it depends on the pond watercolour and pH.
Prior to water exchange if not sure about water quality.	Broadcasting dolomite 200 kg/ha to prevent sudden change in water quality

 

Quantity of lime to be added based on soil and water pH

Sl No.	Soil and water pH	Soil and water type	Quick lime required (kg/ha)
1	4.0-5.0	Highly acidic	2000
2	5.0-6.0	Acidic	1200
3	6.0-6.5	A little acidic	1000
4	6.5-7.0	neutral	400

Applying of lime in the stocking pond

Watering

• After the lime has been applied to the pond bottom for at least two weeks, the water should be let in slowly.
• The water should fall from the water inlet into the pond, so that the water mixes with oxygen from the air as it falls into the pond.
• The water should not go in to the pond too quickly. If the water enters too fast, the pond bottom will get stirred up and thus make the water muddy.
• Screens should be used at inlets, so that the unwanted fishes and other organisms will not enter into the pond.
• The pond should be allowed to be free for a few days after it has been filled. The quality of water in the pond should be checked before the fish is released into it.

Watering in the stocking pond