Freshwater aquaculture (2+1)

Unit 3 - Nursery, Rearing and grow-out ponds

3.2.1. Draining, drying, Ploughing and Liming
Draining and drying
Pond needs to be drained a dried before culture operations begin
Drying facilitates in

• Oxidation of organic matter
• Degassing of toxic gases such as ammonia and hydrogen sulphide
• It kills pathogenic micro organisms
• Kills predatory and weed fish
• Kills unwanted aquatic plants

Ponds should be dried for 7-10 days till the soil cracks the ponds with clayey soil; in sandy soils they should be dried till the soil supports a person and foot prints do not form on the soil.

Ploughing
The ponds should be ploughed using wooden ploughs or power tillers or tractors
Ploughing helps in

• Mixing up of soil which helps in oxidation of organic matter
• Proper degassing of soil from toxic gases
• Mineralization of nutrients.

Liming
The productivity of fish ponds depends on soil qualities such as

• Texture
• Water retention
• pH
• Organic carbon
• Available nitrogen
• Available phosphorous

Pond bottom is important for productivity since process of mineralization of organic matter and release of nutrients to the overlying water takes place
Liming helps in improving the quality of the pond soil, thus enhancing productivity.
It also corrects soil pH; the desirable pH is 6.5 – 7.00

A range of liming materials are used such as

• Agricultural lime or calcite (CaCO3)
• Dolomite [CaMg(CO3)]
• Calcium hydroxide/slaked line Ca(OH)2
• Calcium oxide/quicklime - CaO

The dose of a particular variety of lime depends on its effectiveness and soil pH
Generally 200-500 kg/ha of line is used for application to pond soil
After application, the lime should be mixed with the top soil with light ploughing.
Quick lime is preferred for applying to soil and calcite agricultural lime for application to water after stocking of the ponds

Liming helps in

• Correcting soil pH
• Mineralization of organic matter
• Release of soil sound phosphorous to water
• Disinfection of the pond bottom