VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

NURSERY POND PREPARATION

The various steps in pond preparation include deweeding, drying, filling the pond with water, liming and fertilization. 

Deweeding 

• The aquatic weeds and the weed fishes that are present in the pond should be cleared off. The bottom of the pond should be sun dried until the soil cracks. Then the pond has to be filled with water through the inlet followed by liming and fertilization.

Liming

• Liming is an important part of nursery pond maintenance which increases the natural productivity of the ponds and has a favourable effect on the health of the fry. Some of the beneficial effects of liming can be summarized as follows:
  • Disinfection of the pond bottom (using quick lime).
  • Increases the pH of the water and pond bottom to an optimum level (pH 7-9) for plankton and fish production.
  • Increases the alkalinity of the water; adequate alkalinity is required so as to ensure pH stability and neutralize the harmful effects of magnesium, sodium and potassium salts.
  • Increases pond productivity through increased biological activity and availability of minerals in the pond bottom and water column.
• The most commonly used liming compounds are quicklime (CaO), caustic lime, also called slaked lime or hydrated lime (Ca(OH)₂) and agricultural lime. The required amount of lime depends upon the acidity of the water and soil and the alkalinity of the soil, and consequently varies from region to region and from pond to pond. The average estimated quantity required depending upon pH is as follows:

Quick lime          :	7 - 10 kg/100 m2
Caustic lime       :	7 - 13 kg/100 m2
Agriculture lime:	20 - 30 kg/100 m2

Fertilization

• Phosphorus (P) and nitrogen (N) are required in minimum quantities for optimum primary production in fish ponds. Since the required quantities of these minerals are not always available in ponds, it is necessary to add them to promote the growth of plankton, i.e., phytoplankton and zooplankton which are the natural live food for the fish fry. This can be achieved by adding minerals either directly (chemical fertilizers) or indirectly (organic fertilizers).
• Some of the chemical fertilizers that are widely used include : superphosphate (containing about 20% P₂O₅), triple superphosphate (containing about 45% P₂O₅), urea (containing about 45% N) and NPK 15:15:15 (15% N, 15% P₂O₅, 15% K₂O).
• Commonly used organic fertilizers include poultry manure, duck manure, pig dung, sheep dung and cow dung. The quantity of organic and inorganic fertilizers required varies from place to place and from pond to pond. Dry chicken manure at a rate of 50 kg/100 m² one week prior to stocking results in a good phytoplankton bloom resulting in  the pond water containing about 1.5-2 ml of plankton per 100 litre of water and having a secchi disk reading of 20-25 cm. Fertilization with 10-20 kg manure/100 m², 0.4-0.8 kg N/100 m² and 0.1-0.2 kg P₂O₅/100 m² can be done in addition. The fertilizers have to be dissolved in water after which they are spread evenly over the surface. The phytoplankton will develop within a week time.