Preparation and maintenance of a pond for carp farming in Sri Lanka
For natural aeration of pond water, the pond should be oriented east to west. The length to width ratio of the pond should be 2: 1 and the depth of the pond should be 1.5 m. The pond wall should be 3 m wide.
In order to prepare a pond, eradication is required. There are two types of eradication: physical eradication and chemical eradication. Physical eradication is achieved by Sun drying for 2-3 weeks until the formation of soil cracks.
Bleaching powder (25g/m2) is used to do chemical eradication. The pond bottom should be thoroughly wetted before bleaching and then bleach for 1-3 days. Then fill the pond to 12 inches with water and after 2 days, water should be released to minimize the bleaching powder toxicity, and water should be filled to 48 inches level again. As another chemical eradication method, can use bleaching powder with urea (1g/m2 urea and after 24 hrs 12g/m2 bleaching powder). The ponds should be free from aquatic feeds, wild fish, and predators. Ammonia 25g/m2 is sometimes used to kill wild fish like stinging catfish. Lime (50 g/m2) is a good pesticide to use.
Fertilization has a bigger role in semi-intensive carp farming. Fertilizers might be inorganic or organic. Organic fertilizer consists of fresh cow manure, poultry manure, green leaves, and compost. For early fertilizing of ponds to grow planktons, cow dung (750g/m2) or poultry manure (250g/m2) could be used. Auxin and cytokinin hormones are found in fresh cow dung and are beneficial to phytoplankton growth. Use 1g of TSP (powder form) and 3g of urea per m2 in combination with organic fertilizers for quick results. Weekly manuring is advised if necessary. Before applying fertilizer water level in the pond should be 1.5m and then the water level in the tank should be gradually raised.
After two weeks there is a significant change in color of the pond water (immediately dark brown and then yellow after that green), and after two weeks, excellent culture ponds can be obtained by this method. The visibility of the Secchi disk should be between 25 and 30 cm. Plankton density must be 20-25cm in brood and brood ponds and 45cm in brooders ponds. The pH of the medium can be adjusted by adding lime. Eichhornia sp. can also grow in corner of the ponds to absorb excess ammonia produced by excess feed, however, as Eichhornia sp. is an invasive alien species, that should be planted in small quantities.
