Explanation:

Production of natural food through fertilization is one of the important factors for better survival and growth of fish in ponds. Good phytoplankton growth is pivotal for sustained zooplankton density in a pond. This requires an adequate availability of nutrients such as phosphorous and nitrogen including certain micronutrients. Since the natural availability of these nutrients is low, ponds must be adequately fertilized to sustain good plankton growth.
Grow-out ponds are usually fertilized with cow dung at 10 000-20 000 kg/ha/year or poultry manure at 4 000-8 000 kg/ha/year and in combination with inorganic fertilizers such as urea at 100 N kg/ha/year and super phosphate at 50 P kg/ha/year.
Bio-processed organic manure (e.g. bio-gas slurry) has also been tested and application rates have been standardized. It has been reported that the application of bio-gas slurry at a rate of 30 000 – 45 000 kg/ha/year has the same beneficial effect as other manures, although the BOD is lower and the nutrient release rate is faster (Jena and Das, 2006).