Biogas slurry in fish culture

Cowdung is commonly used as a fertilizer for fish ponds in India but fish production is limited to 15002000 kg/ha. These yields can, however, be more than doubled if the dung is first fed to a biogas plant and the digested slurry then used instead of the raw dung. The following methodology for a 0.4 ha pond exemplifies the technology.

Figure

1. Prepare the pond using the urea-bleaching powder

· method or by draining-drying in June.

2. Stock the pond with 2000 (5-8 9) fingerlings of six Asiatic carps: catla 20, rohu 25, mrigal 20, silver carp 20, grass carp 5 and common carp 10.

3. Fertilize the pond daily with 30 litres of biogas slurry. The slurry is rich in nitrogen and phosphorus, and is free from toxic gases which are produced when cowdung decomposes in ponds.

Excess slurry is used for the field while the gas is used both in the kitchen and for lighting the house.

The slurry is not applied on a cloudy day or when the fish come to the surface gulping air.

4. Surface feeders will be about 1 kg in six months. All marketable fish are then harvested every two months and replenished with an equal number of fingerlings. A total of 2000 kg of fish is obtained using biogas slurry as against 800 kg if raw cowdung were used.

ADVANTAGES

· Saving on inorganic fertilizers and feed (60% of operation costs).

· Environment-friendly—no oxygen demand.

· Saving on fuel and electricity.

· Cooking with biogas removes drudgery of womenfolk and helps in keeping the kitchen and environment clean.

LIMITATION

· Slurry/gas production is poor during cloudy days or when temperatures are low.

Biogas slurry.babed fish culture on a 0.4 ha pond.

Note: 1 U$ = 25.50 Rs