Grass carp - Fertilizers and fertilization

Because grass carp are herbivorous, ponds have to be fertilized to produce duckweed and other macrophytes to ensure good growth. Animal manure is generally used for this purpose. About one week before stocking fry, approximately 9 000 kg/ha fermented pig manure is added to the pond, where after the water level is increased to about 1.2 m. Grass carp is normally produced in polyculture and under the above fertilization schedule the ponds are stocked with 60 000 grass carp, 30 000 bighead carp and 1 500 common carp fry. In addition the ponds are stocked with 1 500 kg duckweed seedlings. Alternatively, one week after stocking the juvenile fish are fed with duckweed at 330-660 kg/ha per day. After twenty days the fish reach around 7 cm TL, at which stage duckweed must be provided at a rate of around 1 650 kg/ha. When the fish reach around 17 cm TL they should be fed with grass (Liang, 2002).