region and used by farmers in the upland fields, were also used in these studies, with
organic and chemical fertilizers applied at an N/P ratio of about 3:1. The amounts of
fertilizer used were varied according to the on-farm availability of organic fertilizer,
as well as current ammonia, total nitrogen and total phosphorus concentrations in the
pond. The total amounts applied were calculated to provide 1.0 ppm total nitrogen
and 0.5 ppm total phosphorus (Kumar et al. 2004a).
Under the traditional carp polyculture system of northern Vietnam, grass carp
has been reported to be the main species (Steinbronn 2009; Kumar et al. 2005a, b;
Tripathi and Mishra 1986); grown to augment the internal nutrient recycling
processes of the ponds, and can be raised cost efficiently with the use of on-farm
resources (Kumar et al. 2005b; Pomeroy et al. 2000).
Farmers in the research area reported the occurrence of a disease specific to grass
carp after 1996 (Steinbronn 2009), one which led to mass mortalities in the region.
In order to reduce the risks of farmers being impacted by the grass carp disease,
grass carp was replaced almost entirely by common carp within the traditional carp
polyculture system, and was then stocked only as a supplementary species. In this
region, the common carp is considered a suitable principal species, because it is
well accepted as food and fetches a good price on the local market, a price similar to
that of grass carp. Farmers are familiar with its habits and ecological requirements
and it is readily available from local traders as fingerlings for stocking, or can be
reproduced naturally in farmers’ ponds. Ponds were stocked at a density of 1.5 fish
per m
2 as recommended by Rahman et al. (2008b), with common carp eventually
accounting for around 50 % of fish stocked in the area. Other carp species (such as
silver carp, bighead carp, mud carp, grass carp) and also tilapia – all important as a
supply of animal protein for domestic consumption, were stocked to similar levels.
8.5.2 Implementation of a Modified Feeding Regime
The common carp is an omnivorous fish and prefers to scavenge pond bottoms in
search of benthic organisms like oligochaetes, nematodes and insects, but is also
capable of digesting zooplankton, plant derived diets and detritus (Rahman et al.
2008a). Common carp in carp polyculture systems has been reported to increase the
bio-availability of nitrogen and phosphorus through its scavenging activities, which
increase bioturbation and recirculate sedimented nutrients (Rahman et al. 2008b;
Jana and Sahu 1993; Milstein et al. 2002). This stimulates primary production
(Chumchal and Drenner 2004) and the accumulation of nutrient in plankton
(Rahman et al. 2008a), but also increases turbidity by recirculating sedimented
material (Chumchal et al. 2005).
Due to the ability of common carp to utilize carbohydrates for their energy
requirements (Kaushik 1995; Ufodike and Matty 1983) and to digest plant-derived
proteins for their anabolism (Degani et al. 1997), only a small amount of animal
derived protein is required in the diet of common carp to supply essential amino
acids. Sulphur containing amino acids are most essential for fish, as the acids are not
298
J. Pucher et al.
organic and chemical fertilizers applied at an N/P ratio of about 3:1. The amounts of
fertilizer used were varied according to the on-farm availability of organic fertilizer,
as well as current ammonia, total nitrogen and total phosphorus concentrations in the
pond. The total amounts applied were calculated to provide 1.0 ppm total nitrogen
and 0.5 ppm total phosphorus (Kumar et al. 2004a).
Under the traditional carp polyculture system of northern Vietnam, grass carp
has been reported to be the main species (Steinbronn 2009; Kumar et al. 2005a, b;
Tripathi and Mishra 1986); grown to augment the internal nutrient recycling
processes of the ponds, and can be raised cost efficiently with the use of on-farm
resources (Kumar et al. 2005b; Pomeroy et al. 2000).
Farmers in the research area reported the occurrence of a disease specific to grass
carp after 1996 (Steinbronn 2009), one which led to mass mortalities in the region.
In order to reduce the risks of farmers being impacted by the grass carp disease,
grass carp was replaced almost entirely by common carp within the traditional carp
polyculture system, and was then stocked only as a supplementary species. In this
region, the common carp is considered a suitable principal species, because it is
well accepted as food and fetches a good price on the local market, a price similar to
that of grass carp. Farmers are familiar with its habits and ecological requirements
and it is readily available from local traders as fingerlings for stocking, or can be
reproduced naturally in farmers’ ponds. Ponds were stocked at a density of 1.5 fish
per m
2 as recommended by Rahman et al. (2008b), with common carp eventually
accounting for around 50 % of fish stocked in the area. Other carp species (such as
silver carp, bighead carp, mud carp, grass carp) and also tilapia – all important as a
supply of animal protein for domestic consumption, were stocked to similar levels.
8.5.2 Implementation of a Modified Feeding Regime
The common carp is an omnivorous fish and prefers to scavenge pond bottoms in
search of benthic organisms like oligochaetes, nematodes and insects, but is also
capable of digesting zooplankton, plant derived diets and detritus (Rahman et al.
2008a). Common carp in carp polyculture systems has been reported to increase the
bio-availability of nitrogen and phosphorus through its scavenging activities, which
increase bioturbation and recirculate sedimented nutrients (Rahman et al. 2008b;
Jana and Sahu 1993; Milstein et al. 2002). This stimulates primary production
(Chumchal and Drenner 2004) and the accumulation of nutrient in plankton
(Rahman et al. 2008a), but also increases turbidity by recirculating sedimented
material (Chumchal et al. 2005).
Due to the ability of common carp to utilize carbohydrates for their energy
requirements (Kaushik 1995; Ufodike and Matty 1983) and to digest plant-derived
proteins for their anabolism (Degani et al. 1997), only a small amount of animal
derived protein is required in the diet of common carp to supply essential amino
acids. Sulphur containing amino acids are most essential for fish, as the acids are not
298
J. Pucher et al.