completely drained for harvests and drying purposes. The constant water flowthrough system was replaced by the periodic exchange of pond water, and channels
were installed around the ponds to inhibit the inflow of run-off waters from
surrounding upland fields. A persistent ground cover was established to stabilize
the pond dikes and reduce the erosive effects of heavy rain. Such ground cover for
upland fields and pond dikes not only minimizes erosion but also increases the feed
base for grass carp and ruminants in the dry season, when green fodder is limited.
The aims of the water management scheme were to reduce the turbidity of the
pond water, thus enhancing primary production, and to reduce the loss of nutrients
caused by flushing out. Every 2–4 weeks, water was fed into the ponds to compensate for seepage, and to minimize turbulence in the pond water, accelerate the
sedimentation of suspended particles and minimize the flushing out of nutrients.
Only clear and clean water was fed into the pond; externally present water was not
used during rains in order to inhibit the inflow of water containing eroded soil
particles. Farmers apply pesticides on their fields in response to the weather, the
occurrence of pests, based upon recommendations from the national extension
service and on the advice of neighbors or family members. As a result, water
was only used to fill ponds at times when no pesticides had been applied above
the ponds.
Steinbronn (2009) reported poor growth among non-herbivore fish species under
traditional pond management systems, and during net cage trials in the research
area Yen Chau district, Pucher et al. (2011a, b) also showed that traditional pond
aquaculture practices were not appropriate for raising common carp due to a limited
natural food base. In this study, pond productivity and natural food availability was
shown to be not sufficient to raise common carp under the traditional fertilization
techniques used and with ruminant manure used in combination with constant water
flow-through. The common carp lost weight without supplemental feeding and
grew only slowly under supplemental feeding – by 3 % of their body mass each
day. However, the fish grew better when chemical fertilizers were applied in
stagnant water (Pucher et al. 2010a, 2011a).
To enable primary and secondary production in water with reduced turbidity,
ponds were fertilized using locally available resources. In certain regions of Son La
province with good market access, Black Thai raise locally adapted pig breeds as
livestock for income generation (Lemke et al. 2006), and Kumar and colleagues
reported pig manure to be a better organic fertilizer than ruminant manure (2004a, b,
2005b), while in our research area (Yen Chau district), Steinbronn (2009) reported
pig manure to contain less crude protein than ruminant manure due to the poor feed
base of pigs. As only a few households kept pigs, pig manure was applied in small
quantities during trials in the research area, with organic fertilization performed
through the application of cow and buffalo manure and through the stocking of grass
carp (stocked at a density of 10–20 % of the carp polyculture). Several researchers’
studies reported that stocking grass carp had a significant impact on the fertility of
ponds by enhancing decomposition rates and directly releasing nutrients from the
undigested leaf parts used as feed (Tripathi and Mishra 1986; Kumar et al. 2005b;
Pomeroy et al. 2000). Urea and single super-phosphate, which are available in the
8 Improved Sustainable Aquaculture Systems for Small-Scale Farmers . . .
297
were installed around the ponds to inhibit the inflow of run-off waters from
surrounding upland fields. A persistent ground cover was established to stabilize
the pond dikes and reduce the erosive effects of heavy rain. Such ground cover for
upland fields and pond dikes not only minimizes erosion but also increases the feed
base for grass carp and ruminants in the dry season, when green fodder is limited.
The aims of the water management scheme were to reduce the turbidity of the
pond water, thus enhancing primary production, and to reduce the loss of nutrients
caused by flushing out. Every 2–4 weeks, water was fed into the ponds to compensate for seepage, and to minimize turbulence in the pond water, accelerate the
sedimentation of suspended particles and minimize the flushing out of nutrients.
Only clear and clean water was fed into the pond; externally present water was not
used during rains in order to inhibit the inflow of water containing eroded soil
particles. Farmers apply pesticides on their fields in response to the weather, the
occurrence of pests, based upon recommendations from the national extension
service and on the advice of neighbors or family members. As a result, water
was only used to fill ponds at times when no pesticides had been applied above
the ponds.
Steinbronn (2009) reported poor growth among non-herbivore fish species under
traditional pond management systems, and during net cage trials in the research
area Yen Chau district, Pucher et al. (2011a, b) also showed that traditional pond
aquaculture practices were not appropriate for raising common carp due to a limited
natural food base. In this study, pond productivity and natural food availability was
shown to be not sufficient to raise common carp under the traditional fertilization
techniques used and with ruminant manure used in combination with constant water
flow-through. The common carp lost weight without supplemental feeding and
grew only slowly under supplemental feeding – by 3 % of their body mass each
day. However, the fish grew better when chemical fertilizers were applied in
stagnant water (Pucher et al. 2010a, 2011a).
To enable primary and secondary production in water with reduced turbidity,
ponds were fertilized using locally available resources. In certain regions of Son La
province with good market access, Black Thai raise locally adapted pig breeds as
livestock for income generation (Lemke et al. 2006), and Kumar and colleagues
reported pig manure to be a better organic fertilizer than ruminant manure (2004a, b,
2005b), while in our research area (Yen Chau district), Steinbronn (2009) reported
pig manure to contain less crude protein than ruminant manure due to the poor feed
base of pigs. As only a few households kept pigs, pig manure was applied in small
quantities during trials in the research area, with organic fertilization performed
through the application of cow and buffalo manure and through the stocking of grass
carp (stocked at a density of 10–20 % of the carp polyculture). Several researchers’
studies reported that stocking grass carp had a significant impact on the fertility of
ponds by enhancing decomposition rates and directly releasing nutrients from the
undigested leaf parts used as feed (Tripathi and Mishra 1986; Kumar et al. 2005b;
Pomeroy et al. 2000). Urea and single super-phosphate, which are available in the
8 Improved Sustainable Aquaculture Systems for Small-Scale Farmers . . .
297