38 %. Under the traditional pond management system, the recovery rate for the
common carp was around 20 %, and; therefore, even lower. As under the semiintensive pond management system, the average specific growth rate for the common carp was 2.4 %, while under the traditional pond management system it was
significantly lower at1.9 %. This may have been caused by high inter-specific and
intra-specific competition for the supplemental feed pellets and natural food
resources, especially for the macro-zoobenthos. It may also have been caused by a
reduction in the genetic variability of the fish hatchery populations due to
inbreeding, and this was mentioned by farmers and has been described as typical
for rural hatchery brood stock populations (Kohlmann et al. 2003; Eknath and Doyle
1985) resulting in a low growth potential or a suppression of the immune defense
system. In Son La province, most fish seed is produced either in the Son La city
hatchery or transported from hatcheries in Bac Ninh province (approximately
300 km away from the research area). In contrast to reports from local farmers in
Son La province (Steinbronn 2009; Thai et al. 2006), Thai et al. (2006) found that the
common carp population at the Son La city hatchery exhibits greater genetic
diversity than the three experimental lines at the Research Institute for Aquaculture
No. 1 (RIA 1), or in the wild populations of Vietnamese common carp. Thai et al.
(2006, 2007) attributed this finding to the successful dissemination of imported
genetically improved stocks. The findings of Thai et al. (2006, 2007) indicated
that the poor growth of common carp reported by farmers in Son La province was
caused by a poor feed base and low water quality.
Despite the low growth rate among common carp in the field trials, the modified
pond management system did lead to significantly higher fish production levels
overall (on average 4.5 times higher) and less variable financial net benefits from
aquaculture activities when compared to farming activities (Pucher et al. 2010a).
This was a result of the use of higher quality resources as feed inputs and of the
introduction of measures to increase primary production. Financial net benefit
accounted for 367 Æ 133 USD per 1,000 m
2 of pond under modified management
for a year, and 83 Æ 356 USD per 1,000 m
2 of pond under traditional management
for a year (based on local prices from 2009; 1 USD ¼ 18,000 VND, leaf material
was not taken into account). Both fish production levels and financial net benefit
showed a very high variability under the traditional pond management system,
caused by different environmental land use conditions surrounding the ponds
(Pucher et al. 2010a; Steinbronn 2009). Under the modified pond management
system, the uncoupling of the pond from the surrounding land use activities through
the minimizing of water inflows into the pond, resulted in a lower variability in
terms of both fish production levels and financial net benefits across ponds.
The acceptability of the overall modified pond management scheme in the
research area, as well as the improvements implemented by the Black Thai trial
farmers are discussed in Sect. 8.6. For the farmers, there are several areas of
uncertainty associated with the use of the modified pond management which
might impact their level of acceptance of such a system, such as the need for
constant investment in higher quality feeds, especially the expensive, high protein
feed ingredients like fish meal and heated soybean meal. There is some evidence
302
J. Pucher et al.
common carp was around 20 %, and; therefore, even lower. As under the semiintensive pond management system, the average specific growth rate for the common carp was 2.4 %, while under the traditional pond management system it was
significantly lower at1.9 %. This may have been caused by high inter-specific and
intra-specific competition for the supplemental feed pellets and natural food
resources, especially for the macro-zoobenthos. It may also have been caused by a
reduction in the genetic variability of the fish hatchery populations due to
inbreeding, and this was mentioned by farmers and has been described as typical
for rural hatchery brood stock populations (Kohlmann et al. 2003; Eknath and Doyle
1985) resulting in a low growth potential or a suppression of the immune defense
system. In Son La province, most fish seed is produced either in the Son La city
hatchery or transported from hatcheries in Bac Ninh province (approximately
300 km away from the research area). In contrast to reports from local farmers in
Son La province (Steinbronn 2009; Thai et al. 2006), Thai et al. (2006) found that the
common carp population at the Son La city hatchery exhibits greater genetic
diversity than the three experimental lines at the Research Institute for Aquaculture
No. 1 (RIA 1), or in the wild populations of Vietnamese common carp. Thai et al.
(2006, 2007) attributed this finding to the successful dissemination of imported
genetically improved stocks. The findings of Thai et al. (2006, 2007) indicated
that the poor growth of common carp reported by farmers in Son La province was
caused by a poor feed base and low water quality.
Despite the low growth rate among common carp in the field trials, the modified
pond management system did lead to significantly higher fish production levels
overall (on average 4.5 times higher) and less variable financial net benefits from
aquaculture activities when compared to farming activities (Pucher et al. 2010a).
This was a result of the use of higher quality resources as feed inputs and of the
introduction of measures to increase primary production. Financial net benefit
accounted for 367 Æ 133 USD per 1,000 m
2 of pond under modified management
for a year, and 83 Æ 356 USD per 1,000 m
2 of pond under traditional management
for a year (based on local prices from 2009; 1 USD ¼ 18,000 VND, leaf material
was not taken into account). Both fish production levels and financial net benefit
showed a very high variability under the traditional pond management system,
caused by different environmental land use conditions surrounding the ponds
(Pucher et al. 2010a; Steinbronn 2009). Under the modified pond management
system, the uncoupling of the pond from the surrounding land use activities through
the minimizing of water inflows into the pond, resulted in a lower variability in
terms of both fish production levels and financial net benefits across ponds.
The acceptability of the overall modified pond management scheme in the
research area, as well as the improvements implemented by the Black Thai trial
farmers are discussed in Sect. 8.6. For the farmers, there are several areas of
uncertainty associated with the use of the modified pond management which
might impact their level of acceptance of such a system, such as the need for
constant investment in higher quality feeds, especially the expensive, high protein
feed ingredients like fish meal and heated soybean meal. There is some evidence
302
J. Pucher et al.