(Dongmeza 2009), with leaves from banana or bamboo (Dongmeza 2009), or with
the leaves of maize or barnyard grass (Dongmeza et al. 2010). In all these trials, the
leaves and weeds used, with the exception of the maize leaves, came from the
farmers in Yen Chau. In a feeding trial at Hanoi University of Agriculture, grass
carp fingerlings were fed solely on fresh banana leaves, barnyard grass or Napier
grass (Tuan et al. 2007).
In the experiment carried out by Dongmeza (2009), grass carp that were
supplemented with banana leaves had a significantly higher body weight gain
compared to the control group fed the same amount of standard feed only.
In contrast, the growth and feed conversion rate for grass carp supplemented with
dried cassava leaves was generally lower in the cassava-supplemented fish as
compared to the control group, even though these fish received leaves in addition
to the same amount of standard diet as the control group and; thus, a larger amount of
nutrients (Dongmeza 2009). In this case, the authors attributed the lower level of
growth to the intake of anti-nutrients. Lower growth rates were also observed in
grass carp supplemented with either bamboo leaves, barnyard grass or mixed weeds
from the paddy fields, as compared to the respective control groups (Dongmeza
2009; Dongmeza et al. 2010). Groups of young grass carp (~ 20 g) fed solely on
barnyard or Napier grass showed low fish growth rates and many of the fish died
(Tuan et al. 2007). Tuan et al. (2007) concluded that these grasses are probably not
able to support the growth of young grass carp when they are the sole source of food.
Although most of the feed supplied to the ponds in the study area is intended for
grass carp, the observed growth rates were rather low, with an average specific
growth rate of only 0.24 %. While some of the feeds appear to exhibit good
potential as supplementary feed, such as banana leaves and duckweed, others
such as bamboo leaves, cassava leaves, barnyard grass and mixed weeds probably
do not contribute significantly to the growth of fish.
While the feed items that have been discussed so far are most likely eaten almost
exclusively by the herbivorous fish, the by-products of cassava, maize and rice
(other than the leaves) are thought to play a major role as supplementary feed for the
other fish species in the present system. In addition, most of these species are also
known to feed on the natural food available in the ponds.
Quantitatively, the most important supplementary feed types in the case study
ponds were rice bran and cassava peel. The rice bran was usually of low quality and
had low crude protein content, and the peel from cassava tubers was found to be low
in protein and fat and contained considerable amounts of fiber and lignin as well as
cyanides (Dongmeza et al. 2009). Although tilapia, common carp, mud carp and
mrigal are known to be able to make use of agricultural by-products (FAO 2006b),
it is unlikely in the present case that either of these feeds contributed significantly to
fish growth.
In the study area, the availability of livestock manure for pond use is limited by a
low number of livestock and the competition with other use types such as paddy rice
or gardening within the farm household. Manure from buffalo was by far the most
commonly applied manure in the case study ponds and accounted on average
for 94 % of the total. The dry matter (19.2 % of FM) and nitrogen (N)-content
292
J. Pucher et al.
the leaves of maize or barnyard grass (Dongmeza et al. 2010). In all these trials, the
leaves and weeds used, with the exception of the maize leaves, came from the
farmers in Yen Chau. In a feeding trial at Hanoi University of Agriculture, grass
carp fingerlings were fed solely on fresh banana leaves, barnyard grass or Napier
grass (Tuan et al. 2007).
In the experiment carried out by Dongmeza (2009), grass carp that were
supplemented with banana leaves had a significantly higher body weight gain
compared to the control group fed the same amount of standard feed only.
In contrast, the growth and feed conversion rate for grass carp supplemented with
dried cassava leaves was generally lower in the cassava-supplemented fish as
compared to the control group, even though these fish received leaves in addition
to the same amount of standard diet as the control group and; thus, a larger amount of
nutrients (Dongmeza 2009). In this case, the authors attributed the lower level of
growth to the intake of anti-nutrients. Lower growth rates were also observed in
grass carp supplemented with either bamboo leaves, barnyard grass or mixed weeds
from the paddy fields, as compared to the respective control groups (Dongmeza
2009; Dongmeza et al. 2010). Groups of young grass carp (~ 20 g) fed solely on
barnyard or Napier grass showed low fish growth rates and many of the fish died
(Tuan et al. 2007). Tuan et al. (2007) concluded that these grasses are probably not
able to support the growth of young grass carp when they are the sole source of food.
Although most of the feed supplied to the ponds in the study area is intended for
grass carp, the observed growth rates were rather low, with an average specific
growth rate of only 0.24 %. While some of the feeds appear to exhibit good
potential as supplementary feed, such as banana leaves and duckweed, others
such as bamboo leaves, cassava leaves, barnyard grass and mixed weeds probably
do not contribute significantly to the growth of fish.
While the feed items that have been discussed so far are most likely eaten almost
exclusively by the herbivorous fish, the by-products of cassava, maize and rice
(other than the leaves) are thought to play a major role as supplementary feed for the
other fish species in the present system. In addition, most of these species are also
known to feed on the natural food available in the ponds.
Quantitatively, the most important supplementary feed types in the case study
ponds were rice bran and cassava peel. The rice bran was usually of low quality and
had low crude protein content, and the peel from cassava tubers was found to be low
in protein and fat and contained considerable amounts of fiber and lignin as well as
cyanides (Dongmeza et al. 2009). Although tilapia, common carp, mud carp and
mrigal are known to be able to make use of agricultural by-products (FAO 2006b),
it is unlikely in the present case that either of these feeds contributed significantly to
fish growth.
In the study area, the availability of livestock manure for pond use is limited by a
low number of livestock and the competition with other use types such as paddy rice
or gardening within the farm household. Manure from buffalo was by far the most
commonly applied manure in the case study ponds and accounted on average
for 94 % of the total. The dry matter (19.2 % of FM) and nitrogen (N)-content
292
J. Pucher et al.