According to the classification of integrated agriculture-aquaculture systems
provided by Prein (2002), the system in the study area is plant based since mainly
aquatic or terrestrial macrophytes are used as feed. The herbivorous grass carp,
which is able to process raw plant material, is the major species that feeds on the
applied green fodder in the study area. However, not all of the plant materials
currently applied have been found to be suitable as feed for the grass carp. Some of
the leaves and grasses applied in the study area showed a limited feed value
(Dongmeza et al. 2009) and several feeds even turned out to have a negative impact
on fish growth (Tuan et al. 2007; Dongmeza 2009; Dongmeza et al. 2010). Further,
the feed base for the non-grass carp species in this pond system is rather limited.
These topics are discussed in Sect. 8.3.
Farmers’ decisions regarding the use of a certain feed at a certain time of the year
are often based on the availability of feed – such as the use of maize leaves during
the growing period, the availability of labor – such as the use of rice bran during
times of higher workloads, and current farming activities – including the use of
weeds after hand-weeding of the crop fields has taken place. Fish diets vary
between ponds, which can usually be explained by the ponds’ locations. Ponds
located next to the farmers’ houses often receive more diverse feed inputs
(e.g., kitchen waste or manure from nearby livestock pens) than those situated
further away.
During our study, the average daily feed application was 196 kg of leaf material
per hectare, which is a third of the feed amount used in intensive leaf-based
aquaculture systems such as the Chinese mulberry dike-carp pond farming system
described by Ruddle and Christensen (1993) or the Napier grass based tilapia
culture described by Van Dam (1993). However, the feed conversion rate of leaf
material used within the Black Thai polyculture was found to be 8.8 (feed DM),
which is comparable to the Chinese leaf-based aquaculture system (Ruddle and
Christensen 1993), but is magnitudes higher than in aquaculture systems that use
higher quality feeds. The high moisture content and the bulky nature of many of the
applied feeds means they require large amounts of labor for their collection and
transportation; for example, during the wet season, farmers spend around 2 h per
day just collecting and transporting fish fodder. However, in some cases, aquaculture activities can be combined with other farming tasks, such as the weeding of
paddy fields which simultaneously produces feed for the fish.
Typically, farmers regularly catch aquatic products for their household consumption and then harvest larger amounts for sale at the end of the major rearing period,
which usually lasts between 1 and 2 years. The produce is sold when the fish reach
marketable size, when money is needed, when farmers have fixed harvest dates with
the fish traders, or when water shortages or fish diseases force farmers to take action.
In general, only big fish are caught, while small fish are kept in the ponds to allow
further growth. During our study, average annual net production of the aquatic
species, including ‘self-recruiting’ species (see below), was 1.54 Æ 0.33 tons per
ha, of which roughly two thirds was sold. Besides the cultured species, farmers also
harvest naturally entering self-recruiting species which can be fish or other aquatic
organisms such as snails, mussels, crabs or shrimps. These self-recruiting species as
8 Improved Sustainable Aquaculture Systems for Small-Scale Farmers . . .
287
provided by Prein (2002), the system in the study area is plant based since mainly
aquatic or terrestrial macrophytes are used as feed. The herbivorous grass carp,
which is able to process raw plant material, is the major species that feeds on the
applied green fodder in the study area. However, not all of the plant materials
currently applied have been found to be suitable as feed for the grass carp. Some of
the leaves and grasses applied in the study area showed a limited feed value
(Dongmeza et al. 2009) and several feeds even turned out to have a negative impact
on fish growth (Tuan et al. 2007; Dongmeza 2009; Dongmeza et al. 2010). Further,
the feed base for the non-grass carp species in this pond system is rather limited.
These topics are discussed in Sect. 8.3.
Farmers’ decisions regarding the use of a certain feed at a certain time of the year
are often based on the availability of feed – such as the use of maize leaves during
the growing period, the availability of labor – such as the use of rice bran during
times of higher workloads, and current farming activities – including the use of
weeds after hand-weeding of the crop fields has taken place. Fish diets vary
between ponds, which can usually be explained by the ponds’ locations. Ponds
located next to the farmers’ houses often receive more diverse feed inputs
(e.g., kitchen waste or manure from nearby livestock pens) than those situated
further away.
During our study, the average daily feed application was 196 kg of leaf material
per hectare, which is a third of the feed amount used in intensive leaf-based
aquaculture systems such as the Chinese mulberry dike-carp pond farming system
described by Ruddle and Christensen (1993) or the Napier grass based tilapia
culture described by Van Dam (1993). However, the feed conversion rate of leaf
material used within the Black Thai polyculture was found to be 8.8 (feed DM),
which is comparable to the Chinese leaf-based aquaculture system (Ruddle and
Christensen 1993), but is magnitudes higher than in aquaculture systems that use
higher quality feeds. The high moisture content and the bulky nature of many of the
applied feeds means they require large amounts of labor for their collection and
transportation; for example, during the wet season, farmers spend around 2 h per
day just collecting and transporting fish fodder. However, in some cases, aquaculture activities can be combined with other farming tasks, such as the weeding of
paddy fields which simultaneously produces feed for the fish.
Typically, farmers regularly catch aquatic products for their household consumption and then harvest larger amounts for sale at the end of the major rearing period,
which usually lasts between 1 and 2 years. The produce is sold when the fish reach
marketable size, when money is needed, when farmers have fixed harvest dates with
the fish traders, or when water shortages or fish diseases force farmers to take action.
In general, only big fish are caught, while small fish are kept in the ponds to allow
further growth. During our study, average annual net production of the aquatic
species, including ‘self-recruiting’ species (see below), was 1.54 Æ 0.33 tons per
ha, of which roughly two thirds was sold. Besides the cultured species, farmers also
harvest naturally entering self-recruiting species which can be fish or other aquatic
organisms such as snails, mussels, crabs or shrimps. These self-recruiting species as
8 Improved Sustainable Aquaculture Systems for Small-Scale Farmers . . .
287