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Rice-fish aqua culture improves farm income
By
Ahmed Yar Anjum, Muhanmmad Amin & Rashad Mehmood
 RICE-Fish
aqua culture is practised mainly to improve the income
of farmers and to make an essential item available in
the diet of rural people in areas where ‘rice and fish’
form the staple food. It requires very little input and
provides off-season employment to farm labours.
It has been observed that combination of rice and fish
farming is mutually beneficial. Fish feed on organisms
which grow in fields and on many noxious insects and
their larva, thus saving the crop from harmful organisms
and promoting better rice yield. By culturing
herbivorous fish, the weed growth can be controlled to a
considerable extent. Where there is proper water
management it is possible to control the growth of
molluscs and breeding of mosquitoes, thus reducing
public health hazards.
Movement of fish in inundated rice fields increases
tillering, which is helpful in higher rice production.
Greater depth of water maintained in fields prevents
pests like rodents from digging holes in bunds, and
floods their existing holes. Despite benefits, the two
cultures entail additional cost for farmers,
particularly in management and labour, which may easily
be overcome by income from fish farming.
At present three major types of rice-field aqua culture
are practised. The first which is the simplest form is
by using flooded rice fields after harvest, to raise one
or more crop of fish or shrimp. The second is growing
fish along with rice and harvesting rice and fish at the
end of the rice-growing season. The third and
complicated system, which ensures a prolonged period of
fish culture, involves transferring the stock to
specially prepared ditches, channels or pools at the
time of rice harvest, and restocking them in fields for
a further growing period. By this system, fish is grown
to a larger size than is possible in the short duration
of one rice crop.
In rice-cum-fish farming, the main crop is rice and
therefore fish farming techniques have to be modified to
make them compatible with rice farming. In some cases
,it is needed to reinforce and increase the height of
bunds to prevent the escape of fish, but this will not
affect rice farming. Construction of ditches and canals
reduces the area available for rice planting, as they
may occupy 5-10 per cent of the land. Higher levels of
water have to be maintained (10-25 cm) for growing fish
together with rice.
In areas where water supply is limited, this may prove
to be a major handicap. Also the short-stemmed,
high-yielding varieties used by farmers may tolerate
only moderate water depths, even when water supply is
not a constraint. The duration of cultivation of such
varieties is shorter (105-125 days) and may not be long
enough to grow fish to a marketable size. Deep water
(floating) rice is suitable for combined farming.
Fertility of the soil is equally important for this
culture. The small additional fertiliser needed to
stimulate adequate growth of fish food may not affect
production costs very much. Water quality in fields has
to be maintained at a level suitable for fish and its
food organisms. A serious problem which has affected the
culture, and contributed to its decline in many
countries, is the excessive use of pesticides which
kills fish. There is also risk of accumulation of
pesticides in fish which may be harmful for consumers.
In rice fields irrigated with fresh water, either mono-
or poly-culture of finfish is cultured. The most common
species are carp, tilapia and Trichogaster. Snake-head (murrel)
and catfish are also used.
As fields when flooded after rice harvest, serve as
shallow ponds, some pond culture practices such as
fertilisation and supplementary feeding can be adopted.
Through proper water management, a suitable water
temperature and oxygen content have to be maintained.
Depending on the period available for fish farming, the
stocking rate and size can be determined. The duration
of culture is generally three to four months. Fish yield
varies with species and culture practices etc. In well
managed fields a yield of up to 700 kg/ha can be
expected.
Rice and fish culture: For the combined culture some
additional constructions are needed. As in the case of
rotational culture, bunds around the field have to be
strengthened and the height increased. Straw may be
embedded along the inside walls of the bunds to make
them water-tight. A height of 25-60 cm is suitable
depending on water level required and the species to be
cultured.
Usually the inlets and outlets are provided with pipes
and screens to prevent escape of fish and ingress of
undesirable animals. A series of trenches are dug to
serve as fish refuge when water in field gets too cold
or too warm, or when water level in rest of the fields
has to be reduced. They may be built along the
peripheries or across the field. A width of 50 cm and a
depth of 30 cm are normally enough, but for extreme
temperature conditions deeper trenches (up to 90 cm) are
recommended. Depending on the type of soil, a side slope
of 30-45 degrees may be necessary
Although several species are cropped from rice fields,
the main specie used at present rice-fish culture in
fresh waters are: carp, tilapia, nielm carps (Osteochilus
hassltii), kissing gourami (Helostoma temmincki) and
sepat siam (Trichogaster pectoralis) and less frequently
the Java carp (Puntius gonionotus), snakehead (Channa)
and catfish (Clarias).
The most successful species in rice fields are those
which can thrive in shallow waters and tolerate fairly
high turbidity and high temperatures. As the duration of
culture is rather limited, they should have high growth
rates and reach marketable size in a few months. In
general, fish are stocked no earlier than five days
after the transplantation of rice seedlings, to give
enough time for the seedlings to root properly. It is
recommended that stocking should be done only after 10
days if fry or fingerlings are used, and in the case of
fingerlings about three weeks after transplantation of
rice.
The rate of stocking varies considerably, depending on
species and size of age of the fry or fingerlings used.
According to recent records, when small fry are stocked
for rearing to fingerling size, 2.2-7.6 kg per ha of fry
are stocked. If the duration of culture is one month,
6.5-15 kg per ha of fingerlings can be harvested. When
larger fry or fingerlings are stocked and reared to
consumption size a yield of about 100 kg/ha, after two
or three months, has been reported. This is a
comparatively low production, but is probably due to
lack of any supplementary feeding and less intensive
management. The yield per ha is generally higher when
fish are grown alone in the rice fields as a rotational
crop.
Courtesy: The DAWN |
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Pakissan.com;
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