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Simultaneous Culture
For simultaneous culture, rice fields of 0.1 ha area may be economical. Normally
four rice plots of 250 m2 (25 x 10 m) each may be formed in such an area. In each
plot, a ditch of 0.75 m width and 0.5 m depth is dug. The dikes enclosing the rice
plots may be 0.3 m high and 0.3 m wide and are strengthened by embedding straw.
The ditches have connections with the main supply or drain canal, on either side
of which, the rice plots are located, through inlet-outlet structures of the dikes.
The depth and width of the supply or drain canal may be slightly smaller than that
of the ditches. Suitable bamboo pipes and screens are placed in the inlet and outlet
structures to avoid the entry of predatory fish and the escape of fish under culture.
The ditches serve not only as a refuge when the fish are not foraging among rice
plants, but also serve as capture channels in which the fish collect when water
level goes down. The water depth of the rice plot may vary from 5 to 25 cm depending
on the type of rice and size and species of fish to be cultured.
The fish species which could be cultured in rice fields must be capable of tolerating
shallow water (15 cm), high temperatures (up to 35ºC), low dissolved oxygen
and high turbidity. Species such as Catla catla, Labeo rohita, Cirrhina mrigala,
Cyprinus carpio, Chanos chanos, Oreochromis mossambicus, Anabas testudineus, Mugil
spp., Clarias batrachus, C. macrocephalus, Lates calcarifer, Channa striatus
and C. marulius have been widely cultured in rice fields.
Simultaneous Culture Of Fresh-Water Prawn And Rice
Semi-intensive culture of Macrobrachium rosenbergii could be undertaken
in rice fields. Unlike for fish-rice culture, bunds for fish-prawn culture are raised
so as to enclose 12 cm of water for four months, the period of rice culture. Further,
inlets and outlets should be provided with extended screen, say, 0.3 m above water
surface to prevent climbing and escape of prawns. One or two small sump pits (1
x 2 x 0.5 m) should also be constructed near the outlet for trapping prawns when
water is drained at the time of harvesting. The stocking of juvenile prawns (2-3
cm size) at the rate of 1,000/ha may be done after the rice seedlings are well rooted.
No supplementary feeding of prawns is required in this system.
The simultaneous culture has the following advantages:
- Fish increases rice yield by 5 to 15 per cent, which is chiefly due to the indirect
organic fertilisation through the fish excrement and also the control of unwanted
filamentous algae which may otherwise compete for the nutrients.
- Tilapia and common carp control the unwanted aquatic weeds which may otherwise reduce
the rice yield up to 50 per cent.
- Insect pests of rice like stem borers are controlled by fish feeding on them like
murrels and catfish.
- Fish feed on the aquatic intermediate hosts such as malaria causing mosquito larvae,
thereby controlling water-borne diseases of human beings.
- Rice fields may also serve as fish nurseries to grow fry into fingerlings. The fingerlings,
if and when produced in large quantities may either be sold or stocked in production
ponds for obtaining better fish yield under composite fish culture.
Limitations in simultaneous culture: The simultaneous fish-rice culture may have
some limitations, like (a) use of agrochemicals is often not feasible, (b) maintaining
high water level may not be always possible, considering the size and growth of
fish, (c) fish like grass carp may feed on rice seedlings, and (d) fish like common
carp and tilapia may uproot the rice seedlings. However, these constraints may be
overcome through judicious management.
Culture procedure: Five days
after transplanatation of rice, fish fry (1 cm) are stocked at the rate of 5,000/ha
or fingerlings (8-10 cm) at the rate of 2,000/ha. The stocking density can, however,
be doubled if supplemental feed is given daily, particularly if plankton is found
depleted after 10 days of stocking fish. The plankton production in rice fields
could, however, be increased if some amount of fertiliser more than what is required
for rice fields is added. To control the menace of insects, the insecticide Furadon
(Carbofuran) may be used at the rate of 1 kg/ha. The insecticide is mixed with basal
fertilisers and applied once during the final harrowing. It may be stated that fish
grown in insecticide-applied rice fields are safe for human consumption.
After a period of 10 weeks (if stocked with fry) or six weeks (if stocked with fingerlings),
the rice fields are slowly drained off and the fish are harvested. The harvesting
of fish may be done about a week before the harvest of rice. The growth rate of
fish is also moderate in rice fields as the production of plankton, the fish food
organisms, is rich. Individual growth of 60 g and a per hectare yield of 500 kg
have been reported under the simultaneous culture practice.
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