studies on improved practices of prawn farming for higher ...

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Penaeid shrimps are generally cultured in impoundments less
expensive to construct and operate, with stagnant or semi-stagnant
water in comparison to running water systems.
Shrimps can also be cultured in pens ie, artificial enclosures
implanted at the substratum of estuaries, bays, swamps and coastal
waters. But the greatest disadvantage is that these are at the mercy
of natural environment over which the aquaculturist has very little
control. Hence it is not possible to anploy advancedtechnologies. The
widely practised pen culture organised in Japan (Felix, 1975) and is in
vogue in Cambodia, Thailand and Indonesia (Devaraj, 1974) is done on an
experimental basis in lagoons of southern India by enclosing suitable
intertidal areas by net fencing using nylon/metal mesh and wooden
poles. Shanmugham and Bensam (1982) based on their <strong>studies</strong> on pen
culture of prawns in coastal lagoons at Tuticorin have suggested many
improvements. Japanese pens are made of vertical concrete walls of l M
height to hold water during low tides and covered by wooden frames with
nylon netting to prevent escape of shrimp. larvae (Kungvankij, 1985).
These pens resembling tidal ponds often cover an area of 10000 m‘ and
is capable of producing 3-4 tonnes per ha/year when stocked with a
density of 20-30/m‘.
Cages originated in -Kampuchia (Coche, 1979) are enclosed
structures of several types (Beveridge, 1987), varying shapes,
dimensions and areas usually made of bamboo, wood, nylon or metal in
which shrimps can be stocked in higher densities. These are floated in
suitable areas either inshore or off shore where sufficient water
exchange is assured.
Siddharaju and Ramachandra Menon (1982) assumed that the nylon
cages could be used for raising 2 crops of shrimps with artificial feed
and could give an average annual production of 736 g/m’ in 2 crops.
Nursery rearing experiments conducted in collapsible 36 meshes
per cm nylon screen cages of Sx2x1 m size at Kovalam near Madras proved