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Wednesday, April 24, 2024
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മലയാളം
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Nursery Rearing
Nurseries are ponds for rearing the fry until they attain 5-7 cm in length.
The area of nursery ponds ranges from 500 to 5,000 m2. At the nursery
site the fry are acclimatized to the salinity of the pond water. Preparation of
pond for stocking with fry has to be started about one or two months in advance.
The ponds are drained and dried for about 10 to 15 days and later tilled and raked.
Lime is added @ 1000 kg/ha and fresh water is let in. Pond water is fertilized with
organic and inorganic fertilizers. Once the algal bloom develops more saline water
is added to a height of 10 cm. Within 3-7 days, a complex of blue green algae, diatom,
bacteria, nematode worms develop at the bottom of the pond called “Lab-Lab”.
This algal consortium is most vital for developing frys of milkfish. Stocking to
the nursery pond is usually done only after “Lab-Lab” has developed
in the pond. The fry are stocked at densities of 20-50/ m2. The threat
of predatory fishes, crabs and snakes can be screened from entering the pond using
nets. Erecting poles along the embankments and crisscrossing with strings can discourage
predatory birds. One serious cause of mortality of seeds in fry ponds is the sudden
reduction of temperature and salinity due to heavy rains. Filling the ponds with
brackishwater before rains may prevent such an eventuality.
The fry feed actively on Lab-Lab and phytoplankton and grow rapidly. By the end
of one month they measure 5-8 cm long and weigh 1.5-5 gm, when they are ready for
transfer to the production pond or pen structures for rearing. They are captured
by partially draining the fry ponds at low tides, when the fry usually congregate
near the water gates, for which seine nets are used.
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