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Thursday, November 21, 2024
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മലയാളം
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Hatchery Production
of Spat
The criteria for site selection, the technology for spawning and rearing the larvae/spat
of clams are similar to those described for other molluscs. In clams, spawning occurs
both at the elevated water temperature of about 34°C and also at the lower temperature
of about 24°C on transfer to the conditioning room, after the thermal shock.
Spat settlement takes place between 7th and 16th day after spawning in different
clam species. The clam spat attain 2-3 mm in length in the hatchery in two months
after fertilization and are transferred to the nursery. A survival rate of 15-20%
in spat production in the hatchery is considered as satisfactory. Microalga Isochrysis
galbana is given as food to the larvae and mixed microalgae, reared in
outdoor tanks as food to the spat.
Clams in hatchery
Nursery rearing
The 2-3 mm hatchery produced clam seed are transferred to 40 x 40 x 10 cm box type
cages. These cages are covered with fine velon screen mesh and for additional protection
against damage by crabs and fishes; a 10 mm mesh nylon fish net is stitched over
the cage. The cages are suspended from racks in shallow calm waters. They are periodically
cleaned of silt, predators and foulers, which enter the cages as larvae. In 6-8
weeks, the clams grow to about 10 mm in length and are ready for planting on the
grow-out grounds. They are stocked in milkfish ponds; bamboo sticks are planted
to serve as markers. To enhance the pond productivity fertilizers are used. After
about 6 months nursery rearing they are harvested (survival 50-60%) and sold for
stocking in clam farms.
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