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Fisheries > Culture Fisheries > Clams

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.

nursery

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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