Crab farming has become an integral part of aquaculture in the country. This practice began in the early seventies when some fishpond operators in Bicol, Visayas, and Southern Tagalog started to culture crab as a subsidiary crop in milk fish or bangus ponds.
The crab species Scylla serrata is the biggest and most important member of the family of edible crabs in the Philippines.
Mud crab, or alimango, is considered a delicacy and has become a popular fare in seafood restaurants. It is sought for its very tasty aligue or ripe eggs in the ovary.
Crabs abound in estuaries, mangroves, swamps and tidal waters, living both as a scavenger and a cannibal.
Breeding and Spawning
The mating period of crabs is usually long. When mating, the female is carried by the male, clasping her with three pairs of walking legs. In this condition, it is very easy to catch them. After five days, the female is finally released by the male. Mating usually occurs for four months, during the period May to September. Prior to that, in April, the females develops eggs or aligue.
Crabs spawn in the sea. The newly hatched larvae called zoea are free-swimming. They are carried by the tide to the coast where they migrate to live-in estuaries, swamps and mangroves. Fertility is very high among females. As much as a million eggs can be laid but mortality is also high because of inclement climatic conditions.
This is an indispensable stage in the life cycle of crabs. During molting, they shed their covering or carapace. This happens when there is an abrupt increases in the size of their body. After shedding the old carapace, the crab is left with a very soft covering. It becomes an easy prey to other animals and survive, the crab buries itself under the mud until the soft shell hardens.
Culture and Cultivation Methods
Small crabs or crab seeds are caught by fishermen in seashores, swamps and other natural habitats. They are gathered and sold to fishponds operators.
Crabs are raised in brackish water fishponds. Crab and can be raised simultaneously. It is, however, not advisable to culture crabs together with prawns or sugpo, because when prawns undergo molting, crabs eat them.
Choosing the Crab Farm
Choosing a site for crab farming is not difficult. First, there should be adequate supply of estuarine water because good and stable salinity is conducive to growth. Smaller ponds are advisable since they are easier to manage. Make sure the soil is clay or clay loam. This kind of soil is capable of retaining water. If possible, the site should be free from floods. The depth of water is also important. Advisable depth is one meter to prevent exposure of cultured crabs and stop them from boring holes through the dikes. For easy harvesting, the site should have good drainage. This also facilities the practice of pond freshening whereby the water is cleansed by letting in fresh seawater. Available of crab seeds in the area is also important. This ensures a steady number of young crabs for rearing and the continued operation of your farm.
Managing the Crab Farm
For crab farming, the ponds are prepared just like any bangus fishpond but the side of the dikes should be very firm to discourage the crabs from burrowing through. Place banatan or bamboo screen along main dikes to prevent escape of crabs. About 2,000 to 4,000 crab seeds, 2 to 5 cm in length and size, would be needed initially. Stock them directly in the rearing ponds. Feeding is not a problem since young crabs feed on algae and decaying organic matter. As they grow, crabs become carnivorous. Supplement their feed with trash fish and leftover food. Their rate of growth is rather slow. It takes five to six months for crabs to grow into marketable sizes.
Application of fertilizer is helpful. This enhanced the growth of natural food like moss in the ponds.
This is done with different kinds of trap like the bamboo cage, lift net, scissors net, fish corrals and gill nets. Crabs are ready for the harvest and marketing when the piece or two reaches up to a kilo. They are sold alive and can stay out of the water even for a week. They should, however, be kept in damp containers and periodic moistening is important. Feed them with trash fish and other kitchen refuse.
Adult crabs in captivity are tied with dried nipa strings. Both pincers are tied close to the abdominal cavity to prevent crawling. When transported, proper handling is important. Place them in baskets or tiklis to avoid getting trampled or crushed.
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Agri-Aqua Network International
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For more information contact:
PCAMRD – Philippine Council for Aquatic and Marine Research and Development
Department of Science and Technology (DOST
Jamboree rd., Brgy. Timugan, Los Banos, Laguna
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PCAMRD Liaison Office
2nd Floor, Rm. 205 PTRI Bldg.
Gen. Santos Ave., Bicutan, Taguig, Metro Manila, Philippines
Telephone Number: (63 2) 837-2071 up to 82 local 2430
BFAR – Bureau of Fisheries and Aquatic Resources
Arcadia Building, 860 Quezon Avenue, Quezon City
Tel No. : (02) 372-5043, Fax: (2) 372-5048
Email : [email protected]