Mudcrab culture provides income and livelihood to many Filipinos. What was considered as a minor fishery product is now an export commodity and a foreign exchange earner. Mudcrab being a supplementary crop from brackishwater milkfish and shrimp ponds, it has virtually been overlooked as a potential species for culture. With the increase in prices and demand from both domestic and foreign markets, the attitudes towards mudcrab has been changed. This has triggered the development of the mudcrab industry in the Philippines.
Mudcrabs are widely distributed in the Philippines and are easily available in the markets throughout the year. In 2000, total mudcrab production (Scylla spp.) in the country reached 4,495 tonns (BFAR 2000). These provinces were Bulacan, Capiz, Masbate, Pampanga, Pangasinan, Sorsogon, Surigao del Sur, Catanduanes, and Zamboanga del Sur.
There are several species of mudcrab in the Philippines and not all of them are ideal for aquaculture. Estampador (1949a) identified three species and one variety. This, however, was revised by Keenan et al in 1998. Below is a comparison:
Estampador (1949a) Keenan et al (1998)
S. serrata S. olivacea
S. oceanica S. serrata
S. serrata var. paramamosain S. paramamosain
S. tranquebarica S. tranquebarica
In this paper, the classification of mudcrabs follows that of Keenan, et al (1998). The mudcrab industry uses the term King Crab as the local name for S. serrata (“Putian” or “Bulik”), considered as the biggest and fastest growing mudcrab in the Philippines. This species is greenish with white polygonal markings on the swimming and walking legs, chelipeds, carapace, and with orange claws. Locally named “pulahan” or native alimango is the Scylla olivacea. It has deep green to grayish green color of the carapace, rusty brown chelipeds, swimming, and walking legs.
Collecting areas are situated in Northern Samar, Sorsogon, Albay, Camarines Norte, Camarines Sur, Catanduanes, Cagayan, Aklan, and Surigao. Other areas include some municipalities of Negros Occidental, Negros Oriental, Lanao, Misamis, and Zamboanga.
Mudcrab growers still depend on seedstocks coming from the wild for pond stocking. Native mudcrabs are distributed in mangroves and in estuaries. King crabs (S. serrata) come mostly from provinces facing the Pacific Ocean, the reason perhaps, why mudcrab growers believe they are oceanic species.
Production and Technology
Mudcrabs have been cultured in ponds, cages, and pens. Production data for mudcrab for the period 1998 to 2000 showed increasing production from brackishwater ponds. Production for the same period ranged from 3,996 to 4,495 metric tons.
The commercial production of mudcrab in bamboo-fenced brackishwater ponds has already been established, and is being practiced in the Philippines. Mudcrab grow-out in ponds can yield as much as 1,200 kg per ha per crop (10,000 mudcrab juveniles per ha per crop).
Mudcrab culture in mangroves or tidal flats has been also practiced in some parts of the country. It is ecologically friendly because it does not destroy mangroves and uses locally available materials. The net enclosure requires small financial investment to construct and operate.
Nets were installed enclosing the area as specified in the design by SEAFDEC-AQD. The mangrove area (which can have 0.5-1.0 ha water area) was enclosed with “A” net (1-2cm mesh size) with bamboo or wooden post as structural framework. The upper end of the net extends about 30 cm above the waterline and is fitted with thick plastic sheets (50 cm) to prevent mudcrab from escaping. The lower end of the net is staked 50-60 cm deep into the pond bottom.
The mangrove area goes through the usual pond preparation protocol. It is to be drained during the lowest tide to eradicate predators. Flooding should follow the normal tidal cycle but water depth should be maintained at 0.70 to 1.0 meter. Stocking density of 10,000 monosize mudcrab juveniles weighing 25-30 grams per piece can be stocked per hectare. Chopped trash fish, animal hide or entrails and snails are used as feeds. After 4-5 months, marketable sizes (300-350 g) may be harvested by handpicking during low tide. A production yield of 1,200 kgs. may be achieved with survival rate of 70%. Return of Investment (ROI) is placed at 60% and payback period of 1.4 year.
Research & Development
There have been sporadic R&D work on mudcrabs in the country. Experiments to establish stocking density of mudcrabs raised in brackishwater ponds were set up by SEAFDEC-AQD and BFAR. More and more attention is now given to mudcrab aquaculture research and development. Development of appropriate technologies is one of priorities of most R&D institutions in the Philippines namely; SEAFDEC-AQD, UPV College of Fisheries, BFAR-NFRDI, PSU, Bicol University, and UEP in Catarman, Samar.
SEAFDEC-AQD and UPV have successfully spawned mudcrab in captivity. However, mass production of juveniles is still hampered by the low larval survival and production of crablets in the hatchery. Recent improvements indicated a 1-4% survival from hatching to crablets stage which is economically feasible considering that a female crab releases about 2 million eggs per spawning. BFAR-NFRDI is conducting a study to refined the breeding and hatchery techniques on mudcrab in order to increase larval survival and growth under controlled conditions. Private sector collaboration to pilot test the mudcrab hatchery technology will be implemented next year.
Due to the availability of several species of mudcrab in the Philippines, the author is conducting mudcrab seedstocks resource assessment to determine the geographical areas where each of the mudcrab species is dominant.
The market price of firm and fat crabs is usually higher hence techniques in improving the quality of harvestable size through fattening has been developed. Moreover, this technique is oftentimes more preferred than actual crab culture due to fast rate of return and minimal investment cost.
Lean mudcrabs do not possess the fat conditions demanded for by consumers, hence, the domestic price is low and the export market rejects it. Growers fatten lean crabs before they are sold for export. Fattening culture of mudcrab takes a minimum of 15 days and a maximum of 30 days. One of the common features of mudcrab fattening in pond or mangrove is selective or progressive harvesting and restocking.
More practical method of fattening is done in bamboo cages (138.5 cm long x 70 cm wide x 23 cm deep) with 18 compartments. Each compartment measured 23 cm x 23 cm ans stocked with thin crabs at one crab per compartment. Daily feeding is done in the morning and afternoon using any or a combination of the following food items: trash fish, snails, and animal entrails. From an initial body weight of 150-200 g apiece, crabs averaged 250 g in weight after 10-15 days.