MudCrab Pen Culture in Mangroves

Over the years, commercial production of mudcrab (Scyllaspp.) has been undertaken only in bamboo – or net-fenced brackish water ponds. Its feasibility was proven trough a series of verification trials conducted in commercial ponds by SEAFDEC/AQD researchers and is now practiced elsewhere in the country.

Of late, the introduction of using net enclosure to grow mudcrabs in mangroves or tidal zone offers a bright prospect in aquasilviculture. Using mangroves as a natural resource paves the way for creating livelihood among the fisherfolk in the coastal areas. While this method is not very popular in the Philippines, as it ha only recently been introduced, the same has been carried out for quite some time in Indonesia, Malaysia, Vietnam and China successfully.
The advantages of this livelihood option include low investment cost, easy construction, easy operation and it is environment- friendly.

Site Selection

Mangrove areas should have a sufficient supply of marine or brackish water throughout the year. Water depth at high tide should range between 0.8 to 1.0 m. Salinity should range between 18 to 30 ppt and temperature between 25 to 30°C. The site must be free from any source of pollution, protected from environmental hazards such as typhoon, flood erosion and from vandals and poachers. Materials

  • 6 rolls of green polyethylene (PE) net, 1-2 mesh size and 2 mm twine diameter
  • 2 rolls of plastic sheets
  • 30 pieces of bamboo (10-15m) for structural framework (horizontal bracing)Wooden posts, 3-4m long (vertical post)

Net enclosure – 4,000 sq m (50 m x 80 m)

Constructing a Pen

  1. Design the enclosure with a shape that varies from square, rectangular, etc. depending on the contour and vegetation of the area. The manageable area ranges from 0.2-1.0 ha.
  2. Install a net enclosure (polynet 1-2 cm mesh size) using bamboo or wooden of the net should extend not less than 30 cm above the waterline during the highest high tide level.
  3. Along the top edge of the net enclosure, install a plastic strip/sheet of about 50cm to prevent mudcrabs from climbing over the top. Embed the lower and of the net about 50-70 cm along the base of the enclosure.
  4. Dig ditches/puddle trenches (libaong) at a depth of about 20-40 cm representing at least 20 to 30 percent of the total area of the enclosure. These are intended to hold water in the enclosed area during the lowest tide for the crabs to withdraw and take refuge. Avoid cutting the main roots of the mangroves during digging.
  5. Install catwalk around or perpendicular to the enclosure for ease in feeding and monitoring the stocks during high tide.

REARING OPERATION

Transplanting Mudcrab Juveniles for Grow-out Culture

Mudcrab juveniles for stocking are normally placed in bamboo wicket baskets (bakag/kaing) or in plastic/padan (bayong) bags during transport. A pandan bag can carry about 150 to 200 pcs of 20-50 g of juveniles.

Place fresh mangrove leaves inside the basket or bag to reduce the temperature, serve as a cushion and prevent juveniles from fighting each other. Do not cut or remove the chelipids or pincers of young juveniles below 30g so they are protected from stress or infection, which could cause mortality.

However, juveniles weighing more than 30g must have their pincers tied using strips of soaked coconut sheath (suwak) or plastic straw. Sprinkling them with brackish water during transport or storage keeps them alive and active.

Stocking and Acclimatization

Before stocking, ensure that the enclosure is cleared of debris, unwanted species and predators. Check nets all around for possible holes or scouring. Stock monosize mudcrab juveniles weighing 30-50g per piece or measuring 5-10cm (capable length) at the recommended rate 5,000 – 10,000 per ha.

Stocking must be done in early morning or late in the afternoon when the temperature is cool and the tidal water is available.

Before releasing the juveniles, place them inside plastic basins and sprinkle with seawater until they are completely submerged for about 1 hour. Make sure that crabs have adopted to the pen water temperature and salinity before releasing them.

During stocking, tilt the basin to allow crabs to crawl out freely. Cut the ties on pincers before releasing them.

Feeds and Feeding

Feeds comprise 40-60 percent of the total cost of production. Chopped trash fish, animal hides or entrails, mussel meat and snails (golden apple snail) are cheap and effective locally available feeds for mudcrab culture.

Broadcast feeds evenly everyday, using half the total feed in the morning between 6-8a.m. and the other half in the afternoon between 4-6 p.m.

Feeding rate is 10 percent of the average body weight per day. Reduce the feed by 1 percent and adjust monthly down to 5 percent up to the end of the culture period.

Stock Sampling

Take a stock sample every 30 days, using bintol or bamboo traps, to determine the growth and feed requirement. Take 30-50 crabs samples and measure their increase in body weight and carapace size.

Pen Management

Monitor the crabs for feed consumption, swimming behavior, presence of berried female crabs, etc. Inspect enclosure daily for destruction debris, scouring and torn nets where stocks could possibly escape. Secure them against possible poachers by making routine inspections of the area, especially during the night.

Harvesting

Partial harvesting is done when mudcrabs reach marketable size of 200g and above. This could start, at the earliest, after 45 to 60 culture days.

Handpick the crabs during low tide and/or by catching those using baited traps like bintol during high tide. Fat crabs are detected by pressing the abdomen. The presence of gonands (orange mass called alique) indicates fat female crabs. Fat male crabs have massive pincers.

Total harvest may be done after 4-6 months of culture. Tie the pincers of newly-harvested crabs using plastic straw or suwak before transporting them to the market.

Mudcrabs sold in restaurants are 350g and above. Prices vary with markets and seasons.

Marketing

In all cases, mudcrabs are marketed live. In the Philippines, female crabs with mature gonands are relatively expensive. Mudcrabs are sold in market year-round, but generally, those found in domestic markets are grouped in mixed sizes and are smaller than exportable crab. Usually during the Christmas season, the price is relatively high because of the increased demand.

The major market for the Philippine mudcrab is Taiwan, Hongkong, Guam, Japan and the USA. Other markets include Singapore, Brunei, Germany Korea and neighboring countries. Taiwan has been the biggest buyer of mudcrab from the Philippines the trading pattern of maudcrab industry throughout the Asia region involves a series of intermediaries between the fishermen/supplier and the local consumers or exporter.

Cost and Return Analysis

a. Technical Information

  • Project location: Manalo Multi-Purpose Cooperative, Puerto Princesa, Palawan
  • Total area: 4,000 sq.m.
  • Initial stock: 2,040 pieces
  • Size at stocking: 9-22 g/crablet
  • Method of harvest: Partial starting 2nd to 5th month, in total in the 6th month
  • Survival rate: 85%
  • ABW: 275 g
  • Yield: 477 kg
  • FCR: 1.5
  • Cropping/year: 2

b. Investment Requirement (Pen Construction)

  • Nylon nets (5 rolls) – 8,000.00
  • Bamboos for horizontal bracing (25 pcs) – 750.00
  • Wooden post 4 m in length (130 pcs @30/pc) – 3,900.00
  • Monofilament #150 mm (5 kg @120/kg) – 600.00
  • Plastic sheet #5 (2 rolls) – 4,000.00
  • Labor – 33,900.00
  • Canal excavation for fence – 5,500.00
  • Fencing – 26,000.00
  • Backfilling – 2,400.00
  • Total investment requirement – P85,050.00

Cost

a. Labor

  • Feeder – 7,500.00
  • Caretaker – 3,000.00

b. Predator eradication of undrainable area

  • Hydrated lime – 600.00
  • Ammonium sulfate – 400.00

c. Materials

  • Crab juveniles (P8/pc) – 32,640.00
  • Trash fish 2,425 kg x 2 @P7/kg –  33,950.00

d. Others

  • Maintenance and repairs – 500.00
  • Transportation – 1,000.00
  • Depreciation – 17,010.00
  • Contingencies – 500.00

Total cost – P97,100.00

Returns (477kg x 2 @P170/kg) – 162,180.00

  • Net return – 65,080.00
  • Return on investment – 76
  • Payback period – 18 months

For more information, contact:

Bureau of Fisheries and Aquatic Resources (BFAR)
PCA Building, Elliptical Road, Diliman, Quezon City
Tel. Nos. (02) 929-8074/9597
Email: [email protected]
Web: www.bfar.gov.ph

source: DA-BFAR FIDSD flyer (prepared by SEAFDEC/AQD)

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