Mud crabs, locally known as alimango, inhabit brackishwater and marine environments and prefer muddy and sandy bottoms. They dig deep burrows in mangroves and soft substrates in shallow or intertidal waters. Mud crab juveniles (crablets) are obtained from the wild and recently from the hatchery. Crablets are cultured for 4-5 months. Lean crabs are fattened for 30-45 days.
The four mud crab species are the following:
- Giant or king mud crab (Scylla serrata)
- Purple mud crab (Scylla traquebarica)
- Orange mud crab (Scylla olivacea)
- Green mud crab (Scyall paramamosain)
Technology Profile
Mudcrab from the wild or from the hatchery may be stocked in brackishwater ponds at a stocking density of 1,000 per hectare.
Ponds have to be carefully prepared, including the digging up of trench canals parallel to the dikes when polycultured with milkfish. In monoculture, trenches are not needed but ponds should be provided with water depth of 80-100 cm. Shelters would also be provided.
To prevent escape of crabs, each pond is fenced by bamboo or nylon net, and above the water line, a plastic sheet covers the bamboo support. Water management is based on the tides. Selective harvesting is best. Culture period lasts 4-5 months.
Site Selection
A typical brackishwater earthen pond designed for the culture of shrimps or fish can be used for the farming of mud crab. The following are the characteristics of a suitable site:
- Clay, clay-loam or sandy-clay soil to retain water
- Adequate source of brackishwater
- Free from possible source of pollution
- Protected from typhoon, flood and siltation
- Accessible but free from poachers
- Flat land 1 meter above the sea level of the highest tide to allow drainage and harvest
Culture Conditions
The conditions for rearing mud crab in brackishwater ponds should fall within the optimum range to ensure growth and survival of stocks.The recommended values of water parameters are:
- temperature: 26-32°C
- pH: 7.5-8.5
- salinity: 16-30 ppt
- dissolved oxygen: >=4 ppm
Culture Methods
- Prepare the pond and install nets.
- Select uniform-size S. serrata crablets (3-5 cm carapace width), acclimatize and stock in pond.
- Feed crabs with low-value fish, snails or chicken entrails with or without twice daily at 10% of total biomass initially. Reduce to 8% on 2nd month, 5% on 3rd month and 3% on the last months of culture.
- Change 30-50% of the water every spring tide. Conduct regular sampling, monitoring and record-keeping
- Harvest marketable size crabs (>=400 g female and >=500 g male) starting on the 4th month.
Financial Indicators
Technical assumptions for s. serrata culture:
- Project duration : 5 years
- Production area : 1 ha
- No. of crops/yr : 2
- Days of culture/crop : 150
- Stocking density/ha : 1,000
- Survival rate : 70%
- Feed conversion ratio : 2
- Ave. body weight at harvest : 400g
- Productlon/ha/crop : 280 kg
- Farm gate price (P/kg) : 420
Costs-and-returns
- Revenue from sales (@P420/kg) : 134,400
- Total variable cost : 51,180
- Total fixed cost : 30,980
- Net Income per crop : 52,240
- I ncome per year : 104,480
- Return-on-investment (%) : 134
- Payback period (years) : 0.63
- Break-even price : 256.75
- Break-even production (kg/crop) : 195.62
For more information, contact:
SEAFDEC Aquaculture Dept.
Tel: (033) 511-9171/9170
Email: aqdchief@seafdec.org.ph
Web: www.seafdec.org.ph
photo from myhealthblog.org
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