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Mud Crab Culture – Beginner’s Guide
Mud crabs are considered abominable by people who have no idea they can be consumed, just only known to be visible one-sided walkers when it had rained heavily and were washed out of the water. It takes one to be adventurous to actually educated that crabs have the most exotic white meat which is healthy just like fish.
About Mud Crabs
Mud crabs are also known as ‘alimango’ which inhabit in brackish water or marine environment with a preference of sandy and muddy bottoms. They dig deep burrows into 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 in earthen ponds, mangrove pens or cages set in ponds or protected coastal waters for 30–45 days.
The Four Mud Crab Species Are The Following:
- Giant or king mud crab Scylla serrata
- Purple mud crab Scylla tranquebarica
- Orange mud crab Scylla olivacea
- Green mud crab Scylla paramamosain
Site Selection
A typical brackish water 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 brackish water
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 optimum conditions for rearing mud crab in brackish water ponds are as follows:
Temperatures between 26 – 32 degrees Celsius
Salinity between 16 – 30 ppt (parts per thousand)
pH balance range of 7.5 – 8.5
Oxygen ≥ 4 ppm (parts per million)
Technology Profile
Mud crab from the wild or from the hatchery may be stocked in brackish water ponds at a stocking density of 1,000 per hectare usually with milkfish. Ponds have to be carefully prepared, including the digging up of trench canals parallel to the dikes when polyculture with milkfish.
In monoculture, trenches are not needed but ponds should be provided with water depth of 80–100 cm. To prevent escape of crabs, each pond is fenced with bamboo or nylon net. Above the water level, a plastic sheet covers the bamboo support. Water management is based on the tides. Selective harvesting can be done prior to final harvest, which is 4–5 months after stocking.
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 SEAFDEC formulated diet twice daily at 10% of total biomass initially. Reduce to 8% on 2nd month, 5% on 3rd month and 3% until harvest.
- 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.
Mangrove system was found to be a good location to collect juvenile S. serrata. The juvenile crabs typically sheltered under loose slabs of sandstone and other rocks, or within clumps of mangrove roots, shaded by mangrove trees) between mean high water and mean spring low water. Deep soils alongside a river, branches, logs and hollow mangrove trunks provided the best habitat for S. serrata as determined by burrow density.
Larger S. serrata were found in fringe channels near the edge of the mangrove forest, compared with the interior of the forest. Chemical tracers have been used to show that while some adult populations of S. serrata feed predominantly within mangroves, others forage more on reef flats and sea grass beds.
Apart from spawning migrations, mud crabs appear to move little within their habitat, most remaining on site in distinct populations. However, longer-term tagging has shown that crabs can move several kilometres from their home range over time.
Nightly movements of S. serrata fitted with transmitters averaged 461 m, with average speeds in the range of 10–19 m per hour.
Distinct differences have been reported for the habitat preferences of S. Paramamosain of different sizes. Small crablets (carapace width [CW] 0.5 cm) settle on the outer edge of mangroves, gradually moving deeper into the forests living on the surface of mangroves (CW 1.5 cm), while larger crabs dig burrows or live in the sub-tidal zone migrating in to feed in the mangroves at high tide (CW 4.5 cm), with the main adult crab population living sub-tidally, offshore (CW 12.5 cm).
How To Raise Crabs The boundary between the mangroves and mud crab flats is identified as an area that can support higher densities of crabs.
While several species of mud crab can be present in any one location, it appears common that one species makes up a dominant percentage of the overall crab population.
As mud crabs appear to have an interdependent relationship with mangrove forests, the loss of mangroves, for whatever reason, will typically be followed by lower crab-catches. However, mud crabs are found in estuaries without mangroves, so they are not essential for their colonization or survival.
The most widely distributed species of mud crab, S. serrata, is found as far west as South Africa, east to Tahiti, French Polynesia, as far north as Okinawa, Japan, and south to Sydney, Australia.
Life History Of Mud Crabs
While mud crab megalopae appear not to be selective among estuarine habitats (sea grass, mud or sand), crablets (juvenile mud crabs) strongly select for a sea grass habitat, indicating that living within sea grass beds likely increases their survival.
This supports the theory that mud crabs settle out of the plankton in the near shore region of the coastal shelf and it is the crablets that colonize the estuaries.
Crablets have also been reported to shelter in a variety of inshore habitats including reed beds, areas of aquatic macrophytes, under stones and within the mud and sandy sediments.
An interesting aspect of the maturation of mud crabs is their apparently step-wise maturation process, where they pass through an apparent physiological maturation, before becoming functionally mature.
Here are frequently asked questions (FAQs) about mud crab (Scylla spp.) culture that are commonly raised by farmers and enthusiasts:
General Questions
- What are the common species of mud crab used in aquaculture?
- Answer: The most commonly cultured species are Scylla serrata, Scylla tranquebarica, and Scylla olivacea.
- What is the ideal water salinity for mud crab farming?
- Answer: Mud crabs thrive in brackish water (10–30 ppt salinity), but they can adapt to a wide range (5–35 ppt).
- What type of pond is best for mud crab culture?
- Answer: Earthen ponds with proper water exchange, mangrove-like environments, or tidal-influenced systems are ideal.
Stocking & Growth
- What is the recommended stocking density for mud crab grow-out ponds?
- Answer: Typically 1–2 crabs/m² to avoid cannibalism; higher densities require proper shelter.
- How long does it take for mud crabs to reach market size?
- Answer: About 4–6 months (from juvenile to 300–500 g), depending on feeding and environmental conditions.
- What is the survival rate in mud crab farming?
- Answer: Survival rates range from 40–70%, depending on management (cannibalism is a major issue).
Feeding & Nutrition
- What is the best feed for mud crabs in captivity?
- Answer: They are omnivorous but prefer trash fish, mollusks, shrimp head, and formulated crab pellets.
- How often should mud crabs be fed?
- Answer: Twice daily (morning and evening), with 5–10% of their body weight.
- Can mud crabs be fed with commercial feeds?
- Answer: Yes, but they prefer high-protein (30–40%) feeds; some farmers mix commercial pellets with natural food.
Diseases & Health Management
- What are the common diseases in mud crab farming?
- Answer: Shell rot, bacterial infections, parasitic infestations (like barnacles), and fungal issues.
- How can I prevent cannibalism in mud crab culture?
- Answer: Provide hiding places (PVC pipes, coconut shells), size grading, and adequate feeding.
Harvesting & Marketing
- When is the best time to harvest mud crabs?
- Answer: During molting stages (soft-shell crabs) or when they reach hard-shell market size (300–800 g).
- How are mud crabs usually sold?
- Answer: Live crabs (highest value), chilled, or frozen; export markets prefer hard-shell males (for higher price).
Economic & Sustainability
- Is mud crab farming profitable?
- Answer: Yes, if managed well (low feed cost, high market demand), but risks include diseases and price fluctuations.
- Can mud crab farming be integrated with other aquaculture systems?
- Answer: Yes, they can be co-cultured with shrimp, milkfish, or mangrove-based systems (silvofisheries).