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Mud Crab Fattening


Mud crabs of genus Scylla, also known as green crabs or mangroove crabs constitute an important secondary crop in the traditional prawn or fish culture systems in the Asian countries. In India the mud crabs have come into prominence since early eighties with the commencement of live crab export to the South East Asian countries which has created a renewed interest in the exploitation as well as in the production of mud crabs through aquaculture. The importance of live mud crabs as an export commodity has opened up great opportunities for crab farming. It has high demand and price in the export market. The present exports are to a tune of Rs.46.2 crores. The product wise break up of exports is as follows:

Quantity in metric tones
Value (Rs.crores)
Live crab 1,948 33.8
Frozen crab 556 8.4
Stuffed crab 343 4.0


(source: MPEDA)


The mud crabs inhabit marine as well as brackish water environments. Two species of mud crabs, namely Scylla tanquebarica and Scylla serrata are found in the inshore sea, estuaries, backwaters, coastal lakes and mangroove swamps of all maritime states on the main land and the creeks and bays of Andaman and Nicobar Islands. Both the species co-exist in the inshore sea as well as in the inland brackish waters preferring muddy or sandy bottom.

Crab fattening is essentially a holding operation during which post-moult or water crabs are kept for a short period of 20 days until they 'flesh out' or immature female crabs are held until their gonads develop and fill the mantle cavity. This type of activity has become very popular throughout the Asian countries due to increasing demand for gravid females and large size hard shelled ones in seafood restaurants. Fattening of mud crab is undertaken in the states of Andhra Pradesh, Tamil Nadu, Kerala, Karnataka, Orissa and West Bengal.

Technical Parameters

Mud crabs grow to a very large size of about 22 cm in carapace and about 2 kg in weight. The crabs belonging to the species S.tranquebarica is free living and grows to a large size with carapace width of 22 cm and those of species S. serrata have borrowing habit and grow to about 12.7 cm in carapace width. Mud crabs are omnivorous and they feed on a wide variety of food items such as shrimps, crabs, bivalve molluscs and fish.

The females reach sexual maturity at a size of about 12 cm in S. tranquebarica and 8.5 cm in S.serrata in the brackish water. Both the species are continuous breeders with peak breeding seasons which vary from place to place. The peak seasons of seed abundance is May to October along the southwest coast, December to May in Madras coast and March to June in Chilka Lake. Each crab spawns once in two months. The number of eggs carried by S. tranquebarica are about 1.1 to 7.0 million and by S. serrata are 0.5 to 0.9 million. The berried females migrate from estuarine areas to the inshore sea. The eggs hatch out in the sea and undergo metamorphosis and then they migrate to brackish water areas and spread to different parts of the estuarine systems.

Crab seed are available in the nature at all sizes. Juvenile crabs can be collected from estuaries, lakes, backwaters, creeks, mangrooves and salt water lagoons by using bamboo traps, lift nets or scissor nets. A hatchery is being set up at the Central Marine Fisheries Research Institute, Kochi for commercial production of crab seed.

Mud crab fattening is done by stocking soft shelled crabs or water crabs that are held in smaller impoundments for 20-30 days till the shells are hardened. The techno-economic parameters required for crab fattening are briefly described.

Soil quality

The soil suitable for crab fattening is sandy or sandy clay. A sand bottom inhibits burrowing.

Water quality

There should be availability of abundant and good quality water. Mud crabs are highly tolerant to varying salinity conditions, so brackish water would be ideal for crab fattening operation.

Salinity - 10 to34 ppt.

PH - 8.0 to 8.5.

Temperature - 23oC to 30oC.

Dissolved oxygen content - should be more than 3 ppm.

Size of pond and Pond construction

Crab fattening is carried out in ponds, cages or pens. Small ponds ranging from 0.1 to 0.5 ha in size with a water depth of 1.5 m are generally selected for the purpose. The pond should preferably have a sandy bottom. Bunds should have a minimum of 1.0 m width at the top to prevent crabs from escaping by borrowing through the bunds. Crabs are capable of climbing over the bunds, which is prevented by fixing overhanging fences on dykes. Fencing of height between 0.5 to 1.0 m over the dyke is done with materials like bamboo sticks, bamboo poles and knotless nets, asbestos sheets, fibreglass panels, etc. As the crabs are highly cannibalistic especially on freshly moulted animals, 'refugee cages' made out of hollow bamboo pieces, cement pipes or stones are placed inside the pond to minimise mortality.

Water supply and drainage

Water exchange is through tidal water. Sluice gates may be used to regulate the inflow and outflow of the tidal water. The sluice gates are fitted with bamboo screens to prevent the escape of crabs. In regions where tidal influence is less, sea water is pumped in.

Pond management

The pond is prepared by draining out the water. The pond is then allowed to dry or bake in sunlight before the liming is done. The water is let in during the high tide or sea water is pumped in to a height of 1.5 m.


Soft-shelled crabs of size 8 cm Carapace Width and above or crabs of more than 550 gm are stocked in the density of 1 crab/m2. The stocking density is normally 1 crab/1 to 3 m2.


Crabs are fed with bivalve meat or trash fish. Feeding is done daily at the rate of 5 to 10% of body weight. The duration of fattening is 20 days.


The crabs are harvested after the shell becomes sufficiently hardened and before next moulting. The harvesting is done by draining the pond and using scoop nets and ring nets with baits. Harvesting should be done in the early morning hours or evening to prevent mortality of crabs due to overheating of water at noon time. In a year 9 to 10 cycles of fattening can be taken from a pond.

Production & Income

The expected production par crop for an area of 0.1 ha. is around 320 kg. The income parcrop from 0.1 ha. has been assessed to be Rs.48000/-. (annexure II)


In India, the importance of live mud crabs as an export commodity has opened up great opportunities for crab farming / fattening. At present crab has good market and in the future crab is poised to be the next potential sea food in the world market among the edible marine crustaceans after shrimp and lobster.

Financial outlay

Details of the financial requirement for fattening in 0.1 ha. area have been indicated in Annexure I. The items and cost indicated under the model are indicative and not exhaustive. While preparing projects for financial assistance the costs have to be assessed taking into account actual field conditions. The projected capital cost for 0.1 ha. unit has been estimated to be Rs.63,750 and operational cost for one crop to be Rs.38,450.

Financial viability

The following assumptions have been made for working out the financial viability of the activity.

Pond Size 0.1 ha
Culture Period 20 days
Stocking density (1000 nos of 350 gm each) 1 crab/m2
Survival 80%
Weight at harvest 400 gm.
Expected production 320 kg /0.1 ha /crop
Crops per year  
1 st year 4
2 nd year 8
Farm gate price Rs. 150 / kg

The financial analysis (annexure III) reveals that net profit is to the tune of Rs.76,400 from the activity with IRR (>50%) and BCR (1.61:1)


Margin money and bank loan

The farmer is expected to bring margin money out of his own resources. The rates of margin money stipulated are 5% for small farmers, 10% for medium farmers and 15% for other farmers.

Rate of Refinance

NABARD provides refinance assistance for mud crab fattening to commercial banks, cooperative banks and Regional Rural Banks. The rate of refinance is charged as fixed by NABARD from time to time.

Rate of Interest

Interest rate to be charged would be as stipulated by bank/ RBI/ NABARD from time to time.

Repayment Period

Repayment of bank loan is possible in 3 years with no moratorium.


Security from the ultimate beneficiaries may be obtained as per the guidelines of RBI issued from time to time.

Annexure - I

Estimated financial outlay for Mud Crab Fattening in 0.1 ha water area

Capital Cost

  Units Quantum Rate (Rs.) Total
Construction of pond including digging, bund construction and compaction & consolidation Cum 800 25 20,000
Inlet / outlet sluices (lumpsum) Nos 2 5,000 10,000
Cost of 5 HP Diesel pumpset Nos 1 18,000 18,000
Bamboo fencing     LS 3,000
Nylon nets for fencing     LS 2,000
Casurina poles @ 1 pole/m Nos 250 15 3,750
Watchman's shed     LS 5,000
Miscellaneous     LS 2,000
Total       63,750

Operational Cost for one cycle ( 20 days)


  Units Quantum Rate (Rs.) Total
Pond preparation     LS 600
Cost of soft crab 1000 nos of 350 gm each 350 kg Rs 80/kg 28,000
Feed 35 kg/day 700 kg Rs 10/kg 7,000
Diesel cost (for pump)     LS 500
Labour charges   one Rs 100/day 2,000
Harvesting charges   350 kg LS 350
Total       38,450

Annexure II

Production & Income

1 Survival 80%
2 Average weight at harvest (gms) 400
3 Total production (kg) 320
4 Farm gate price (Rs) 150
5 Number of crops per annum 8
6 Income per crop (Rs.) 48,000
7 Income during 1 st year (4 crops) 192,000
8 Income from 2 nd year onwards 384,000

Anneure III

Financial Analysis

Items Years      
  1 2 3 4
Capital cost 63,750      
Recurring cost 153,800 307,600 307,600 307,600
Total cost 217,550 307,600 307,600 307,600
Income 192,000 384,000 384,000 384,000
Net Benefits -25,550 76,400 76,400 76,400
PW of costs @ 15% DF 799,887      
PW of benefits @ 15% DF 929,355      
NPW 129,468      
BCR 1.16:1      
IRR >50%      

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