Mud Crab Farming
Mud Crab Farming in IndiaPresented by- Tarang Kumar Shah M.F.Sc(Aquaculture)CREDIT SEMINAR ON
Mud Crab is also known as Mangrove Crab. Scylla serrata and Scylla tranquebarica are the common mud crabs occurring in the estuarine and mangrove areas along the coast of India.Scylla serrata is commonly called as Red crab and it prefers to live in low saline waters.Scylla tranquebarica the Green crab lives in high saline waters.Mud Crab farming is widely practiced in Thailand, Taiwan, Malaysia, Singapore and Indonesia.
Item/Year2003-042004-052005-062006-072007-082008-092009-102010-112011-12Live Crab (MT)159917492022190919182230286329633054FrozenOther (MT)478151524797428540664758450532512848Total Crab (MT)638069016819619459846988736862145902
World Mud Crab ProductionIndia Mud Crab Production
2.Distribution in IndiaTwo species mud crab(Scylla Serrata and Scylla tranquebarica ) occur along the Indian Coasts. Mainly distributed in Andhra Pradesh, Tamil Nadu and Kerala.
Scientific classificationScylla SerrataScylla tranquebaricaKingdom:Animalia PhylumArthropoda Subphylum: Crustacea Class: Malacostraca Order: Decapoda Family: Portunidae Genus: ScyllaSpecies Serrata, tranquebarica
Scientific Name: Scylla SerrataCommon Name: Red Mud CrabScientific Name: S. tranquebaricaCommon Name: Green Mud Crab
4. Identifying Characters
Character Scylla serrataScylla tranquebaricaSizeSmaller SizeLarger sizeFirst sexual maturity83mm120mmWeight0.5 to 0.75 kg2.5 kgColour of upper surface of body (carapace)greenish brown to ferrugenous brownlight to dark greenPolygonal markings No Polygonal markingslimbsPresent Polygonal markingsall limbsNumber of SpinesOne spines on the outer margin of wrist of chelipedsTwo spines on the outer margin of wrist of chelipeds
5. Habitat and feeding HabitsMud Crab are found both in the seas and estuarine system.The Mature female mud crabs emigrate to inshore seas for hatching of the larvae.Mud crabs in their megalope stage (post larva) migrate into the estuaries, coastal lagoons and backwaters.Mud crabs are nocturnal feeder feeding mainly on bottom dwelling, slow moving animals such as bivalve, small crabs and dead decayed animal matter.
6. ReproductionThe sex are separate and there is distinct sexual dimorphism.The size at first sexual maturity is 120mm (carapace width) for larger species (Scylla tranquebarica) and 83 mm (carapace width) for Scylla serrata.The early maturing ovary is bright orange whereas in mature ready to spawn female it is deep yellow. Mud crab is able to breed throughout the year.The peak spawning periods of the mud crab Kerala coast is from September-February.Tamil Nadu coast from September-AprilAndhra Pradesh coast from Oct.-Feb. & May-June.
Life cycle of mud crab
B) Farming Techniques of Mud Crab
Site selection for Mud crab Culture
Site selection is an important process in farming as it decides the success or failure of the mud crab farming.Silt - clay, clay loam or clayey soil is ideal for both mud crab framing.Clear seawater with high plankton production is ideal for mud crabs. No new farms to be established within 200 meter from high tide line.Water of good quality should be adequate all year round, coming directly from the sea or river. The following range are required such as.
CategoryRangeWater temperature23-32cWater Salinity15-30 pptDO concentration>4pH8.0-8.5Water depth (cm)>80
2. Seed collectionFor culture purpose crab seed are mainly collected from natural resources.Juvenile crabs can be collected from estuaries, lakes, backwaters, creeks, mangroves and salt water lagoons.Juvenile crab can be collected by using bamboo traps, lift nets or scissor nets.
Hatchery production of Mud crab
A hatchery has been set up at the Central Marine Fisheries Research Institute, Kochi for the commercial production of crab seed.Seeds are available in commercial scale in RGCA.(Rajiv Gandhi Centre for Aquaculture)
3. Culture Method
a) Pond Culture
The pond size depends on the production type.Pond size of 0.5 to 2 hectares is most suitable for crab culture. Small sized ponds are very suitable for crab farming.Sandy soils with a mixture of 50% clay are ideal for culture of these crabs. The maximum stocking density should be 1 crab/m2.
Young crabs are raised and grown for a certain period of 5 to 6 months till they reach marketing size and weight.A water inlet system and an outlet system to drain out water during water exchange should be constructed as in the case of shrimps.In addition, about 1000 numbers of stone wire, pipes of 6 inch diameter and 1.5 feet length etc. should be kept at the bottom of the pond throughout the dike.
b) Pond culture in mangrove areaThe ponds could be constructed as described above around the mangrove plants.Maximum pond area of 100 m2 is suitable for this type of culture.A canal of 1 m wide and 0.5 m deep.In which water will be available even during low tide should be dug around the edge of the pond.Polythene nettings could be used to prevent the escape of the crabs.Feeding depends on the availability of organisms namely low-value fishes, mangrove snails, clams, mussels etc.
Pond culture in mangrove area
c) Pen culture in pondCrab Culture can also be done in pens. Pens size of 4 X 4 X 2.5 m could be made inside the ponds using bamboo strips.Bamboo strips are driven 1-1.5 m deep into the soil to prevent the escape of the crabs by burrowing. The pens could be made nearer to the dykes for easy stocking and monitoring.
d) Pen culture in mangrove areaThe pens could be constructed using the locally available bamboo splits or arecanut logs or cane.These strips should be driven 1-1.5 m deep into the soil to keep the crabs inside and the potential predators outside.
Mangrove trees in the Centre of the pen provide shade for the crabs.The crab could be fed once a day during high tide with low-cost fishes, mussels, clams, snails etc. The crabs could be selectively harvested after they reach 400 g or more.This system is eco-friendly, survival rate of only 47 to 50 % could be expected.The crabs could be harvested after 47 months.
e) Cage culture (Suspended or Fixed type)Cage Design:-Crab fattening can be carried out in Cell-type Cane Cages of 1 m (L) X 1 m (W) X 20 cm (H) size.Cages can be partitioned into nine equal compartments.
Crab fattening can also be done in floating net cages, bamboo cages in shallow estuarine waterway.3 m X 2 m X 1 m (3 m long, 2 m wide and 1 m height) is ideal cage size for crab fattening.
One crab should be placed in each compartment of the cages. In this method of fattening, higher number of crabs can be fattened in a square meter area, i.e. 9 crabs/m2. Different types of feeds such as trash fish, mussel, chicken waste, clams etc. can be given to the crabs.
Stocking and feeding in cages
Marketing:- Generally the mud crabs are sold in live condition.The first pair of largest legs (chelate legs) of each live crab are firmly tied up with the body by jute/nylon thread .The basket packed crabs are transported from remote fishing villages to the major cities by road or rail.The mud crab are sold through the middlemen to retailers. Export:- The live mud crab export from India has started in 1987-88 . Exported mostly to South east-Asian countries. The live crabs are packed in perforated carton boxes lined with thermocol sheets and air-lifted from Chennai and Kolkata.
Culture methodCrab cultureCrab FatteningSpeciesScylla Serrata S. tranquebaricaScylla Serrata S.tranquebaricaCulture periods(days)12038Expenditure(Rs.)(seed,feed,pond preparation,labour)43,86056,200Production(tonnes)0.780.56Income(Rs.)1,57,2001,22,850Net profit/crop (Rs.)1,13,34066,650
ReferencesAllan, G. and Fielder, D. 2004. Mud crab aquaculture in Southeast Asia. Proceedings of the ACIAR Crab Aquaculture Workshop.2829 April 2003.Angel,C.A(1992).Report of the seminar on mud crab culture and trade. Bay of Bengal programme BOBP/REP/51,246pp.Blackshaw, A. (Eds.), Mud Crab Aquaculture and Biology, ACIAR Proceedings No.78. Canberra, Australia, pp. 14-20.FAO (2013) Fisheries and Aquaculture Department, Statistics and Information Service Fish Stat J: Universal software for fishery statistical time series. FAO. Rome.