Mud Crab Fattening:
The following write-up is all about Mud Crab Fattening.
Introduction to Mud Crab Fattening
What are mud crabs? well, mud crabs belong to the genus of Scylla, also popularly known as green crabs or mangrove crabs. This crab industry constitutes an important secondary crop in the traditional system of fish culture (aquaculture) from Asian countries. Basically, the mud crabs have become popular since the early ’80s with the commencement of live crab export into the South East Asia regions which has generated a renewed interest in the manipulation as well as in the creation of sand crabs through the aquaculture system. The live mud crabs as an export product have opened up huge opportunities for crab farming /cultivation in India. Mud crabs have high demand and price in the export market as well as in local markets due to their flesh and high rapid growth rate. Commercial mud crab cultivation is one of the lucrative and profitable aquaculture businesses in India. These mud crabs are found from South Africa, around the coast of the Indian Ocean to the Malay Archipelago, as well as from southern Japan to south-eastern Australia. Currently, mud crabs are being farmed commercially in many parts of the world. These mud crabs are exported in three forms such as live crab, frozen crab, and stuffed crab.
The mud crabs occupy marine as well as brackish water environments. Scylla tanquebarica and Scylla Serrata are two species of mud crab that co-exist both in the inshore sea as well as in the inland brackish waters. These species usually prefer muddy or sandy bottom.
Crab fattening is basically a holding procedure during which post-moult or water fishes are retained for a short period of 20 to 21 days till they ‘flesh out’ or immature female crabs are held till their gonads develop and fill out the mantle cavity. This type of action has become remarkably popular throughout the Asian regions due to growing demand for gravid females and large-size hard-shelled ones in crab/fish restaurants. Fattening of sand crab is undertaken from the states of AP, Kerala, Karnataka, Tamil Nadu, Orissa, and West Bengal of India and other coastal areas.
About Mud Crab Parameters
Usually, mud crabs grow about 22 to 25 cm in carapace and about 2 to 2.5 kg in weight, which is considered very large in size. Mud crabs mostly feed on prawns (shrimp) crabs, fish, and bivalve mollusks. The female mud crabs reach maturity at the size of 12 to 13 cm in the species S.tranquebarica whereas the maturity is 8.5 cm in the species S.serrata.
Both the mud crab species S. tranquebarica and S.serrata are continuous breeders. The peak seasons of breeding vary from place to place. Generally, Each crab spawns once in 60 days. Both crab species will carry a good number of eggs for breeding. On average, mud crabs of S. tranquebarica will carry about 1 to 7 million eggs whereas S. Serrata species carry about 0.5 to 0.8 million eggs.
Where can we buy the crab seed? well, they are available naturally in backwaters, estuaries, lakes, creeks, mangroves, and saltwater lagoons. However, you buy crab seed for commercial farming from crab hatcheries or at any central marine fisheries.
How is mud crab fattening done? well, it is carried out by stocking soft-shelled crabs which are kept in smaller impoundments(a body of water confined within an enclosure) for 25 to 30 days until the shells of crabs are hardened.
Scientific / Botanical Name of Mud Crab
- Scylla Serrata.
Other Names / Common Names of Mud Crab
- Mud crab.
- Mangrove crab.
- Green crab.
Soil Quality for Mud Crab Fattening
Quality of soil plays a major role in mud crab fattening. Sandy or sandy clay soils are best suited for mud crab fattening. Generally, a sand bottom restrains from burrowing.
Water Quality for Mud Crab Fattening
Abundant and good quality water is required for commercial mud crab fattening business. Brackish water is best suited for mud crab fattening as they are highly tolerant to varying salinity conditions.
The water used for mud crab fattening should have the following technical parameters for best growth.
- The pH of water: 8.0 to 8.5.
- The temperature of water: 22°C to 30°C.
- The salinity of water: 10 ppt to 34 ppt.
- The dissolved oxygen content of water: More than 3 ppm.
Size and Construction of a Pond for Mud Crab Fattening
Mud crab fattening is done in cages, pens, and ponds. You can select a pond with a size of 0.1 to 0.6 hectares. The water depth of the pond is about 5 feet (1.5 meters). Make sure to build a pond with a sandy bottom.
For preventing mud crabs from escaping through bunds (by burrowing/digging), make sure the bunds have a minimum of 3 feet width at the top. Fix overhanging fences on dykes to prevent the crab from climbing over the bunds. Maintain a fencing height of 0.5 meters to 1 meter over the dyke. What kind of fencing material can be used? well, materials such as bamboo poles /sticks, asbestos sheets, fiberglass panels, and knotless nets. Make refugee cages with hollow bamboo pieces, or stones and place them in the prepared pond for freshly moulted animals as mud crabs are highly cannibalistic in nature.
How to Supply and Control the Water in Mud Crab Fattening
Water exchange in the pond is carried through tidal water and sluice gates are used for this purpose. These gates can regulate the inflow and outflow of the tidal water. Usually, the sluice gates should be fitted with bamboo screens to prevent the escape of mud crabs. In areas where tidal water is not possible, then seawater can be pumped in.
Pond Management Activities in Mud Crab Fattening
The pond should be prepared by draining out all the water in it to allow it to dry in sunlight before the liming is carried out. The water should be allowed during the high tide. In the case where tidal influence is less, you must pump seawater to a height of 5 feet (1.5 meters).
Stocking in Mud Crab Fattening
Usually, soft-shelled mud crabs with a size of 8 cm carapace width and above or mud crabs with more than 500 grams should be stocked. The crab density should be is about 1 crab/1 square meter area. You can also stock them at 1 crab /1 to 3 sq. meter.
Feeding Management in Mud Crab Fattening
You can feed mud crabs in the pond with small fishes or bivalve meat. You can feed the crabs based on their weight. Feeding of the crabs should be done daily @ 5 to 10% of body weight. Usually, the crab fattening duration is about 20 to 25 days.
When and How to Harvest in Mud Crab Fattening Business
Generally, the mud crabs should be collected after the shell becomes hardened enough and before the next moulting. The collection of crabs should be done by taking the water out of the pond (draining) and using scoop nets, and ring nets with baits. It is recommended to harvest mud crabs in the early morning hours or late evening hours. This can prevent crab deaths due to overheating of water in the afternoon time. You can carry 9 to 10 cycles of crab fattening operations in a year from a pond.
Yield and Income from Mud Crab Fattening
You can obtain a production (yield) of 300 to 350 kg of mud crop for raising are of 0.1 ha. The price of mud crab is from 150 to 200 Rs at the farm gate. The income or profits in mud crab farming depends on the size and current market demand.
Marketing in Mud Crab Fattening Business
There is a huge demand for live mud crabs in export markets even this business can skyrocket in near future after the prawns (shrimp) and lobsters. For crab marketing procedure, contact central marine fisheries.
Subsidies and Loans in Mud Crab Fattening Business
You can talk to any NABARD professional about the procedure of getting loans and any subsidies for commercial mud crab fattening. You should spend some margin money from your pocket. In the case of small farmers 5%, medium-scale farmers 10%, and 15% of the total cost of the project for other farmers. Interest rates and re-payments are fixed by the Reserve Bank of India.
Cost and Profits in Mud Crab Fattening
Read this: Tilapia Fish Farming.
The following is a sample project report of mud crab fattening in the 0.1-hectare pond area.
Assumption of the sample mud crab project report
- Pond Size = 0.1 ha.
- Crab culture Period = 20 days.
- Crab stocking density = 1000 numbers of 350 grams each; 1 crab/m2.
- Survival percentage = 80%.
- Weight at harvest time = 400 grams.
- Expected production = 320 kg /0.1 ha /crop(cycle).
- Crops for first-year = 4.
- Crops for second year = 8.
- Assumed farm gate price = 150 Rs/kg.
|Inputs||Cost (Indian Rupees)|
|Pond construction, digging, bund construction, and compaction, and consolidation.||20,000|
|Inlet/outlet sluice gates for water exchange||10,000|
|Diesel pump set (5 HP)||18,000|
|Fencing (Nylon nets)||2,000|
|Casurina poles @ 1 pole/m||4,000|
Operational cost for one cycle of mud crab fattening (20 days period):
|Operations||Cost (in Indian Rupees)|
|Preparation of pond||1000|
|Cost of soft crabs||28,000|
|Diesel for pumping||500|
Production and returns in mud crab fattening
|Average weight at harvest in grams||400|
|Total production in kg’s/crop||320|
|Farmgate crab price in rupees||150|
|Number of crops/production cycles/ year||8|
|Income/crop (cycle) in rupees||48,000|
|Income during the first year for 4 crops||1,92,000|
|Income from 2nd year onwards||3,84,000|
Note: The above sample project is just for reference, the numbers can change from time to time and region to region.
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