Wednesday, August 22, 2012

Crab Fattening

Crab Fattening
The fattening of Crabs is basically a culture in the time they moult their outer covers/shells or water crabs are kept in captivity for a short time of 15 or more days till they become fleshy or female_crabs that are not matured are kept for a short time being till their gonads are developed and fill up the mantle cavity. The system is well known in Asian countries for growing demand of gravid females as well as big_size hard_shelled crabs in the sea-food restaurants. 
Technical Parameters of Crab fattening:
Seeds of crab (all size) can get in sufficient quantity from nature. We can get Juvenile crabs from all kinds of salt water sources such as sea shore, backwaters, lakes, mangroves, creeks, estuaries and salt lagoon. By applying bamboo_traps, scissors_nets and lift_nets seeds can collect easily. The seed supply of mud crab cultivation depends generally on the nature. It is the main limitation of mud/green crab culture/cultivation. The parameters required for crab fattening are briefly described below.
Soil quality:
The appropriate soil for the project of the pond is sandy and sandy_clay. This kinds of soil protect burrowing holes.

Water quality:
Good quality sufficient water is needed for this project. Mud crabs can tolerate highly saline conditions. So sea water or brackish water is suitable with crab fattening.
15 – 30 ppt (must >10 ppt)
7.8 – 8.5
 28 – 30 0 C
Dissolved oxygen
> 5 ppm.
 Pond (size and constructions):
Generally fattening of crab is cultured in ponds. Generally 250 - 1000 square meters of area and 500 - 1000 cm depth pond are used for this system. The pond bottom should be sandy. It discourages burrowing of crabs. Pond boundary should have at least 1 meter width. It prevent burrowing the boundary through mud for escaping. We should attached bamboo fence along with boundary of height 1.5 meter. The fence should fix with 0.5 meter deep in mud and 1 meter over the mud. A net is fixed over the fence so that crab can't escape over the fence.
The crabs can fight any time so we should put hollow materials i.e. plastics pipes, bamboo_pieces or cement_pipes. When they make fight the weaken crabs take shelter in to it. It reduces fight among them.
Water management:
If we make pond besides the tidal river then tidal water can easily exchange through sluice gate. River current can flux or influx through the gate easily without any coast. This system minimizes the project cost.  The gate are affix with bamboo nets (i.e. nets made of bamboo-sticks in parallel) for the prevention of crabs escaping. In the low tidal influenced region brackish or sea water should pumped up at the one end of the pond and the water lay out at other end of the pond so that water can exchange easily.
Pond management:
We should flux water by sluice gate or pump out water completely of the pond for drying pond bottom. Lime is scattered over pond bottom as well as boundaries for a few days. This process helps cultured crabs to free from harmful gases. Then we should influx tidal saline water in to the pond through sluice gate or by pump. Water height is 1 - 1.6 m is appropriate for the pond. 
The crabs with soft_shelled of carapace width 8 cm and more or 550 gm and more weight crabs are stocked in the pond. We can stock 3 or less crabs in a square meter area. We can divide ponds into chambers in order to reserve the same_size crabs together. It reduces cannibalism or quarrel among them. We can separate same gendered crabs in different compartments/chambers.
Supply food 2 – 3 times a day with five(5) to ten(10) percent(%) of their body weight (8% - 10% at first week and next 5% - 7%). Generally a fattening cycle requires 15 – 20 days. We can provide kitchen leftovers like rice, vegetables, fish and animal entrails, swine manure, snails, oyster etc. We should take care when providing food. we should put food in multiple places or scatter in the pond to avoid fighting. We supply adequate food for their proper growth. 
We should collect crabs when their shell become hard. The general survival ratio is about 80 -85 %. We should collect crabs when the shell become hard and before next moulting time (the shell become soft). During high_tide water can influx easily in to the pond through sluice gate. In the time the collection can easy in a tide_fed ponds. When water begin to influx in to the pond the crabs start swimming across the influx water. They gather near bamboo-stick net (partition made of bamboo sticks). We can catch crabs with nets and hand_picking by expert labors.
We should collect crabs in the evening or early morning. It is possible 5/6 rounds per year of fattening. 

At first we have to clean thoroughly the crabs with water carefully. Then their largest legs should be tied carefully with nylon thread by expert labors so that they can't make cannibalism. Then we have to put in to bamboo baskets in less numbers as their died rate become very less. In transporting we must take steps about humidity condition. 
We can produce about 240 kg of crabs in a circle from 0.1 hector of pond area.

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