Introduction to Mud Crab Project Report, Culture Practices: This article content is useful for sharing the knowledge to many aqua farmers, fisheries entrepreneurs for the commercial hatchery production of mud crabs. Mud crab is a profitable and promising aqua business for its fast growth and market demand along with good export potential. If you want to go for a commercial mud farming business, make sure to have good knowledge in water quality control, husbandry of crabs, food and pond management, crab processing, and crab marketing. Mud crab has a smooth outer shell (carapace), has big claws and their last pair of legs are flattened for swimming.
Mud Crab Project Report, Culture Practices, and Pond Management
Types of Mud Crabs: Scylla serrata, Scylla olivacea, Scylla tranquebarica, and Scylla paramamosain are the four mud crab species. Scylla Serrata (green mud crab) and Scylla Olivacea (Brown mud crab) are the most commercially grown species in aquaculture in the coastal regions.
Green Mud Crab (Scylla Serrata): This is the most common and larger species that are grown commercially. They have a shell width of 20 to 25 centimeters and grow over 2.0 to 2.5 kg in weight. Green Mud Crab can be identified by its elbow, which has a prominent sharp spine on the claws and the claws are dark-green to purple colored. These species are free-living animals with polygonal markings on all appendages
Brown Mud Crab (Scylla Olivacea): This is also known as red claw and these crabs are more aggressive. Usually, these types can grow half the size of green mud crab. They have a shell width of 10 to 15 centimeters and grow over 1.0 to 1.5 kg in weight. They can be identified by their elbow which has a blunt spine or no spines at all on their claws and the claws are light brownish-orange in color. This species has a burrowing habit and no polygonal markings.
Understanding Lifecycle of Mud Crab Culture
Zoeae: The first stage of the mud crab after hatching from the egg as larvae, which is called zoea. The zoeae feed on planktonic animals or brine shrimp in the water. At this phase in the hatchery, water must be maintained same as seawater conditions including pH, salinity, ammonia, oxygen, and water temperature (27° to 28°C). At this stage, the mud crab is about one millimeter long with no resemblance to a crab as it has no developed limbs but looks more like a tadpole. It remains at this stage for about 12 to 15 days while undergoing some changes. Zoea larvae when crowded in the hatchery, usually lead to heavy losses due to cannibalism.
Megalopa: The next stage after zoea is megalopa, while in the zoea stage the larva undergoes four moltings in a period of two weeks. In the final fifth molting stage, the larva transforms into a megalopa having functional claws. At this stage, it starts resembling a crab with a tail. In a weeks’ time, megalopa moves inside the waters and settles on the seabed. Megalopa starts feeding voraciously on juvenile shrimps, zoea larvae, and artificial diet. By next molting that takes place in a weeks’ time, it transforms from megalopa to a juvenile crab4 mm wide, which is the first crab stage.
Juvenile Crab: In this stage, it completely resembles an adult crab but in a miniature size. All the organs are well developed and can walk around on the seabed and also can swim in the water. The juvenile crab will be about 10 to 40 millimeters by now. Due to cannibalistic behavior, a density of 50 per square meter must be maintained. The crablets can be fed on formulated feeds, freshly minced mussel, or fish meat. The juvenile crab starts to settle down in a sheltered area by moving to an estuary or brackish waters.
Young Adult: The juvenile crab grows over the coming days and grows both in weight and carapace width. It takes about 18 to 24 months for crabs to attain maturity. A matured green mud crab has a carapace width of about 180 to 250 millimeters while a brown mud crab has a carapace width of 90 to 150 millimeters.
Mating: During warmer months or in the warm season, matured mud crabs start to mate. To attract males, the female crab releases a chemical attractant called pheromone in the water. A suitable male climbs on top of the female by clasping her with his hind legs and carries her for up to three to four days till she begins to molt. The male turns the female upside down to mate after she sheds her shell. Sperms of the male are deposited inside the reproductive opening of the female like a capsule that will remain for a month till the developing eggs are ready to be fertilized. After mating the male flips the female and still holds the female for some more days till her carapace (shell) hardens.
Spawning and Hatching: The female digs a hole with her abdominal flap in the sand and releases the fertilized eggs. Till she releases the fertilized eggs, it uses her swimming legs to carry them for about two to four weeks under her abdomen that looks like a dark spongy mass. When the eggs begin to hatch, the female crab stands on her legs. You can expect 3 to 5 million eggs to be released by moving her abdominal flap in the water.
Mud Crab Culture Feed and Diet
Usually, mud crabs search for food at night times. Apart from the artificial formulated feed, they feed on small and slow-moving animals such as juvenile shrimps, mollusks, worms, plant material, and juvenile crabs. While in search for food they use different senses such as eyes which give them 360° vision both in and out of the water, by antennae they detect minute changes in water movement around them, tiny hairs on their legs are sensitive to touch and taste. Mud crabs travel up to 500 meters at night looking for food. Crab’s claws are so powerful that a medium-size crab can crush shells that may require a force of forty kilograms to break. Their large claws are used to break shells or crush while the smaller ones are used to cut.
Frozen or fresh fish trash or 75% of brown mussel meat along with 25% trash fish can be given as feed. Feed is given depending on the crab’s weight. Crabs whose shell length is less than six centimeters can be fed up to 10% of their body weight per day while crabs whose shell length is greater than six centimeters can be fed up to 5% of their body weight per day. Feed must be given two doses in a day; the first dose is given at the evening time about 60% out of the daily ration and the remaining 40% at late evening.
Mud Crab Culture Methods
In case if you miss this: Prawn Cultivation.
You can grow mud crabs in two possible systems: 1) grow-out culture system and, 2) fattening system.
Grow-Out Crab Culture System
Ponds: Crabs can be grown in earthen ponds used for marine shrimp culture. Generally, one can grow mud crabs in half to 1-acre ponds without much difficulty. Similar to shrimp farming sites, sandy soils with 50 percent clay are ideal sites. The pond must have a water inlet and outlet for water exchange. Place a netting barrier to prevent the crabs from getting out of the water, this is because. at times, the crabs might walk away from the aquaculture pond site that will directly lead to farmer’s financial loss. To overcome this loss, farmers have to place netting with plastic topping around the pond up to 20 to 50 cm in height which will prevent crabs from walking away from the culture site.
Mud Crab Culture of Raised Dry Platforms inside the Ponds: In this system, the ponds are designed with raised mounds or platforms within the pond. These raised platforms are also used as feeding stations for mud crabs. The design will reduce the water usage in the pond and these designs are also helpful in places where water resources are limited. The water levels in the pond can vary in height just like the tidal cycles giving mud crab a natural environment. There is no documented research on whether this design is beneficial over conventional ponds.
Mud Crab Culture Pens in Mangrove Areas: Mangrove forests are the best suitable natural habitats for juvenile and adult mud crabs, the pen design will be an ideal pond culture in mangrove areas to raise mud crabs. Each mangrove pen can be 100 sq. meters with mangrove vegetation in the center which will provide shelter for crabs during low tides. These designs will retain the crab stock while monitoring their feed and growth within the mangrove specific area. As the pens are constructed in the mangrove forest area, the pen’s fencing is constructed with complete bamboo or wood or netting with a wooden frame structure. Netting mesh size must be small enough to hold the smallest crab in the farm stock. To ensure that no crabs escape by swimming out on a maximum king tide, the height of the fence must be higher than the king tides. Mangrove pens are constructed with walls buried deep in the mud about 40 to 60 cm and support posts every three meters with horizontal bamboos or bracing structures to support the walls. It is recommended to construct ditches inside the mangrove pens which will hold water for crabs to stay immersed even at low tide and about 20 to 30% of the total pen area must consist of such ditches. If not ditches, a canal can be dug around the edge of the pond about one meter wide and half a meter in depth that will hold water during low tide. The crab survival rate in this mangrove pen culture is 45 to 50% and the loss is due to escape of crabs and cannibalism, it is suggested the density of stock should be lower to lower the survival rate.
Crab Fattening in Mud Crab Culture System
After molting, the crab exoskeleton takes some time to grow and get hardened. These soft-shelled crabs do not fetch the market price as the little meat and a lot of water content in them. Mud crab fattening is a process where these soft-shelled crabs which are identified at the time of harvest are reared for a period of time till their exoskeleton gets hardened and are full of meat and ready to market.
Fattening in Cage and Pen Mud Crab Culture: Cages of about 100 x 100 x 20 cm size divided into nine equal cell-type partitions can be used for carrying out the crab fattening process. The crab cage can be made of non-corrosive materials with each cage having a lid at the top and no gaps in the flooring for easy crab movement. Each cell or compartment in the cage must hold only one crab i.e. nine crabs per cage. Cages can also be made without cells making them as pens but this will lead to cannibalism which will lower the survival rate. In pens, stocking of five crabs per square meter is ideal. Cages can be suspended from a raft or can be made fixed in ponds, backwaters, or mangrove areas.
Mud Crab Culture Fattening in Ponds
Crabs weighing 150 to 200 grams are stocked in ponds either in the early morning or in the evening time. Usually, 2 or 3 crabs can be accommodated /sq. Meter and, empty cans can be placed in the pond to hide themselves to prevent cannibalism and fighting. Crabs are fed at a rate of five to eight percent of their body weight thrice a day. By two weeks the body weight increases and the crabs attain marketable weight.
It is found and recommended for all crab culture owners, the fattening system is profitable and has more advantages over the grow-out system. The fattening system is more popular as it takes less time for crabs to grow and will be ready for marketing while in the grow-out system the production of crabs for marketing takes considerable time. As for commercial production, harvesting in less time with good body weight will give high profits to aqua farmers.
Water Quality in Mud Crab Culture
For successful crab production and profits, water quality in the culture plays an important role. Crab culture must have proper water recycling with water an inlet and an outlet. You must maintain the ideal water quality with a salinity of 15 to 25 ppt and with more than 5 ppm of oxygen levels in the water for better crab yield. Crabs grow well in water temperatures ranging between 26° to 30°C and with 7.5 to 8.5 water pH ranges.
Health Management in Mud Crab Culture
Though there is not much documented source regarding diseased in mud crabs and is still at an early stage of development. However, compared with diseases in shrimp farming can be incorporated into mud crab rearing. Some diseases such as white spot syndrome virus (WSSV) and Taura syndrome virus (TSV) are common diseases with no mortality.
Disease management and Treatment in Mud Crab Culture: As said earlier that there’s no knowledge regarding diseases and treatment is still at an early stage of development. Much of the disease management has been developed at hatchery level operations in improving mud crab larvae survival. Controlling for bacterial and fungal diseases and infections is critical at the hatchery stage; less mortality in the hatchery stage will give more crab production at the later stages. Prophylactic treatments such as antibiotics for bacteria and fungicides for fungi were successful in improving the survival rates of mud crab larva in hatcheries. For improved survival rate in ponds, using quicklime to disinfect the ponds as preparation before stocking and filling of juveniles and adult crabs has led to a high survival rate. Some of the recommended strategies for minimizing disease risks in mud crab farming are:
- Pond or Cage or Pen Management
- Water Quality Management
- Feed Management
- Stock Density and Husbandry Practices
- Source of Stock and Record-keeping
Mud Crab Project Report/ Economics of Mud Crab Culture in India
The mud crab culture model project is for fattening in a 1000 sq.m size pond, the cost and items are not actual figures but are indicative project figures. While preparing the project model for a 1000 sq. meter pond; the estimation of capital cost and operational cost is Rs. 65,000 and Rs. 40,000 respectively.
The financial viability of mud crab culture is based on the following assumptions:
|Size of the pond
|Culture / Crop Period
|Stock Density ( 1000 nos of 300 to 350 grams each)
|1 crab / m2
|75 – 80%
|Weight of Crab at the time of Harvest
|Expected Production per Crop
|No.of Crops in the first year
|4 – 5
|No.of Crops in the second year
|8 – 10
|Rs. 190 / kg
Capital Investment Cost for a Mud Crab Culture of 1000 sq.m pond:
|Construction of pond ( digging, bund construction )
|Water inlet and outlet Sluices ( 2 x 6000)
|Water pumps ( 5 HP diesel )
|Fencing (bamboo, nylon netting, casuarina poles)
|Shed for watchman
Operational Cost for Mud Crab Culture of One Crop:
|Pond preparation and sanitizing with quicklime
|Cost of soft crab (1000 nos of 350 gm each @ 85 / kg)
|Crab Feed 735 kg (35 kg/day @ Rs. 12.50 / kg)
|Labor cost (Rs. 250 / day)
Mud Crab Culture Production and Profit Margin:
Cost of Production on First Crop in First Year = 75,500+45,450 = Rs. 1,20,950/-
Cost of Production on second Crop onwards = Rs. 45,450 /-
Income on One Crop in the First Year = 400 x 190 = Rs. 76,000 /-
Income in the First Year = Rs. 1,22,700 /-.
Income on each crop(21 days) from Third Crop onwards = Rs. 30,550 /-. Income and profit generation are still higher (more than 5 times) in mud crab culture which practices fattening of crab culture in cage methods. Although initial one-time capital investment will be high which can be recovered in the first 2 crops and from then onwards the profit margin will be very high.
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