Mangrove Mud crab Farming discusses two main methods of mud crab farming: grow-out culture and fattening. In grow-out culture, juvenile crabs are grown for 5-6 months in ponds until they reach market size, while fattening involves rearing soft-shelled crabs for a few weeks in ponds or cages until their shells harden. The document provides details on nursery rearing, feeding practices, water quality parameters, health management, and harvesting techniques for both grow-out culture and fattening operations.

1. Mangrove Mud crab Farming
BY:
Bhukya Bhaskar
Fisheries

2. Distribution and habitat of Scylla species

3. Four species of Scylla and
details of their claw

4. Identification of Mud crabs
• Mud crabs in the genus Scylla inhabit coastal areas, estuaries and
backwaters.
• i. Larger species :
• The larger species is locally known as `green mud crab'.
• It grows to a maximum size of 22 cm carapace width and 2 kg in
weight.
• These are free living and distinguished by the polygonal markings
present on all appendages.
• ii. Smaller species :
• The smaller species is known as `red claw'.
• This grows to a maximum size of 12.7 cm carapace width and 1.2
kg in weight.
• It is without polygonal markings and has a burrowing habit.
• Both species have good demand in the domestic as well as in the
foreign market.

5. NURSERY REARING MUD CRAB
• Commonly, nursery tanks are
rectangular, with a flat base
constructed from concrete or
fibreglass, with a sloping floor to a
sump (simplifying drainage.
• Net cages (hapa nets) Square or
rectangular net cages (or Hapa nets)
typically of 1–2 mm mesh opening,
are set in earthen ponds, the base of
the net buried into the bottom of the
pond. Ponds should be used or
designed so that a water depth of 80–
120 cm of water can be maintained to
support moderate water temperature
fluctuations and steady plankton
populations. Zooplankton populations
should be established in the ponds to
provide feed for the megalopae once
they are stocked.
• Nursery ponds should be surrounded, typically
around their banks, by a short fence (height 20–40
cm) constructed of relatively fine mesh (1–2 cm)
netting or similar to ensure crablets cannot walk
away from the ponds should water conditions in
them deteriorate for any reason. The fence is made
more effective if the top of the net is covered with
plastic sheeting, which crablets cannot climb over.
If multiple nursery areas are set up in one pond,
fencing, buried into the pond floor, can be used to
separate them and manage the stock in each area
independently

6. Feeding and Harvesting of Crab lets
• Feeding: Advanced Artemia (5 days old)
at 20–25 per millilitre and formulated
shrimp larval feeds are provided to the
megalopa stage mud crab larvae, prior
to settlement.
• Once settled, formulated feeds (at
present, formulated prawn starter diets
as few crab-specific diets have been
developed), or diets of trash fish, and/or
molluscs can be used to feed crablets.
• On-grown Artemia, up to adult size, can
also be fed throughout the megalops
and early crablet stages. Diets of 45–55
percent crude protein and 9–15 percent
lipid appear to support optimal growth
in crablets of S. serrata.
• HARVEST OF CRABLETS Crablets are
typically harvested from nursery
systems after a 3–4-week period and
moved to grow-out systems having
grown to over 1 cm and to weights up
to 0.3 g, at the C3–C4 stage.
• For S. serrata in China, crablets are
harvested earlier at C1–C2 and then
transferred to ponds to grow to C7–
C8, then moved again to other ponds
for final grow-out.
• In net cages, lift nets with feed on
them can be used to attract and
harvest crablets.
• For the final harvest from a net cage,
one end of the cage can be lifted and
crablets scooped from the other.
• To minimize the risk of death in
transit, any soft-shell, recently
moulted crablets should not be
transported until their shell has
hardened.

7. Mud crab farming is done by two methods.
i. Grow- out culture
• In this method, young crabs are grown for a period of 5 to 6 months till they attain desirable size.
• Mud crab grow-out systems are generally pond based, with or without mangroves.
• The pond size varies between 0.5-2 ha, with proper bunds and tidal water exchange.
• Fencing is advisable if the pond is small. In large ponds where natural conditions are prevailing, strengthening is
necessary along the outlet area.
• Wild collected juvenile crabs of 10-100 g size are used for stocking.
• The duration of the culture varies between 3-6 months.
• mud crabs are stocked at relatively low densities (0.5–1.5 crabs/m2 ) with survival rates as high as 67 percent.
• These stocking densities reflect both the size of individual mud crabs and their tendency to cannibalistic
behaviour.
• Stocking at higher rates of 1–3 crabs/m2 has been used with survival from 40 to 60 percent. Stocking mud crabs
from 0.5 to 3.0 crabs/m2 is considered semi-intensive, compared with extensive mud crab culture commonly
practised
• The stocking rates are commonly between 1-3 crabs/m2, with supplementary feeding.
• Feeding is usually with trash fish (wet weight feeding rate-5% per day of the biomass), along with other locally
available items.
• Regular sampling is necessary to monitor the growth and general health, and to adjust the feeding rate.
• Partial harvesting of marketable sized crabs can be started from 3rd month onwards. This 'stock-thinning'
provides chances for better survival by reducing the mutual attacks and cannibalism.
ii. Fattening
• Soft shelled crabs are reared for a period of a few weeks till their exoskeleton gets hardened. These 'hard' crabs
are locally known as "mud" (meat) and fetch three to four times better price than the soft crabs.

9. Fattening
a. Fattening in ponds
• Fattening can be done in small tidal ponds between 0.025-0.2 ha with a water depth of 1 to 1.5 m.
• Before stocking the soft crabs in the pond, the bottom is prepared by draining the pond water, sun-drying and adding sufficient
quantity of lime.
• Care is taken in strengthening the pond bunds without any holes and crevices. Special care is taken in the sluice area as these
crabs have a tendency to escape through nearby areas of sluice gate. The inlet areas should be reinforced with bamboo matting
inside the bund.
• The ponds are fenced properly using bamboo poles and nets along the sides of the bund, which incline towards the pond to
prevent the escape of crabs.
• Soft crabs collected from local fishermen / crab merchants are stocked in the ponds preferably in the morning hours @ 0.5-2
crabs / m2 according to the size of the crabs.
• For crabs of 550g and above, market demand is more. Hence it is ideal to stock
crabs belonging to this size group. In this case, the stocking density should not be more than 1 crab /m2.
• Depending upon the location and availability of water crabs, 6-8 cycles of "fattening" can be carried out in a pond by repetitive
stocking and harvesting.
• If the culture pond is big, it is better to divide the pond into different compartments of suitable sizes for stocking crabs of
uniform sizes in the same compartment. This is good for manipulating the feeding and is easy to monitor and harvest.
• When the interval between stockings is wide, crabs of similar sizes can be stocked in one compartment.
• Sex-wise stocking in compartments is advantageous to reduce the attacks from more
aggressive male crabs. It's better to provide shelters like old tyres, bamboo baskets, tiles etc. to minimize mutual attacks and
cannibalism.
b. Fattening in pens and cages
• Fattening also can be carried out in pens, floating net cages or bamboo cages in shallow estuarine waterways and inside large
shrimp ponds with good tidal water influx.
• HDPE, netlon or bamboo splits can be used as the netting material.
• The size of the cage shall be preferably 3 m x 2 m x 1 m.
• The cages have to be arranged in a row so that feeding and monitoring can be easily carried out.
• A stocking of 10 crab/m2 in cages and 5 crabs/m2 for pens is recommended. Since the stocking rate is higher in cages, and to
minimize the mutual attacks, the tips of the chelae can be removed while stocking.
• However, these methods are not commercialized like `fattening' in ponds.
• Between these two methods, Fattening is more advantageous since the culture period is short and profitable, when enough
stocking material is assured. In India, grow-out culture is not popular, mainly due to non-availability of crab seeds and
commercial feed.

10. Pens, tanks and cages for crab fattening

11. Percentage composition of natural food of Scylla
serrata of different ontogenetic stages
• While mud crabs can survive a
wide salinity range in culture (5–40
ppt), optimal growth appears to be
in the range of 10–25 ppt for S.
serrata

12. Suggested water quality parameters for
mud crab pond management

13. Feeding, Water Quality and Health Management and Harvesting of market size crabs
 Feeding
• Crabs are daily fed with trash fish, brackish water clams or boiled chicken
waste @ 5-8% of their body weight.
• If the feed is given twice a day, major share must be given during evening
hours.
• Water quality parameters shall be maintained within the range shown
below:
• Salinity-15-25%
• Temperature: 26-30° C
• Oxygen: > 3 ppm
• pH: 7.8-8.5
• Periodically crabs are to be checked for their hardening.
• Harvesting should be done in the early morning hours or evening hours.
• The harvested crabs should be washed in good brackish water to remove
the dirt and mud and carefully tied without breaking its legs.
• The harvested crabs have to be kept in moist conditions. It has to be kept
away from sunlight, which has a negative effect on survival.
•

14. Harvest techniques
• mud crabs are reasonably tolerant to a wide range of environmental variables, it is
recommended that unnecessary stress be avoided during harvest.
• Wherever possible, avoid harvest activities during high temperatures, typically experienced
during the day.
• In addition, preliminary grading at harvest should be undertaken as quickly as possible and
unsuitable mud crabs returned to the pond to complete grow-out.
• Once some of the crabs in a pond are identified as large enough to harvest, harvesting of
crabs can commence.
• Crab pots of various designs can be used to harvest crabs.
• These are baited with food attractive to crabs.
• It is found that the largest crabs in a pond tend to enter traps first. As this is the case,
ponds can be partially or selectively harvested on a regular basis, progressively removing
the larger crabs from the pond.
• To complete the harvest, either trapping is continued until no more crabs are trapped, or
the pond is drain harvested, with crabs collected from the pond’s drain or the lowest part
of the pond.
• As premium prices can be obtained for female “egg-crabs”, females may be monitored and
are only harvested when mature ovaries (red-orange) can be viewed through the carapace.

15. Diseases of mud crabs

16. Useful Video links for Mud crab farming
• Indoor Vertical Crab Farming | Modern Mud Crab
Farming: - https://youtu.be/redAuBjbC5Y
• RAS Vertical Farming, Mud Crab Farming, Pond Culture, Cage
Culture, Raceway Culture
:https://youtu.be/KJRf61oBfb8?si=kEe9L7SNy9cMFoq9
• Feeding and Monitoring Scylla Serrata (Mud Crab
Farming) in RAS Vertical Farm:
https://youtu.be/do62eZY_Q_k?si=TFQhl3EUlrJRrX
2N
• https://youtu.be/EkFe4CX1HZM?si=1d6OnmcvAbX
GFB86

17. Economics of Mud Crab Farming

18. References
• https://vikaspedia.in/agriculture/fisheries/brackish-water-fisheries/culture-fisheries/mud-
crabculture#:~:text=Mud%20crab%20grow%2Dout%20systems,necessary%20along%20the%
20outlet%20area.
• https://www.fao.org/3/ba0110e/ba0110e.pdf
• https://www.agrifarming.in/mud-crab-fattening-profits-cost