Crab in Mangrove & Pond

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Mud Crab (Alimango) Culture in Pond

and in Mangroves

April 4, 2008 byLeo 6,454 Views

14 Comments

Among the larger species of crabs that are known to

be of commercial value in the Philippines are the Neptunus pelagicus (alimasag) and the

Scylla serrata . Both belong to the swimming crab family Portunidae, but the latter has

been an incident product of brackish water fishpond.

Occasionally, juveniles are collected in tidal flats and marshes and stocked in fishponds,

but usually at their own accord. The recent years, over fishing, of Scylla serrata has

threatened the fishery, industry so possibility of culturing them in ponds was givenattention.

Biology of Mud Crab

Mudcrab is a swamp crab that spawns in the sea but the larvae are carried by tide alongthe seashore. Juveniles migrate to the tidal flats and marshy lands along rivers. It

becomes sexually mature in the first year of its life after the female undergoes theprecopulatory molt which cannot be readily distinguished from ordinary molting. At thisstage the abdomen of the female changes from its triangular shape into broad rounded

form.

Mudcrab spawns throughout the year with a peak season for about four months staring

from the last week of to the third week of September. As early as April, the stageprecopulatory molt which cannot be readily distinguished from ordinary molting. At this

stage the abdomen of the female changes from triangular shape into broad rounded form.

During spawning season, the fertilized eggs get out of the ovary and attached to the

pleopods where they hatch within a few weeks. The eggs hatched into a planktonic zoea.After passing through several zoea stages and a single megalopa stage within about a

month, the larvae metamorphose to benthic juvenile crabs that are found crawling in the

shallow areas.

The mudcrab is a voracious feeder. It crawls on the pond or seabed searching food ormay also be seen swimming on the surface hunting for food. They feed on natural food,

such as: algae, decaying animals, crustacean, or decaying matter.
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Suitable Crab Farm Site

Mudcrab prefers brackish water ponds with no less than one meter depth of water. It is

the usual practice of fishpond operators to stock mudcrab juveniles in newly constructedor partially developed fishponds, although they are also cultivated in developed ones. In

fully developed fishponds, some operators placed hollow-blocks along the dikes toprevent the crab from burrowing along the dikes thus causing leakages. These blocks

serve as refuge or hideouts when not actively feeding.

Generally, the most suitable places for mudcrab culture are underdeveloped fishponds

with numerous high mounts and submerged region which the animal can take shelter.

Culture Method

The culture of mudcrab in the Philippines is only incidental to bangus culture, except in

not fully developed fishponds. Young crabs or juvenile stages are allowed to enter in the

pond during high tide when water is admitted to the fishpond. In some cases, seeds arepurchased from fry collectors or fishermen with size ranging from 2 to 7 cm along the

length of the carapace.

They are caught by scissors nets (sakag) along the sandy shores. Young crabs whenpurchased have no pinchers as they are removed for ease of handling and to prevent them

from fighting or hunting each other during transport. This is no problem, whatsoever,

because they have ability of regeneration and other pair of pinchers will grow withinthree weeks after stocking in the ponds.

Pond Management

As previously mentioned, mudcrab are usually cultured along with bangus, the pond

management employed is primarily for milkfish. In developed fishponds, where alimangois solely cultured not much preparation on growing the natural food is done but water

freshening is made during high tide.

In ponds, alimango aside from feeding on the natural foods can be given artificial feeds

like trash fish, kitchen refuse, by products of slaughters houses and other feeds of animalorigin.

Harvesting

Alimango reared in ponds, if properly fed can reach marketable size in six months.

Alimango are usually harvested using different kinds of traps like bintol or liftnets

baited with meat or small fish or shrimp or by bare hands. Only the big ones areharvested and the smaller ones are set free in the ponds to attain bigger sizes.

MUD CRAB CULTURE IN MANGROVE


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Over the years, commercial production of mudcrab (Scyllaspp.)Has been undertaken only

in bamboo or net-fenced brackish water ponds. Its feasibility was proven trough a series

of verification trials conducted in commercial ponds by SEAFDEC/AQD researchers andis now practiced elsewhere in the country.

Of late, the introduction of using net enclosure to grow mudcrabs in mangroves or tidalzone offers a bright prospect in aquasilviculture. Using mangroves as a natural resource

paves the way for creating livelihood among the fisherfolk in the coastal areas. While thismethod is not very popular in the Philippines, as it ha only recently been introduced, the

same has been carried out for quite some time in Indonesia, Malaysia, Vietnam and China

successfully. The advantages of this livelihood option include low investment cost, easyconstruction, easy operation and it is environment- friendly. Site selection.

Mangrove areas should have a sufficient supply of marine or brackish water throughout

the year. Water depth at high tide should range between 0.8 to 1.0 m. Salinity should

range between 18 to 30 ppt and temperature between 25 to 30C. The site must be free

from any source of pollution, protected from environmental hazards such as typhoon,flood erosion and from vandals and poachers. Materials

6 rolls of green polyethylene (PE) net, 1-2 mesh size and 2 mm twine diameter

2 rolls of plastic sheets 30 pieces of bamboo (10-15m) for structural framework (horizontal

bracing)Wooden posts, 3-4m long (vertical post)

Net enclosure 4,000 sq m (50 m x 80 m) Constructing a Pen

1. Design the enclosure with a shape that varies from square, rectangular, etc.

depending on the contour and vegetation of the area. The manageable area rangesfrom 0.2-1.0 ha.

2. Install a net enclosure (polynet 1-2 cm mesh size) using bamboo or wooden of thenet should extend not less than 30 cm above the waterline during the highest high

tide level.

3. Along the top edge of the net enclosure, install a plastic strip/sheet of about 50cm

to prevent mudcrabs from climbing over the top. Embed the lower and of the netabout 50-70 cm along the base of the enclosure.

4. Dig ditches/puddle trenches (libaong) at a depth of about 20-40 cm representing at

least 20 to 30 percent of the total area of the enclosure. These are intended to holdwater in the enclosed area during the lowest tide for the crabs to withdraw and

take refuge. Avoid cutting the main roots of the mangroves during digging.

5. Install catwalk around or perpendicular to the enclosure for ease in feeding andmonitoring the stocks during high tide.

Rearing Operation Transplanting Mudcrab Juveniles for Grow-out Culture
http://www.seafdec.org.ph/http://www.seafdec.org.ph/


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Take a stock sample every 30 days, using bintol or bamboo traps, to determine the

growth and feed requirement. Take 30-50 crabs samples and measure their increase in

body weight and carapace size.

Pen Management

Monitor the crabs for feed consumption, swimming behavior, presence of berried female

crabs, etc. Inspect enclosure daily for destruction debris, scouring and torn nets where

stocks could possibly escape. Secure them against possible poachers by making routineinspections of the area, especially during the night.

Harvesting

Partial harvesting is done when mudcrabs reach marketable size of 200g and above. This

could start, at the earliest, after 45 to 60 culture days.

Handpick the crabs during low tide and/or by catching those using baited traps like bintolduring high tide. Fat crabs are detected by pressing the abdomen. The presence of

gonands (orange mass called alique) indicates fat female crabs. Fat male crabs have

massive pincers.

Total harvest may be done after 4-6 months of culture. Tie the pincers of newly-harvestedcrabs using plastic straw or suwak before transporting them to the market.

Mudcrabs sold in restaurants are 350g and above. Prices vary with markets and seasons.

Marketing

In all cases, mudcrabs are marketed live. In the Philippines, female crabs with mature

gonands are relatively expensive. Mudcrabs are sold in market year-round, but generally,those found in domestic markets are grouped in mixed sizes and are smaller than

exportable crab. Usually during the Christmas season, the price is relatively high because

of the increased demand.

The major market for the Philippine mudcrab is Taiwan, Hongkong, Guam, Japan and theUSA. Other markets include Singapore, Brunei, Germany Korea and neighboring

countries. Taiwan has been the biggest buyer of mudcrab from the Philippines the trading

pattern of maudcrab industry throughout the Asia region involves a series of

intermediaries between the fishermen/supplier and the local consumers or exporter.

For more information, contact:

Bureau of Fisheries and Aquatic Resources (BFAR)

PCA Building, Elliptical Road, Diliman, Quezon City

Tel. Nos. (632) 929-8074 / 929-9597


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Email :[email protected]

Web: www.bfar.gov.ph

photo from seafoodtreasure.com

Crab in Mangrove & Pond

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