Mud crab fattening is a relatively new practice in the Philippines. The technology has been pioneered by the private sector, primarily to meet the demands of the domestic and foreign markets by culturing marketable crab in a short span of time. Mud crab fattening pertains to culturing mud crab from 15 days to 1 month so that they put on additional weight after moulting. Ovigorous females are highly prized for their bright red roe.
Fattening has also been resorted to by Filipino exporters to avoid confiscation of underweight mud crab, export of mud crab weighing less than 200 g being prohibited. However, due to limited baseline research studies in mud crab culture and fattening, practices vary widely in different parts of the country. The only documented technology verification studies on fattening in bamboo cages was conducted in Capiz by Joey and Sylvia de la Cruz of the Department of Agriculture, Roxas City.
Mud Crab Fattening Practices
Early methods involved placing crab in holes along the seashore. The holes were covered and food was given as often as possible. The earliest recorded mud crab breeding and fattening project was by Catalino Catanoan of Bolinao, Pangasinan. His crab project was part of an integrated fish farm he tried out in this area with crab and milkfish. Tanks were constructed in his backyard, the mud crab breeding and nursery tank covering an area of 136 m2 and the fattening tank covering an area of 41 m2.
All sides of the tanks were cemented to prevent crab from burrowing. Drain pipes were provided in each tank to drain off foul water. Overhangs were positioned along the upper sides of the tank to prevent the crab escaping.
The water entering the tanks was fertilized and its depth maintained at 0.5 -1.0 m. About 1,000 animals were stocked, those of bigger size fattened, and the smaller ones cultured further. About ten berried crab were bought for breeding purposes and stocked in other tanks.
Feed was provided daily and consisted of kitchen leftovers, like rice, vegetables, fish and animal entrails, as well as swine manure from his piggery. During the rainy months, from May-October, about 2 kg of African snails were given.
The stock was periodically harvested to thin the tanks. Water was also changed, as often as possible, to prevent fouling.
In all, 320 crab were harvested. each with an average weight of 950 g. Because this was purely a private experimental effort. no scientific data was maintained on the duration of culture, and the size and weight of the crab.
Mud Crab Fattening in Fish Ponds
In New Washington, Aklan. mud crab fattening activities were initiated by fish pond owners using a series of crude trial and error methods. Small undeveloped ponds measuring 500 m2 were utilized for fattening. Bamboo or plastic polyethylene netting was used as fencing material.
The ponds were prepared in similar fashion to milkfish and prawn ponds. After fertilization, crab weighing 150-200 g were stocked during the early mornings or late afternoons. The stocking rate was 2-3 crab/m3 To prevent cannibalism and fighting amongst themselves, the tips of their pincers were cut off. Sometimes hollow blocks or old cans were placed at the pond bottom to serve as hiding areas for the crab.
The crab were fed three times a day at a rate of 5-8 per cent of bodyweight. Water was changed as often as possible to prevent fouling. The crab were fattened for 10-15 days and a growth increment of 110g/crab was achieved. After 15 days, the crab were harvested using crab liftnets.
Panquil Bay in Mindanao is another mud crab producing region where mud crab fattening is widely practiced. About 20 t of exportable mud crab are shipped every month from this area to Cebu or Manila.
Mud crab fattening is widely practiced here because of financial assistance under the LEAD-Buklod Yaman Project of the Department of Agriculture. Assistance has been granted to four or five fishermen’s associations in this area. Each association has a membership of 25 fishermen.
The method of fattening in Panquil Bay differs from elsewhere. Instead of earthen ponds, square pens are used. These 2 x 2 x 1.5m pens, made with bamboo poles, are erected in the muddy, intertidal areas near the fishermen’s houses. In order to facilitate entry, exit and feeding, especially during high tides. there is a catwalk set up near the pens.
Crab weighing 150-300 g are fattened over 15-8-day periods. Chopped trashfish is given at 10 per cent hodyweight as feed twice daily. Crab liftnets are used to harvest the mud crab.
In Basilan Province. mud crab for fattening are penned underneath the homes of the Muslim fisherfolk. These houses are often constructed on stilts and the space underneath is fenced from top to bottom with chicken wire and discarded netting. There is an opening in the floor of the house through which trash fish. kitchen refuse and fruit peelings are dropped as feed. When the crab have attained the desired weight. they are harvested.
Mud Crab Fattening in Bamboo Cages
Mud crab fattening in bamboo cages is one of the technology verification studies tried out by Joey and Sylvia de la Cruz in Barangay Napapao, Ponteverdra Capiz. This project was conducted to provide a standard culture method for fattening crab.
Mud crab grow best in brackishwater, such as tidal flats, estuarine areas, bays and lagoons. Sheltered bays and coves are selected to protect the bamboo cages from strong winds and waves during adverse weather conditions. The water at such sites should be 0.5-lm deep.
Areas with low salinities should be preferred, as saline water inhibits the growth of mud crab. Areas with sufficient crab for fattening as well as trash fish for feed should be considered. The area should also be accessible to the growers and target markets.
A modified bamboo cage (140 x 70 x 25 cm) subdivided into 18 compartments is fixed firmly by its comers to the substratum to prevent it from being washed away during inclement weather. The compartments are covered with 140 x 70 cm split bamboo. Holes are provided in the compartment covers for feeding.
One advantage of using bamboo cages is that selective harvesting can be done. If the desired weight has not been attained, the crab could easily be returned to their compartments and fattened further.
About 18 crab can be stocked per unit. Stocking is done during the early morning or late in the afternoon. In Capiz, 185 crab, each of average weight 175 g. were stocked. The weight increase after 15 days was I 10 g.
Feed and Feeding
Mud crab are fed twice a day at 5 per cent bodyweight for 10-15 days. Feeds may be trash fish, soft-shelled snails, kitchen leftovers, mussel meat, animal entrails or almost any other kind of food.
Cage and Maintenance
Periodic checks should be made during the culture period. Drifting seaweed, logs and other debris should be removed to facilitate easy circulation of water and prevent damage to the cages. After use, the crab cages should be lifted periodically and dried.
Harvest and Handling
After the fattening period, mud crab can be harvested individually by hand. The crab are then bound with straw or string to enable easy handling. A skilled laborer is hired to bind the pincers of the crab. Exposure of the crab to sun and wind should be avoided, as this may lead to weakening and eventual death.
For more information, contact:
2/F PCA Annex Bldg.,Diliman Q.C.
photo from seafoodtreasure.com