Mud Crab Culture, Part 2 Managing Farm and Fattening Practices

Managing Farm

Once decided on the farming method and when the oyster spats have settled

  1. Condition ponds/pens before stocking mudcrabs. Plant Gracilaria or other macrophytes to serve as shelter for crabs. Stock crabs when luxurious growth of macrophytes is observed.
  2. To insure high survival of crab juveniles for grow-out culture while in transport, provide transport containers with fronds of mangroves. Remove chilepeds of crabs weighing less than 30g. Do not remove chilepeds of crabs weighing more than 30g but tie them firmly to prevent antagonistic behavior during transport. Frequently pour seawater into containers while in transport to keep crabs moist.
  3. Stock marketable size lean crabs for fattening culture at 2.0 crabs per sq m. Stock together male and female but remove movable part of the claw and apply Povidone-iodine (betadine) to the injured part to prevent infection. Acclimate before releasing them in ponds/pen.
  4. Stock crab juveniles (7-11g or 16-20g) at 1.5 per sq m for pond grow-out culture and 2.0 per sq m for pen (mangroves). Stock males separately from females. Stock monospecies, more or less monosize crabs. Acclimate to pond/pen water temperature and salinity before releasing them.
  5. Feed crabs with frozen or freshtrash fishor a mixed diet of 75% brown mussel meat and 25% trash fish. Feed grow-out culture crabs at 10% of the crab biomass per day when carapace length is less than 6cm and 5% when carapace length is 6cm or more. Feed fattening culture crabs at 10% of the crab biomass per day through out the culture period. Feed crabs in the grow-out or fattening culture twice per day: 60% of the daily ration at 5:00 PM and 40% at 7:00 PM.
  6. Select and remove marketable size and fat crabs several times over the grow-out culture period: 150g or more female and 200g or more for male pulang alimango; 350g or more for female and 400g or more for male giant crabs.
  7. Harvest fat crabs from fattening culture 20 days after stocking. Not all crabs fatten at the same time but expect to harvest about 50% fat crabs of your total stock. Replace harvested fat crabs with lean ones but remove the movable claw, disinfect, and acclimate them before releasing in ponds/pens. Harvest and replace every 10 days thereafter; this time you can harvest fat crabs of about 30% of your total stock. You can maintain this cycle for five months.
  8. Harvesting is done with different kinds of trap like the bamboo cage, lift net, scissors net, fish corrals and gill nets. Crabs are ready for the harvest and marketing when the piece or two reaches up to a kilo. They are sold alive and can stay out of the water even for a week. They should, however, be kept in damp containers and periodic moistening is important. Feed them with trash fish and other kitchen refuse.
  9. Handling adult crabs in captivity are tied with dried nipa strings. Both pincers are tied close to the abdominal cavity to prevent crawling. When transported, proper handling is important. Place them in baskets or tiklis to avoid getting trampled or crushed.

Mudcrab Fattenning Practices

A. 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 polyethelene 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/m‘ 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.

B. Mud crab fattening in square pens

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 LEADBuklod 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 trash fish is given at 10 per cent body weight as feed twice daily. Crab lift nets 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.

C. 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:

C1. Site Selection

Mud crab grow best in brackish water, 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.

C2. Cage Design

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.

C3. Stocking

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.

C4. Feed and Feeding

Mud crab are fed twice a day at 5 per cent body weight 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.

C5. Cage 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.

C6. 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.

source: www.bar.gov.ph

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