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Mudcrab Farming

Scylla serrata is the common mudcrab occurring in the estuarine and  mangrove areas and is commonly called as “red crab” and it prefers to live in  low saline waters. Male crabs of S. serrata grow to 700 to 800 gm at  the maximum The export size of the crab  is 500 g and above for males and 250 g and above for females.

Crab fattening is widely practiced in Thailand, Taiwan, Malaysia, Singapore  and Indonesia. Gravid female mud crabs with full orange-red egg masses are in  great demand in seafood restaurants of  South East Asian countries. Due to its  high price, people started to hold immature female crabs in some kind of  enclosures and fed them until the gonads developed and filled the mantle cavity.  This is how crab “fattening” spread, initially, throughout South East Asian  countries. Subsequently, the practice of holding post-moult “water” crab of  market size, in some enclosures, for short period of time and feeding them until  they completely “flesh out” for getting quick returns also became popular.  Cages, pens and small ponds with net are being used for holding crabs for a  short period of 3-4 weeks.

The mud crab resource is a natural bounty for our country, which has a  potential to change the socio-economic status of the coastal communities. The  coastal poor fishermen and educated unemployed youths should realize this fact  and take up crab culture or fattening in eco-friendly way to raise their  economic status.

Culture

This is the process of stocking juvenile crabs (10 g to 250 g) and allowing  them to moult and grow. Harvest is done after 3-8 months or once the crab  reaches 400 g to 500 g size. Mud crab fattening is the most suitable  method for small-scale aquaculture because:

* Turnover is fast, hence, the period between investment and returns is short. * Fattened crabs can  be stocked at higher densities (15 crabs/sq m) compared to grow-out systems (1  crab/sq m) as no molting occurs and therefore losses due to cannibalism are  dramatically reduced. * Short production time reduces the risk of losing  crabs to disease, thus, rendering a higher survival rate for fattening (>90%)  compared to grow-out systems (40%).

Different Methods of Crab Culture

Four methods of oyster culture are practiced in the Philippines; broadcast (sabong), stake (tulos),  lattice and hanging (bitin, sampayan, horizontal, and tray) methods.

Pond Culture. Pond size of ½ to 1 acre is most  suitable for crab culture. However, large size ponds of more than one acre can  also be used for this purpose. Sandy soils with a mixture of 50% clay are ideal  for culture of these crabs. A water inlet system and an outlet system to drain  out water during water exchange should be constructed as in the case of shrimps.  The pond should be constructed in such a way that it should hold 3 ½ to 4 feet  of water towards the inlet and 4 ½ to 5 feet towards the outlet. A flow through  mechanism of water exchange should be there in order to remove any left over  organic food material and also to efficiently remove excretory material. A  fencing of nylon net used for fishing can be placed on the dike to prevent the  escape of the crabs during nighttime. In addition, about 1000 numbers of stone  ware, pipes of 6 inch diameter and 1 ½ feet length, worn- out tyres, etc.,  should be kept at the bottom of the pond through out the dike. The nylon screen  fencing should be supported with split bamboos of 1.5-meter height around the  pond periphery for preventing the escape of the crabs from climbing over the  bunds. The maximum stocking density should be 1crab per sq. meter.

Pen Culture in Ponds. Several units of pens of 4 X  4 X 2.5 m could be made inside the ponds using bamboo strips which are driven  1-1.5 m deep into the soil to prevent the escape of the crabs by burrowing. The  pens could be made nearer to the dykes for easy stocking and monitoring.

Pond Culture in Mangrove Areas. The ponds could be  constructed as described above around the mangrove plants. But a maximum pond  area of 100 Sq. meters is suitable for this type of culture. A canal of 1 m wide  and 0.5 m deep, in which water will be available even during low tide, should be  dug around the edge of the pond. The center of the pond forms a raised platform  with mangrove vegetation, which the crabs would use as a refuge during low tide.  Water exchange could be tidally controlled. Polythene nettings could be used to  prevent the escape of the crabs. Feeding depends on the availability of  organisms namely low-value fishes, mangrove snails, clams, mussels, etc.

Pen Culture in Mangrove Areas. The pens could be  constructed using the locally available bamboo splits or arecanut logs or cane.  These strips should be driven 1-1.5 m deep into the soil to keep the crabs  inside and the potential predators outside. The manageable area of the pen could  be 100 to 150Sq. m. With in the pen, a ditch of about 0.3 to 0.9 m wide and 0.3  m deep should be dug. Mangrove trees in the center of the pen provide shade for  the crabs. Roughly 1000 to1500 crabs of 100 g each could be stocked per pen. The  stocking should be continuous. The crab could be fed once a day during high tide  with low-cost fishes, mussels, clams, snails, etc. The crabs could be harvested  after 4 – 7 months. The crabs could be selectively harvested after they reach  400g or more. Although this system is eco-friendly, survival rate of only 47 to  50 % could be expected. The loss could be mainly due to cannibalism, and escape  of crabs. Lower stocking density is suggested to be a remedy for the low  survival rate.

Cage Culture (suspended or fixed type)

Cage design. Crab fattening can be carried out in  Cell-type Cane Cages of 1m (L) X 1m (W) X 20 cm(H) size, which can be  partitioned into nine equal compartments. Each of these cages should be provided  with a lid to prevent the escape of crabs. A gap of 5 mm is to be provided  between the canes at the top and 2.5 cm at the sides of the cages to enable free  movement of water through the cages. But, no gap should be provided at the  bottom to enable easy movement of the crabs.

Stocking and feeding in cages. One crab should be  placed in each compartment of the cages. In this method of fattening, higher  number of crabs can be fattened in a square meter area, i.e. 9 crabs / m2. Based  on the local availability, different types of feeds such as trash fish, mussel,  chicken waste, clams etc. can be given to the crabs.

Deployment of cages. These cages can either be  suspended from a raft deployed in bays or backwaters or mangrove areas. These  cages could also be made as a fixed type in ponds, mangrove areas or coastal  regions of the bays. The cages could be made without cells inside. But the  survival would reduce in this method due to cannibalism.

Cage Maintenance

* Clean the cages as frequently as possible using brushes enabling free  movement of water inside. * If nails are used in the cages, use only the  anodized MS/ copper / SS nails for increased longevity of cages in seawater.   * Repair the damages in the cages immediately when it happens. * Deploy the  cages where there is mild water current. * If algal growth is found on the  crabs, clean them using a brush.

Managing the Crab Farm

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

Mud Crab Fattening Practices

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. 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 bodyweight 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.

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:

Site Selection

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 salinity 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.

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.

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.

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 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:

1. SEAFDEC Aquaculture Department. Tigbauan, Iloilo, Philippines

2. BFAR-FIDSD. 2/F PCA Annex Bldg., Diliman, Quezon City


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Freshwater Prawn Culture

Growing freshwater prawn is a promising alternative to the expensive  lobster and tiger prawn. The freshwater prawn, locally known as ulang,  can be substituted for lobster and tiger prawn (sugpo) because of their  appearance and excellent taste. Among the 15 species of freshwater prawn in the  Philippines, the most popular to culture is the macrobrachium rosenbergii, also  known as udang in ilocano, kising-kising in Pangasinan, and swahe in other  regions.

Grow out Farming of the Giant Freshwater Prawn aquabusiness The  macrobrachium rosenbergii is appealing to culture because of its rapid growth  performance and ability to survive and grow in turbid water conditions. Ulang  can tolerate moderate temperature and salinity changes, and can be caught in  tributaries and cultured in ponds, tanks, cages, and rice paddies. They feed on  anything such as terrestrial animal feeds, fish feeds, kitchen leftovers, and  vegetables like carrots, winged beans, etc.

Freshwater prawn can be used in polyculture together with tilapia and carp.  They can tolerate temperature up to 34oC and actively feed at night.  They consumed less feed than tilapia since they are nibblers and slow feeder.  They grow to a maximum size of more than 1 kilogram per piece and they command  high price in the market.

Grow-Out Operation of Ulang

Factors affecting success of grow-out operation:

1. Feasibility of the site

2. Water Supply/Water Quality

3.  Topography

4. Quality of soil

5. Free from flooding

6. Quality of  Stock

7. Market acceptance

8. High level Management practices

9.  Peace and order situation

I. Procedures in Pond Operation:

Pond Preparation

1. Pond draining – To collect eliminate old stocks,  predators and unwanted species.

2. Pond poisoning – Application of biodegradable organic materials such as tea seed cake and tobacco  dust to kill all unwanted species.

3. Pond washing – to  remove the effect of toxic chemicals when insecticides were used.

4. Leveling of pond bottom – removes excess mud and dirt, ensure complete drainage and facilitate ease of  seining during harvesting.

5. Sun drying – helps eliminate  and evaporates toxic gases & ammonia especially in old ponds

6. Screening of water inlet and outlet – prevent entrance of  unwanted species and escape of stocks

7. Filling the pond with  water –Fill the pond with water from 0.8 to 1.5 meters depth.

8. Application of lime- The rate of application is 100g / m2 or  1,000 kg/ hectare.

9. Basal fertilization

 Grow out Farming of the Giant Freshwater Prawn aquabusiness

10. Installation of Artificial shelters – arrange the shelters  in the pond (30 – 50 pcs/1000m2).

II. Nursing of Post Larvae (PL) to Juvenile

Nursing of PL to Juvenile Prawn- The size of the Post larvae  ranging from 1.5 to 2.0 cm must be reared to juvenile size of 5 cm to 8 cm  before transferring them into the grow-out ponds to attain marketable size.

a. Nursery Ponds. The size of the pond must be 50 sq.m. with  a depth; 0.8-1.5 m

b. Artificial shelters. This are placed in the nursery ponds  to serve as hiding place of the Post larvae during molting. Artificial shelter  is needed because when prawns are soft shelled they will be eaten or  cannibalized by the hard shells prawn. The following can be used as artificial  shelters:

  • twigs, bamboos , sampaloc twigs
  • pipes, PVC, or recycled materials  like nets
  • bricks or stones
  • used mineral water bottles (250-300  ml)

c. Nets used for substrate can be suspended from float across the pond  and weighted with sinkers to serve as hiding place for molting prawns to prevent  or reduce cannibalism.

III. Growing of Juvenile to Marketable Size

Stocking Density

Extensive – The stocking density is 1-3 pcs/m2, with the use  of fertilization only (chicken manure and 16-20-0) at a rate of 1,000-2,000  kg/ha and 100-200 kg/ha respectively for basal application.

Semi- intensive – A stocking density of 4-8 pcs/m2 with the  use of fertilization and feeding. A monthly exchange of 30% of water in the pond  is done to maintain water quality

Intensive – The stocking density of 10 pcs /m2 and above  with feeding, fertilization, frequent water exchange and aeration using paddle  wheel is also done to ensure enough supply of dissolve oxygen for the prawn.

Stocking Procedure

Acclimatize the prawn juveniles into the pond water for 10-15 min. before  releasing the prawn in the pond water to prevent thermal stress that will cause  mortality.

CAUSES OF MORTALITY:

a. Cannibalism- due to lack of food and shelters b. Predators – mudfish,  catfish, frogs c. Water pollution – insecticide, pesticide, industrial waste  products

Types of Feeds for Commercial Farming of Ulang

1. Live or fresh food (termites, earthworm, insects 2. Plant vegetable  feedstuffs 3. Formulated diets 4. Reformulated diets (ground tilapia  feeds mixed with fish meal & starch as binder) 5. Chicken pellets (to be  given during the first 2 mos. of culture) 6. Ground fish flesh mixed with  cooked broken rice (to be given after two mos. of stocking) 7. Tilapia  sinking pellets 8. Trash fish

Initial feeding rate using trash fish: • 5% of total body weight

For dried diet, chicken pellets/fish feed: • 3% of total body weight • prawn are nocturnal feeder 40 % of feed ration must be given at night.

Regular water quality monitoring and  feeding activities of the prawn must be properly observed.

DETERMINATION OF AVERAGE BODY WEIGHT (ABW), DAILY FEED RATION (DFR),  TOTAL FEED REQUIREMENTS (TFR) FEED CONVERSION RATIO (FCR)

Grow out Farming of the Giant Freshwater Prawn aquabusiness * The  closer the FCR to 1.0 kg. The better is the feeds. Good feed have FCR’s of  between 1.5 to 2.0 kgs.

Harvesting of Ulang

Harvesting of ulang can be done when they reached its marketable size. After  4to 5 months of stocking, ulang can be harvested through selective harvesting or  total harvesting.

Methods of harvesting

1. Selective – this is done by seining the prawns using size  17 net. The bottom of the seine net should be kept intact on the pond bottom to  avoid escape of the prawn.

2. Total harvesting – this is done by total draining of the  pond. The prawns can be collected in the catch basin manually by using scoop net  or with bare hands.

Marketable Sizes of Prawn After 4 To 5 Months Culture Grow out Farming of the Giant Freshwater Prawn aquabusiness

Measurement of length is from tip of the rostrum to end of the telson

Simple Cost Estimate (1,000 sqm Ulang Fishpond  Project) Grow out Farming of the Giant Freshwater Prawn aquabusiness

For more information please write to:

The Project Manager BFAR-NFFTC CLSU, Muñoz, Nueva Ecija, Philippines

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