CRAB CULTURE

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CRAB CULTURE:

CRAB CULTURE Larval rearing of crab , S. serrata Though a number of species of marine crabs are edible, the biggest and most highly esteemed species suitable for costal aquaculture is Scylla serrata commonly known as mud crab, green crab or mangrove crab The crab meats are of export value and highly relished by foreigners. The early larval development of Scylla serrata has five zoeal and one megalopa stages.

CRAB CULTURE:

CRAB CULTURE Larval rearing of crab , S. serrata The newly hatched zoea are placed in suitable tank containing filtered sea water (32 to 35%o) and aeration at the rate of 30 to 50/lit and are fed with Chlorella, milk powder or egg yolk. The first and fifth zoea measure 1 and 3.5 mm respectively and stalked compounds eye are visible in all stages except 1 st zoea. The planktonic megalopa stage is attained in a period of 20 days with an interval about 3 days for two successive stages

CRAB CULTURE:

CRAB CULTURE Pond culture Crab ponds may be sandy bottom, the size of pond may be 400-800 m 2 and water depth of 30 cm may be enough. In pond bottom, ditches of 3m width and 0.5-1m depth may be formed along the dykes and two ditches are made in the middle of the pond. These ditches provide shelter for growing crabs On the dyke tops, chicken wire mesh screen of about 1m high are erected to prevent the escape of growing crabs Fencing with 1.8m high bamboo mattingmay be placed obliquely about 1m inside from the edge of the dyke. This would prevent the crabs from escaping by climbing

CRAB CULTURE:

CRAB CULTURE Pond culture Large square ponds may also be divided into four smaller crab ponds with a concrete tank of about 1.5 m square. In the centre to serve as a water inlet tank for all the four ponds. The central concrete tank would serve as a harvesting pit as when water is let in, the crabs concrete here and can be caught easily The walls of the large square ponds area of 1m high and are made of bricks or concrete to prevent escape of crabs. The algae and detritus are the natural food source of crabs.

CRAB CULTURE:

CRAB CULTURE Stocking of seeds The seeds of crabs (2 to 10 cm carapace width) collected from the wild are produced through the induced breeding The seeds are stocked at the rate of 10,000 to 30,000/ha. It is advisable to rear the female crabs in separate pond because that have just had copulation for a period of about the 45 to 60 day Different sizes may be stocked and grown in smaller ponds until they are suitable for transfer in production.

CRAB CULTURE:

CRAB CULTURE Feeding of growing crabs S. serrata is a voracious feeder. Though it prefers to crawl on bottom in search of food, it may also be seen swimming on the surface of the ponds In ponds, the crabs feed on the naturally available algae, decaying animals, crustaceans etc. To enhance the growth of crabs, they may fed with trash fish, fish offals, fish visceras, snails, chank meat etc., The supplementary diet is given at the rate of 5-7% total body weight of growing crabs. Feeding is given daily especially during late evening.

CRAB CULTURE:

CRAB CULTURE Harvesting and Transportation Male crabs, copulated several times will have only little meat and fetch low price. Hence they harvested before that stage. Catching the grown crabs at the inlet tank of large square ponds is the most efficient method The marketable size crabs of earthen ponds are captured on the other hand by hand with the help of small dip net or large dip net baited with trash fish Specially designed traps made of old cycle wheel and coir bags and bamboo traps are also commonly used in the shallow brackish water ponds for the harvesting the crabs Harvested crabs may be transported live in wetted gunny bags or heavy straw ropes

CRAB CULTURE:

CRAB CULTURE Growth and yield Under monoculture, survival rates of 70-90% have been reported Properly fed crab, reached a carapace length of 70 mm and with of 100 mm within six months Female crabs reared for 45 to 60 days have given on yield of 1000 kg/ha.

CRAB CULTURE:

CRAB CULTURE Poly culture of crab-prawn-fish Milkfish nursery ponds of 2500m 2 with earthen dykes could also be stocked with crab seeds at 1/m 2 and grown to marketable size In brackishwater ponds of 0.5-2ha ponds, S. serrata can be stocked at 2000-5000/ha along with prawns and milkfish, but ponds are to be modified with bamboo fences In polyculture, crabs fed with supplementary diets for a period of 6 months, they attain carapace width of 12 cm and weight of 220g with 50% survival