Soft-shell crab production is being practiced in many Asian countries but the major source of seedstock is from the wild, which could no longer sustain the increasing demand. Commercial scale soft-shell crab production can become sustainable only if there is a continuous supply of seedstock not dependent on wild stock. Rajiv Gandhi Centre for Aquaculture (RGCA) under the Marine Products Export Development Authority (MPEDA) has established a pilot-scale mud crab hatchery at Thoduvai, Nagapattinam District, Tamilnadu in 2004 with the technical assistance from SEAFDEC/AQD. At present, RGCA has the biggest mud crab hatchery in India and a demonstration farm at Karaikal, U.T. of Puducherry, where nursery rearing, grow-out and soft-shell crab production are conducted using hatchery- produced mangrove crabs or mud crabs, Scylla serrata. This paper presents the results of the soft-shell crab production using hatcheryproduced S. serrata juveniles maintained in perforated low density polyethylene (LDPE) boxes. The duration of the molt interval, time of molt (day or night) and the increase in body weight and carapace width of each size group (40-60, 61-80, 81-100, 101-120, 121-140, 141-160, 161-180 g) after molting were determined. Results showed that the percentage increase in body weight and carapace width increased as the crabs grew bigger. Likewise, the molt interval was longer in bigger-sized groups of crabs. Sixty to seventy percent of the population molted during night time and the next molt occurred within 25 days in 80-160 g size groups. Soft-shell crabs in boxes within the water surface and juvenile crabs (2.5 cm CW initial size) for culture until market size in the pond can be a viable technology technology for mud crab growers.

Mud crab is an economically important portunid crab species found in estuaries, coastal lagoons and nearshore waters of India. The genetics team of RGCA recently made an attempt to decipher the taxonomic ambiguity of mud crab species commonly available in Indian coastal waters using multiple molecular genetic markers and concluded that only two species of mud crabs, Scylla serrata and S. olivacea are commonly available in India. India has about 8,103 km of coastline with shallow coastal waters, brackishwater lakes, estuaries and intertidal swampy areas along the east and west coasts. It has been estimated that the potential resources of crabs particularly from the 7,770 km² of estuaries and backwaters is 13,209 tonnes out of the total potential resources of 43,816 tonnes from Indian coastal waters. The southern part of the coast is potentially richer than the northern part. Estimated brackish water area in India is about 1,190,900 ha, out of which 167,193 ha developed for shrimp farming may become suitable for crab farming as evidently seen in Tuticorin, Tamil Nadu. Estimated mud crab culture area in Andhra Pradesh is more than 2,833 ha covering nearly 50 villages. Live mud crab export from India was higher in 2011-2012 (3,054 mt) compared to 2010-2011 (2,963 mt). Frozen and other forms of crab export declined in 2011-2012 (2,848 mt) compared to 2010- 2011 (3,251 mt). Apart from shrimp culture, mud crab farming, fattening and soft-shell crab production are now emerging as feasible business ventures in India. About 11 types of crab products are being exported from India with an average unit value realization of US$ 3.73 kg⁻¹, highlighting its importance in the foreign exchange earnings. There has been a noticeable decline in the mud crab populations in the natural habitat throughout Indian coastal waters due to over exploitation and indiscriminate fishing of juvenile crabs by artisanal fishermen. Wild seeds are collected throughout the year in backwater zones of Sundarbans, Kakdwip and Namkhana of West Bengal; Chilika Lake of Odisha; coastal waters of Kakinada, Visakhapatnam and Rajahmundry of Andhra Pradesh; Pulicat Lake, Killai backwaters, Muthupet saline swamps, Punnakayal estuarine complex and Colachel coastal waters of Tamil Nadu; Neendakara, Cochin and Kozhikode backwaters of Kerala to meet the demand of culture operations. There is an urgent need to produce good quality hatchery seed to meet the demand of farmers. To address this, the Rajiv Gandhi Centre for Aquaculture (RGCA) established a state-ofthe- art mud crab hatchery for commercial scale production of seedstock to promote the adoption of the technology by the private entrepreneurs in the country.

Mud crab farming has long been established in the Philippines. Scylla serrata, S. tranquebarica and S. olivacea are the common species found in the Philippines. S. serrata is the preferred species for farming by crab growers. The total production of mud crab from aquaculture was estimated at 13,720 valued at US$77,025,000 and 14,437 tons valued at US$86,511,000 in 2009 and 2010, respectively. The sources of crab seeds for farming are from the wild and in recent years, from the hatchery although in small percentage. The overexploitation of mud crabs and habitat losses have resulted in both reduced landings and mean capture size. To stem the wild harvest, the provincial and municipal government along with the Bureau of Fisheries and Aquatic Resources have introduced ordinances that prohibit the gathering and selling of crablets (≤ 3 cm) outside the municipality of origin. This resulted to increased acceptability of hatchery-reared crabs by crab growers. Basic technologies in all phases of culture (hatchery, nursery and grow-out) have been developed. However, there are still several issues that need to be addressed. In the hatchery phase, one of the major causes of low survival are the Molt Death Syndrome in which zoea 5 has difficulty molting to megalopa and diseases due to bacterial and fungal infection in eggs and larvae. The use of antibiotics as treatment for Vibrio spp. has proven to improve larval survival. However, the use of antibiotics can lead to the development of resistant strains of bacteria and abnormalities that become apparent at the juvenile stage. In the nursery phase, economic losses have been attributed to cannibalism. Providing sufficient food and shelters, reducing stocking density, size grading and removal or trimming of claws are the common strategies used to mitigate the high level of cannibalism. Recent findings showed that incorporating tryptophan in the diet can reduce the aggressive behavior of crabs. In the grow-out phase, culture of juvenile crabs to market size with one or two more commodities in earthen brackishwater ponds is the most prevalent practice. Due to the cannibalistic nature of mud crab, polyculture (usually with milkfish and shrimp) pond is carried out. Stocking density of each commodity varies with the size and the number of seed stock available and the abundance of natural food growth in the pond. Culture period ranges from 4-5 months. Monoculture of crabs is usually done for short term culture as in fattening in various systems. Mud crab culture is also integrated with the existing mangroves. Formulated diets have been verified in commercial grow-out ponds and showed promising results. Mud crabs are commonly fed with low value fish, molluscs and other unprocessed natural foods. Mortality in mud crabs in grow-out phase is oftentimes due to the white spot syndrome virus. The domestication of S. serrata has been done at SEAFDEC/AQD. The duration from spawning of the base population to F1 broodstock size was 10-14 months and from F1 to F2 was 11-12 months. Selective breeding of S. serrata is currently being done. The results serve as guide to understand and eliminate the obstacles to broodstock management and seed production. Recently, The Department of Science and Technology has funded the National Mud Crab Science and Technology Program being implemented by SEAFDEC/AQD and University of the Philippines Visayas to refine the existing technologies in all phases of culture and to aggressively promote the establishment of several mud crab hatcheries and nurseries in the Philippines. The Bureau of Fisheries and Aquatic Resources is also implementing the Philippine National Aquasilviculture Program, which includes the rehabilitation of mangrove forests and culture of commercially important aquatic animals including mud crab in established mangrove areas. On-site training on all phases of culture of mud crab has also been done by SEAFDEC/AQD not only in the Philippines but also in other countries like Brunei, Myanmar, India and Timor Leste. With the establishment of several hatcheries and nurseries, there will be sufficient seed stock supply for farming, thereby decreasing the dependence on wild stock.