The study was carried out to determine the reproductive biology of the mud crab Scylla tranquebarica to provide baseline information that are useful in the seed production activities. Size at first maturation was observed in male crabs with 11 cm carapace width (CW) and in female crabs with 10 cm CW. The highest GSI values in male crabs (6.17) and females (5.12) were observed in October. The maximum number of eggs produced by females was up to 5 million. The egg diameter ranged from 0.69 to 0.76 mm at the heartbeat stage. Embryonic development was classified into five major stages: blastula, gastrula, nauplius pigmentation and heartbeat. The color of newly spawned eggs was orange. As the embryo developed, the color changed from orange to brown and finally to black prior to hatching. The incubation period was 11-13 days and the hatching success was 80%. The temperature and salinity during the incubation period ranged from 27 to 30°C and 30 to 35 ppt, respectively.

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 is an economically important crustacean commodity in Thailand due to its high nutritional and market value. All the four species of mud crab, Scylla paramamosain, S. olivacea, S. serrata and S. tranquebarica are found in Thailand. The production areas are along the coasts of Gulf of Thailand where S. paramamosain or white mud crab is abundant, and Andaman Sea where S. olivacea or black mud crab is dominant. Data from the Thai Department of Fisheries estimated that the total mud crab production in 2010 was 2,130 mt valued at Baht 322.7 million (US$10.84 million). In the last decade, the production from coastal aquaculture was 6,921 mt valued at Bath 491.4 million (US$16.51 million). The probable cause of the decrease in production is the over exploitation of the wild population. Mud crab culture systems commonly practiced are grow-out (culture from juveniles to market size crabs in ponds), fattening of lean crabs and production of soft-shell crabs. In the past, seedstocks for grow-out culture were collected from the wild. Recently, both wild and hatchery-reared seedstocks are being utilized for farming. Mud crabs for fattening and production of soft-shell rely mainly on wild resources. All culture practices are considered extensive or semiintensive except for soft-shell crab farming which is intensive. The current research and development activities include broodstock and seed production techniques, and formulated feed production. Further technical and financial support are required to improve the survival and production of mud crab. Likewise, support for the transfer of technology to farmers is needed. The lack of seed supply is a major issue facing the mud crab industry in Thailand. A few mud crab hatcheries, which belong to the government, have been established. It is becoming difficult to collect ovigerous females from the wild. Hence, most females are obtained from ponds. Collection of ovigerous females in the wild is prohibited from October to December. Restocking of mud crabs in the natural habitat has become a routine activity to increase the resources.