Mud crabs, Scylla spp., also known as mangrove crabs, occur naturally in association with mangrove swamps and nearby intertidal and subtidal muddy habitats. Mud crabs can exceed 3kg in body weight, yielding high volumes of delicate flavoured meat and are accordingly sought after as a quality food item. Easily caught with simple traps or nets, they remain alive for considerable periods after capture and they are highly valued as an important income source for small-scale fishers throughout the Asia-Pacific region.
Scylla spp. seem to adapt to an aquaculture regime reasonably well, and they have been cultured in China for at least 100 years, and throughout the rest of the region for decades. In Japan, sea-ranching of hatchery reared mud crab seed has been employed but seed production has not proved reliable. Almost all crab aquaculture production relies on wild-caught stock, as larval rearing has not yet reached a commercially viable level for stocking into aquaculture farms. Megumi Minagawa, Takeshi Hayashibara, Motohiko Sano, Motoya Tamaki, Kouki Fukuoka, and Katsuyuki Hamasaki, from the Seikai National Fisheries Research Institute, have published a brief report (in English) entitled Habitat characters of juvenile mud crab, Scylla serrata.
In Australia, Clive P. Keenan, from the Bribie Island Aquaculture Research Center, has published a report entitled Aquaculture of the Mud Crab, Genus Scylla – Past, Present and Future. From the abstract:
Crabs of the genus Scylla are strongly associated with mangrove areas throughout the Pacific and Indian oceans and form the basis of substantial fishery and aquaculture operations. Aquaculture production currently relies on wild-caught seed for stocking ponds, as larval rearing at a commercial scale is still difficult. One of the major problems for effective mud crab management and aquaculture is the likelihood that there are a number of genetically distinct species. Research has demonstrated the presence of at least four distinct species. Laboratory experiments of the larval stages of each species should provide valuable information on each species’ biological and ecological requirements. There are two basic forms of land-based mud crab aquaculture: fattening of crabs with a low flesh content, and grow-out of juveniles to market size. Fattening is a very profitable activity, employing high densities of crabs and low costs. However, total production is low because of mortalities due to cannibalism. Grow-out systems for mud crabs show much more variety and production can be very high. Grow-out systems are usually pond-based, with or without mangroves, although intertidal pens can also be used. Without mangroves, lower stocking rates provide the best return. In shallow mangrove ponds, there are two distinct forms of aquaculture: (i) intensive, with higher stocking rates and supplemental feeding; and (ii) extensive, in large mangrove silviculture ponds where the stocking rate is very low, and no supplemental feeding is involved. Growth rates under all systems are comparable, with production of commercial-sized crabs three to four months after stocking with seed crabs. Further research is required into the habitat preferences of each species so that production techniques can be modified to suit their respective requirements. With advances in the hatchery production of mud crab juveniles for stocking into ponds and enclosures, the future of mud crab aquaculture looks promising.