Scylla serrata is an ecologically important species of crab found in the estuaries and mangroves of Africa, Australasia and Asia. In their most common form, the shell colour varies from a deep, mottled green to very dark brown.
Distribution
The natural range of Scylla serrata is in the Indo-Pacific. It is found from South Africa, around the coast of the Indian Ocean to the Southeast Asian Archipelago, as well as from southern Japan to south-eastern Australia, northern New Zealand, and as far east as Fiji and Samoa. The species has also been introduced to Hawaii and Florida. In Hawai'i, mud crabs are colloquially known as Samoan crabs as they were originally imported from American Samoa. As these crabs are known for their robust size and dense meat content, they have been greatly sought after over the years. As a result of over-crabbing, local government efforts have restricted harvesting of crabs smaller than 6 inches and it is illegal to harvest females of any size.
Ecology
A study on tidal flats in Deception Bay in Queensland found juvenile crabs were resident in the mangrove zone, remaining there during low tide, while subadults migrated into the intertidal zone to feed at high tide and retreated to subtidal waters at low tide. Adults were caught mainly below the low tide mark, with small numbers captured in the intertidal zone at high tide. These crabs are highly cannibalistic in nature; when crabs undergo molting, other hard-shelled ones sometimes attack the molting crabs and devour them. The females can give birth to a million offspring which can grow up to in size and have a shell width of up to wide.
Aquaculture and consumption
Interest in the aquaculture of this species has been high due to the high demand/price for them, high flesh content, and rapidgrowth rates in captivity. In addition, they have a high tolerance to both nitrate and ammonia, which is beneficial because ammonia-N is often the most limiting factor on closed aquaculture systems. Their high ammonia-N tolerance may be attributed to various unique physiological responses which may have arisen due to their habitat preferences. However, their aquaculture has been limited due to the often low and unpredictable larval survival. This may be due to inadequate nutrition, disease, "moult death syndrome", inadequate protocols, or a combination of all. S. Serrata can be kept easily in home aquaria when smaller but will outgrow small setups. They are very active and will eat almost any conventional sinking pellets; they also consume some small fish pieces and vegetable matter. They are tolerant of most water conditions and are generally a very hardy and entertaining species. Generally cooked with their shells on, when they molt their shells, they can be served as one of many types of soft-shell crab. Mud crabs can be killed by placing them in a freezer for up to two hours before cooking.
