MUD CRAB

Scylla serrata (often called mud crab or mangrove crab, although both terms are highly ambiguous, as well as black crab) is an economically important species of crab found in the estuaries and mangroves of Africa, Australia 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 Oceanto the Malay Archipelago, as well as from southern Japan to south-eastern Australia, and as far east as Fiji and Samoa.The species has also been introduced to Hawaii and Florida.

Ecology

A study on tidal flats in Deception Bay in Queensland found juvenile crabs (20–99 mm or 0.8–3.9 in carapace width) were resident in the mangrove zone, remaining there during low tide, while subadults (100–149 mm or 3.9–5.9 in) migrated into the intertidal zone to feed at high tide and retreated to subtidal waters at low tide. Adults (150 mm or 5.9 in and larger) 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 moulting, other hard-shelled ones sometimes attack the moulting crabs and devour them. The females can give birth to a million offspring which can grow up to 3.5 kg (7.7 lb) in size and have a shell width of up to 24 cm (9.4 in) wide.

Aquaculture and consumption

Scylla serrata from Karwar, India.

Interest in the aquaculture of this species has been high due to the high demand/price for them, high flesh content, and rapid growth rates in captivity. In addition, they have a high tolerance to both nitrate and ammonia (twice that of the similar sized Portunus pelagicus), 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" (due to their highly cannibalistic behaviour during the megalopa stage), inadequate protocols (e.g. suboptimal environmental conditions), 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 moult their shells, they can be served as one of many types of soft shell crab. Some consider them to be among the tastiest of crab species, and demand for them is large in South and Southeast Asian countries, where they are often bought alive in the markets. In the northern states of Australia and especially Queensland, mud crabs are relatively common and generally prized above other seafood by the general public.

Mud crabs can be killed by placing them in a freezer for up to two hours before cooking.

The mud crab is one of the best shellfish you could wish for. Its moist meat, mostly found in the body and claws, has a marvellous distinct and sweet flavour.

The mud crab is one of the best seafoods for presentation, with graceful legs and ornate claws that can be kept whole and used as a garnish. A crab claw protruding from a bowl of hearty mud crab bisque can be very appealing to the eye.

One of the best cooking methods is to steam, boil or poach mud crabs in salted water (25 g of salt per litre), then season with lemon, black pepper, garlic and onion. The crab can be finished off for the final dish by a variety of methods including barbecuing or pan-frying. Be careful not to overcook the crab in the initial stages, when adding a little vinegar will make the meat easier to remove.

Mud crab is delicious in soups and bisques, or as a filling for seafood tortellini. In a salad, dress with light vinaigrettes using flavoured oils such as walnut, and cascade the flesh over a mound of curly endive with a selection of citrus fruits. Mud crab can also be served whole on a platter, often feeding a number of people.

Never put live crabs directly into boiling water or the meat will toughen and the legs or claws may fall off. Kill them before cooking (refer to p. 235 of the Preparation chapter for recommended killing methods).

Taste

Flavour	Oiliness	Moisture
Medium to Strong	Low	Moist

Wines

The accompanying wine should not overpower the sweetness of the flavour of the mud crab, although there is a strength of flavour that would be complemented by some of the unwooded, dry white styles. Suitable examples include Semillons from New South Wales, or Chardonnay from Western Australia. The pronounced flavour of mud crab bisque allows for more robust flavours in the wine, such as those of wooded Chardonnay s.

Nutrition Information (average quantity per 100g)

Energy	372* (89* Calories)	Fat (total)	0.7 g	Alpha‐linolenic acid	15 mg
Protein	18.0* g	Saturated fat	31% of total fat	Docosahexaenoic acid	58 mg
Cholesterol	45 mg	Monounsaturated fat	31% of total fat	Eicosapentaenoic acid	22 mg
Sodium	355* mg	Polyunsaturated fat	38% of total fat