Crabs make up 20 percent of all crustaceans caught and farmed worldwide, with about 1.4 million tonnes being consumed annually. The horse crab accounts for one quarter of that total. Other important species include flower, snow, blue, queen, edible, Dungeness and mud crabs, each of which provides more than 20,000 tonnes annually .
The FAO groups fishery catches using the ISSCAAP classification (International Standard Statistical Classification of Aquatic Animals and Plants). ISSCAAP has a group for crabs and sea-spiders, and another group for king crabs and squat-lobsters.
The following table summarises the capture in recent years by commercial fisheries in tonnes.
|Commercial crabs captured in tonnes|
|Crabs, sea spiders||1 061 042||1 101 880||1 093 256||1 122 414||1 334 001||1 332 932||1 323 616|
|King crabs, squat lobsters||77 644||67 932||46 382||41 853||43 993||36 457||52 064|
Horse crabs (Portunus trituberculatus), also known as the gazami crab or Japanese blue crab, is the most widely fished species of crab in the world, with over 300,000 tonnes being caught annually, 98% of it off the coast of China .
Horse crabs are found from Hokkaidō to South India, throughout the Malay Archipelago and as far south as Australia. In the Malay language, it is known as ketam bunga or "flower crab". It lives on shallow sandy or muddy bottoms, less than 50 m deep, where it feeds on seaweeds and predates upon small fish, worms and bivalves. The carapace may reach 15 cm (6 inches) wide, and 7 cm (2¾ in) from front to back.
Flower crabs (Portunus pelagicus), also known as blue crabs, blue swimmer crabs, blue manna crabs or sand crabs, are a large crab found in the intertidal estuaries of the Indian and Pacific Oceans (Asian coasts) and the Middle-Eastern coast of the Mediterranean Sea. The name flower crab is used in east Asian countries while the latter names are used in Australia. The crabs are widely distributed in eastern Africa, Southeast Asia, Japan, Australia and New Zealand.
The species is commercially important throughout the Indo-Pacific where they may be sold as traditional hard shells, or as "soft shelled" crabs, which are considered a delicacy throughout Asia. The species is highly prized as the meat is almost as sweet as the blue crab, although P. pelagicus is physically much larger.
These characteristics, along with their fast growth, ease of larviculture, high fecundity and relatively high tolerance to both nitrate   and ammonia , (particularly NH3-N, which is typically more toxic than NH4+, as it can more easily diffuse across the gill membranes), makes this species ideal for aquaculture.
Snow crab are caught as far north as the Arctic Ocean, from Newfoundland to Greenland in the Atlantic Ocean, and across the Pacific Ocean, including the Sea of Japan, the Bering Sea, the Gulf of Alaska, Norton Sound, and even as far south as California for Chionoecetes bairdi. Fishing for opilio (and rarely bairdi) crab has been the focus of the second half of all four seasons of Deadliest Catch on the Discovery Channel.
The Chesapeake Bay, located in Maryland and Virginia,is famous for its blue crabs, and they are one of the most important economic items harvested from it. In 1993, the combined harvest of the blue crabs was valued at around 100 million U.S. dollars. Over the years the harvests of the blue crab dropped; in 2000, the combined harvest was around 45 million dollars. Late in the twentieth century, the Maryland Department of Natural Resources created stricter guidelines for harvesting blue crabs to help increase populations. These include raising the legal size from 5 to 5¼ inches (from 12.7 to 13.3 cm) and limiting the days and times they may be caught.
While blue crabs remain a popular food in the Chesapeake Bay area, the Bay is not capable of meeting local demand. Crabs are shipped into the region from North Carolina, Louisiana, Florida and Texas to supplement the local harvest.
Edible crabs (Cancer pagurus), also known as Cromer crabs or chancre, is a species of crab found in the North Sea, North Atlantic and the Mediterranean Sea. It is a robust crab of a reddish-brown colour, having an oval carapace with a characteristic "pie crust" edge and black tips to the claws . Mature adults may have a carapace width of up to about 25 cm and weigh up to 3 kg. The edible crab is abundant throughout the northeast Atlantic as far as Norway in the north and northern Africa in the south, on mixed coarse grounds, mud and sand from shallow sublittoral to about 100 m. It is frequently found inhabiting cracks and holes in rocks but occasionally also in open areas. Smaller specimens may be found under rocks in the littoral zone .
Edible crabs are heavily exploited commercially throughout their range. It is illegal to catch crabs of too small a size around the coast of Britain, a conservation measure brought in the 1870s. Crabs with a shell diameter of less than 100 mm should not be taken.
The Dungeness crab inhabits eelgrass beds and water bottoms from the Aleutian Islands in Alaska to Santa Cruz, California . Its binomial name, Cancer magister, simply means "master crab" in Latin.
They measure as much as 25 cm (10 inches) in some areas off the coast of Washington, but typically are under 20 cm (8 inches). They are a popular delicacy, and are the most commercially important crab in the Pacific Northwest, as well as the western states generally .
They are named after Dungeness, Washington , which is located approximately five miles north of Sequim and 15 miles east of Port Angeles. The annual Dungeness Crab and Seafood Festival  is held in Port Angeles each October.
Mud crabs (Scylla serrata), also known (ambiguously) as mangrove crabs or black crabs, are an economically important crab species 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. Generally cooked with their shells on, when they moult their shells, they can be served as a seafood delicacy, one of many types of soft shell crab. They are among the tastiest crab species and have a huge demand in South 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 within the general public.
There has been a huge interest in the aquaculutre of this species due to their high demand/price, high flesh content and rapid growth rates in captivity. In addition they have a high tolerance to both nitrate  and ammonia (particularly NH3) tolerance (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 larvae survival.
King crabs are not true crabs and squat lobsters are not lobsters. Both may be more closely related to hermit crabs, which are also not true crabs. However, they have been included in this article because the common perception is that king crabs are crabs, and because squat lobsters are more closely related to crabs than lobsters and the FAO classifies them together with king crabs.
In Alaska, three species of king crab are caught commercially
Most prized is the red king crab.
Squat lobsters are not lobsters, but are related to porcelain crabs, hermit crabs and, more distantly, to true crabs. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents. There are currently 870 described species. Squat lobsters are much smaller than commercially-harvested true lobsters. They are often sold commercially as "langostino lobster," and are sometimes called "lobster" when included in seafood dishes, which irritates the Maine lobster industry.
Species with commercial significance include Cervimunida johnii, Pleuroncodes monodon and Pleuroncodes planipes.