European Green Crab

The European Green crab is a common littoral crab. It is also known by many different names in different parts of the world. It’s common names include the Shore crab, Green Shore crab, Green crab, European Shore crab etc. It is actually a widespread invasive species, and listed among the 100 ‘world’s worst alien invasive species’.

The European Green crab is actually native to the north-east Atlantic Ocean and Baltic Sea. But it has colonized similar habitats in Australia, South Africa, South America and both Atlantic and Pacific coasts of North America. Read some more information about this crab species below.

Characteristics
The carapace of the European Green crab has five short teeth along the rim behind each eye, and three undulations between the eyes. The undulations, which protrude beyond the eyes, are the simplest means of distinguishing C. maenas from the closely related C. aestuarii, which can also be an invasive species.

The color of the European Green crab varies greatly from green to brown, grey or red. This color variation has a genetic component, but is largely due to local environmental factors. On average the juvenile crabs display greater patterning than adults. Generally the crabs which delay molting become red-colored rather than green. The red crabs are stronger and more aggressive, but are less tolerant of environmental stresses (such as low salinity or hypoxia).







On average, the carapace of the European Green crab is up to 60 mm long and around 90 mm wide. But some crabs can reach around 10.1 cm wide outside their native range in British Columbia. Photo and info from Wikipedia.
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Diet
The European Green crabs are mainly feed on a variety of molluscs, worms and small crustaceans.

Breeding
The European Green crabs generally mate between spring and fall, though timing varies. Generally a male crab mate with a smaller female by holding her underneath him and carrying her around until she molts. And after the molting the female crab turns over and they mate. The female crab extrudes the eggs in a mass that she carries under her abdomen. On an average under favorable conditions, a large female crab can spawn up to 0.2 million eggs at a time.

Uses
The European Green crab is used for food. It is also commercially harvested and used for bait in Europe and sometimes in the eastern United States.

Special Notes
The European Green crab is fished on small scale in the north-east Atlantic Ocean, with approximately 1200 tonnes being caught annually. Countries with largest catches are France and the United Kingdom.







The European Green crabs can live in all types of protected and semi-protected marine and estuarine habitats (including habitats with mud, sand or rock substrates, emergent marsh and submerged aquatic vegetation. They prefer soft bottoms for living.

European Green crab are used for food and popular in some countries. But it is potentially impacting a number of fisheries. Its successful dispersion has occurred via a variety of mechanisms, such as on ships’ hulls, sea planes, packing materials, and bivalves moved for aquaculture. However, review full breed profile of the European Green crab in the table below.

European Green Crab | Breed Profile

Name European Green Crab
Kingdom Animalia
Phylum Arthropoda
Class Malacostraca
Order Decapoda
Family Portunidae
Genus Carcinus
Species C. maenas
Binomial Name Carcinus maenas
Other Names Also known as Shore crab, Green Shore crab, Gren crab, European Shore crab etc.
Breed Purpose Food
Special Notes Fished in small scale in the northeast Atlantic Ocean, can live in all types of protected and semi-protected marine and estuarine habitats, prefer soft bottoms for living, used for food
Breeding Method Natural
Climate Tolerance Native climate
Body Color Varies greatly from green to brown, grey or red
Rarity Common
Availability Europe

Chinese Mitten Crab

The Chinese mitten crab is a medium-sized burrowing crab that is named for it’s furry claws, which resemble mittens. It is also known as the Shanghai hairy crab, and it is native to rivers, estuaries and other coastal habitats of eastern Asia from Korea in the north to the Fujian province of China in the south. It has also been introduced to Europe and North America. And it is considered an invasive species there.

The Chinese mitten crabs can be found in both freshwater and saltwater. They are walking crabs, and they can emerge from the water to move upstream of barriers and are capable of moving several hundred miles upstream from saltwater. However, read some more information about the Chinese mitten crab below.

Characteristics
The Chinese mitten crab is a medium-sized crab, and it’s body is the size of a human palm. It’s most distinguishing features are the dense patches of dark setae on it’s claws. The carapace is 3-10 cm wide, and the legs are about twice as long as the carapace is wide. These crabs have 8 sharp pointed walking legs (4 on each side), and they have no swimming legs. They are brownish-orange to greenish-brown in color. Average live body weight of the mature Chinese mitten crab is around or up to 45 grams. Photo and info from Wikipedia.
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Feeding
Chinese mitten crabs are omnivorous and opportunistic. Generally they consume a wide variety of plant and animal material. Their food include algae, macrophytes, terrestrially derived detritus, invertebrates, fish carcasses and also steal a wide rage of bait from fishermen.

Breeding
The Chinese mitten crab spend most of it’s life in freshwater, and return to sea for breeding. In late August, the mature crabs begin migrating downstream to sea (away from their feeding grounds). These crabs reach puberty and develop their reproductive organs during this migration. They begin to breed in the brakish water in late fall. The male crabs arrive first and stay in the brackish water all winter, and the females arrive later. After successful mating, the females lay eggs within 24 hours.







Uses
The Chinese mitten crab is mainly used for food. It is an autumn delicacy in Shanghai cuisine and eastern China. It is prized for the female crab roe.

Special Notes
The Chinese mitten crab has been spread rapidly from Asia to North America and Europe (raising concerns that it competes with local species). And burrowing nature of these crabs damages embankments and clogs drainage systems. Management efforts have shown to be very difficult. This is due to its abundance, high reproductive rate, and high physiological tolerance. However, review full breed profile of the Chinese mitten crab in the chart below.

Chinese Mitten Crab | Breed Profile

Name Chinese Mitten Crab
Kingdom Animalia
Phylum Arthropoda
Class Malacostraca
Order Decapoda
Family Varunidae
Genus Eriocheir
Species E. sinensis
Binomial Name Eriocheir sinensis
Other Names Also known as the Shanghai hairy crab
Breed Purpose Mainly food
Special Notes Mainly used for food, an autumn delicacy in Shanghai cuisine and eastern China, prized for the female crab roe, it has been spread rapidly from Asia to North America and Europe, high reproductive rate
Breeding Method Natural
Weight Around 45 grams
Body Color Brownish-orange to greenish-brown
Rarity Common
Availability Native area (worldwide)

Gazami Crab

The Gazami Crab is the most widely fished species of crab in the world. It is also known by some other names such as Japanese Blue Crab, Horse Crab and the binomial name is Portunus trituberculatus. It is mainly found off the coasts of East Asia (Japan, Korea, China and Taiwan). It was first described by Edward J. Miers in the year of 1876, under the name Neptunus trituberculatus. Read some more information about this crab below.

Characteristics
Carapace of the Gazami Crab is rough to granulose with regions discernible. Generally the carapace is of dull green to brown color. This crab is closely related to the Portunus pelagicus. But it may be distinguished from the Portunus pelagicus by the number of broad teeth on the front of the carapace.
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On an average the carapace may reach about 15 cm wide, and around 7 cm form front to back. Photo and info from Wikipedia.

Uses
The Gazami Crab is mainly used for food.







Special Notes
The Gazami Crab is the world’s most heavily fished crab species, with more than 300,000 tonnes being caught annually. And most of the catches (around 98 percent) are from off the coast of China. It is mainly caught by trawling. It is also a very important commercial crab species in Japan. It is common edible crab in Japan, and it is collected in large numbers in some areas. The Gazami Crab generally inhabit in sandy and sand-muddydepths in shallow waters to 50 m depth. However, review full breed profile of this crab species below.

Gazami Crab | Breed Profile

Name Gazami
Kingdom Animalia
Phylum Arthropoda
Class Malacostraca
Order Decapoda
Family Portunidae
Genus Portunus
Species P. trituberculatus
Binomial Name Portunus trituberculatus
Other Names Also known as Japanese Blue Crab, Horse Crab
Breed Purpose Mainly food
Special Notes The world’s most heavily fished crab species with more than 300,000 tonnes being caught annually, most of the catches are from China, mainly caught by trawling, also an important commercial crab species in Japan, used mainly for food
Breeding Method Natural
Climate Tolerance Native climates
Body Color Dull green to brown
Rarity Common
Availability East Asia

Mud Crab Farming

Mud crab farming is very popular in some Asian countries like Bangladesh, India, Thailand, Philippine etc. Mud crab has huge demand and price in international market. Crab is very tasty and many countries of the world import huge amount of crabs for consumption every year. As a result, there are huge possibilities of earning foreign currencies by exporting crabs.

The main benefits of crab farming are, labor cost is very low, production cost is comparatively lower and they grow very fast. Commercial crab farming business is developing the lifestyle of the people of coastal areas. By proper care and management we can earn more from crab farming business than shrimp farming. And small scale crab farming is gaining popularity day by day. Mud crab farming systems in coastal areas are described below.

Types of Mud Crabs
Mud crab can be found on estuaries, backwaters and coastal ares. They are member of Scylla genus. There are two species of crabs available that are suitable for commercial production. Two species of crabs are red claw and green mud crab.

Green Mud Crab

Green mud crabs are larger in size.
A green mud crab can grow to a maximum size of 22 centimeter carapace width. And it can weights about 2 kg.
These are free living and distinguished by the polygonal markings present on all appendages.
Red Claw

Generally red claws are smaller in size than green mud crab.
A red claw can grow to a maximum size of 12.7 centimeter carapace width. And it can weights about 1.2 kg.
It has a burrowing habit and there are no polygonal markings on it.






Both species are suitable for commercial crab farming business. And both have good value and huge demand in the foreign market.
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Mud Crab Farming Methods
You can raise mud crabs in two systems. Grow out farming and fattening systems. The systems of farming in this two methods are shortly described below.

Grow Out System
In grow out farming system, young crabs are raised and grown for a certain period of 5 to 6 months till they reach marketing size and weight. This type of crab farming system is generally pond based. The pond size depends on the production type. Generally ponds for crab farming sized between 0.5 to 2 hectors. Proper bunds and tidal water exchange is a must. Small sized ponds are very suitable for crab farming. Because they are easily maintained. Make a suitable fence if the size of pond become small. In larger sized ponds where natural conditions are prevailing, strengthening is necessary along the outlet area. You can stock wild collected juvenile crabs that weights around 10 to 100 grams. Depending on the size of crabs and available facilities the duration of production may varies between 3 to 6 months. In commercial production with supplementary feeding you can stock 1-3 crabs per square meter. You can feed your crabs low cost fish, shrimps, small sized crabs etc. You can visit your nearest local market and collect rotted fish and innards of birds and animals from slaughter house. Provide the crabs 5% feed daily of their total body weight. For example, if there are 100 kg crabs in the pond then feed 5 kg food daily. Collect some crabs and try to determine an average weight. Regular sampling is very necessary for monitoring the growth and general health, and to adjust the feeding rate. Keep some pipes in the pond for shelter and the purpose of reducing mutual attacks and cannibalism. Within 3 to 5 months they will reach marketing weight and become suitable for selling.







Fattening System
Raising soft shelled crabs for a certain period until their exoskeleton gets hardened is known as crab fattening system. Hard shelled crabs has four to five times more value in the market than soft shelled crabs. Farming crabs in this system take less time and the process is very profitable. You can do crab fattening business in two systems that are described below.

Fattening in Pond: Fattening can be done in any types of ponds between 0.025 to 0.2 hector size. Small tidal ponds with a depth of 1 to 1.5 meter is very suitable for crab farming. Prepare the pond perfectly before stocking crabs in the pond. Pond preparation can be done by draining the pond water, sun-drying and adding sufficient quantity of lime. Make a fence around the pond for fattening purpose. Because the crabs have a tendency to escape by making hole and digging the soil. Reinforce the inlet areas with bamboo matting inside the bund. For stocking, collect soft crabs from local fisherman or crab merchants. Collect the crabs in morning. 1-2 per squire meter stocking density is ideal for crab fattening purpose. Divide the pond into different compartments according to the size of crabs if it is big sized. Keeping male and female crabs separated from each other will make good results and reduce mutual attacks and cannibalism. Depending on your location and crabs availability 8 to 12 fattening cycles can be done in a year. Generally, crabs weight between 300 grams to 500 grams have high demand and value in the market. Collect and sell all the crabs when they reach the marketing weight. Always try to sell the crabs when they are in hard shelled condition. This will ensure high profit form crab farming business.
Fattening in Pens or Cages: Crab fattening can also be done in pens, floating net cages, bamboo cages in shallow estuarine waterways and inside large shrimp ponds with good tidal water influx and in tanks. You can use bamboo splits, netlon or HDPE as netting material. 3 m * 2 m *1 m (3 m long, 2 m wide and 1 m height) is ideal cage size for crab fattening. Arrange the cages in a row so that you can easily feed and monitor the crabs. Stocking density of 10 crabs per squire meter in cage and 5 crabs per squire meter in pens is ideal. Maximum stocking density can result mutual attacks and cannibalism. Fattening in cages or pens in only used in small sale production. For commercial production fattening in ponds is perfect and more profitable.
Between these two crab farming methods, fattening system is more profitable than grow out system and has many advantages. Grow out crab farming system takes more time than fattening system. But fattening system is very popular to the farmer as it take less time and highly profitable.

Water Quality
Water quality plays an important role in the production of crabs. Change water occasionally if possible or apply proper medicines or chemicals. See the following chart.
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Feeding
For commercial purpose, crabs need 5-8% food of their body weight. You can feed your crabs low cost trash fish, chicken waste, animal innards collected form slaughter house, brackish water clams etc. Don’t served all the feed at once. Instead give it twice a day. Give major part of the total feeds during evening hours.







Marketing
After a certain period check the crabs for their hardening. In grow out crab farming system they become suitable for marketing purpose within their 3 to 6 months of age. And in fattening system the time depends on crab’s size. However, collect the crabs when they reach proper weight and when their price remain high. Collect the crabs in the early morning hours or evening hours. You can collect crabs from pond by using scoop net or by using alluring bait. Wash the collected crabs with good brackish water and remove all types of dirt and mud. And then carefully tie the crabs very carefully without breaking its legs. Then try to keep those crabs in moist conditions. Keep them away from sunlight. Because direct sunlight has a negative effect on their survival. After that send them to the market.

Commercial crab farming business is gaining popularity day by day in many coastal areas around the world. Because it is a very easy, profitable and takes less time. Mud crabs have huge demand and high value in international market. So, you can earn some extra money and make an employment opportunity by doing commercial crab farming business. Have a good day!