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This profile was written by Ken Tweddle an active contributor to the site.  



Red Claw Crab

Perisesarma (Sesarma) bidens



    The Red Claw Crab is a forager. They use fine hairs on their legs and claws to taste the sand and will spend a large amount of time scavenging the substrate for food. These crabs like to make small tight fitting caves under rocks and logs and will quickly scurry to safety when threatened. They also spend a few days in their burrows during molting and should not be disturbed during this process. There should be a place above the waterline such as a pile or rocks, wood or other substrate so the crab can climb out of the water. The Red Claw Crab is a good climber and will go exploring outside of your tank if it finds a way out. Run air tubes and power cords through small holes in your hood and keep the aquarium sealed to the best of your abilities.

Quick stats:

    Listed tank sizes are the minimum
    Size: Leg span up to 4" (10 cm)
    Tank: 10 gal minimum
    Strata: Benthic
    PH: 7.5 to 8.5
    Hardness: dKH 8+
    Temperature: 75°F to 80°F (24°-27° C)


    Order: Decapoda
    Suborder: Labroidei
    Family: Sesarmidae
    Genus: Sesarma
    Species: Bidens
Red Claw Crab

Common name:

    Red Claw Crab, Thai Crab

Image gallery:

    Additional species photographs


    Badmans' Forum


    Red Claw Crab


    Mangroves and Mudflats of South China Sea From Hong Kong to Singapore.

General Body Form:
    Flattened shell with protruding eye stalks and Two equal sized claws.

Red Claw Crab
A crab biotope set up
Red Claw Crab
Males in front females in back

    Dull red with brown patterns and bright red claws.

Red Claw Crab

    Best kept in brackish conditions with land access. The addition of Marine Salt in the amount of 2 tbs/gal or a Specific Gravity of 1.005 is sufficient. The use of Marine Grade Salt will help to provide trace minerals needed for proper development. As the crab grows it must shed its exoskeleton. The new shell is soft and the crab will hide for a few days until this hardens. The use of a sand or soil substrate will allow for more natural feeding habits as well as facilitate burrowing. Red Claw Crabs are Omnivorous and enjoy brine shrimp, bloodworms, peas, beans, spinach and raw fish. They will also eat commercial flake foods and crab pellets as well as bits of driftwood and aquarium plants.

    Mangrove swamp or Mud Flats. P.bidens make good companions for Mud Skippers, Knight Gobies Bumblebee Gobies, Indian Glass Fish, Halfbeaks, Mollies, Guppies, Amano and shrimp and other Brackish fish that do not prey on large invertebrates. These types of setups are most easily filtered with canister, or in-tank filtration as Hang On Back types do not work well with lowered water levels. Keep the water well below the rim of the tank and allow for safe perches above the waterline.


    Special breeding requirements will not likely be met in the home aquarium. Larva of The Red Claw Crab live for a time as Plankton in the water column.


Your comments:


Please remember that the following comments are personal experiences and may or may not apply to your setup. Use them as guide to help better understand your fish, like us all individuals will behave differently under different circumstances.


From: Teri
Last week I watched as one of my crabs rubbed thousands of gray specks from her underside against their tree. I thought it looked like some type of eggs. Now I am quite sure as another now has thousands of red specks on her underside. She appears to be eating some...very bizarre to watch!
From: Nina
I purchased two RCCs; a male and female, maybe six months ago or so. About one month ago, my male died, for some unknown reason. He started tipping over and noticed him upside down one night, and then I pushed him back the right way, only to find him dead the next day. ;0( I keep them in an open top tank that is stocked with a few bamboo like plants that grow out of the water. They have only crawled out once, in which I found them on the floor, and just put them back in. They have never tried to come out again. Tank is well planted. I had just noticed that my female crab has eggs all under her pouch. I am not sure if they are fertilized or not because the male had died already. I have noticed she had been hiding for very long periods of time recently. These are great little creatures! I can't believe people keep saying they like to crawl out of the tank because mine never do, and they totally can get out so easily because there is no top. They do sometimes cling on to the edge with their legs, and rest on the top, but they never come out. I guess they remembered what happened the first time they did.
From: Kassie
I recently bought one of these for our aquarium. They are so cute and so adventurous!! So far he has climbed to the top of EVERYTHING in our aquarium.. Things you would think "There's no way" ..He has did it.. Just a few seconds ago he climbed to the top of the aquarium thermometer and sat up there for awhile and then proceeded back down just as easy as he got up. They are Great to watch. I've read a lot about them and a lot says they like to hide in caves.. Hehe mine likes to climb mountains ;)
From: Matt
LISTEN to me very cheerfully! These little love monsters will find any way out the tank thatís conceivably possible! I can't stress enough how clever they are. Cover even the smallest of gaps, otherwise they will be running around outside the tank, and they will die of dehydration within hours of their great escape! They're absolutely brilliant little creatures to watch and enjoy. Feed them all sorts of sea food twice a week and they will be happy. They especially love prawns; they literally smile when they see a big juicy piece of sea food. You can also add peas, sweet corn, and cucumber; just about anything. They do chop your plants up as they love a bit of greenery too. If you bury your plants deep enough they will survive, and continue to grow to give your crabs a healthy balanced diet... The crabs will shed their shells quite often and they love to eat their old shell which provides calcium for their new shell to harden. Donít be surprised if you donít see them for a few days after shedding! They very rarely nip at fish, but will eat slow moving fish if theyíre not feed regularly. They love sitting out of the water for hours on end and my crabs love to watch me losing at poker lol. (Enjoy)...............
From: Tony
I would think carefully before adding these to your tank. I bought 2 of these crabs for my 10 gallon freshwater. They will escape and standard tank setup. They destroyed my plants especially the frill. They are very cool but I wouldn't recommend them unless your tank is set up to accommodate them.
From: Sarah
We bought one of these crabs about 6 months ago and changed our freshwater tank to a brackish one (using Marine salt). Mr. Crabs is very entertaining! We feed him algae tablets which he steals from the mollies in the tank. He loves our alkaline water (from our own well). We change water weekly (25%) and avoid using any products with copper. He has been exposed to Melafix (used to treat our fish) with no apparent ill effects. These crabs can definitely escape, we have found ours in the filter on more than one occasion. Our crab also appreciates the small piece of wood we bought for the tank which sticks out above the water level. He crawls up there to take a dry-land break. He also eats pieces of the wood. We also have two rocks which lie one on top of the other so as to make him a small cave. He spends most of his time in there and uses it to hoard his food away from the other fish. He also hides in here during a molt for protection while his new shell hardens. We have noticed that he will dig out the cave by removing the rocks just before a molt is about to begin, basically creating a protected spot during this critical period. Our crab has molted twice already and seems to be growing, with this getting bolder and braver. Our crab has been a great addition to our tank. Happy crab-days!
From: Melanie Sheppard
My husband got this crab because he saw it had so much personality, it does!! VERY good escape artist!!! He's fun to watch eat and protect his dwelling, he'll wave his claws in the air and run at the fish if they get too close.. Neat to watch!! DEFINITELY seal your tank as best as you can, he WILL get out!!
From: Steve
If you want your crab to live, you need to add iodine and calcium supplement to the water. They love (must be boiled to remove parasites) soil, and appreciate a little hollow tube above water to live in. Mine also have a saltwater dish to soak in. Very intelligent once they lose their fear; They have claw gestures for mating, and will even wave their claws in the air, happy to see you - if you give them a little bloodworm or other treat once in a while that is. I use Kents marine iodine and calcium; 3 drops per four litres. Make sure they have land space as they really are more land crab than water. Keep them separated when they molt. I have had mine for two years so far, but then I give them fresh water, food and boiled soil EVERY day. Too lovable.
From: Carl
Red crabs do add that something extra. I have made a rocky beach for them to climb out onto, they love it, they come up to sun-bathe, dry off, go for a swim and then back sunning themselves. Great to watch very colorful
From: Aaron
What a wonderful addition to my tank. If you want something interesting to watch besides fish this is great. I highly recommend sealing the tank up well, this little guy is like harry houdini. I woke up one day with him in bed with me.




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