Red Claw Crab Complete Caresheet




Red Claw Crab Caresheet

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If you’re looking for an interesting, quirky pet and you fancy a change from keeping tropical fish, you might consider the Red Claw crab. 

These attractive little creatures are often kept in freshwater community tanks. However, the crabs’ natural habitat is brackish bodies of water. These aquatic animals don’t play well with others and are best-suited to a single species paludarium.

Keep reading to learn everything you need to know about keeping Red Claw crabs and setting up a suitable home for them. 

Red Claw Crab Fact Sheet

Red Claw Crab Background and Natural Habitat

The Red Claw Crab is also known as the Red-Clawed crab and the Mini crab. Sometimes, the creatures are also referred to as Sesarma bidens or (pseudo) Sesarma moeshi.

The little crustacean’s scientific name is Perisesarma bidens

Red claw crabs are naturally found in mangrove swamps in Asia. In these estuaries, rivers flow into the sea, creating a mix of fresh and saltwater. The water is relatively shallow, temperatures are tropical, and the ground is usually covered with fine sand.

All this provides you with some excellent guidelines for creating the perfect environment in a red claw crab paludarium.

What Do Red Claw Crabs Look Like?

These beautiful little crabs are smaller than other aquarium crab species, and grow to measure just 4 inches, including their leg span. The actual carapace of the creature is much smaller than that, measuring just 2 to 2.5 inches wide.

The crab’s body and head are shades of dark brown camouflaged with spots. On the corners of the head are two bulging eyes set on antennae. The crab has ten legs, eight of which are used for walking around on the substrate and for climbing. The other two legs end in large, bright red claws tipped with yellow or orange. 

Although all Red Claw crabs have the same basic coloration, each individual is slightly different in the intensity of color and shade.

Boys Or Girls?

Male and female crabs look slightly different. It’s imperative to tell the difference between them, as you don’t want to have more than one male crab in your tank. These critters are aggressive, and males will not tolerate each other, often fighting to the death.

Males typically have larger claws and have more vivid coloration. On the underside of the crab is a small flap. In males, the flap is pointed, whereas with females, it’s rounder and broader, and they have darker claws.

What’s The Lifespan Of Red Claw Crabs?

You can expect your crabs to live for between two and two and a half years with proper care and a high-quality diet.

Although Red Claw crabs can survive in a purely freshwater tank environment, they won’t thrive, and they certainly won’t live for very long. So, you need to set up brackish water conditions or paludarium for these creatures.

Red Claw Crab Care Guide

In this section of our guide, we explain how to care for Red Claw crabs.

Tank Size

If you plan on keeping Red Claw crabs, you should house them in an aquarium tank of at least 10 gallons. Although these crabs are pretty small, they can be very territorial and aggressive, so the more space they have, the better.

A 10-gallon tank is large enough to house a single male crab and two females. If you want to keep more, then you need a larger tank. An overcrowded tank does not make for happy crabs.

However, ideally, these semi-aquatic crabs should be kept in a paludarium. A paludarium basically features underwater and dry land environments, which is a perfect tank setup for the semi-aquatic Red Claw crabs. Your paludarium should measure around 24 inches wide.

Make sure that your tank has a tightly fitting lid, and be sure to plug any gaps, as these active critters are accomplished escape artists. The crabs mustn’t get out of the tank, as they need access to water to survive, and they will die if they become dehydrated.

If you have an internal filtration system, you’ll need to cover the intake and outflow, as the crabs will surely find their way inside if you don’t!


Just like fish, crabs need a tank that has an efficient filtration system that’s adequate for the tank size and water volume.

A marine-specific filtration system is the best choice, as that will cycle the water without impacting the salinity level too much. To keep things on an even keel, carry out a 10% water change every week. 

Water Parameters

The most important aspect of Red Claw crab husbandry is providing the correct water parameters that closely replicate what the crabs are accustomed to in nature.

Wild crabs live in the shallow, tropical, brackish waters of the coastal mangrove swamps where the water quality is hard and slightly alkaline. You can achieve the salinity the crabs need by adding a small quantity of marine salt to the water. Ideally, the water should be about one-sixth of the salinity of seawater.

The ideal water parameters for Red Claw crabs are:

  • Water temperature should be between 70° and 88°F
  • pH in the range of 7.6 to 8.5
  • Water hardness of 8 to 25 dGH
  • Specific gravity (saltiness) of 1.005

Be sure to test the water parameters at least once a week using an aquarium water testing kit and make any necessary adjustments.

Do Red Claw Crabs Need A Heat Lamp?

Red Claw crabs are a tropical species that need a water temperature of between 70° and 88°F. These crabs are semi-aquatic, venturing out onto land periodically, so although it’s not essential, your crabs will enjoy a heat lamp placed over a terrestrial area of your setup.

Ideal Habitat For Red Claw Crabs

As previously mentioned, Red Claw crabs are happiest and more likely to thrive when kept in conditions that closely replicate their natural habitat. 

In the case of these semi-aquatic crabs, the ratio of water to land should be roughly 3:1. So, you want mostly water with some raised land surfaces that the crabs can climb up onto.


The best substrate for Red Claw crabs is sand. These critters love to burrow, dig, and scavenge, so sand is a soft, safe material for them.

If you’re creating a habitat for the crabs in a standard fish tank, you can build a landmass from the sand or use special floating perches instead. Most purpose-built paludariums contain shelves that you can landscape if you decide to take that route.

Tank decoration

When choosing decorations for the tank, rocks and driftwood are a good choice, and you should also include some caves that the crabs can use as shelter. 

Several times during their life, the crabs go through a molting process when they outgrow their shells. The new carapace takes a few days to harden, during which time the crab is very vulnerable to predation and attack from other crabs. So, you need to provide dense planting, caves, upturned plant pots, and the like that the crabs can hide in while their new shell hardens.

If you notice a molted shell in the tank, leave it there for a few days. Sometimes, the crabs eat the shell as a source of calcium, which is essential for their shell health and growth.

Although live plants are an excellent addition to any fish tank or paludarium, Red Claw crabs are destructive and will uproot and shred your plants. So, either use tough plant species or silk ones instead.

Red Crab Behavior

Red Crabs are fun to watch, but they can be somewhat skittish, and they tend to be nocturnal, spending much of the daylight hours hiding away.

You can sometimes encourage the crabs to become more active during the day by using moonlighting if you have that option on your aquarium lighting unit. When the crabs do show themselves, you can enjoy watching them scavenging, digging, burrowing, and generally exploring their environment. 

If these crabs feel threatened, they will raise their claws in a gesture of aggression toward whatever critter has alarmed them. That could be your finger if you’re carrying out tank maintenance! 

Are Red Claw Crabs Aggressive?

Red Claw crabs are pretty feisty characters that can be very aggressive toward other crabs and fish. That’s mainly because the crabs are very territorial, and they will fight to the death.

These crabs have even been known to kill fish and other invertebrates, so make sure you don’t overcrowd the habitat and provide lots of hiding places that the crabs can claim as their patch.

What Are Good Tank Mates For Red Claw Crabs?

Since these crabs are aggressive and live in brackish water, your choice of compatible tank mates is somewhat limited.

However, you can keep Mollies, Flagfish, and larger species of gobies relatively safely with Red Claw crabs. We recommend that you don’t keep any other species of freshwater crabs in the same tank as Red Claw crabs, as that’s almost certain to end in disaster.

Can Red Claw Crabs Live Together?

Yes, it is possible to keep a few Red Claw crabs together, provided that you have a large tank with plenty of space and hiding places.

Ideally, you should keep one male to two females. Never keep multiple male crabs in the same tank. They will fight until only one remains!

Do Red Claw Crabs Sleep?

You might notice that your Red Claw crabs are not very active during the daytime, hiding away in caves and other secluded areas of your tank. That’s because these creatures are primarily nocturnal, coming out at night to feed.

So, do these critters sleep?

Yes, Red Claw crabs do sleep. Like most creatures, crabs need to rest and recuperate between bouts of activity.

Why Is My Red Claw Crab On Its Back?

Many species of crabs spend some of their time laying upside down or on their back, and they do that for various reasons. So a Red Claw crab on its back is not necessarily stuck. However, crabs are curious creatures that like to spend time exploring their environment, so you wouldn’t want to see your crab upside down for too long.

There are several reasons why your Red Claw crab is upside down:


Some crabs prefer to go on their backs while molting. It might simply be that the crabs feel vulnerable without their exoskeleton, so turning over is an effective defense strategy. 

However, it’s more usual for the crabs to hide somewhere safe for the duration of their molting process. That offers the crabs protection and privacy while they are at their most vulnerable to predators, including other crabs. 

The following behavioral signs might indicate that your crab is molting:

  • Digging
  • Lethargy
  • Drinking and eating more than usual
  • A glazed expression in the crab’s eye
  • Exoskeleton fading to a dull color

If the crab is trapped out in the open, you might want to consider gently relocating it to a safer location.


Crabs are notorious escape artists, sneaking out through any gaps in the tank to explore your home. If you spot one of your Red crabs dangling from the tank lid, it’s likely attempting a breakout!

Constant escape attempts can indicate that there’s a problem with the crabs’ habitat. Possible reasons for a crab to seek pastures new include:

  • Insufficient space: the tank is too small for the crabs and other residents
  • Poor conditions: the aquarium is too cold, not humid, too light or too dark
  • Boredom: the habitat lacks stimulation for the crab
  • Poor diet: Red crabs need a varied diet. A boring diet could encourage a crab to look elsewhere for food
  • Stress: Not all crabs settle into life in captivity, becoming stressed and anxious

If your crabs are trying to escape, take action by weighing down the aquarium lid and blocking any gaps. 


Crabs are climbers, exploring their habitat and scrambling up and down your aquarium decorations. However, accidents can happen and crabs can sometimes suffer falls, ending up on their backs.

Protect your crabs by using a four to six-inch layer of a soft substrate to cushion any falls, and always check your crab for injury if you witness a fall.


Although crabs can usually right themselves, there’s the chance that the creature has become stuck on its back or is wedged between two surfaces. 

Can Red Claw Crabs Right Themselves?

Red Claw crabs are usually able to flip themselves over, although they do need help to right themselves sometimes. Usually, that help comes in the form of a piece of aquarium decoration or even from another crab.

Sometimes, you can tempt a tired or reluctant crab to right itself by offering food.

How To Turn Your Red Claw Crab Over

If the hermit crab can’t right itself, you might need to intervene.

When handling the crab, always do so with the utmost care. Never try to pull the crab over by its legs! You might finish up by tearing the leg off completely, seriously injuring your pet and possibly even killing it.

Instead, push your hand into the substrate underneath the crab. Once the crab is in your hand, slowly rotate the crab by moving it onto its side, and then turning it over completely. Carefully, replace the crab in its tank.

Red Claw Crab Diet

Although red claw crabs do actively hunt, they are not strict carnivores. 

A healthy red claw crab diet should include plenty of protein such as bloodworms and small pieces of uncooked fish or prawns. That should be supplemented with a variety of food, including veggies such as leafy greens, peas, and spinach.

Red Claw crabs will usually also eat regular fish food and algae pellets. You should also include commercial crab food, such as Hikari crab cuisine, in the crabs’ diet, which should help supply them with enough calcium to grow and molt successfully.


How Often Do You Feed Red Claw Crabs?

These critters are scavengers, foraging around the tank and picking up whatever scraps of food they can find.

To prevent the water from becoming polluted, offer the crabs food once a day and remove anything that’s not been eaten after a day or so.

Health And Disease

Red Claw crabs are hardy creatures that are very resistant to most diseases that can affect crustaceans. They will even eat sick or dead fish without contracting any form of disease themselves.

That being said, these crabs can suffer from fungal and bacterial infections, and parasites may occasionally attack them. However, thankfully, such instances are pretty uncommon.

You mustn’t overcrowd your crabs’ tank. Overcrowding causes stress, which increases the chances of the Red Claw crabs becoming sick. Generally, if you keep the tank clean and keep up with your regular water changes, the crabs should remain healthy.


Unfortunately, breeding Red Claw crabs in the home aquarium or paludarium environment is pretty much impossible to achieve. 

Some hobbyists report seeing their crabs spawn in tanks. However, any eggs that are produced generally don’t hatch, and those that do usually die off very quickly. Juvenile crabs start life as larvae, meaning that they are very vulnerable to predators. 

And like most crab species, Red Claw crabs don’t display any parental behavior at all. The parents will often eat the larvae, so your baby crabs chances of survival are, sadly, virtually nil.


Red Claw crabs are readily available to buy in your local fish store and online. 

Before you choose your pet crabs, double-check their sex so that you don’t end up with more than one male. Also, look very carefully to see that the crabs do not have any signs of injury or damage and that all their legs are intact.

You can expect to pay around $10 per crab, depending on where you buy them.

Final Thoughts

Red Claw crabs are a fascinating species of crustacean that can make a nice addition to a single-species tank or paludarium with a few suitable tank mates. 

These are semi-aquatic crabs that must have access to land if they are to thrive. Also, although Red Claw crabs are frequently sold as freshwater species, they actually hail from brackish coastal waters. 

These interesting little creatures can make great pets if you keep them in the proper environment and provide them with a diet that contains sufficient calcium and nutrients for a healthy shell and growth.

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121 thoughts on “Red Claw Crab Complete Caresheet”

  1. Hello, thank you for all the details. They started out in fresh water, thanks to an uneducated pet store but I have a pair in a 10 gallon tank. I’m having a hard time keeping the gravel clean & would like to move them to another aquarium with sand and a better paludarium setup. What sand would you recommend? Also if the new tank has the proper salinity how should I drip acclimate them to avoid too much stress? Thanks so much!

    • Hi Christina!
      Red claw crabs will do best on a sand substrate, yes. What kind of sand you get isn’t too important; hobbyists have luck using play sand though I like to stick with aquarium-specific brands. Sand lets them dig and forage so it’s much more maneuverable than gravel.
      Cleaning sand is a little trickier than gravel, but you can just lightly siphon it every week or two and you shouldn’t pick up too much sand that way.

      If the tanks are identical in parameters, including salinity and temperature, you can theoretically just transfer them over with a net. I would probably drip acclimate them for ~30 minutes or so personally.

  2. Hi,
    My 10-year-old has been researching red clawed crabs for months and we have almost agreed to let him set up a red clawed crab tank. He would like to know how it is best to introduce them to a new tank (i.e. is it like with fish that you have to let acclimatise slowly?). Can anyone offer advice?

    • Hi Christine!
      It would first be good to ask the pet store if your crabs are being kept in freshwater or brackish water. Even though they are supposed to be kept in slightly salty water, not all pet stores take the time to get the salinity right.
      If they are being kept in a salinity much different from the tank you have set up, then you will want to acclimate very slowly, over a couple of hours.
      Even if your salinities are close, you will still want to take your time with acclimation. The best way to do this is by drip acclimation.
      Empty your crab and its water into a bucket. Get a piece of airline tubing and make a loose knot in it. This will keep the water flowing, but slow down the speed to create a slow drip.
      Allow your crab to relax for 1-2 hours or until parameters match between tanks (usually when the water volume has doubled). Keep the aquarium lights off for a while, and with any luck, your crab should be fine.
      Alternatively, you can match the salinity of the pet store and then slowly raise the salt content every week.
      Good luck and let us know how it goes!

  3. Hi I have a question. Can my Red Clawed Crab live in a tank that has no filter in less than 24 hours the filter broke yesterday when i got him and i got it again and my filter broke again so im going to get a small 5 gallon filter today so will he be fine until after 6:00 P.M

    • Hi Mitchel!
      Your crab should be fine! Many tanks don’t have any filter at all. If you’re really concerned, you can do a bunch of small water changes and/or move around the water every few hours. Most importantly, you don’t want the water to be stagnant for too long as gas exchange decreases dramatically. The water change will help remove possible waste and help introduce oxygen, but you should be fine with some hourly stirrings.
      Let us know how it goes!

  4. hiii i have a red clawed crab and i have had it for around 5 months now i watch him reguarly and i have noticed that he is starting to grow somthing purple on the belly is that bad? have i done somthing wrong?

    • Hi Lili,
      It’s a little hard to say without knowing more. Are you sure that it’s a male? It’s possible that it’s actually a female and this ‘growth’ is developing eggs; try searching for some images of red claw crabs with eggs and compare.
      Otherwise, it could be anything.. an injury, a parasite, a tumor, or even just dirt. I would monitor your crabs very closely to see if there are any changes in behavior. Also, pay attention to molts and see if the bump disappears with the next shedding.
      Can you tell us more about your setup? Have you added any new livestock lately? Is there any way this crab could have gotten injured? Are other crabs/fish acting normal?
      Thank you!

      • Srry this is a bit late but I later figured out she was a female after coming back to this comment i just relized that she looks a awful lot pregnate and im wondering how that is because sadly she is alone at the moment. I will keep in touch she hasnt really molted lately and has been more shy than normal.

        • That’s okay!
          If she’s alone, then it’s not likely to be eggs as most crabs are not asexual; however, this depends on how long she’s been alone. It’s still possible that they’re eggs if she was with a male not too long ago.
          I would continue to monitor her overall health and behavior and check to see if the growth gets larger. Unfortunately, if it doesn’t start to show signs of improvement, then it could very well be a tumor.
          Keep us updated!

          • Somehow i woke up one day and she was free of the purple stuff she now starting to come out more including actually running around her cage. Before when she had the “purple stuff” she would not come out of underneath her rock (that has an opening) now she is hapily living thanks for the advise though!

          • Hmm.. maybe it was an injury and she just had to molt. Make sure to continue to keep an eye on her, but it sounds like everything sorted itself out! Good luck.

    • Hi Ashley!

      Whether or not your crab will survive is probably going to be entirely up to fate; losing both claws is kind of worst-case scenario since there’s no way for the crab to protect itself for the time being. However, crabs will regenerate missing limbs and other appendages through molting in time. If you’re able to, I would isolate that crab from any other animals in the tank and keep super close attention on it, making sure it’s still getting enough to eat and that there’s no abnormal behavior.
      I wish the best for your crab!!

  5. I have been trying to slowly rise the salt level / transition from fresh water for my crab, but have become a bit confused on the calculations. With the target of 1.005 and the increase of .001 that you mention I want to be precise as possible. But the product I have (seachem brackish salt) only gives amounts for certain species rather that how much it affects the water. I’ve tried some online salt calculators as well but i’m not super confident in the results. How can I calculate the correct amount of this product per gallon for a red claw crab?

    • Hi Kalani,
      I have a saltwater tank so I know how sensitive salinity can be, but it’s really nothing to be scared about! Especially with crabs, they’re used to living in estuaries where water conditions can change by the hour, but your crab will definitely appreciate the changes you’re making.
      First, I would suggest you look into Instant Ocean Sea Salt–you might end up saving some money switching from Seachem, and it does the same exact thing. Second, I would suggest getting a refractometer. They’re very easy to use and very accurate.
      From here, I would add salt in small amounts to my new water during a water change, allowing it to dissolve, and then checking the salinity. Because this only accounts for ~25% of your tank, you’ll actually want to make that new water more than .001 so it actually makes a difference. I would maybe make it so that my new water reaches the first or second line on the right column of bars on the refractometer, so 1 or 2. And then test the water in your tank and keep note of it.
      Remember that only freshwater evaporates from saltwater, leaving the salt behind; so as time passes between your water changes, the salinity will continue to rise. Though like I said, your crabs should do just fine. Just don’t let it increase more than ~4. To fix this, just add freshwater.
      I hope this helps! It’s just a matter of taking and giving until you find that sweet 1.005 spot. Then it gets much easier to maintain.
      Let me know if you have anymore questions!

  6. I have 65bgallon tank, can red claw crabs survive? I have plants they can climb to reach to a floater for air. Or are they just mainly for smaller tanks?

    • Hi Felicia,
      While a 65 gallon gives plenty of space for these crabs underwater, it’s more important that they have plenty of places (about 50% of the tank) to sit out of the water. Secondly, your tank should be set up as brackish as this is when they really thrive. However, if you’re really wanting them, a 10 gallon will be fine!

      Happy crab-keeping!

      • Hello one of my Red Clawed Crabs is missing both claws and a leg from where she was originally kept and I wanted to know if I should worry or not because I have 2 and the other one bully’s her!

        • Hello!
          I would definitely separate the crabs if they’re fighting. Your crab is defenseless right now. However, it should regrow them with the next molt.

    • Hello.. I’m confused.. I have 2 red crabs and every now and again I see a crab but its just an empty shell… Do they break out their shells and carry on?? I’m baffled as I still have 2 crabs and I’ve taken out 2 crab shells..

      • Hi Chauntelle,

        This is a natural phenomenon known as molting performed by crustaceans (crabs, shrimps, lobsters, etc.). This happens when your crab is growing and its shell cannot expand with it. So every month or so your crab will shed its exoskeleton and become a little bigger. While it’s okay that you took out the shell to make sure it’s not dead, your crabs will actually eat the shell to reuptake nutrients such as calcium. So next time, don’t worry!

        Happy crab-keeping!

  7. Actually, my son bought 2 red claw crabs a couple of days ago from the pet store. They had them in freshwater tanks and advertised them as fresh water. So we too put them in a freshwater tank. Now I’m concerned about their well being. I assume this can be corrected. They have been active, appear to be doing well, and seem to be eating. However, One of them has lost at least one front claw which is why I was on this site to begin with. Will it regenerate or is he a lost cause. I’m not sure if we have males or females.

    • Hello. Sorry to hear you were misinformed, it happens a lot!

      Are they alone in their tank? If they are, it’s going to be an easy process to convert them to brackish. If they’re not you’re going to have to set up a separate tank for them so as to not hurt their freshwater tankmates. Instructions on setting up a brackish aquarium can be found in this article. I recommend increasing the salt grade slowly, like 0.001 with every water change for example.

      Also be sure to have a look at the other instructions here, like the bit about giving them plenty of land space. That’s not always mentioned in pet stores either, they’re often said to be fully aquatic.

      As for the front claw, in a healthy environment with high quality foods they will regenerate limbs during their next molt, yes. So he might well recover completely.

      Good luck, I hope it works out!

  8. Dang wish I had found this article sooner! I got one of these crabs at Pet’s Mart for my forest Paludarium. I put this crab in and haven’t seen it after the first night. My paludarium has tree’s and wood sticking out of the open top and two waterfalls that come up out of the top. I am guessing this guy is running around my house somewhere.

    • Ah yikes, sounds like that might be the case 🙁 they dry out quite quickly so there’s a good chance he’s already passed. They can hide for quite a while but if the paludarium is open top then I do fear the worst.

  9. I have a 20-gallon tank that is not in use right now, but I am looking into turning it into a red claw crab habitat. Any tips for how long I should cycle it, how much land area they should have, and how many crabs would be happy in this tank? Thank you so much for this care sheet, as there is so much miss-information around!

    • Hi! Good to hear you’re doing your research beforehand and great choice on red claws for your tank, you’ll enjoy keeping them. As for cycling, you cycle the aquarium just as you usually would: the time it takes depends on when it’s done, basically. You can read more about it here. Half land, half water would work well and you could try starting with three or four specimens. Just make sure they all have caves to hide out in.

      I hope that helps, good luck!

  10. I’m wanting to get some crabs but I have a few questions. First, how do I clean the tank? Should I just replace the water or should I scrub hides? Also, what is the correct ratio of salt to water? Should I put a over water heater or an in water heater? How many crabs would be comfortable in a 15 gal? Do they need humid air? Finally, should I put their food in the water or on the land? Does it matter?Sorry, I’m just full of questions.

    • Hi! Great to hear you’re serious about doing your research.

      Cleaning consists of a water change as well as filter cleaning (instructions on the latter can be found here). Scrubbing is not that much of an integral part unless things are getting a bit too dirty for your own liking.

      With regards to salt, I recommend you do some further research into setting up a brackish aquarium. I don’t have any articles on the set-up process right now but I’m sure there’s plenty out there that’ll help you understand what goes into it! Heater-wise, an in water one should usually be enough since the lights help keep up the temperature of the land area.

      In a 15 gal, if it’s a long tank, you could do three. If it has less land area maybe try 2. The air will be humid by itself because the tank should be quite well-sealed to avoid escape attempts, so paying extra attention to that is usually not really needed. Food should go on land, even if it’s just because it’s easier and avoids fouling the water!

      I hope that clears things up a bit. If you have any more questions feel free to get back to me 🙂

  11. I have a red clawed crab and it is molting, it has white hair like stuff growing on the bottom of it and I don’t know what it is.

    • Hi, sorry to hear your crab isn’t feeling well! Sounds like a fungal infection. Have you checked all the care guidelines in this articles and confimed you are following them? If you’re not, your crab can fall ill with problems like this.

      • Hi.

        I’ve recently bought 2 of these crabs (160l Tropical planted tank). I’ve a tall tank so I was looking for something to help keep the base clear. The shop assistant insisted these would be perfect and won’t bother the fish too much unless they’re ill.

        I’ve created some land space by placing bog wood to create a platform and dropping the water level in the tank to give some space. Both crabs seem happy at the moment picking up left over plant mass or food that gets caught up in rocks and roots.

        My concern is with the brackish water. If I were to hollow out a bit of the wood above the tank level and make a pool, would this suffice? The sales assistant didn’t mention this and the crabs were kept in communal tropical tanks .

        • Hi! Sorry to hear you were misinformed at the pet store, my family had the same issue with red claw crabs years ago. And there we were wondering why the crabs climbed out of the tank and ended up on the living room floor… glad to hear yours seem to be doing alright for now at least.

          These crabs naturally occur in brackish water and will eventually perish in a freshwater tank. Your idea sounds like it might get a little messy… not wanting to set up an entirely different tank for just two crabs makes sense, but it would be the best thing for them if you’re up for it. If you don’t want to buy an aquarium you can always set everything up in a food-safe tub, you’d still be able to view them from above. It doesn’t have to be complicated – a set-up like the one in this video would be fine, although I’d prefer going for 15 gallons instead of 10 personally. 🙂

          Good luck, nice to see you’re at least looking to correct the damage done by the pet store.

  12. Hi. I recently put a heater in my red claw crab tank and it says it will keep the temp between 76-80F. Will that be too hot for my crab? I live in FL but it is starting to get cold at night. Thanks.

    • As mentioned in this caresheet that’s actually a pretty good temperature range. Is it an underwater heater or an above water one? Whichever it is, make sure the water and air temperature match reasonably well. It’s not good for your crab do constantly be shocked by big temperature differences (a few degrees is fine).

      Good luck! 🙂

  13. Hey, so I’ve had two crabs for like two weeks and they started as an impulse buy but I’m really really trying to give them a good life.
    They seem to be doing pretty well but how do I know that’s true. Is there any sign to see regarding their happiness or that they’re stressed?

    • Very good question! With these inverts it’s a little difficult to see at a glance since they’re usually not THAT active. Signs to look out for are that they’re eating, moving about regularly and molting successfully. There might be times where you don’t see them much – the annoying thing is that this can either be a sign that they’re molting, or a sign that they’re not doing well. It gets confusing sometimes! If you’ve followed all the instructions in this caresheet your crabs should hopefully do just fine though 🙂

    • There’s a link to a post that explains it in the caresheet 🙂 it’s this one. Be sure to increase the salinity in small increments – you don’t want to shock the crab too much!

      Good luck!

    • As with all inverts it really depends on their age. Younger crabs molt pretty frequently, probably monthly-ish or even weekly if they’re really small. Then after that it slows a lot to once every few months or so!

  14. Is a three gallon tank big enough for two female red clawed crabs? I have been told that they only need one gallon but I don’t know if there social or not. She looks so lonely.

    • Hi,

      Did you read the article? The minimum tank size to keep red claw crabs is around 23.5″ which comes down to about 15 gallons. I recommend returning the crab you’ve got now or setting up a better aquarium (following the guidelines from this article, NOT pet store advice) ASAP. Sorry I don’t have better news!

  15. Would a 20L gallon be enough room for 3-4 red claw crabs? I have one cycling right now, my son wants 4 of them but I’m worried that there won’t be enough space. I’m using sand but the dry side is still some what wet, I’m waiting for more sand to come that I ordered because the pet store was out. Also the dry side feels so much colder then the water side. Is that going to be a problem? Will I have to get a basking light or anything like that? I know this is a lot of questions sorry

    • Hey! A 20 gallon long tank would be great for 3-4 red claws. It’s alright if the sand on the dry side is wet as long as it’s not underwater. Have you measured the temperature on the dry side? It should ideally be similar to that of the water, so if it’s really significantly colder then maybe a basking lamp would help. Or you could try a regular fluorescent light that gets relatively warm? Just thinking out loud here, I haven’t experimented with this!

      Hope that helps, it seems like you’ve done your research so all should be well. I’m sure I don’t have to tell you, but just in case: brackish water is necessary 🙂

    • Hi,

      Yes, the air temp shouldn’t be too far removed from the water temp. You can just use regular aquarium lights for them 🙂

    • Can I use a reptile thermometer to measure the temperature in the tank? Would it be accurate? I currently have a water heater in a 20 gallon with 3 (one male 2 female) crabs. Also how do recommend cleaning the rocks and decorations before adding them to a tank? I usually use really hot water to rinse them until the water looks clean but I am afraid that is not enough? Also what kind of fish do you recommend I can add to the tank, I have a couple of guppies but I see one has been aten will any fish be safe? Lastly do you recommend removing half the water and leaving in the other 1/2 to clean the water should I add salt to the clean water always? How many times a month should I do this? Thank you so much.

      • Hello!

        A reptile thermometer should work for the land part as far as I know. For décor I always use actual boiling water, not just really hot. That should be enough to kill any nasties. As for fish, yeah. The crabs do hunt and they love a fish snack. Guppies are actually the only species that I would recommend for a tank your size as tankmates for red claws, so if you’re not really having success with them I’m not sure if there really are other good options.

        As for water salinity during cleaning, your water should always be at the same salinity, which you should be measuring with a salinity meter. When you remove water during cleaning and put new water back in, the new water should be pre-mixed to the same salinity as the rest of the tank. So if your water is at 1.005, the new water should also be 1.005. The only time you DON’T put salt in new water is when you’re replacing water that has evaporated (referred to as a top off). This is because salt doesn’t evaporate, so you need to add saltless water to prevent the salinity from creeping up.

        I hope that all made sense. If you still have any questions, feel free to ask 🙂

  16. Hi, I just got two red claw crabs two days ago. We put them in a freshwater tank with a rock decoration that they can (and have) climb up to get out of the water if they want. We don’t have a heater yet. When we brought them home, both crabs were active, and were exploring the tank, occasionally hiding, etc. we have been dropping crab food pellets near each of them twice a day but they don’t seem to be eating much. Yesterday one seemed to become pretty inactive, but he would move a little if prompted to. Today, both crabs are not moving at all, and are both staying underwater. They both seem to have flaps of their shell loose- does this mean they’re molting? How long should this last, and what should we do while they’re molting?

    • Hi,

      Why did you put your red claw crabs in a freshwater tank? It seems their setup is not suitable for them at all. As described in this article they need a brackish paludarium with a large land area and a cycled, heated water area. So that probably explains why they aren’t doing well.

        • No one was an “asshole” here. A lot of commenters comment with questions that can be answered quite easily by reading the post they’re replying to, so that’s why my replies can be short. The long and very polite explanation is in the caresheet 🙂

          • One of my crabs have died and the 3 others have been hiding a but more since he passed. Is it normal or should i be concern

          • That does not sound entirely normal to me considering that you’ve already lost one. They could be getting ready to molt but I would definitely check my water values using a liquid test kit, check both water and air temperature and make sure I’m following all the guidelines in this article. It sounds like the three remaining crabs might not be entirely healthy. Good luck!

      • I have two crabs in a freshwater tank with four big goldfish, their only access to “dry land” is a small underwater island in a glass jar with an airstone to supply oxygen. They’ve been in there for about 2 months and have successfully molted. Clearly brackish water and “a large land area” are not required. ‍♂️

        • Well… I’m not sure what to say to this. 2 months is not exactly a feat… the ones I had in an unsuitable set-up when I was little survived for quite a while as well. Doesn’t mean they weren’t suffering. They naturally occur in brackish habitats and spend much of their lives on land. They are not compatible with goldfish temperature-wise. With four big goldfish the tank would also have to be quite massive.

          Anyway, glad you feel things are going well with your crabs, just please don’t go and comment misinformation.

  17. I have a question,.
    So I have a sort of double mound beach setup in a 10 gallon tank. It has one mound on one side and another mound on the other that connect to one another through a small narrow path connecting to one another. I’ve counted about 5 hiding spots. My male doesn’t seem aggressive and shares spaces with the other 2females at times. I’m hoping to get 2 more crabs but I really want a fiddler. Would a male fiddler and a female fiddler work well in this situation? I know red claw crabs ate nocturnal while fiddlers are diurnal. That’s also a factor I’m having to consider

    • Hi,

      As discussed in the article, I wouldn’t recommend anything less than a 60cm/15-ish gallon setup for red claw crabs. So your tank is already too small for red claws in my opinion, which means I most definitely wouldn’t recommend also adding fiddlers. I wouldn’t combine the two regardless, but your tank size makes it even less of an option. So just set up a new tank for those if you want to keep them!

      Good luck.

      • Thank you for the response!
        I have another question though.
        So I got an internal filter for the water half of the tank but the water is still looking very murky. I have the Caribsea substrate. Not sure if it’s the substrate or something. I just got this filter today. I’ve also noticed most people have crystal clear water and I can’t seem to figure out how

        • Hi,

          So you just hooked up the filter yesterday? Yikes! That is not good. Your tank isn’t cycled. Please read this article very thorougly. The murky water is not what you should be worried about right now, that will probably clear up by itself. Your water quality is your main priority.

    • Hi! Yes, you can use fine gravel. However, gravel is actually more difficult to clean than sand because debris falls between the grains. With sand, it just stays on top and you can easily remove it. Good luck 🙂

  18. Hi! I have a question. We have our red claw crab set up with a “beach” and a large shop ornament to hide in. He liked it for a few days, but no he has stopped moving much. We have only had him for a week, and I’m concerned about temp. I have a water heater but it’s still only at 72. I have another on the way by mail because the store didn’t offer a large range.

    But my main question, is do they need the air temp to be 75 F as well? I live in a northern climate and the house temp is currently at 69 F. Could this cause lethargia?

    Thank you!

    • Hi! I’d expect things to improve temperature-wise once you get the new heater and can get the water temp up a bit. Obviously that will also raise the air temp a bit to what is probably an acceptable level.

      As for inverts and lethargia – it can also be related to molting, which can cause issues especially with new crabs. They don’t always receive proper care at the aquarium store and as a result are sometimes too weak/nutrient depleted to molt properly. In any case, it’s normal for them to remain in hiding for a while when they’re attempting to molt. If it really is molting there isn’t much you can do, it either works out or it doesn’t.

      Finally – did you cycle the tank before getting the crab? The water area should be cycled properly like any other aquarium. Have you performed a water test with a liquid test kit to check whether the water values are still where they should be?

      I hope the crab is doing better by now! Good luck.

  19. Hi Mari! I’ve never had a crab before, but I’m in a marine biology class and I came across these crabs for a project I was working on, they seem cute so I was interested in getting two or three! I read everything extensively and I have some questions to ask, I don’t want this to be an impulse buy and I really want to know how to care for the crabs the right way. First, will a 20.2×10.5×12.5 tank be suitable enough for the crabs? Second, how often should I change the water and where should I keep the crabs when I do change it? If I got two male crabs would it be super dangerous to keep them in the same tank? How many ornaments sound I buy and how much sand if I’m using the tank size listed above? I’m sorry if these are a lot of questions, I hope you can answer most of them!

    • Hi!

      Are those measurements in centimeters or inches? If it’s cm that definitely won’t cut it unfortunately, if it’s inched then I think you should be fine. Water changes completely depend on the way you set up the tank, but you usually do a weekly water change based on how much nitrate has built up. There is no need to move the crabs when you change the water, as you won’t replace all of it so they just stay in there.

      I would definitely try to avoid getting two males – you can sex them relatively easily (described in the article). Hide-wise, I’d do at least two caves or other hiding places per crab. As for sand, that also depends on what you want to do with the tank. You’ll need to get enough to provide a nice big land area for the crabs.

      I’m not sure what a marine biology class entails, but just to be sure: don’t forget to cycle the tank, even though the crabs won’t be in the water all the time it should still be filtered and heated.

      Good luck! Nice to hear you’re doing your research 🙂

    • Hello,

      As you can read in the article, red claw crabs are very good climbers. I’m not surprised they managed to climb the plastic wall. Why do you have plastic walls in between anyway?

  20. I have just recently got a crab and it molted not long ago. For a couple days now he’s barely been moving and has been going upside down, a few times I thought he has been dead. I don’t think he’s eaten for a few days and I left for the weekend and when I came back he was upside down in the same spot I left him, yet still moving his claws and mouth (he won’t move his legs). He’s just recently molted about a week ago so I’m not sure if he could be trying to again. It’s been at least four days of not moving anything but his claws. He has also spewed out a black liquid from his mouth, and his belly flap was open at one point (not sure if it’s a male or female but I’m pretty sure female). Do you know what’s going on?

    • Hi! I’m sorry to hear your crab isn’t doing well 🙁 If your water values look normal (have you checked?) and your setup is in order I think you might be dealing with a bad molt here. This can happen when an invertebrate is in bad health and/or has a calcium deficiency. It might not have enough energy to recover or not enough calcium to produce a proper new shell. Besides keeping the water clean and maybe offering food once in a while I don’t think there is much else you can do for now. I hope it recovers!

  21. Hi, I have one red clawed crab, this hasn’t happened yet but what would it mean if a crabs claws start turning a darker color, also I have one of those habitats for hermit crabs, it’s like 2-3 feet long and 1 and 1/2 foot wide, is this a good enough space or should I get it something better

    • Hi! I’m not sure about the claw thing, it might have to do with the molting cycle. As for the hermit crab habitat, if it’s just a regular glass tank that can hold water for the aquatic part it should be fine. 🙂

      • Yeah it can hold water, also how do I keep my water warm, from what I’ve been told these crabs prefer warm water, I’m constantly changing the water to keep it some what warm, or is cool water fine?

        • You use an aquarium heater just as you normally would! If you’re not familiar with maintaining an aquarium it would be a good idea to read up on that a bit. For example, even though red claw crabs don’t spend all of their time in the water the tank should still be fully cycled.

          Good luck!

  22. Great page very insightful I’ve had 2 red claw crabs for just over a week due to an impulse buy and they are sloop interesting to watch there is very little or contradicting information around the internet on how to care for them but this page is defiantly the best help I could find thank you .
    Going to introduce them to fresh prawn tonight see how they like them

  23. A few questions. Do they breathe in or out of water? Do they need to be fed in or out of water? How often will my crab come out of water and use the beach I’ve made for it?

    • Hi! I think they have gills and can breathe both underwater and out of the water but I’m not entirely sure. You can feed them both underwater and out of the water (also depends on what kind of food you’re giving, whatever is more convenient!). They usually spend around half their time out of the water.

      Hope that helps!

  24. My crabs keep dying and I’m really not sure why. The tank is healthy and clean and water is brackish and everything but every crab I got keeps dying :-/

    • I can’t really help you out without more info! Is the tank cycled and what are the water values? What is the salt grade? What does the layout look like?

  25. Why did my female Biden die with her eggs? 🙁 she was perfectly fine but she did turn into a brownish color and lost a claw for some strange reason 🙁 help?

    • I can’t tell you much about that without more specific info, sorry! You could try asking on an invertebrate/aquarium forum.

  26. Is it normal for the crabs to be a sandy color a few days after molting? My female just molted and she is paler than usual, but still very active.

    • I’ve never seen a red claw crab right after molting so I can’t confirm whether a sandy color is normal, but a lighter color in general is definitely normal yes! Their new exoskeleton is still relatively soft and weak.

    • I have a female red claw introduced a male an within the hour she just stopped all movement I can touch her an she moves but it is almost like just a twitch what is this can they go from fine to moltin just in the blink of an eye

  27. hi there, nice website.

    one of my crabs had a big fight and lost his 2 claws, you have anny idea how and what to feef him?
    don’t want to loose him 🙁

    kind regards

    • Sorry about the late reply, I was out of town for a few days. How is the crab doing? Just feed calcium-rich foods. Crabs aren’t supposed to fight so be sure to reassess your setup!

  28. I’m considering getting a thirty gallon tank for a figure 8 puffer, and I’m wondering if these would make good cleaners, as I’ve heard that the puffers get very messy

    • I suggest doing a little more research on the puffer! You’ll find out that their diet consists almost entirely of crustaceans, so not an ideal combo at all 😉 these crabs are also not great cleaners. With puffers and all aquarium fish, the cleaning is ultimately up to you! Vacuuming the bottom of the tank frequently, keeping up with water changes and removing any uneaten foods quickly are the key here. Good luck!

      • aw darn
        i knew that they ate crustaceans, but I keep dwarfs with cherry shrimp w/o too much trouble, and the cherries save me the trouble of cleaning for the most part

        • We keep a dwarf puffer with cherry shrimp too, but they really can’t be compared with any of the larger puffer species. None of those can be kept with any tankmates, they’re pretty much killing machines unfortunately haha. :/

    • Hi! Great to hear you’re thinking about getting some red claw crabs. I’m sorry about the dead link – Fish Girl’s Koi Pond was changed to Fish Girl Writes, you can now find my guest post with all the info you need to set up a brackish paludarium for your red claw crabs here 🙂 it should answer all your questions relating to setting up the tank. Also be sure to have a look at the article about cycling an aquarium, as this has to be done with brackish aquariums as well.

      As for your question about tankmates – that doesn’t sound like a good idea. I don’t know of any peaceful, small brackish crayfish/lobsters and other crabs will surely end up causing trouble. As mentioned in the caresheet, red claw crabs are best suited to a single species setup! If you had a larger tank there would have been some brackish fish species that could work in the aquatic part, but unfortunately for a 60L I would definitely recommend just the crabs. But don’t worry, they provide plenty of action and your tank won’t become boring!

      • Thanks for all your help and the links were very helpful to I cant wait to get my tank and get it set up. thanks a lot 🙂

  29. Hi thanks for the info sheet I have bought a 60 ltr tank waiting for it to arrive to have it for the red claw crabs. I have a tropical fish tank with fish and have had a marine tank years ago. would like some advise on how to set it up and how long to wait till I get crabs please the link above doesn’t work unfortunately many thanks
    caroline 🙂

  30. Thanks for the info. I have a red claw crab which I bought four days ago. He was moving about fine in the tank then once I made access for him to go out of the water on a piece of wood he hasn’t yet come down. He does sometimes go on the side of the wood so gets wet and I’ve put some food up where he is but the wood is only about 2″x2″ and he has just been up there for days. Is this normal? Should I be worried or put him back down into the water?

    • No, there is no need to worry. As mentioned in the caresheet, red claw crabs are not fully aquatic and will spend a lot of time on land. You may actually want to provide a bit more land area! Also, is the water in the tank brackish?

  31. I have a five gallon tank that I am setting up for them I already have a ten gallon tank full of fish I want to set up an old five gallon tank for the crabs how many crabs would be acceptable for this tank

    • As mentioned in the caresheet, 15 gallons is unfortunately the minimum size for red claw crabs! In a five gallon, none would fit.

      • I got a 15 gallon tank for the crabs like u said and set it up I fed them lettuce because they were eating my live plant what are som other vegetables I can feed them the crabs screen very happy

  32. I am a some what experienced aquarist with two 125 gal and two 55 gal other tropical tanks running. I am also experienced with some salt water years ago.
    I am starting up a tropical crab aquarium . It is a 20 gal. half full of water with 1 table spoon of salt to 5 gal of water. My question is, with such a low water level in the tank how do I create & keep a biological bacteria filter going with out using a under gravel or over the edge box filter? Thank You

    • Sounds like a fun project! You could use a normal internal filter and replace part of the sponge with biological filter material or you could go for an external filter, those have tons of room for biological filter material. You’ll also need to use a bit more salt, maybe around 1 table spoon per five LITERS instead of gallons. Be sure to get a device to measure salinity too!

        • I’m missing the greens here, they’re not carnivores! Veggies like leafy greens and peas should be included in their diet. I’m also not sure how nutritious dried shrimp are, try going for fresh shrimp instead. As for the mealworms, not sure about those honestly! I don’t know enough about them to figure out whether they work well in red claw crab diet.

          Good luck!

    • Hi Mari, I don’t know if you’re still replying on this article. But I have a red claw crab that I got as an impulse buy and I was looking for a good heater for his tank. Do you have any recommendations or suggestions?

      • I am, no worries! My go to are the Eheim Jäger heaters and Aquadistri’s Superfish heaters, though the latter are not sold in the US unfortunately. Just try to calculate the volume of the submerged part of your tank and go off that to determine the required wattage 🙂 good luck, hope it turns out well despite the impulse buy.


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