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Caresheet: Red Claw Crab | Perisesarma bidens

Last Updated June 24, 2020
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Red claw crabs are very interesting to keep and a very easy impulse buy, but unfortunately there is still a lot of misinformation about their care to be found in aquarium stores and on the Internet. They are often kept in freshwater community aquariums, but their ideal habitat is actually a single species low-end brackish paludarium!

Keep reading for more information about keeping red claw crabs and setting up a suitable home for them.

Note: Red claw crabs need brackish water. A list of freshwater crabs can be found here.

Minimum tank size15 gal (57 L), long, paludarium
Temperature75-80 °F/24-26.5 °C


Perisesarma bidens, red claw crab, red clawed crab, mini crab.

They’re also sometimes still referred to as Sesarma bidens or (Pseudo)sesarma moeschi.

Red claw crab natural habitat

One of the best ways to figure out how to keep an animal in captivity is to have a look at what its natural habitat looks like. After all, it has evolved to live there and will benefit from a similar environment in our home!

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 salt water. The water is quite shallow, temperatures are tropical and the ground is usually covered with fine sand.

All this gives us some great guidelines for what a red claw crab paludarium should look like.

Red claw crab appearance

With a size of no more than around 4 inches (10cm), red claw crabs stay smaller than some of the other crab species available in aquarium stores, which is why they’re sometimes referred to as “mini crab”.

Males are easy to tell apart from females. Their characteristic red claws will be larger and the underside of their shell is pointy instead of broad and round.

Brackish paludarium for red claw crabs

As mentioned before, red claw crabs are not fully aquatic and should ideally be housed in at least a 23.5/60cm paludarium with plenty of access to land. They are also not freshwater crabs: water salinity should actually be around 1.005. This means you’ll need to set up a brackish aquarium if you want to keep them.

As with all types of tropical aquarium setups, the water should be heated, filtered and cycled. Water changes should be done regularly. For more information about setting up a brackish aquarium or paludarium (which is actually not as difficult as it sounds), check out this post. You don’t need a lot to go brackish: a simple salinity meter and some aquarium salt will get you a pretty long way.

The funky red claw crab is the perfect species for a brackish paludarium. The red claw <a href=crab caresheet contains everything you need to know! #aquariums” class=”wp-image-10186″ width=”512″ height=”650″/>
Hover over image to pin to Pinterest!

Red claw crab requirements

Mimicking the natural habitat of your red claw crabs is quite easy and results in a very beachy looking paludarium. The land area should be sandy. Multiple hiding places are a must because crabs need a quiet place when they are molting and vulnerable.

For a realistic effect, you can add rocks, aquarium plants such as Java fern that can withstand brackish water and mangrove ornaments. Real mangrove is possible too, but it’s not the easiest plant to grow and it gets very large.

Important! Red claw crabs are the ultimate aquarium escape artists. When setting up their tank, seal off any and all possible escape routes or you will find your crabs on your floor sooner or later. They dehydrate very quickly, so this can potentially be fatal.

The water line should never be up to the rim of the tank, keep openings for filter/heater cords as small as possible and avoid placing decorations in a way that allows the crabs to climb all the way to the top of the tank.

DSC02185 by captkodak on Flickr.

Red claw crab tankmates

When choosing red claw crabs it’s very important to try to avoid getting multiple males, as territorial fights are not uncommon and can sometimes result in injury or death. In a 23.5″/60cm paludarium, 1 male and 2 females or 3 females should work well. It’s easiest to keep your red claw crabs in a single species setup, but if your water area is large enough it is possible to keep additional tankmates.

When choosing, keep in mind that crabs do hunt fish, especially when they’re slow or sick. Tankmates that can withstand low-end brackish water and aren’t bottom dwellers, such as guppies, should be able to avoid any nippy claws.

Keep in mind that because red claw crabs need paludariums, the water area will be limited. The actual water volume can be pretty small, so keep that in mind while choosing tankmates. Calculate how much water is actually in your tank before you head out to buy fish.

Red Claw Crab
RockStarRei at English Wikipedia [GFDL or CC BY-SA 3.0], via Wikimedia Commons

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 proteins such as bloodworms and small pieces of uncooked fish or prawn. This should be supplemented with veggies like leafy greens, peas and spinach.

Red claw crabs will usually also eat regular fish food, algae pellets and commercial crab foods like Hikari crab cuisine, which should help supply them with enough calcium to grow and molt succesfully.

Red-clawed crab
Red-clawed crab by Björn König

Red claw crab behavior

Although they do spend a portion of their time hiding, especially when molting or scared, these crabs are very fun to watch and interesting to keep once they come out. If you use a soil substrate you’ll see your crabs displaying their natural scavenging behavior for most of the day. When they encounter another crab or a fish they will usually get defensive, raising their claws and chasing the intruder away.

Some aquarists report their crabs getting used to them and losing their fear after a while. However, if you ever have to handle your red claw crab for any reason don’t forget that they will still pinch hard enough to startle you!

Breeding red claw crab

Breeding red claw crabs is unfortunately very challenging and virtually impossible to do at home. Similar to some other invertebrate species like Amano shrimp, red claw crabs start their lives as larvae and will likely not survive in your aquarium.

Females will often carry eggs, but these don’t hatch or the young die off almost instantly.

If you have any more questions about keeping red claw crabs or if you want to share your own experiences, be sure to leave a comment below. Happy fishkeeping!

Cover photo: meanandpinchy

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  • ReplyAshley GormanSeptember 14, 2020 at 5:24 am

    Can Red Claw crabs survive if they lose both claws??

    • ReplyJennifer DollSeptember 15, 2020 at 9:06 pm

      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!!

  • ReplyKalaniMay 3, 2020 at 5:28 am

    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?

    • ReplyJennifer DollMay 3, 2020 at 4:50 pm

      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!

  • ReplyFelicia mcentireMarch 2, 2020 at 3:50 am

    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?

    • ReplyJennifer DollMarch 7, 2020 at 3:39 pm

      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!

  • Reply10 Types Of Pet Crabs + Interesting Facts » Learn MoreSeptember 26, 2019 at 1:13 pm

    […] These tiny crabs aren’t picky eaters and like most aquatic pet crabs, they require a dry space in the aquarium where they can come out of the water from time to time. […]

    • ReplyChauntelle EmeryMarch 4, 2020 at 4:08 pm

      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..

      • ReplyJennifer DollMarch 7, 2020 at 3:45 pm

        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!

  • ReplyJoAnn S. ArmstrongJuly 20, 2019 at 3:29 pm

    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.

    • ReplyMariJuly 23, 2019 at 3:51 pm

      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!

  • ReplyNeowindJune 6, 2019 at 3:17 pm

    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.

    • ReplyMariJune 7, 2019 at 1:17 pm

      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.

  • ReplyDylanMay 17, 2019 at 6:06 pm

    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!

    • ReplyMariMay 20, 2019 at 6:44 pm

      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!

      • ReplyDylanMay 20, 2019 at 10:02 pm

        Thank you! It’s nice to see an admin who responds quickly to questions.

  • ReplyCurious About CrabsApril 9, 2019 at 3:06 am

    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.

    • ReplyMariApril 9, 2019 at 2:46 pm

      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 🙂

  • ReplyCoonorMarch 8, 2019 at 7:11 pm

    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.

    • ReplyMariMarch 11, 2019 at 4:38 pm

      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.

      • ReplyScott LaityMarch 17, 2019 at 7:53 pm


        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 .

        • ReplyMariMarch 18, 2019 at 1:38 pm

          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.

  • ReplyJacquelineOctober 25, 2018 at 9:49 pm

    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.

    • ReplyMariOctober 26, 2018 at 4:01 pm

      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! 🙂

  • ReplyEmorySeptember 20, 2018 at 9:10 pm

    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?

    • ReplyMariSeptember 21, 2018 at 5:27 pm

      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 🙂

  • ReplyCrissy DSeptember 14, 2018 at 1:20 am

    I just got a red claw crab but I didn’t know they needed brackish water. How do I get my water to be brackish.

    • ReplyMariSeptember 14, 2018 at 10:27 pm

      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!

  • ReplyCJAugust 6, 2018 at 3:41 am

    Does anyone know how frequently these crabs typically molt? I can’t seem to find much info.

    • ReplyMariAugust 6, 2018 at 11:21 am

      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!

  • ReplyHelenaMay 16, 2018 at 4:24 am

    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.

    • ReplyMariMay 16, 2018 at 5:12 pm


      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!

  • ReplyShelbyMay 9, 2018 at 9:29 am

    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

    • ReplyMariMay 10, 2018 at 4:51 pm

      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 🙂

  • ReplySteve DoubleMarch 25, 2018 at 1:52 pm

    Should the water heater keep the air temp in the tank @ a safe range?

    • ReplyMariMarch 25, 2018 at 2:52 pm


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

  • ReplySteve DoubleMarch 25, 2018 at 1:38 pm

    Do red claw crabs need a UVA/UVB day & night light or day ONLY?

    • ReplyMelOctober 18, 2019 at 8:55 am

      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.

      • ReplyMariOctober 18, 2019 at 6:34 pm


        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 🙂

  • ReplyHollyFebruary 12, 2018 at 10:36 pm

    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?

    • ReplyMariFebruary 13, 2018 at 10:34 am


      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.

      • ReplyalleyJuly 1, 2018 at 3:54 am

        You don’t have to be an asshole to people, politely inform them of the proper ways to care for such.

        • ReplyMariJuly 1, 2018 at 12:04 pm

          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 🙂

          • AbbyOctober 19, 2019 at 9:48 pm

            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

          • MariOctober 20, 2019 at 8:12 pm

            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!

        • ReplyA CrabApril 9, 2019 at 2:54 am

          Nobody’s being rude.

          • MariApril 9, 2019 at 2:40 pm

            No worries, this comment is almost a year old! People will be people 🙂

      • ReplyCaleb HolmesMarch 7, 2019 at 2:57 am

        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. ‍♂️

        • ReplyMariMarch 7, 2019 at 10:27 pm

          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.

  • ReplyVFebruary 7, 2018 at 2:31 am

    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

    • ReplyMariFebruary 7, 2018 at 11:36 am


      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.

      • ReplyVFebruary 8, 2018 at 12:26 am

        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

        • ReplyMariFebruary 9, 2018 at 9:28 am


          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.

  • ReplyCodyFebruary 4, 2018 at 5:54 pm

    Can i use fine gravel in the tank? i heard sand gets looks dirty relatively quick.

    • ReplyMariFebruary 4, 2018 at 7:12 pm

      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 🙂

  • ReplyAlyssaJanuary 16, 2018 at 4:38 am

    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!

    • ReplyMariJanuary 19, 2018 at 5:46 pm

      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.

  • ReplyJeannaDecember 18, 2017 at 4:06 am

    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!

    • ReplyMariDecember 21, 2017 at 12:00 pm


      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 🙂

  • ReplyAmirNovember 15, 2017 at 2:32 am

    Hey i had 3 red claws in a setup but i put plastic walls inbetween and they all somehow climbed into the center area why and how

    • ReplyMariNovember 22, 2017 at 11:42 am


      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?

  • ReplyEmilyJune 20, 2017 at 4:07 am

    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?

    • ReplyMariJune 20, 2017 at 12:10 pm

      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!

  • ReplyJesusMay 9, 2017 at 7:12 pm

    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

    • ReplyMariMay 10, 2017 at 11:08 am

      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. 🙂

      • ReplyJesusMay 10, 2017 at 3:11 pm

        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?

        • ReplyMariMay 10, 2017 at 3:34 pm

          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!

  • ReplyLlamaMarch 24, 2017 at 11:36 am

    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

    • ReplyMariMarch 24, 2017 at 2:06 pm

      Glad it was helpful to you! Good luck with your new crabs. 🙂

  • ReplyThe Photostory – Zoe CurryJanuary 26, 2017 at 6:10 pm

    […] /caresheet-red-claw-crab/ […]

  • ReplyKalebJanuary 24, 2017 at 11:45 pm

    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?

    • ReplyMariJanuary 26, 2017 at 2:44 pm

      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!

  • ReplyDeebsNovember 21, 2016 at 12:42 am

    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 :-/

    • ReplyMariNovember 23, 2016 at 2:48 pm

      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?

  • ReplyJoeAugust 30, 2016 at 6:23 pm

    Hey, I want to know if I can have them in a slightly salinated water with some land and house with some crays and turtles

    • ReplyMariAugust 31, 2016 at 5:58 pm

      Hi! No, crays/crabs and turtles cannot be combined. Crays and crabs can’t either. Sorry!

  • ReplyMichael CAugust 4, 2016 at 11:57 pm

    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?

    • ReplyMariAugust 9, 2016 at 9:50 am

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

  • ReplyAndiJune 4, 2016 at 9:50 am

    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.

    • ReplyMariJune 4, 2016 at 2:05 pm

      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.

    • ReplyStephenJuly 31, 2016 at 6:09 am

      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

      • ReplyMariAugust 1, 2016 at 11:16 am

        That doesn’t seem like she’s molting. Have you done a water test?

  • ReplykennyMay 22, 2016 at 5:57 pm

    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

    • ReplyMariMay 29, 2016 at 7:37 pm

      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!

  • ReplyblucanaryApril 9, 2016 at 12:19 pm

    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

    • ReplyMariApril 9, 2016 at 10:52 pm

      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!

      • ReplyblucanaryApril 10, 2016 at 10:25 am

        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

        • ReplyMariApril 10, 2016 at 10:33 am

          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. :/

          • blucanaryApril 10, 2016 at 12:31 pm

            oh okay

  • Replycaroline murrayMarch 4, 2016 at 7:22 am

    sorry another question can I keep a lobster or other crabs with the red claws please??

    • ReplyMariMarch 4, 2016 at 12:43 pm

      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!

      • Replycaroline murrayMarch 5, 2016 at 8:34 am

        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 🙂

  • Replycaroline murrayMarch 4, 2016 at 7:20 am

    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 🙂

  • ReplyKateFebruary 11, 2016 at 6:18 pm

    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?

    • ReplyMariFebruary 13, 2016 at 2:44 pm

      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?

  • ReplyElwoodJanuary 5, 2016 at 12:46 am

    Thanks for the info

  • ReplyPaytonJanuary 4, 2016 at 7:54 pm

    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

    • ReplyMariJanuary 4, 2016 at 8:52 pm

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

      • ReplyPaytonJanuary 5, 2016 at 2:32 am

        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

  • ReplyElwoodDecember 29, 2015 at 1:23 am

    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

    • ReplyMariJanuary 2, 2016 at 3:40 pm

      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!

      • ReplyElwoodJanuary 5, 2016 at 12:45 am

        Thanks for the info

      • ReplyJulian munozNovember 25, 2016 at 10:13 am

        I was wondering if my red clawed crabs can eat a unique blend of pellets, dried shrimp, and mealworms .

        • ReplyMariNovember 25, 2016 at 11:01 am

          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!

    • ReplyKellyJuly 14, 2019 at 10:55 am

      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?

      • ReplyMariJuly 15, 2019 at 1:55 pm

        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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