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FAQs on Freshwater, Terrestrial Crab Systems

Related Articles: Fresh to Brackish Crabs, Freshwater Crustaceans, Invertebrates for Freshwater Aquariums by Neale Monks, Forget Crawfish Pie, Let's Make a Crawfish Tank! By Gage Harford

Related FAQs: Freshwater Crabs 1, Freshwater Crabs 2, & FAQs on: FW Crab Identification, FW Crab Behavior, FW Crab Compatibility, FW Crab Selection, FW Crab Feeding, FW Crab Disease, FW Crab Reproduction, & Fresh to Brackish Water Crabs, FW Crustaceans 1, FW Crustaceans 2, Terrestrial Hermit Crabs, & Marine: Hermit ID, Hermit Behavior, Hermit Compatibility, Hermit Selection, Hermit Systems, Hermit Feeding, Hermit Reproduction, Hermit Disease/Health, & Crayfish FAQs, Crayfish 2, Crayfish ID, Crayfish Behavior, Crayfish Compatibility, Crayfish Selection, Crayfish Systems, Crayfish Feeding, Crayfish Disease, Crayfish Reproduction,

Calcium in Crab & Shrimp Tanks     6/2/16
I keep a few crustaceans (Panther crabs, Rainbows crabs, Geosesarma crabs, Crayfish and Cherry Shrimp). I know that calcium is important for the proper development of their shells. I have looked all over the net and can't find any definitive information on how much calcium and how often it's needed, so I'm hoping you can help.
I bought some small calcium tablets (1" long by .5" wide), but I haven't put them in the tanks yet. I need to know how often I should be giving my crustaceans calcium and how much. So far they've been doing good but I want to make sure they have the best care possible.
Any help is much appreciated. Thank you.
Kind Regards,
<As with humans, it's the "bio-available" Ca that is important; and for freshwater organisms this takes the form of both dissolved and macro-sources. Unless you have a Calcium concentration test assay, I'd rely on "hardness" as a measure here; and aim for "medium hardness" (measured in various ways: https://en.wikipedia.org/wiki/Hard_water
AND I would use the small calcium tablets you mention (or softer sea shells, cuttle bone) as an exogenous source these animals can/may pick on.
Bob Fenner>

Parathelphusa pantherina Biotope Aquarium      6/15/14
Hello, I've emailed you before and have had great service from you and you seem to know your stuff, so I thought I might run a few things by you again to see what you thought.
<Fire away.>
I am planning a biotope aquarium based on Lake Matano with the prime species being Parathelphusa pantherina (Panther Crab). I have had some of these before and have learned quite a bit and hope to succeed in breeding them this time.
Last time I kept them, one was a female and released her pheromones in a too small of an aquarium and drove the males crazy. Needless to say, I found her limbless and she didn't make it.
<Some potential to separate them is surely a good idea, e.g., with egg crate. Do read on similar problems with cichlids.>
Anyways, I plan to keep them in a DIY acrylic aquarium measuring approximately 74 inches by 52 inches by 18 to 20 inches tall. I plan on housing three trios in this aquarium (trio = one male, two females). I've
done the math and this should leave plenty of space for them.
<Let's hope the crabs understand the maths too. Seriously, the hobby's track record of keeping amphibious crabs together is very poor. Many were shipped in soap boxes once upon a time, singly, so they couldn't interact with any others. During moulting they are all especially vulnerable, because a moulting crab is defenceless and viewed as an easy meal for any other crab. In the wild moulting crabs use deep burrows or something else to hide in.>
It's recommended you have one square foot of surface area to each inch of crab, so for these crabs being three inches, they need approximately three square feet of area each.
<While this recommendation sounds good, I suspect surface area is less important than topology. A crab isn't going to ignore one that's an inch outside "it's" square foot. So while providing space is important, you
probably also need rockwork, caves, 3D climbing structures and space above the waterline. This latter is important. A crab feeding on land can't see one below the waterline, and vice versa. I'm no expert on crab behaviour, but I'd also suspect they have different sets of behaviours used above and below the waterline because the predators, resources and stresses will be different.>
In the aquarium I have planned, this leaves just enough room for all nine crabs. I plan to replicate Lake Matano as much as possible including aquarium inhabitants but as of yet have not researched what other species of aquatic life are endemic/native to the lake, but I am open to suggestions (fish spp, shrimp spp, maybe some good substitutes).
<Snails and shrimps are definitely crab food, so a non-runner. Fish will be highly risky, as ever with crabs. While these crabs aren't fish predators, they are fish scavengers, and if a crab comes across a sleepy fish or manages to corner one... we'll, that fish becomes dinner. One crab might be tenable with a bunch of (initially inexpensive) fast moving midwater species along the lines of big barbs, but the more crabs, the less peace the fish will have. I think you're trying to do too much here. Breeding will require one set of criteria: potential to isolate "picked on" individuals; easy cleaning to reduce bacterial and fungal infections of eggs; countless hiding places to break up lines of sight; and some degree of flexibility so you can change the tank decor as needed when the unexpected happens. A biotope aquarium is designed for aesthetics, usually as a caricature of a particular place or habitat. That tends to force you to decorate an aquarium in a way that is less easy to maintain, rearrange or divide up with egg crate.>
I hope to create as much of a fully sustaining ecosystem as possible in all future aquariums but will be prepared to intervene if necessary.
<Do read "Dynamic Aquaria" if at all possible; the science behind microcosms that sustain themselves has been done, is extremely complex, and for home hobbyists, overwhelming. That said, if you're prepared for the extra cost needed for a biotope aquarium (e.g., in optimising plant growth) and stock the tank very lightly (understocking is virtually essential) then you can create tanks that more or less manage themselves in some regards, such as algae control and even population if the fish or shrimps breed.>
I know you recommend housing crabs alone,
<With good reason.>
but I feel confident about what I am embarking on.
<Which is fine. But have a Plan B.>
I plan to use driftwood with some sticking out of the water so the crabs can climb on them if they want, some sort of sand (open to suggestions)
that is natural-like, and rocks (what kinds of rocks are in Lake Matano?).
<No idea! But use neutral rocks regardless, such as granite or slate since the water isn't especially hard.>
I am open to suggestions on my setup. I will not be putting anything near the edges for them to climb out of the aquarium (to help prevent fatalities).
I will have a sump with heaters and plants for filtration.
<How will you keep the crabs out of the sump?>
A drip system will continuously cycle my aquarium to help reduce concentrations of hormones and prevent need of water changes (water will be dripped into aquarium and excess overflowed out through the sump).
<Unless the hormones are diluted with fresh water, and old water continually leaves your aquarium (and sump) for the drains, hormone levels in the tank will not go down. Honestly, I suspect managing crab behaviour this way is dubious. Indeed, I can't find anything on Google Scholar about Parathelphusa hormones. Is this something brewed on the Internet or some cutting-edge scientific research? All the crustaceans I've ever worked with have been visually-oriented animals that use body postures, claw waving and so on to communicate. So while Panther Crabs aren't nearly as lethal as, say, Soap Box/Rainbow Crabs, I'd still be focusing on ensuring a complex, 3D habitat with lots of objects breaking lines of sight, as well as plenty of suitable caves and burrows. Might end up looking less like the Lake
Matano, but would nonetheless be more suitable for keeping crabs in numbers greater than 1 specimen.>
Any suggestions? I appreciate you answering my questions and giving me advice on how this may or may not work out. Have an awesome day!
<Most welcome, Neale.>
Re: Parathelphusa pantherina Biotope Aquarium      6/19/14

So, I've decided to play it safe and focus on breeding the crabs first. I was reading up on a few things and came across your article about the freshwater deep sand bed. I was wondering if it'd be possible for me to set up one of these in a 10 gallon aquarium with one crab?
<Do you mean Deirdre Kylie's article?
Doable, yes; worthwhile, debatable. A 10-gallon tank isn't especially large; the standard US version has a depth of 12 inches (about 30 cm).
Since you need 3 inches (at least) for the DSB, that leaves you relatively little for the water. It would certainly be fun trying, but think about any potential compromises you might have to make. I will also observe that crabs are almost always deposit feeders to some degree, which means they sift mud and eat any organic material they find. That's great in the wild, but will make a full-featured DSB somewhat less easy to create because things like worms and micro-crustaceans are going to be eaten.>
I plan on putting one crab in a 10 gallon with a 10 gallon sump.
<Ah now, the DSB in the sump *would* work, and could work great.>
The 10 aquariums would be connected to each other via an overflow in each aquarium.
<Sounds good.>
I may put in a water bridge, but just thought of this as I was typing this, so I'm still undecided on this. Anyways, what are your thoughts on the deep sand bed? Will the crabs burrow too much?
<Not sure these are deep burrowing crabs, and don't look like them, but most crabs do usually move about the top layer of mud as indicated above. I have no idea how much movement this species is likely to carry out, but I'd be aware of the possibility.>
Should I just have it in the sump? I plan on a three inch deep substrate for the DSB, and in case the crabs want to burrow. Thank you for your time.
Have an awesome day!
<Breeding projects are most easily done in the cleanest possible tanks for various reasons including minimising opportunistic bacteria and making it easy to see eggs/fry. If this was me, and breeding was my goal, I'd probably look at plain tanks, sponge filters (great for aufwuchs growth) and easy to clean climbing surfaces for the crabs. But if breeding is a welcome spin-off rather than the prime goal, then a "freshwater reef tank" project with the focus on microbial life could be very worthwhile, and might provide opportunistically useful food and niches for crab eggs/zoea.
I think you will need to consult Google Scholar to find out whether Parathelphusa spp have a marine larval stage; I do not know if they do (many amphibious crabs do) and that may be a complicating factor that
requires collecting eggs, transferring to brackish then salt water, and rearing accordingly. Has been done, rarely, in the case of some freshwater Gobies and Amano Shrimps, but obviously a major project. Cheers, Neale.>

Fully Aquatic Freshwater Crab? 8/10/11
Well, I'm using a different e-mail but I wrote you awhile ago, twice. (I forgot the address and password of the e-mail.) Both times it involved things in my aquarium dying.. (First my Crab, then all my Neon Tetras)
I recently re-visited the place I buy my crabs, shrimps, and fishes from. (I don't buy fish anymore after that Neon Tetra incident.) After you told me that crabs should have land I noticed that the crabs I buy have only water in their buying tank and no land. I decided to buy another and pay a lot closer attention to them. The new one I bought is a lot smaller than the old one, but still the same species. Are there any fully aquatic freshwater Crabs?
<Mmm; none that I'm aware of, no>
If so, is mine? I don't know the scientific name for it but I can describe him.. it looks a lot like the female Flower Crab. (Portunus pelagicus)
<... this isn't a freshwater animal: http://en.wikipedia.org/wiki/Portunus_pelagicus>
Since I didn't see a single male among them, or one that looks like a male, I can only assume that the crab is not that species.
It has mainly a light brown color with many small black dots around its body. It has an orange color under its claws and the back of its shell is mainly dominated by those black dots. Its eyes are completely black, its legs are orange, its underbelly is white, and if you were to stretch its legs from side to side and measure it across it would probably be 1 and a half to 2 inches. It's quite shy as whenever I walk by it will run for cover immediately while my other Crayfish just sit there unwavered. It seems very passive and it won't kill anything (At least from what I've seen.) It also likes digging up the ground and creating ditches. It eats all the plants I buy (over a span of around one plant per 2 weeks) One thing I haven't mentioned about the previous incidents is that my crayfish are not the ones with claws. They have no claws and are very, very small. (Around a fourth of an inch!) If you can identify this Crab, what should I do to ensure it lives well and is it fully aquatic?
<See the Net>
Sorry for it being so long but I have one last question... A really long time ago when I was first setting up my aquarium and I finished the starting group of animals I got were: Around 4 mini-Crayfish and one that was about an inch in size, was bright Orange and had claws. It seemed to eat all the crayfish though I never caught it I always noticed the numbers of my Crayfish decreasing. I later asked the owner if these ate those mini-Crayfish and he said they didn't though all my crayfish seemed to die in the same area. (Feeding Ground?) Eventually it passed on and I wanted to know he was responsible for the deaths of my other Crayfish or if there could be another reason.
<Could be... Read here:
and the linked files above>
Really sorry about all these incidents that talk about my crayfish/fish dying, must make me sound like a terrible 'aquariumist'.
<A developing one. Bob Fenner>

Panther Crabs! 6/29/11
Hey there folks! As always, I have a few questions if you don't mind helping me out with! I've looked far and wide for a completely fresh water dependant crab! Parathelphusa panthernia
<Parathelphusa pantherina.>
appears to be just what I've been looking for but is it all of what little I've read it to be?
so here we go!
#1 T or F - I've read it does not require a land portion for its habitat and can purely stay in a fully filled aquarium.
<More or less. They will crawl out onto floating plants and above-the-water wood or stones, but only for short periods. So provided there's at least a bit of land, even if that's just the top of an internal canister filter it can perch on, it'll be happy. Conversely, yes, it can climb, and yes, it will escape from an aquarium given the chance.>
#2 T or F - It IS completely Fresh water, NO BRACKISH or full marine needed.
<Is indeed freshwater. Hard, alkaline freshwater.>
#3 T or F - They grow to a decent size, 3 inch on just the shell, but with legs around 5 inch, and thus the minimum tank size is 5 gallons per crab (2 for a 10 gallon)
<Two will kill each other. One in an 10 gallon tank would be fine. If you get one male and two or more females, allowing 25-30 gallons for the first trio, and another 5-10 gallons per extra female, you should be okay. But two males will fight.>
#4 T or F - They will eat or uproot plants, even the toughest leaves are not safe from their grasp!
<Yes, they are omnivores and view plants as food. But tough plants like Java fern should be okay, and fast-growing plants like Hygrophila and Indian fern should keep up with any damage. Just don't expect to keep one in an Amano tank!>
#5 T or F - They WILL eat any sort of dwarf crayfish, shrimp or fish that it can catch or get a hold of somehow.
<Yes, they are omnivores and view any fish, shrimp or crayfish as potential food.>
Anyone with knowledge on these crabs PLEASE help with these T or F questions! I have a 10 gallon all ready and waiting for either these panther crabs (preferred), dwarf crays, or Aegla sp. argentina (if I could even find any), my tank is a low light set up so it has crypts Anubias and soon to be mosses, so hardy plants for that matter..
I thought you would enjoy a little T or F trivia to change the pace of your email reading haha! -Shovelman (AKA-John)
<Certainly makes a change! Nice animals, by the way. Cheers, Neale.>
Re: Panther Crabs! 6/29/11
Thanks Neale! You don't by chance happen to be on tropical fish forums as well? I always see "Neale" replying to many questions and concerns in the oddballs section most frequently?
<Yep, that would be me! Cheers, Neale.>

Crab identification 11/17/10
Hello, I was wondering if you could help me identify a large crab that I recently bought from Petco. They had it labeled as a "Thai Red Devil Crab" but all my internet searching on this name has not found any results. He is about 4 1/2 to 5 inches across with a purplish red shell. His left claw is much bigger than his right, but not quite as much of a difference in claw size as Fiddler crabs. On a side note, I was wondering if crabs use their large claw for anything other than attracting the ladies. Anyways, I currently have him in a 10-gallon semi brackish tank (he will be upgraded to a 25 soon) with a cave to hid in and one of those small turtle docks to allow him to get out of the water. Is this setup ok or should I switch to a terrarium? I also included some pictures of him and one of my crayfish for your convenience. Any help would be appreciated.
<Hello Zach. You appear to have a male "Thai Devil Crab". They're periodically traded but I have no idea what their Latin name might be. In any case, they get quite large, and they are notoriously aggressive and
predatory. They do appear to be more or less aquatic in the same way as many other estuarine crab species -- i.e., by choice they stay underwater, but that can venture onto land for short periods. An arrangement of rocks above the waterline that allowed the crab to bask under the light should it choose to would be helpful, but otherwise don't worry about providing this beast with a land area. Thai Devil Crabs don't seem to be amphibious in the same way as Soapdish Crabs or Red-Claw Crabs. One clue is their rather flat body compared to the much more boxy, deeper body shape typical of amphibious and land crabs. They do require brackish conditions though, SG 1.005 is ideal, and I'd also recommend using marine aquarium Iodine supplement at about 50% the recommend dosage. Although crabs are carnivorous given the chance, their diet should be distinctly mixed with plenty of green foods alongside meaty treats such as tilapia fillet and unshelled prawns. As for differences in the size of the claws, so far as I know this species has claws of similar size, so your chap has probably lost a claw at some point, and it'll be a few moults until the new claw matches the other claw in size. Crabs do indeed use their claws for all sorts of things, from signaling to one another through to dismembering prey, snipping off vegetation, crushing snail shells, climbing up things, and of course for nipping at anything that attacks them. Crabs are fascinating animals, among the Nature's success stories, and quite a sophisticated and modern group of animals despite their sometimes archaic appearance. Cheers, Neale.>

Re: Crab identification, salt 11/17/10
Hello again and thank you for the quick reply. I don't think my crab lost his claw in a fight as all the other crabs in the tank also had one large and one small claw. He also uses his small claw to pick up food like
fiddler crabs. His large claw has roughly the same proportions to his body as a fiddler but his small claw is a little bigger proportionately. If both his claws were the same size as his left I don't think he could move them. I'm sorry if you didn't get the picture I will paste it to this message. As for the salinity, should I use marine salt or is their a salt specifically made for brackish water? Sorry if that sounds dumb I don't know much about saltwater tanks.
Thanks in advance
<Hi Zach. The claw could easily have been damaged prior to collection.
While it is not uncommon for crabs to have dissimilar sized claws through accidents and fights, Fiddler crabs are exceptional in having one claw massively overdeveloped as a signaling/fighting tool rather than one for feeding and climbing. So far as I know, crabs don't do the lobster thing of having one claw for crushing and one claw for snipping. Yes: marine salt mix is what you need, not "tonic" or "aquarium" salt used for treating freshwater fish. Around nine grammes per litre should be ample, with iodine added. Without the iodine, large crustaceans are extremely prone to moulting problems in captivity. Iodine-rich foods such as Sushi Nori make particularly good supplements to their diet for the same reason. Cheers,
Re: Crab identification, sys 11/17/10
Hi sorry for so many questions (this is the last one) but how long can these crabs live in freshwater? The salt in his tank is "aquarium" salt. I might not be able to get marine salt for a couple days will he be ok until then? I don't know how long Petco had them in freshwater but he's been in my tank 5 days. Thanks.
<Hello Zach. "Aquarium" salt will do for a few weeks, but in the longer term the lack of calcium salts as well as iodine could cause problems. If you can, add 1 teaspoon baking soda (sodium bicarbonate) and 1 tablespoon Epsom salt (magnesium sulfate) per 10 litres alongside the aquarium salt.
These will provide some of the minerals crustaceans need for their shells.
Also, add the iodine, either in the water, or through foods rich in iodine (there are some special crab pellets available from companies like JBL).
Cheers, Neale.>

crab compatibility 11/19/10
Hello, I would like to thank you again for all the info on my Thai Devil Crab. I am going to get him some marine salt this weekend. Anyway, my question is would a devil crab be compatible with a Halloween
crab(Gecarcinus sp.)? I know crabs are aggressive but I figured that since the devil crab is mainly aquatic and the Halloween crab is mainly terrestrial they would pretty much ignore each other. They would both be in a 55 gallon tank, (half water half land) about 4 ft long and 1ft wide.
<Easy one this. No. These large crabs are extremely intolerant of one another and in a small vivarium like yours cannot be reliably kept together. When one crab moults, there's a good chance the other one will
attack it. Cheers, Neale.>

Question about my rainbow crab 6/21/10
Hey, I`ve owned my rainbow crab `Peaches` for 4months now, he's so adorable.
<Cardisoma armatum, I assume? There are, unfortunately, other crabs sold under the "rainbow crab" name.>
I keep him with loads and loads of sand that he happily burrows in and a plant pot for hiding and a lunchbox full of normal tap water.
But I`ve been reading a lot about having to treat the water or use `saltwater`, I love this little guy to pieces and would appreciate any professional help you can give me with his upbringing.
<Actually, while these crabs do come from coastal regions of West Africa, they don't appear to need brackish water to do well, though they may well need brackish or saltwater for breeding. The use of a marine aquarium
iodine supplement in his bathing water, at one-half the dose recommended for marine tanks, would actually be much more useful. With that said, if you wanted to (also) add 2-3 grammes of marine aquarium salt mix per litre
of water, that wouldn't do any harm, and may even do some good.>
He seems quite happy though but I really don't want to risk anything with looking after him. Any help would be much appreciated :-) many thanks,
<Cheers, Neale.>

unknown crab, terr. 4/19/09
I hope you can shed some light on my current dilemma and give me a few pointers and how to take care of this beautiful crab I rescued today. I received a call from a friend that works at PetCo. He says "I have this awesome crab that someone just dropped off in a bucket and have no idea what to do with it. Do you want it?" Of course being the lover of all God's creatures that I am, I said "Yes". Keep in mind, I have zero idea what I have or how to care for it.
<Usually not difficult with crabs. They need something very similar to what you'd offer frogs or newts: shallow pool of water to bathe in; lots of damp moss and rock above the water; a source of warmth; and an enclosure with a tight lid so they can't escape. Virtually none of the species in the trade is aquatic, and all will spend most of the time on land.>
I have six fish tanks, all freshwater and no crab experience. I have searched the web to find not much info. It looks a lot like a soap dish crab, same basic shape, but this one I have is so awesome in color. Not
plain reddish/brown like the pics I have seen online. One call I made said possibly a Thai Devil crab. I am attaching a photo. It is female, I do know that much.
<Very likely a Cardisoma species of some sort, so basically similar to the Soap Dish Crab in terms of being terrestrial, largely herbivorous, and highly aggressive.>
She is currently in a 20g tall tank with a mix of gravel and crushed coral.
<It's a land crab. You can easily tell land crabs from underwater crabs.
Land crabs have tall, boxy bodies. They have that shape to make space for the structures that effectively function as their lungs. By contrast underwater crabs are usually more flattened so they are streamlined and not pushed over by water currents. Another good clue is the back pair of legs; on underwater crabs these are usually flattened into swimmerets, basically paddled; on land crabs they are pointed, just like the walking legs.>
I have a submersible filter running and I have some rocks she can climb out onto so that she isn't constantly submerged and have given a healthy dose of aquarium salt.
<Not a brackish water species, so far as I know. I'd certainly not keep her in an aquatic environment. Honestly, she's a land animal.>
I read in a several of the forums that I may need to get iodine supplements and some different salts. Does she need a heater?
Anyway, so far she seems to prefer being under the surface for the most part. Every now and again she pops up out of the water just far enough to inhale through her "nose" and immediately exhales through her back side. I want to absolutely do right by her as she has obviously had a decent life so far. Can't imagine someone just bailing on her as they did today. She is fairly good sized with her body being about 2.5" across. Many thanks in advance for whatever info you can help me with.
<Read up on Cardisoma species, and keep in the same basic way. These animals like damp, but terrestrial, habitats and feed extensively on soft fruits, dead animals, etc. Couple of inches of filtered water ample. Iodine supplements are useful. Cheers, Neale.>

Re: unknown crab 4/19/09
Thank you so much for the super fast reply.
<Happy to help.>
Beautiful isn't she?
<And how!>
We are just amazed at her colors. I am real concerned about taking care of this crab. Ok, just a couple more questions. Is the 20 tall big enough?
<Should be ample, especially if you use lots of bogwood or whatever to create places to climb.>
I have a 55g that has a crack in the bottom that is not being used. Or is that overkill?
<I'm sure the crab would love that tank, but why not keep things simple and inexpensive for now?>
Is the gravel and crushed coral ok or should I get a bunch of moss instead?
Or both?
<Either. These animals aren't at all fussy. Wild animals burrow into mud.
They burrow into the mud along river banks a lot, so if they can dig, that's great. Here are the things that matter: Firstly, that you can clean the tank out easily. Some folks find "disposable" media like coconut fibre
the ideal in this regard, simply cleaning it all out before it gets smelly.
Other folks prefer substrates they can clean every couple of weeks. Either is fine. What matters more are [a] a hiding place; and [b] humidity. Provided they have these things, they really aren't fussed. So a cave or hollow ornament or whatever where they can hunker down periodically is useful, and as for humidity, a plastic drip tray or even a regular hood should take care of that. Within these restrictions, be creative!>
I have made her a larger land area by making a plateau out of the gravel and siphoning out some of the water out. Seems to work ok with the filter still circulating all the water through the raised gravel area. She wants nothing to do with the "land" area and dives right back into the water.
<Really? That's odd. Well, since I don't recognise the crab to species level, let your observations be your guide. She certainly should have land, but if she's nervous or otherwise fussed about something, she will feel more secure under water. Start off with a 50/50 mix of land and water, and see how you go.>
Maybe that's just what she is used to. I hollowed out a spot in the gravel so there is just a shallow pool. She is staying there for the moment. As far as heat, get a heat rock?
<I'd recommend an under tank heating mat as being a lot easier to use in this context.>
Of course that would require a real land area wouldn't it.
<Indeed. You may find that if the water area is big enough, heating the water, and allowing the warmed air to circulate, will do the trick. Really depends on how cold the air is in your part of the world. If you're in
Southern California or somewhere with a subtropical climate, merely warming the water would be adequate. Elsewhere, you really want to heat up the whole enclosure.>
Again, I really appreciate your input.
<Cheers, Neale.>

Re: unknown crab 4/20/09
You are awesome.
<Modesty forbids...>
We live in Texas, usually around 74, 75 in the house all year round. Should be warm enough I'd think. She ate a nice piece of cantaloupe while we were making breakfast. I feel much better now that she has eaten something.
Here's a link to a site I found helpful as well.
<Have to confess that this isn't one of my favourite sites; while it has a page on just about everything, it also contains myriad errors and the writers seem to have a slap-dash approach to healthcare and animal welfare.
They seem to offer feeder fish to just about everything, which to me is a massive alarm bell that rings "bad fishkeeping".>
We will stick to the 20t for now as I am going to "give" the crab to one of our 12 year old twins. You are of course correct concerning manageability compared to the 55g. The other twin is getting a hand tame pair of
Fischer's lovebirds to "take care of". We all know how that works don't we?
<Indeed... an issue I've commented on here before; by all means share animals with children, but if any parent believes their child will genuinely shoulder all the work (and expense) they're likely to be in for a
Should be fair, we hope...
Again, thank you. We will let ya know how we progress. Have a blessed day.
<I do hope so! And to you, too.>
<Cheers, Neale.>

Re: unknown crab, fdg., sys., beh. 4/22/09
I was mistaken when I said that the crab had eaten a nice piece of cantaloupe.
<Banana! Land crabs seem to love banana, the softer the better! Also try small pieces of white fish, ideally lancefish, which you can buy in pet shops. These have bones in them, and the calcium there is excellent for the crabs. Unshelled prawns, perhaps sliced along the middle to make things easier, are also a good source of calcium. Crabs are scavengers, and generally eat anything that's soft or meaty.>
My wife had removed it as it was getting a bit smelly. The crab has not eaten anything since we got her and has seemingly become very weak.
<Review air temperature and humidity; these are essentially like frogs in terms of care, and cold, dry air does them no good at all. Turning the heater up in the water side of the tank can create more warm, humid
conditions in the land side of the tank. Likewise, keeping the lid more firmly secured will help, too.>
She has not moved much in the past 2 days. Maybe she's getting ready to molt.
<You can actually check this: before they moult, crustaceans absorb extra water. When picked up, you may notice they've both bulked up and yet the shell is softer than normal, and may even yield a bit to the touch. They feel less heavy for their size that you'd expect (a tip you using when buying edible crabs, by the way). While the following link refers to Land Hermits, in terms of generalities, it would hold true for Land Crabs too:
So, prior to moulting, the crab will puff up, become softer, tend to hide away from light, and generally become inactive. Moulting starts with the exoskeleton unzipping, and the crab sort of backs out of its shell,
tail-end first.>
I hope so. We would not feel like very good stewards if she dies.
<I understand!>
Already lost one pet this week :-( One of our Fischer's lovebirds had a seizure and died in my hands.
<Oh, sorry to hear that.>
Of course, I have zero history on the crab. Have tried feeding her a variety of foods to no avail. Any suggestions? Thanks.
<Cheers, Neale.>

FW Crabs Hello again. Thanks for taking a look at my letter. I have a few more questions for you. Using the German crab ID page I found on your site, I have determined that my soap dish crab is the third Thai fresh water crab they have listed, it looks just like my little Carl, right down to the dark zig-zags on his appendages. It says it is of the Demanietta species, but that seems to include a lot of different looking crabs. How can I narrow it down further? < Do a Google search on the web using the Demanietta species you have already found. That should get you closer to a correct ID.> Anyways, I've started adding iodine to all my crab tanks. How often should I add the drop? daily? < Add the drop of iodine every time you change water.> The water I use is well-water with a softener. If this is no good, what type of water should I use? Would adding some sea shells add calcium to the water? < All crabs like brackish water. I would use the softened well water but add some sea salt and micronutrients at about 1/3 to 1/2 the dosage recommended for salt water.> I know the fiddlers prefer brackish water, does Carl need some salinity also? < You bet.> Should I change the water to brackish? < The sooner the better.> Would his feeder minnows tolerate the salt? < They are pretty tolerant to salt and would probably do OK.> He has not molted since I have had him, but I just figured he was big enough that he only molted once a year. Am I incorrect with this assumption? < Sounds like a pretty safe assumption.> How big is this guy supposed to get, anyway? What is this creatures lifespan? well, thanks in advance, Scott < They usually get about 2 to three inches across the body and will probably live between 2 and 5 years depending on how old Carl was when he was caught.-Chuck>

Bettas and brackish This question is threefold, but background first. I have a two-year running planted tank with just about the easiest to grow plants in them (hornwort and Cabomba weeds) and a Betta (who is in heaven). Ten gallons, inexpensive waterfall-type filtration turned all the way down to keep the water filtered but generally undisturbed at the surface, temperature at 82-84F, full spectrum lighting (as I pretty much used to use it as a plant-isolation tank to get the snails out of them... used to have a swarm of apple snails, which has since stabilized as the Betta tends to eat the egg sacs and young snails... basically anything he could fit in his mouth). It was my first foray into plants and gave me the knowledge I needed to go into planting my goldfish tanks. <Outstanding> I am now interested in getting some (generally) bottom-dwelling small crabs, and according to the research I have done, while they can tolerate freshwater (poorly), they prefer brackish. <Most of the species sold in the trade, yes> I've done research into setting up a brackish system and I feel ready for it. I've also been briefed in the requirements of the types of crabs I'm considering (but will eventually settle on a single pair of a single type, most likely the small red-clawed crabs) and feel ready to meet them. <Okay> Question one is: Can the Betta tolerate a brackish or slightly-less-than-brackish salinity? <Yes... as can the hornwort/Ceratophyllum... but the Cabomba may well do its falling apart act> I'd like to keep him (I got him as a fry and know he is around 19 months of age now) where he is, and possibly just slowly up the salinity to desired levels to get him used to it, as well as letting the microorganism population adapt to the change. <Good technique> Question two: Would the Betta be socially compatible with these scavengers? He generally will sleep on the plants and I've almost never seen him sleep on the gravel (I work nights, and keep the room dark on my nights off, so I have observed him during the 'night' part of his cycle). <The Betta should not harm the crabs, but the reverse may well not be so... almost all crabs are opportunistic omnivores... and if hungry, might attack, consume the Betta> Question three: Answered on your brackish plants page, no, the plants will stick around. Thank you, Dan <Be chatting, Bob Fenner>

Crabby Crab? Sabrina Has Crab Envy! - 09/03/2005 Just bought an apparently Yellow Moon crab from the local garden centre. <Research prior to purchase, next time.... I'm impressed, I suspect you have Geothelphusa albogilva. This animal is currently unobtainable in the US.> Guy said it was ok in my tank with 3 goldfish which are very big. <Likely untrue.> Got the heater for him and the right food etc. <Goldfish are coldwater, shouldn't be heated.> He seems to want to get out of the tank all the time, life seems one big struggle to climb to the top and spend some quality time out of the water on top of the heater or filter system. <Yup, this and all other crabs available in the freshwater hobby absolutely require a land mass with hiding space - these are land animals that spend some time in the water. Geothelphusa albogilva is more terrestrial than anything. At least the animal is actually freshwater. I sure wish we got critters like that in the hobby in the US.> Can't find any info on these crabs <Not much out there, from a husbandry point of view - treat this like any other terrestrial semi-aquatic crab.... Give it a large land mass of several inches of sand and wood/leaf debris, with a great deal of cover/hiding and a few gallons of clean, circulating freshwater.> and worried I'm not looking after him right. Can you give me any advice on making sure he has good quality of life? <Just as above - this is an animal worth accommodating.> Would really appreciate your help and comments. <I'd absolutely LOVE some images of this animal.... please.... if you have time and a camera. I have crab envy.> Kind regards, Joanna <Wishing you and your new Decapod well, -Sabrina>

Crabby Crab? Sabrina Has Crab Envy! - II - 09/07/2005 God I feel so naive.....just thought I was buying a funny cute looking crab to live next to my computer and look nice. Guess I was major uninformed. <No worries.... The fact that you are seeking information is wonderful.> Didn't realize I had something unusual! Please excuse my ignorance. <Again, no worries.> I am a total animal lover and now dead worried this poor little creature is not getting the right life. I will transfer him to another tank and somehow arrange land for him to rest on and water when he needs it. How come I can easily buy him here and you can't over there? <I have never heard of Geothelphusa offered for sale anywhere.... But Europe and the UK always tend to get "new" critters a few years prior to the US. There are many shrimp and crabs available in Europe that I'd do a great deal to get my hands on! I suppose I shall just remain patient....> I will take some pictures of him and send them to you... <Much appreciated! I would very much like to see if this is in fact the crab I think it is.> again excuse my ignorance as a first time crab owner but what's the interest? He's not yellow or looks like he's from the moon haha, just a small baby crab that's whitish in colour and likes sitting on the heater. <Once in a proper environment, I suspect you'll find him much more interesting. The interest, to me, is that I have quite a passion/fascination with invertebrates, especially crabs and shrimp.... the interest with Geothelphusa, to me, is that they don't or shouldn't require saltwater access.... If there were more truly freshwater land crabs available in the hobby, folks would be more easily able to care for them properly, which is one of my main desires....> Guess I'm entering a whole new dimension I didn't know existed out there. <Invertebrates are really amazing animals!> Would love to chat more, thanks for replying so quick. <You bet. Sorry for the delay in this response; I've been traveling a bit.> Where about in the US are you? <In California.... In the Santa Cruz mountains. Beautiful place.> I'm over in UK in Yorkshire - God's Country. <Sounds excellent!> Best regards, Joanna <Wishing you and your crabby pal well, -Sabrina>

Crabby Conversion? - 08/07/2005 Can saltwater crabs adapt to fresh water? <Unfortunately, no. Thanks for writing in! -Sabrina>

Halloween Land Crab 03/17/07 Hi, thank you for taking the time to read this. I have what the pet store called a Halloween Land Crab. <Gecarcinus sp., maybe G. lateralis.> He is not set up in some amazing aquarium, he is just in a plastic cage. I have a water dish for him that's 2 inches deep that he climbs in and out of. The bottom of the cage is filled with calcium sand and aquarium pebbles. <Ideally, he needs a sand substrate deep enough and just damp enough to burrow into, and needs enough saltwater and enough freshwater, each in separate containers, deep enough to fully submerge himself - though the land area is by far the most important.> He has been doing really well eating bits of fruit such as apples, oranges, pineapple and also an occasional guppy. <Needs more meaty foods, preferably things like human-consumption shrimp (raw, frozen and then thawed) and fish; krill, meaty fish foods, and also Nori (seaweed) would be other important foods.> But recently three of his legs fell off on his right side! What is going on? <Likely he is very deficient in something that he needs - saltwater, perhaps, or iodine.... Feeding the foods mentioned above, especially shrimp, krill, and Nori which are rich in iodine, will be very important. Supplementing the food with a reptile calcium supplement will be helpful, as well.> He was not in a fight with another crab and I've never experienced him going through the "shedding process"! Is he unhappy or sick? How can I tell what's going on? <sounds like a state of disease, not a normal molting situation at all.... I would urge you to improve this critter's living space and food.> If this is below what you guys do, then I'm sorry to waste your time, <A question is never a waste of time.> I just need simple answers and can't seem to find them anywhere. <Thank you very much for searching for your answers, and for asking questions.> Nick <All the best to you, -Sabrina>

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