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FAQs about Red Claw Crabs 

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Red Claw Crab and salt      2/23/15
I tried to find a similar post on your site sorry if this has already been addressed.
My dad put together an aquarium for my kid and i wanted a crab, well i wanted a blue crayfish but those were $25 and the crabs were $3 and they were equally as cool if not more so.
<Quite so. Land crabs are nifty animals in lots of ways.>
ANYWAY i did do research beforehand and i DID know brackish is preferential if not essential.
<Something like that. Since these crabs are essentially amphibious, assuming the "land" is somewhere humid and warm they only spend part of the time underwater. Brackish water probably helps them, in the long term, but yes, they do seem to live many months with just access to freshwater. That said, their distribution in the wild is apparently coastal rather than inland. Their full common name, "Red Claw Mangrove Crab", is probably accurate, and being cynical for a moment, the missing word "mangrove" surely wasn't dropped accidentally by the exporters!>
Depending on who you ask.
<Indeed, the scientists who collect them versus the people selling them in pet stores!>
Well i got her anyway, as the petstore carrying them was keeping her in a cramped freshwater tank. So i justified putting her in my tank and opposed to the petstore or some more ignorant owner.
Now, more to the point, i was sitting on the floor staring at her for a while and i noticed a bag of rock salt next to me. Being the weirdo i am i shoved some in my mouth and then thought maybe i can give the crab some.
<Sure! Provided that salt is not iodised, it should be fine. Not as good as marine aquarium mix, but better than no salt at all.>
So the question is, can i give some to the crab?
Can i safely put a chunk on her rock and have her not die?
<No, you can't stick a chunk in the tank!
Grab a cheese grater or a chisel, grind off or chip away some bits, allowing 6 grams per litre/3-4 teaspoons per US gallon. So if you have a 3 gallon bucket, then 9-12 teaspoons of salt is about right. That will create slightly brackish conditions (for reference: full seawater is 35 gram salt per litre, so what you're making is about one-sixth normal seawater salinity). Dissolve salty chunks in water completely before adding to the aquarium! Now, each time you do a water change, you can replace plain freshwater with a bucket of this slightly brackish water.>
It seems relatively safe and possibly beneficial to give her some to satisfy her dietary needs.
<Dietary needs are primarily protein and calcium! Bits of white fish fillet, unshelled shrimps, and even things like cooked peas and soft fruit. Iodine is the missing thing here, and a prime cause of deaths with crabs. You can buy "crab food" that contains iodine, but it's cheaper and easier to grab some iodine vitamin supplement as used in marine tanks, and dose at one-half the amount recommended on the bottle. Some "sea vegetables" are iodine rich including Sushi Nori and other seaweeds you can pick up in Asian food markets.>
But im no expert on crustaceans (though i do have a 17 year old hermit crab) Would this be a terrible idea?
<Dumping a sodium chloride lump in the aquarium would be catastrophically bad.>
Do you think she would know to "lick" it? Could she "lick" too much and die? I figure she'd be fine since she's in the water most of the time. Are they're any other options to satisfy her salt needs? Maybe a small dish with saltwater in it on her platform?
<Now you're thinking right!>
Thanks for any input.
<Most welcome, Neale.>

My red claw crab is missing 2 legs      5/27/13
I purchased a red claw crab yesterday at a local fish store and i was feeding the fish tonight and noticed that my crab had 2 legs missing on one side he is still getting around the tank ok and he is eating but will his legs grow back or will he die?
<These legs can be regenerated, through successive molts, IF the conditions are propitious here. A lack of predatory tankmates, enough food, alkalinity and calcium, land to get out of the water, scavenge about on... Read here:
and the linked files above; esp. re foods/feeding and systems. Bob Fenner>

Red claw crab (Perisesarma biden), comp., fdg., beh.   4/17/13
Hello again WWM, I have a 29 gallon tank (about 40% land, water is 4 inches deep at deepest point, sand substrate, brackish water, heater that keeps it 80 degrees during the day, 76 at night, quite humid, plenty of slate rocks, 6 good size grasses in and out of water, hang-on 15 gallon filter that I've modified to work as a waterfall) with 6 crabs (3 females, 2 males and one I haven't checked) in it.
<All sounds good.>
I have a couple questions that I can't seem to find any answers to. First of all one male crab is getting ready to molt and is missing both claws.
<Likely fighting; what these crabs do; isolate the victim if at all possible.>
Will he be able to eat at all without them?
Is there anything I can do to help him if not?
<Could try hand feeding, but crabs aren't real smart, so could be tricky.
Possibly crab will have new claws after moult, but if not, will need feeding.>
Also after reading I'm going to pick up an iodine supplement as soon as possible, but the store is quite a trip. Can the iodine in potatoes provide any help for them in the meantime?
<Some, if they could digest potatoes, which I doubt. Sushi Nori and most seafoods will be better.>
I have included them in their diet along with bloodworms, banana, and occasional orange and avocado.
<All sounds ideal.>
They seem to enjoy them but is this just a wasted effort on my part?
My final question would be is it normal that none of the crabs are burrowing?
<Normal. These crabs prefer to climb, when they aren't killing each other anyway.>
They are all quite active (except the one close to his molt) but I want to make sure this isn't a sign of bad conditions. Thanks for your great information and responses, AA
<And thanks for the kind words. Cheers, Neale.>

Red Claw Crab - Sesarma bidens, gen. captive husbandry... Good     10/20/12
I just wanted to write to share my experience with Red Claw Sesarma bidens crabs.

<Fire away!>
Fellow crab keepers, do not let pet stores tell you the crabs are freshwater....provide brackish water (1.005).
<For sure.>
Color will improve, molting will occur without mortality and frankly, the crabs seem more lively.
I also provide heated water to simulate tropical conditions (I live in a cold weather area).
<Wise, indeed necessary, as well.>
My tank is also set up with little coco moss "islands" and plenty of rocks, crevices, decorations to hide in.  Most important observation...THESE CRABS ARE NOT SOCIAL....I started out with five...I have one left (a male named Spiderman Crab).
<This can be a common problem, yes. Doesn't always happen -- does depend on size of vivarium, sex ratio, availability of moulting spaces. But you are quite right, as with all crabs, you should always assume they'd do better singly than in small groups.>
I have witnessed horrors only seen in movies in relation to keeping these crabs together...they will eat one another...even though my crabs are fed a variety of foods (crab pellet, fresh fruit/veggies, and white fish/shrimp), they eat one another.
<Quite so.>
I used to think it was just "opportunity to clean up" after a natural death...that is until I witnessed Spiderman Crab taking a weaker, smaller crab into his burrow (this crab had two of his tankmates--one mutilated with all legs missing and still alive--on his side of the tank and it did not take CSI to figure out what had happened - I literally caught him eating another crab's leg) of course, this crab I have left also happens to be the largest, healthiest and definitely aggressive (I put a small glass crab collectable into the tank just to see what would happen and he attacked it!)
<Nature red in tooth and claw… and as you've seen, well within the range of "normal" crab behaviour.>
Also they are curious and will definitely hide out in the filter, or even escape, so be extra careful when setting up your tank so minimize accidents.
<Another wise observation. I have kept a crab that literally burrowed through a giant sponge filter in the overflow chute down the side of a large aquarium, creating its own burrow.>
Spiderman Crab escaped via the filter and luckily my dog kept going under the chair and crying so when I investigated I rescued the crab and then redesigned the filter cords to minimize chance of another Houdini escape...recap...one crab per enclosure, brackish warm water, variety in diet, secure enclosure and add variety in decor to occupy crab = one happy crab keeper.
<Thanks for this detailed report. Do think that this will help, inform others considering these animals as pets. Amphibious crabs can be very fun "exotic" pets, particularly if you only have limited space, and their needs are minimal in terms of diet and healthcare. But there are some non-negotiable considerations you've explained here, and when people try to keep them in freshwater community tanks, or with freshwater turtles, or really anything other than a crab-specific vivarium, things can (and usually do) go catastrophically wrong. There are one or two breeding reports for this species online; if you're minded, have a read, and you might find another way to deepen your enjoyment of these unusual animals. It's not easy to do, but it is do-able. Cheers, Neale.>

Red Claw Crabs   1/25/12
Most people on the internet seem to think these crabs are mostly aquatic, I saw that you guys say they are mostly land.
<They will'¦>
The problem I have is that my crabs never come out of the water (I've only had them for four days, so I shouldn't say never).
<Quite so.>
I do have the tank set up as aquatic only with a few bits sticking out of the water.  But still, they seem to only like the water.  So, I guess my main question would be, why do you claim they are mostly land crabs
<Because they are -- in the wild at least. They live in mangrove forests feeding on leaf litter and carrion. Do read up on Perisesarma species, which is what these are.
They're shore crabs, If they don't come on land in your aquarium, then something is amiss. They won't come out if there's something scaring them, or if the air is too cold or too dry. They're also EXTREMELY territorial, and if one crab claims the one small bit of land, the others may not be "allowed" out.>
and is there a resource that can give me a step-by-step on how to set up and care for these crabs?
<Not that difficult. Set up something like you'd create for mudskippers, with a couple inches of warm, brackish water (SG 1.005 at 25 C/77 F is fine). An under tank heater would be ideal. The rest of the tank can be sand, rocks, bogwood. Make sure the air inside the aquarium is warm and damp, but a slight flow of air is important to prevent mould. Keep the hood secure because these animals WILL escape if they can. Use filter floss or plastic mesh to plug any large gaps. Crabs are cannibalistic at times, especially when moulting, so provide lots of caves and such hiding places.>
I am also wondering how you know so much about them, and speak with such authority when there seems to be so much miss-information out there?
<Because I'm clever. More seriously, because I'm a marine biologist by training, an aquarist by inclination, and I've spent some 20-odd years reading scientific as well as hobby literature on brackish water animals. Perisesarma spp are classic brackish water, mangrove crabs. There's really nothing at all mysterious about them. Yet unscrupulous retailers continue to sell them as "freshwater crabs" or "aquatic crabs", and willfully ignorant aquarists vigorously resist any attempt by people like me to tell them what these animals need to do well. It's significant that the people who succeed with them, e.g., actually breed them, are those who understand their ecology and provide brackish water for the adults and marine conditions for the larvae. Cheers, Neale.>

Red Clawed Crab (Pseudosesarma moeshi / Sesarma bidens), sys., fdg.   12/6/11
Thanks for the excellent and informative site. I really don't know how people managed without the web in this hobby. There is just so, so much to learn.
<Thanks for the kind words.>
I recently purchased 4 of the above for my 140L with, what I must confess, was breathtaking newbie stupidity. I thought, being from the coast as I am, a crab's a crab. It lives in the water and eats dead fish. It was in the LFS freshwater area, so I assumed freshwater.
<Ah, yes, indeed. These are brackish-water crabs.>
I now understand that they need an omnivorous diet, land and brackish water. So I went into action to see what I could do. I straightaway got two bits of bogwood stood end on in the tank and secured them above water as a temporary measure and today began construction of Island of the Crab People, Prototype 1. Layered polystyrene sewn together with fishing gut, with a small rim to hold fine gravel, on top of which I placed a few flat rocks for cover. It's elliptical and about 1 foot x 0.5 feet. This was secured to the bogwood with more gut.
<I see.>
The plans for Island of the Crab People, Prototype 2, are to include an area of the same construction and dimensions, only with a deeper rim. All layers will be aquarium siliconed together and the tray filled shallowly with gravel to make a depression for a small brackish water pond.
The finished article will hopefully be both islands incorporated in one kidney-shaped island made from sufficient layers of polystyrene siliconed together for buoyancy, but with a deeper rim than prototype 1 to hold a deeper area of sand instead of gravel, for burrowing. I was thinking of placing ballast underneath to improve the centre of gravity and the exterior will be finished by brushing all over with silicone and rolling in sand, I'll probably do a couple of coats of that.
Anyway, I thought I'd see what you thought about the remedial actions I have made/plan to make and see if you have any suggestions for improvement.
At some point in the distant future I'll set up a proper vivarium. I'm becoming attached to my Crab People already (sorry, too much South Park) and I don't mind giving them a home to themselves.
<Is usually necessary. They aren't really compatible with much else in the long term. In a really big, sandy beach type aquarium you might keep them with salt-tolerant fish like "feeder" Guppies that are fast enough to avoid trouble (fancy Guppies are too dim and too slow). But really, crabs are crabs, and best kept on their own. They're aggressive, territorial, well-armed, omnivorous, opportunistic and persistent. Not a good combination.>
In the meantime the island will have to serve as the cash isn't exactly flowing at the moment.
Now to the other questions. (It does say don't worry about length of the email in the instructions for contacting WWM - you asked for it!)
<Quite so.>
Part of what I thought about the island, except for scuttle space, was an area to place food on to stop them from dropping it in the water.
<Yes, but they will feed under water.>
From my reading and observation, I understand they like to scoff out of the water. Nope, they just drag it off the island back to a crevice in the bogwood, eat a bit and drop it in the water.
I'm assuming this is down to lack of cover on the island. Any suggestions as to what I can use, or will they make their own cover when I get sand?
i.e. burrows.
<Don't worry about it. Feed sparingly, and feed sensibly. For example, a clam on the half shell could feed several crabs. It's shell would prevent it being moved around. Likewise some soft banana smeared on a bit of bogwood would be another good food choice. When hungry, they'll scour the tank for tidbits so don't worry too much about spillage. Just remove uneaten food after an hour. A turkey baster is super-useful for spot cleaning underwater.>
I'm well briefed on what to feed them now, but how long should I leave the food around for?
<See above. Don't worry too much about this. They are scavengers, and to some degree, need time to crunch up things like the bones in whole lancefish and the shells of unshelled krill, both of which provide the calcium they need.>
With fish I give them a minute, but I can easily see that with crabs it's going to be a lot different. Also, how much food should I put down per crab and how often? I'm totally clueless about how much to feed and I can't see anything about it anywhere I've looked.
<A claw-sized hunk once a day is ample.>
I've read about adding iodine to the water during moulting. In the concentrations recommended, would this harm fish?
<Is safe. But you shouldn't be keeping them with fish anyway; at least, not fish you value. Feeder Guppies are a possible bet because they might breed quickly enough to make good any occasional problems. But even then, any Guppies that move slowly or get old will be eaten -- and not everyone enjoys the sight of a still-breathing, still-living fish being dismembered by a crab. Trust me, these crabs can be brutal.>
I have come across suggestions that the amount of salt that the crabs require wouldn't even harm a salt intolerant fish, i.e. salt to SG 1.010.
I'm taking this with a pinch of, um, salt(!). Could you confirm yay or nay on that?
<SG 1.010 at 25 C/77 F is about half-strength seawater. That's ideal, but not essential. SG 1.005 is a good starting point and will cost half as much!>
The other thing is they don't seem to be actually using the island I have made. One has come over, dragged a bit of lettuce back to the bog wood, chomped for a while and dropped it in the water. It then returned, hauled away a bit of salmon (better fed than the cats, these things!) and ate a bit before, yep, it dropped it in the water. Again I think this is maybe due to lack of cover or it could just be early days yet and exploration will occur overnight.
<It is their nature to drag, dismember, and generally make a mess. Don't worry too much.>
Any comments you can make would be appreciated, especially on feeding.
<Best wishes, Neale.>
Re: Red Clawed Crab (Pseudosesarma moeshi / Sesarma bidens)   12/8/11

Hi Neale
Thanks for the advice. I really appreciate you taking the time to help me out. Unfortunately I am going to pickle your head just a little further.
A vivarium with feeder guppies sounds ideal, really. I'm not bothered if the crabs catch the occasional fish but I would object if the guppies had no chance, though.
<Quite so. A lot depends on the size of the tank. If there's only 5 or 6 gallons of water, and it's all just a couple inches deep, then the odds aren't in the favour of the Guppies. But if the vivarium is a 55-gallon tank and there's 6-8 inches of water, so some 20 gallons of the stuff, then the Guppies might be okay. Use some common sense. Basically, if the crabs can catch small fish, they will. Fiddler Crabs tend to be quite safe with fish, but Red Claw Crabs are much more vicious.>
It would be great to see the crabs with damp sand to burrow in and being able to behave a bit more normally than just sulking on a bit of bogwood.
<Yes. Leaf litter, moss or coir (coconut fibre, sold in reptile pet shops) can work for this.>
I've had cats all my life so a bit of predatory brutality isn't exactly unusual for me. Still, "aggressive, territorial, well-armed, omnivorous, opportunistic and persistent" makes it sound like this is going to be a real adventure!
<Ah yes, crabs and cats share very much the same outlook in life, dividing everything into [a] stuff I can kill and [b] stuff I can't kill.>
My only one worry with feeder guppies is WWM's warning to usually steer well clear of them due to ethics and disease.
<Quite so, in terms of using them as live food. This is much different. Where sold, "feeder" Guppies are crossbreed Guppies, and genetically they're much better than fancy Guppies. They're also cheap. So you can try a few out and see what happens.>
I won't be putting the guppies at the mercy of a dedicated killing machine that's much bigger than them, so ethics doesn't really worry me. As long as they are generally able to avoid the crabs that's fine, since it's more or less the way things go in nature. Disease is, however, more of a worry. Are fish likely to pass pathogens/parasites over to inverts or are they too far removed?
<Little to no risk. Crabs are scavengers anyway, so they're pretty resistant to disease right out of the box. They feed primarily on dead and sick animals rather than healthy ones.>
From looking at these little guy's natural habitat, mangrove leaf seems to be their staple diet in the wild. Apparently oak leaf is a suitable substitute but I can't honestly remember where I found that. I've been digging deep on them and read so much that it's becoming a bit of a blur.
<You can actually buy live mangrove plants, though they're mostly sold to marine aquarists.>
It's hard to find any proper scientific literature on them though, sadly. I confirmed the leaf diet with someone's PhD thesis and that's about as good as it's got. From the same thesis, silt would appear to be the natural substrate at the sites that were investigated, i.e. very fine particles, and that stands up for an estuarine environment. Do you or any others have any experience of using silt in aquaria? My first thoughts are anoxia in the sediment and difficulty in keeping plants to break it up owing to the crabs munching them.
<It's doable, but not ideal. For one thing, silty water is murky water, which isn't attractive. A mix of 50/50 silica sand and coral sand will give you an attractive substrate with some buffering capacity, and you can stir in some crushed shells to add interest. Clam shells and mussel shells would both be very authentic. You can also use silicone to glue together "reefs" of oyster shells, either as lumps by themselves or onto fake mangrove roots -- either would be extremely authentic additions to any brackish water system.>
As a related aside, is it possible to get hold of tropical invertebrates other than shrimp, crabs, crayfish and snails.? i.e. worms and other substrate dwellers. Obviously anything that hatches into an adult with wings is out. I'd be barred from stocking anything if a swarm occurred in the living room.
<There are such animals to keep, but selecting them is difficult. But if you know where to look, or can order them, yes, they're out there. There are lots of brackish water Nerite snails, e.g., Clithon species. though crabs will probably eat them. There are brackish water hermit crabs as well, including Clibanarius tricolor, the popular Blue-Legged Hermit kept by most reef tank keepers. It needs high salinity, SG 1.010 upwards, but is cheap and hardy. Again, wouldn't trust this completely with the Red Claws. Then there's the Mangrove Horseshoe Crab, Carcinoscorpius rotundicauda, a species sometimes sold as a freshwater species but like the Red Claw really needing middling to high salinities in the long term.>
Another concern I have with the crabs is that my tank pH is at 6.8, which I know is a little low for them but, as I understand it, brackish will be >7.5 and within their suggested pH range.
If I set up a pool on their island as brackish will they end up suffering pH shock if they are chopping and changing between pool and tank? Or do crabs, being "amphibious", not work that way? If it is an issue, I may be able to persuade wifey-o that a vivarium is essential and is needed soon.
<Just change the water completely. The crabs walk in and out of different puddles in the wild, and really aren't affected by pH, salinity or hardness in the same way as animals that are completely submerged all the time.>
I doubt that they're going to be a real danger to the fish I'm keeping them with now - 1 lonesome blue gourami. I might actually need some help on this little terror too. When the crabs get bigger it might be more of a worry. They're only at 0.75" to 1" carapace width just now.
Would salt to SG 1.005 harm the gourami?
I've read most anabantids are extremely salt intolerant.
<Yes, with very few exceptions, e.g., Anabas testuideus, the Climbing Perch, which is actually quite common in low-end brackish water environments. There's also -- amazingly enough -- a brackish water Betta species, called Betta sp. "Mahachai".>
1.005 doesn't sound like much but it's about 10 000ppm as sodium chloride (not that I'll be using sodium chloride, don't worry).
<Indeed, it's about 9 grammes marine aquarium salt per litre, well above what freshwater fish enjoy. Some can tolerate this, to be sure, but it isn't ideal.>
And the gourami'¦
The gourami bullied her other gourami tankmate, I didn't think much of it, it wasn't too serious. Then the tankmate died. No fault of the bigger gourami, just the fishkeepers who thought that a filter from an already cycled tank meant that the tank we put the filter in was ready to go. We slapped our foreheads, let it cycle and got a couple of Bolivian rams to add. The surviving gourami hounded them to death. The poor little things didn't stand a chance, stressed with the transfer they were gasping a bit, and listless.
<Oh dear oh dear. I have to admit, I'm not a fan of Three-Spot Gouramis in either their Blue or Golden form. One of the first fish I kept, harassed everything in the tank, and haven't touched them since.>
I saw this behavior with newly introduced golden rams before, so I wasn't unduly concerned, but the gourami moved in and started fin-nipping and not giving the rams a chance to stay still and get over the stress. Both were dead the next day. Could it be the gourami now sees the tank as "her's"?
Would adding more gouramis help disperse the aggression amongst the same species?
<Can, yes, but assuming you add so many she can't bully them all, i.e., six or ten of them. Actually, this species does rather well in large groups.>
Would adding some Danios to distract the gourami work?
(Is this what a dither fish is?)
<No. Dither fish convey to bottom-dwelling fish (such as cichlids) that it's safe to come out. The theory is that bottom dwellers can't see above the waterline, so don't know if there's a predator there like a heron or fisherman. But surface-swimmers do, because they're swimming up close. So, if the Danios are nervous and hiding, then the bottom-dwellers will assume there's a danger. If the Danios are happy, the bottom-dwellers will come out of their hiding places.>
I'd like to see her try to nip a Danio! We're also considering that she might just be an evil little sod in character, but we don't really know.
<Could easily be a bad tempered one, yes. Some Three-Spots are lovely, others mean.>
There seems to be a lot of conflicting opinions out there on the net. Admittedly it's been my wife that's been doing most of the research on this front so I'm not fully up to speed. Some are saying gouramis are fairly aggressive and should be kept singly, some to keep them as a school of four, others that the school of four should be different varieties. I trust the judgment of you folks on WWM more than most so a bit of help would be welcome.
<Just isn't a reliable species, but does tend to harass "similar" fish like other Gouramis as well as Cichlids, while generally ignoring dissimilar schooling fish like tetras and barbs and Danios.>
<Cheers, Neale.>
Re: Red Clawed Crab (Pseudosesarma moeshi / Sesarma bidens)  12/9/11

Hi Neale
Don't worry, I'd give the fish in a vivarium plenty room to move.
Thank you for advice on substrate - I really hadn't thought about the display aspects of a silt based vivarium. As for invertebrates, I'll have a look about.
Cheers for the heads up on the brackish Betta. I love anabantids and having seen some pics of Mahachai I think they top splendens in beauty by a long shot. One for the future I think. Do they have a similar character to splendens? e.g. males in a separate tank etc.
<Yes, Mahachai seem very similar to wild-caught Betta splendens. They do well in captivity, but sadly, they're not much traded.>
"Ah yes, crabs and cats share very much the same outlook in life, dividing everything into [a] stuff I can kill and [b] stuff I can't kill" - this cracked me up! I can see my little crabby killing machines and I are going to get on just fine. If the furry killing machines don't get them first, that is.
<Quite so.>
The gourami I really don't know what to do with. I had read about them before she was introduced but I never read about them being evil little sods. We were hoping to make Ctenopoma (spotted climbing perch) the focus of the tank but I fully believe she'd kill one of those. (Obviously crabs and slow-moving Ctenopoma wouldn't be mixed).
<Ctenopoma acutirostre are some of my favourite fish, but yes, they're slow, stealthy fish with very mellow personalities, and shouldn't be kept with anything aggressive. Corydoras, Congo Tetras, that sort of thing make good companions.>
We might have to look at rehoming Madam Gourami. Any suggestions on this front? I've read a lot of American sites that seem to say you can take fish to LFS and they'll take them. Is this the viable in the UK or is it a case of an advert at pets at home?
<The Maidenhead Aquatics chain will normally take unwanted fish and rehome them. Check their web site for a branch near you.>
If you've any experience of keeping Ctenopoma words of wisdom would also be gratefully received. I know - gill spines, BIG mouth, shy and slow to eat but that's all from web pages. If you have any pointers from direct experience I'd love to hear them.
<There are some nice articles here at WWM:
I have kept them, and they're very hardy and easy to keep, except in one regard: they usually don't care for flake or pellets, so you'll need wet-frozen bloodworms, chunks of fish and seafood, earthworms, and so on.
In terms of personality, I find them extremely similar to Angelfish, except with somewhat larger mouths, so tankmates need to be somewhat larger.
Once again, thanks for taking the time out to help this pair of well meaning but inexperienced newbies
Gordon and Denise

Salt, plants, and crabs -- 07/21/11
Dear plant and crab expert,
<Yikes! Quite a combo, there'¦>
I'm converting one of my 10 gallon tanks to a paludarium. Most of the tank will be water (approximately 4 gallons), with lots of shelves on the back (for plants), and a shelf on the left with a ramp for easy access in case a land animal falls in the water.
<I see.>
I'm planting it with hairgrass, several crypts, and any other plants I can think of, even though I want it to be an Asian biotope (Samolus sp, baby tears, etc). I'd like to host red claw crabs (Perisesarma bidens),
<These are best kept as brackish water animals
and don't do well in freshwater indefinitely.>
Hermit crabs (Uca sp.),
<These are 100% brackish/marine animals -- whatever the retailer says -- and will die unless kept in brackish to marine conditions.>
and some aquatic insects (springtails, water louse, water striders).
<May not/will not be compatible with brackish water livestock.>
I can't really find a solid answer about how much salt is needed'¦ I was hoping 1 tsp of reef salt per gallon would be enough.
<SG 1.003 would be the absolute minimum; that's about 6 grammes per litre of water. Teaspoon measurements are very, VERY inaccurate, but 6 grammes is about 1 level teaspoon. Check it yourself using kitchen scales and act accordingly. Above SG 1.003 you'll have problems with plants; below, the Uca and probably the Perisesarma will be less robust, dying.>
I also can't really find out whether that would kill the plants or not.
<May well do unless you choose plants carefully. As it happens, Samolus valerandi is extremely salt tolerant. On the other hand, Hemianthus callitrichoides is not. Eleocharis species sometimes tolerate slightly brackish water but it varies between species. Hardy Cryptocoryne species like C. wendtii tolerate slightly brackish water, and C. ciliata is a true brackish water specialist. So do your research here, for example:
If I use reef salt, would I still need iodine supplements?
I'll also likely add some glass shrimp to the tank- if they get eaten, that's okay.
<These tolerate slightly brackish water well.>
Because the land area is built of shelves, is it ok if the crabs don't have a dry area to tunnel in? The terrestrial and aquatic plants should provide hiding places to help them feel secure.
<The plants will also be food for the crabs, especially the Perisesarma.>
Can you recommend any other inverts that would do well in this setup?
<Crabs generally don't cohabit with anything, and you would be very unwise to mix Perisesarma and Uca; the Uca are essentially non-aggressive (if territorial) deposit feeders that sift mud and algae, while the Perisesarma are aggressive opportunists that will view the Uca as potential food.>
I was also considering Nerite snails'¦
<Can work extremely well with Uca and shrimps.>
Thanks, David
<Cheers, Neale.>
Re: Salt, plants, and crabs -- 07/21/11
What about moon/Halloween crabs?
<Gecarcinus quadratus.>
I was thinking maybe mixing a mostly terrestrial crab with a mostly aquatic crab so the smaller ones could escape'¦
<Not a chance of mixing Gecarcinus quadratus with Uca spp.; do understand that crab species DO NOT cohabit in the wild, and most view one another as either rivals for living space or potential meals. There is an ample literature on this based on crabs in reef tanks; do read.>
It's ironic to me that Uca might be less likely to eat plants, but prefer more salt'¦
<Hmm'¦ not really ironic, merely a reflection of the fact these crabs come from beaches and salt marshes where freshwater aquarium plant species are absent.>
I might have to decide whether to kill my plants with salt or serve the crabs a salad bar. It's a shame. I might end up having to scrap the crabs altogether,
<Do look at Thai Micro Crabs.>
and go with Cambarellus Patzcuarensis var. Orange, also known as the dwarf mexican crawfish.
<A fine beastie, though irregularly traded.>
At least it's plant-safe and peaceful according to everything I've read.
<Hmm'¦ the smaller crayfish are less aggressive and less destructive, but it would be unwise to assume non-aggressive and non-destructive. Potentially safe in mixed species tanks, but do bear in mind these have only been in the trade a year or two, so there's very little experience to draw on, and certainly not every combination of crayfish, fish, and plant hasn't been tried.>
Not sure if it would ever leave the water though..
<Fully aquatic.>
I don't want the land area to go to waste.
<Paludarium systems tend to work best with frogs, to be honest, rather than inverts. You might consider tree frogs alongside, say, similar sized aquatic frogs or newts. Mudskippers are of course another possibility, and can, if species are chosen carefully, cohabit with Uca spp. and certain brackish water livebearers, such as Mollies. Provided the plants above the waterline are insulated from the brackish water and watered with freshwater, there's little risk of salt poisoning them, and conversely, there are true brackish water plants that might be placed under the waterline to green things up there. Cheers, Neale.>
Re: Salt, plants, and crabs 7/23/11

Sorry, I've been doing a lot of research. I think instead of giving the fiddler crabs (Uca sp) the minimum amount of salt, I'll give them whatever is ideal. Do you think 1.008-1.010 would be about right?
After a lot of research, I've found a list of plants that should survive at those levels... I'll put it here so you can share it with others. I assume some of these plants won't make it, but most should, as long as they're
acclimatized slowly.
Variegated Acorus (Acorus gramineus var. 'variegatus') Terrestrial/Emersed
Cryptocoryne pontederiifolia Terrestrial/Emersed
Crinum Calamistratum Submerged
Lilaeopsis novae-zealandiae (Microsword) Terrestrial/Emersed
Glossostigma Terrestrial/Emersed
Java Moss Terrestrial/Emersed
Java Fern 'Windelov' Undecided
Anubias Nana Emersed
Azolla Floating
Various Crypt species (already had) Submerged, will allow to grow emersed
Hairgrass Submerged
<Would be very, VERY surprised if most/any of these would survive above SG 1.005 at 25 C/77 F. Would strongly recommend you run the tank at SG 1.003 at 25 C/77 F to start with, using those plants. That's just short of 20% seawater, and more than ample for most brackish water fishes and livestock.
It'd be acceptable for your Fiddler Crabs, and being relatively benign animals, you'd have lots of options for things like Endler Guppies, Black Mollies, or, if you can get them, oddball livebearers such as Micropoecilia parae melanzona, Micropoecilia picta, and Limia nigrofasciata.>
For livestock, I'm thinking (I know, I can't seem to make up my mind!) 3-5 Fiddlers, 5-10 opae'ula shrimp AKA Halocaridina rubra (I'll have hiding places to let them get away from the fiddlers in case they think they're food)
<Very likely. Do bear in mind Cherry Shrimps adapt well to slightly brackish water, and in fact virtually all shrimps are worth trying at low-end brackish water.>
In addition, Fiddlers are mostly Diurnal, while the Opae'ula shrimp are mostly nocturnal. To wrap it up, I think I'll throw in a couple horned/corona Nerites and a ghost shrimp.
<Clithon corona, Clithon sowerbyana and Neripteron auriculata would all thrive in brackish water.>
The tank is a 10 gallon. I know they like to dig, but I think they'll have to settle for man-made tunnels made out of 1/2" PVC pipe.
<Cheers, Neale.>

My crab isn't moving, BR 1/1/08 Hello crew, <Greetings and happy new year!> I was wondering if you would be able to help me out. I have a crab (*Seserama bidens*), sold to me as a Red Claw Crab. <Ah yes... now known as Perisesarma bidens, though the red-claw crabs traded may be multiple species, given that Perisesarma bidens is primarily from East Asia while most exports are from Southeast Asia and elsewhere.> I bought it close on a month ago and he quickly became my favourite addition, roaming about searching for food and generally acting in a brazen manner. <Quite so. These are rewarding pets when cared for properly, and well worth their own specialised quarters.> However, I recently purchased a 30 gallon tank filled 2/3, bogwood creating a land area and a rock pile for my two crabs to hide in (the other being a golden fiddler (*Uca *sp.) ) and for my dragon goby (*Gobioides broussonetti*). <A nice collection of livestock.> The new tank seems healthy (specific gravity at 1.005). that's the only real thing I measure) the guppies and platys that share it with them are doing fine, and the fiddler is quite lively. Crushed coral for substrate, java fern floating around, trying to get some pieces to take root. <All sounds fine, though strictly speaking Platies aren't brackish water fish, though my experiences agree with yours that they do well at low salinities.> The problem is the red claw, who used to be quite active, scavenging around his log as well as in the water, recently took to hiding. I assumed it was just molting, and after maybe three days, and no actual result, I picked out the rock he'd been holding on to from the rocky pile as he had not been eating or moving and I feared the dragon, who also likes that spot, might stress him out. <Curious. I'd have associated hiding behaviour with moulting, too. Crabs of most sorts are potentially antagonistic towards one another, so do check there isn't bullying between the Perisesarma and Uca crabs.> He looked just as he always did, no colour change, nothing that would indicate molting to me. As I have mentioned he used to spend a good bit of time on land, I thought maybe he just couldn't get up there now (he'd been missing a leg upon purchase, I know it's a no-no, but he was the only one left, and I hadn't really noticed till I got him home). <A missing leg usually isn't a problem when these crabs; they're quite tough and regenerate lost limbs quickly when kept in brackish water. On the other hand, our ability to prevent secondary infections in invertebrates isn't good, given that things like copper are toxic to crustaceans even at very low doses.> So I slipped him onto the wood and sprinkled a few bloodworms in front of him, he stayed for a while and then crawled off and fell into the water where he landed upside down. Despite much flailing he was unable to right himself, so I stuck the net in and he quickly righted himself. He's been there in the open, next to a large shell for over a day, not really moving and I still haven't noticed him eating. He's not being bothered by any of his neighbours. What do you suppose is wrong with him? <Very difficult to say. One problem with these crabs is they're often traded as freshwater animals, and if they've been kept in freshwater at the wholesaler and the retailer, then they can lose condition. Uca crabs are much worse in this regard than Perisesarma, but it is still one more factor beyond the aquarist's control. We don't really know anything much about secondary infections or parasites of crabs. Pretty much they're either healthy or dying. If yours is going to recover, it will, but otherwise the best you can do is watch, keep the water clean, provide suitable food, and if the crab dies, remove it at once.> My mother keeps telling me he's dead, and I try to tell her he's just molting, do you suppose this is so? He'd often sit for a while not moving before hand, but never for days! I don't really know what's typical molting behavior for crabs, I'd always thought they hid away after they molted, or during, not beforehand. <Moulting is very obvious and usually over in a couple of days. One problem with crabs and indeed freshwater crustaceans generally is iodine. While small shrimps seem to get enough iodine out of the water or their food, larger animals like crayfish and crabs apparently benefit from iodine supplements. These supplements can be purchased from stores catering to marine aquarists as iodine supplements are widely used in reef tanks. At this point it might be too late for the red-claw crab, but any new specimens you buy, and the Uca crab as well, will benefit.> I wouldn't think it would be a problem with my levels, as the fiddler and everyone else are doing fine. I heard a rumor of Java ferns being poisonous to fish, he ate a good chunk of one before I moved them, could that be a factor? <Possible, though normally animals stop eating the Java ferns because they taste nasty long before they actually get sick.> I'm just trying to think of everything here, no matter how absurd. I apologize for my lengthiness, but the instructions on your site said include every detail. Any thoughts would be well appreciated, -Collin <Hope this helps, Neale.>
Re: BR crabs... Now: Specific Gravity 1.010... for Hermits, Dragon Goby... 1/2/08
Hello there, <Hello Collin,> I wrote in yesterday about a crab who's not up to his norm, and I will for sure be trying to track down an iodine supplement (as recommended by Neale) to help out at this stage, whatever good that will do. I had heard about this, but there is a slight lack of aquarists specializing in crustaceans or BW tanks in my area and I couldn't find anything locally on it, but I know of one place that probably has it and knows what they're at. <Anywhere specialising in reef tanks should have this, and failing that, you could obtain online.> But! I have another question: I read on your site that the blue-legged hermit crab (Clibanarius tricolor) could be acclimatized to a specific gravity of 1.010 <Apparently so. Do acclimate them carefully, and take great care to identify the crabs carefully before sticking them in a low-salinity environment. SG 1.010 is at the low end of their range, and you will of course need to make sure other things like water quality are "marine standard".> I was wondering if you could tell me if the inhabitants of my brackish tank would be fine with this level of salt, as my findings on the internet have been rather inconclusive with different authors throwing numbers around as if they were just that: numbers. There doesn't seem to be any set specific gravity that people can rely on for these animals. <Uca and Perisesarma should be fine; both spend minimal time in the water and likely breed in the sea anyway. If you're concerned, put a small basin of plain freshwater for them to drink somewhere on the land. An upturned Oyster shell stuck in the sand would be ideal. Guppies can be acclimated to anything up to full strength seawater safely, but you must do this very slowly, over several weeks. You can actually buy "marine guppies" as feeders for marine fish. The Dragon goby will be very happy at SG 1.010. The only chap who can't be kept there is the Platy.> Anywho, my tank has a golden fiddler (*Uca *sp.), dragon goby (*Gobioides broussonetti*), Red claw crab (Perisesarma bidens), two guppies and two platys. So I was wondering if you would be able to tell me if I would be able to house this little guy sometime in the near future with the current inhabitants, maybe rehousing the guppies and platys? Also, would I be able to add the hermit with the current bottom dwellers that are on the go in there given this is all a 29 gallon tank? I may be short one red claw crab within the next week or two, if that's a factor. (Given his current condition. <I would imagine they will ignore each other. Hermits are too well armoured to be molested by small crabs, and since the hermit is fully aquatic, your land crabs won't encounter them much anyway.> Though I was watching him "scratch" his claws off one another, and against his legs. I know the fiddler and red claw both came from the same tank, same store, only the red claw had been in there about a month later till I bought him, I hadn't really been counting. Could have been FW, I wouldn't be surprised, I'll ask them soon.) <Usually these things are sold as freshwater.> So yeah, thanks in advance for reading my email, You guys are awesome -Collin <Glad we could help. Cheers, Neale.>

Red Claw Crab <Hi Anthony, MacL here. The only red claw crab I know of is actually a brackish crab often sold for freshwater. Is this what you have?> I purchased a red claw crab from a local Fish store about 2 weeks ago. I believe the crab is a female due to the very small claws. Anyway, recently she has had her abdomen hanging open. <Maybe releasing eggs?> I figure she was getting ready to molt, but she hasn't done anything for 2 days now. She has already molted once since we have had her and it didn't take long. She has plenty of different kinds of food. Also these past 2 days she is flipping herself over on her back. <Not a really good sign.> Can you tell me what is wrong? <I'm just guessing here but I think you probably have her in fresh water and she needs some salt. I also think it might be a difference in PH as well.> I have searched through the internet, but cannot find any information on Red Claw Crabs. <I did a search on google and came up with tons of thing on them. You might try www.google.com> Thank you for your time and patience. <Anthony you might do the research on them and decide if it needs to be in brackish water or not and make a decision from there.> Anthony <An excellent site re this species: http://wrongcrowd.com/aquaria/crab/ RMF>

Rogue Crab >Hey WWM crew. >>Hi. >I have a slight problem. >>Me too, but I'm not going to talk about it right now. >My red clawed crab has decided to take a walk on the dry side of the tank. >>The "dry side"? As in "the outside"? >I have spent two days looking and am at a loss as to where it is. >>What kind of crab is this, exactly? A land hermit crab? A saltwater hermit crab? A freshwater fiddler crab? Is it a tasty crab, maybe? >Two questions. Will it still be alive this long outside the tank? >>I have no idea, since there are so many crabs we can be talking about, here. If it's a land hermit, and you're keeping it in a tank with NO dry areas, then it's off to find a new flat, better digs and all that. Otherwise.. >And if so, how in the HELL do I track the little bastard down??? >>Find a sexy girl crab, maybe? >I'd like to find him before the cats do, and if he's perished I'd really rather not find him by smell. >>What if the cats already found him, and that's why you can't? >Any help you can pass along would be greatly appreciated. Thanks, Keith P.S. Don't tell my wife..... >>Mum's the word! I'd start checking the kitty dumplings, myself. Marina
Rogue Crabby FOUND!
>Dear crew, Crab found!!! >>Hee! Great. And don't say I spilled the beans to your wife! >More importantly, ALIVE!!! Apparently it had been living in the power filter for the last week... >>Must like it there. >So now, what do I do with it? >>Scold it. >It's not a hermit, but I don't know much more about it than that. It was sold to me as a "red clawed crab," I didn't read the scientific name. Didn't think I'd need to. Best descript. I can give is that it's about 3/4" across the back, and is shaped like a big brown Chiclet (gum), with arms and legs. It has darker brown patterning over a lighter shell, with two big red pinchers up front that are white on the tips. And it's freshwater. >>That's somewhat helpful. >I've offered meaty foods, but it's never showed much interest. Could it be wanting algae, or just anything that's decaying enough to be tasty? >>That may be, or it's also wanting a private flat, a room of his own so to speak. If you don't mind it being in the filter, leave it there. If you do, then give it a hole to call home, and don't worry about feeding it directly at this point. You could try a few things, but let's try that first, see if it's happier having some privacy. When you scold it, don't wag your finger too close to those claws. Marina >As always, any help is welcome. Keith
Rogue Crab goes to the Rogue's Gallery
>Hey Marina, a parting note on my eight legged headache. >>I suppose he's too small of a bit of meat to be enjoyed that way, eh? >After much searching, I have a solid I.D., and another "fish experiment" to irritate the wife with. (Not to say she doesn't enjoy the tanks I have, she's even encouraging a saltwater project. But, She IS jealous of the time it takes to care for, and more importantly view them. And the only reason she wants marine is because she wants, and I quote, "Nemo fish." <sigh>) >>Oh lord, not Nemo again! (A tip, they do NOT need anemones!) >I have discovered myself to be the proud owner of one Sesarma bidens. >>A who? If you can possibly send in some decent pictures, we'd love to have them archived on the site. >A fresh to brackish species from southeast Asia. >>Ah! >Eats anything handy, as long as it's not moving. >>Thank goodness for that, and other small favors. >Not known for chasing fish, fortunately. Likes to trek out on dry land a few hours a day. >>So he might appreciate something more resembling a vivarium, or mangrove setup. >Smart, strong, fast, and hardy apparently makes for a notorious escape artist. But, at least I know why my filter cartridge lasted twice as long as normal, he cleaned it for me... Go figure. Looks like I'm entering the world of <GASP> species tanks! >>Sounds like every filter needs one of these guys. >As if my life wasn't interesting enough. Oh well, something new for the kids to poke at. Keith >>I like the way you think. Glad to know you've nailed him down, so to speak. And thanks for the follow-up. Marina

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