Fiddler and hermit crabs in same home?   12/3/06
We have 2 hermit crabs and now my granddaughter has a chance to obtain a fiddler crab from her teacher at school. Is it possible a fiddler can live with hermit crabs? Please answer soon.
<Mmm, is possible... though not likely within the exact same "habitat"... likely your Hermits are terrestrial (if marine, or land types, please see WWM re their care)... and the fiddlers are highly likely amphibious... need a saltwater environment to dip into at their volition. Behaviorally these species will likely avoid each other, unless their is a shortage of food. Bob Fenner>

Freshwater crab compatibility  - 11/11/06
Hi,
I purchased a large piece of driftwood for my discus tank.  Later in the evening, I noticed that I was now the proud mother of a crab.
1. Is the crab compatible with my discus (7), angels (2), beta (1), Cory cats (2), and Gold Nugget Pleco (1) ?
<... highly unlikely>
2. What kind of crab might it be?  I surfed all over the internet and can't find anything that looks like it.  I have determined that if it's a fiddler, it's female.
<Uca likely... see the Net, Google images with this genus name>
3. it's brown in color to the reddish side.  The body is about 1/2 inch square.  Overall size is about 2 1/2 - 3 inches.  How big will it get?
<Depends on the species, but this is likely near maximum>
Thanks in advance for your help.
Grey
<I would separate this animal... Bob Fenner>

Crab Eating Plec or is it Plec Eating Crab? - 10/21/2006
I have a rather large common-sail fin cross Pleco that is showing signs of discoloration and his armor it starting to stick out. I have tried krill shrimp to boost his color I have treated with a medication made for many illnesses including parasites and scaling. I even tried feeding him algae wafers. I am all out of options. I have seen that one of my fiddlers is missing can a Pleco eat a fiddler by accident if so can this make him sick? He is a male. I was also wondering if I need to get him a mate or another larger Pleco. I have tiny tot the baby Pleco, it is the same breed as he is, which by the way is fat and happy. I did put my Bettas in the tank with him while I cleaned their tank and the female is a bit more aggressive than the male which made them chase each other and the female beta did challenge big boy. Could they of stressed him out? I feel I am running out of options he's not even full growth potential yet, he's supposed to get up to 18 inches and he's only 10 could it be old age he is a rescue fish from a lady that didn't want him anymore. Do I need to get him more tank mates? Please help in stuck up the creek without a paddle... and need as much help as I can get.
<It may be that a bit of crab shell is the underlying problem. Bloating is usually caused by either constipation or an infection. If this is a blockage, and he's still eating, you can try some fresh or frozen veggies. Shelled raw peas work well to get things moving. If he's not eating you can try adding Epsom Salt to his water. One heaping tablespoon per 5 gallons of water. For an internal infection medicated flake is called for. But only if he's eating. Internal infections that progress to a point where the fish is not eating are very difficult to treat. In that case your best chance is keeping his water pristine with very frequent (daily), and very large (50%), water changes and crossing your fingers that his immune system will kick the bug. I doubt a three inch Betta stressed out a ten inch Pleco. Also, there are no crabs that can live a full life in freshwater. So no more crabs, OK? Don>  
This is the edited copy I am sorry I sent it before I checked last time I hope this is better on your eyes.
<Thank you!>

FW Crabs, using WWM 8/2/05
I was wondering what kind of crab this is: little red things in fresh water tanks, they stay in water at all times. I discovered that PetSmart (the worst place for buying fish) had them for $2.00. Very good with plants, keep real clean, always picking out the dead parts and leaving the beautiful green foliage behind. They also eradicate those little pond snails too ^_^.
I don't know what kind of crab these are, but don't put them in with Bettas, or slow moving fish.
Polara_Blues
<Please learn to use the search tool, indices on WWM... and read here: http://wetwebmedia.com/PlantedTksSubWebIndex/fwbraccrabs.htm
and the files linked... Bob Fenner>

Crabby Compatibility - 07/14/2005
Hello:
<Hi.>
Are there any freshwater crabs out there that are compatible with African Cichlids?
<Mm, no, not any that are available in the aquarium hobby in the US, in any case.  There are, however, some different crabs that do live in lake Tanganyika and are pretty neat looking.  I do not believe that any of them are exported for the aquarium trade.  Furthermore, I fear any of them would be quite capable of taking on most cichlids.  The crabs that ARE available in our hobby are all, with one exception, brackish to marine animals that absolutely require land masses (can't stay submerged 100% of the time).  The one exception, the Red Claw Crab (Pseudosesarma moeshi / Sesarma bidens) can survive with only freshwater access, but still requires a land mass.>
Thank you! Pedro
<Wishing you well,  -Sabrina>

Molted Crab - 05/31/2004
I have a Red Claw Crab, he is my first crab and I don't know what to do now that he has molted. His old shell/skin is sitting at the bottom of my tank, I don't know if I should remove the skin or leave it in the tank.
<I would leave it.><<Often are eaten, reincorporated into new exoskeletons... necessary mineral content. RMF>>
I know Hermit crabs need their old skin to eat, but I don't know what to do with this one.
<If it's not gone in a few days, pull it out.  I would assume the crab (or other denizens of the tank) will have made short work of it, by then, but if not, best to get it out.  Wishing you and your crab well,  -Sabrina>
Shelly Warren

Crabby Confusion - Playing With Common Names - 10/11/2004
I recently ran across a Red Thai Crab in my LFS.  
<Hui.  With so little English information on crabs offered in the aquarium trade, I fear "Red Thai Crab" is just about as descriptive as "Small, colorful fish" to describe a neon tetra....  Not your fault at all, just the fact of the matter.>
I have never seen one before.  It was huge and in fresh water, and obviously red.  
<Well, red helps quite a bit.  Getting' some ideas, at least.>
I have no idea what the scientific name might be,
<Sad.  But not unexpected.  I haven't seen a single crab available for sale with a Latin name for a label.>
and my search on the internet has proven well, let's just say made me hungry, I can now prepare crab 100 different ways.
<Great!  You can come make dinner, then!  ;) >
Now the meat of the email.  
<The crabmeat, as it were.>
I have a brackish water tank with a Snowflake eel, a dragon fish, and some Sailfin mollies.  I would like to add one of these crabs to the tank but......  I have no idea if it is truly a freshwater crab and more importantly will it eat my eel and dragon fish.
<Well, let's try to explore *what* this crab is.  Also, a tank size would be of some assistance - also, I'd like to drop a bit of a hint that your eel may prefer saltwater as it matures.>
Does it require a spot to get out of the water on occasion?  The size of the crab was a good 4 inches, could be bigger it was busy moving a large rock in the tank.  
<Alrighty....  You say "obviously red", easily 4", and sounds like a bruiser to be redecorating his digs.  My first, best guess is Gecarcinus ruricola (possibly the genus name is spelled 'Gercacinus'....)  Please see here: http://www.wirbellose.de/arten.cgi?action=show&artNo=115 .  I have seen this species offered for sale quite a few times, now.  Some problems with this animal - and *especially* in keeping it in an aquarium - to my understanding, this crab, surprisingly, is not very aquatic.  In the wild, it rarely enters the water, and instead gets its moisture mostly from humidity in the air.  To keep it totally submerged is a short life sentence.  It should be kept in a terrarium with enough water available to be fully submerged should it choose to do so (for instance, low humidity).  The water available can be plain ol' freshwater, but I think it might be prudent to offer a separate container of brackish water, as well.  If I recall correctly, this crab gets big - roughly an eight inch leg span - and though not horrifically aggressive, I'm sure it would willingly pick off small fishes or land animals.  Feed with aquatic meats, also non-citrus fruits and veggies should be offered.  There is an Aqualog book by Uwe Werner available that has a (small) section on this crab.>
My eel is about 18-19 inches long (of pure hunger) and the dragon fish is about 13 inches (odd fish there), neat how that fish eats.
<Neat indeed!>
Also I just bought a 150 gallon tank for my brackish system (have not changed it over from the 55 yet) Just how big will that Snowflake eel get?
<Big.  Quite big.  I urge you to see here:  http://www.wetwebmedia.com/FWSubWebIndex/fwmorayeels.htm  and make use of http://www.fishbase.org as well.  As you will see, much is dependant upon specifically what fish you have.  Whatever your eel is, a 150 should be adequate; it's mostly just a matter of determining what kind of water it will need as it grows.>
It was only like 5 inches long when I bought it and it just grows and grows and grows, oh and it eats and eats and eats, I love it.
<Glad to hear it.  Amazing animals, aren't they?>
Thanks you guys for any info you can give me.
<Please do write back if you wish, especially if my guess on the crab in question was off - a very detailed description of color, placement and size of the eyes (widely spaced? long eyestalks?), whether one claw is significantly larger than the other, and any details you can muster will help.  And, of course, a picture is worth a thousand words!  Otherwise, you might be able to ID the feller here:  http://www.wirbellose.de/arten.html#Krabben .>
Craig in Peoria ILL
<Wishing you and your fantastic fishes well,  -Sabrina in Boulder Creek, CA>

Anomalous Crab Question - 10/30/2004
Hello, My little red crabs keep getting on the filter and just sit there like they are in a stream.
<Er, do you know what kind of crabs these are?  Can you give me a good description of them?  Size, coloration, markings, anything like that?>
I do not see how they are getting up there unless they can swim. Why and how do you think that they are doing this?
<The how is the easy part.  Crabs are *amazing* for being able to climb nearly anything....  I wouldn't be too terribly shocked if they were simply climbing the glass!  But more likely, they're finding a way up to the filter intake tube, and climbing that.  Now, as for the "why" of it, there are likely a few reasons.  First, is this a fresh, brackish, or saltwater aquarium?  In what country do you live?  In the US, there are nearly - or absolutely - no crabs sold in the hobby that are truly freshwater animals.  Most will survive in freshwater for a time, but they will not thrive and will not live their full life span.  Moreover, nearly - or absolutely - no crabs sold in the trade in the US are truly aquatic.  All are amphibious, or land crabs that only occasionally venture into the water.  Chances are, your little inverts are just trying to find a way out of the water.  At the very, very least, I recommend you drop the water level a bit, and give them a surface to rest on out of the water.  Try to provide them with a few hidey-holes on the surface to help them feel secure.  Remember, crabs are extremely adept escape artists, and they can and will find any way out of the tank, especially if they're not happy with their setup.  Please be sure you have a tight-fitting lid, or you might wake up in the morning to find a crab cuddling you in bed!  ;) >
Thank you
Kayce
<Wishing you well,  -Sabrina>

Got Crabs?
Hi WWM Crew! I have a 20g FW tank. In that tank I have 4 guppies, 5 small goldfish (who will soon have there own tank), and 2 small catfish. I was wondering, can I put some small red crabs in there or will they harm my other fish. The ph is 7.2 and the temperature is consequence at 73* F. Will this cause a problem at all? Please, I would be very happy to hear from you.
Thank you:
~Lena~
<Hi Lena, Don here. Sorry, can't recommend crabs. Although some will thrive in FW, most would do better in at least brackish conditions and all would need a place to get out once in a while. If they were to catch a fish they would kill and eat it. There are plenty of FW shrimp you could keep with the guppies and cats. BTW, You do need to move the goldfish and then increase the temp to 78>

Thai devil Soapdish crab
I know this is not truly an aquatic species, so I don't know if you  can help.  However, I thought that if you didn't know the answer, you may  know someone who does.
<Mmm, am actually one of those "guilty" ex-retailers of yore who used to sell these w/o much knowledge of their husbandry>
My friend has a Thai Devil crab (Soap dish crap).  His large  claw is inflamed at the joint where it attaches to his body.  He is in  a 10 gallon tank, partially filled with water.  He has land access and  spends most of his time there now.  He is still eating as normal and very  active.  The Ph of the water is 7.0, but she does not have any salt  added.
<IS a freshwater animal, that DOES eat various meaty foods>
  He is fed a varied diet of krill and hermit crab pellets.  She  soaks the krill in vitamins before she feeds them to him.
<Good>
I understand  that iodine is important to these crabs.
<A essential micro-nutrient for much life, including you and I. I would add Lugol's solution, potassium iodide/iodate once a week or so... to this animals water.>
Does he need special  lighting?
<No>
And could the inflammation be a sign of an impending molt?  
<Maybe>
He is full grown and they only molt once a year I think.  She is very concerned about his health, she has had him for about 6 months.  Any information would be greatly appreciated.
Thanks,
Caryn
<I encourage you to place the above title words in your computer search tools and read what little there is posted on the Net re this crab/species. Bob Fenner>

Fiddler Crabs, Ich Problems?
Is there a safe medication to treat for ich that will not kill my fiddler crabs?
<Yikes! Ryan here today.  We use a quarantine method to treat infected fish- That involves removing the infected animals, and treating them separately.  In that case, your crabs are safe!>
It's been 20 years since I've had an aquarium, and it seems that many rules about keeping and caring for freshwater fish have changed.  <I'll say!> I did my homework and researched the subject so that I felt comfortable with my choices.  About 2 months ago I purchased a 55 gallon aquarium, and started with about 5 Neons to get the water cycle to do its thing.  I now have several fish: 5 swordtails, 6 mollies, 5 dwarf platies 6 dwarf Gouramis, a Pleco, 6 Cory catfish and 6 fiddler crabs.  (I love the fiddler crabs.) <That Pleco will soon outgrow the 55 gallon tank...I'd inquire early about trading him for a smaller Pleco once he's about 6 inches.>
Everything was going well, including the birth of about 30 babies (black mollies, silver Lyretail mollies and sunset dwarf platies) until last weekend when I did a 25% water change to correct nitrate and total alkalinity levels.  I also rearranged the fake plants, rocks and log to allow the fish to have more swimming room and to ensure a better water flow from the filter.  I must have really stressed my poor fish.  The other day I noticed that 2 of my dwarf Gourami had small slits and little holes in their upper fins.  That evening I noticed my male silver Lyretail had trouble swimming and was at a 45 degree downward angle, and sometimes faced straight down.  I immediately added extra aquarium salt to the tank and increased the water temp to 82 degrees (from 78).  The following day, after work, I purchased a 6 gallon  'hospital tank', Maracyn and Maracyn-Two for my 3 sick fish.  Unfortunately, when I got home, one of the Gourami had died.  It looked to be sick for only 24 hours, so I was pretty shocked to find it dead that quickly.  
I checked all my fish and decided that only 2 of the other Gourami had what is probably Fin and Tail Rot, so I put them, along with my male Molly into the hospital tank, using water from the 55 gallon tank.  (I didn't want to stress them further.)  I've been medicating them for 3 days now and they are looking much better.  My Molly is actually starting to swim somewhat normally, so I believe there is hope for him. <Sounds hopeful!>
Now for the bad part... I came home from work today and found 3 more fish in the 55 gallon tank that look like they have Fin and Tail Rot.  It also looks like there may be a white spot or two on these same fish.  I have CopperSafe that I was going to use in the hospital tank if I needed to treat for Ich, but I can't use it in my 55 gallon tank as it would kill my crabs.  I've started treating the big tank for Fin and Tail Rot, but am not sure what to do about the possible ich, as I don't want to kill my crabs.
<You're going to need to treat all infected fish in the QT tank.  Next time, add the fish to the display tank AFTER they have successfully completed 6 weeks of quarantine.  Then you won't have the same issues.  This time around, it's the long road my friend.  The answer to your question is no- There is no ICH treatment that is truly crab-safe.  Good luck, Ryan>
Chris

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>

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> 

Soapdish Crabs, Fiddlers, Ghost Shrimp
hello:
please, I was wondering if y'all could help me.  I have what was sold to me as a Soapdish crab in a 2' x1' 6" tank with about 4 or 5 inches of fresh water.  Carl, as he is called, has a 2" wide body and is probably about 6" across including legs.  he has relatively short (compared to my fiddler crabs) eye stalks and is a reddish brown color with orange legs and claws that have reddish brown "designs".   the tips of his claws are whitish gray.  he has easy land access but hardly ever comes out of the water.  is that weird?
<Mmm, not necessarily>
  he eats live minnows and frozen peas.  anything else I could feed him for a little more variety?
<Other meaty foods>
  please don't say crabs eat anything, he won't eat carrots or broccoli.   is it safe to feed him hot dog?
<Mmm, no... too fatty>
  he'll eat it and seems to like it but I took it away because I'm wondering if it could be harmful with all that sodium.  should I remove any left over fish parts from the water?  
<Yes, I would>
sometimes he just eats half a minnow and the other half  just floats around in the filter current.  will it muck up the water or make it unsafe for him in any way?   
<Could. I'd remove all uneaten food>
I have had him for probably 8 months and he seems to be doing well.   I just want to know if you guys and girls have any tips to make him happier and/or healthier.  I read something on your site about iodine supplementation for crustaceans? anything else?
<You could monitor, adjust biomineral (mainly calcium) and alkalinity... has this animal molted while in your care?>
what is krill, where do I get it and how do I "soak it in vitamins"?
<Euphausiids... liquid vitamins... just putting a few drops on for ten, fifteen minutes before offering...>
I love my soap dish crab(s) and would really appreciate any help y'all could give as there is virtually zip on the web about them.
also, for anyone wondering, Carl (as with all Soapdish crabs, in my experience: I have 2 males, I lost a female when she wondered into Carl's territory) is extremely aggressive and will decimate anything it can catch, including other Soapdish crabs of equal or  greater size. does not play well with others. I've even heard of one wasting an Oscar.
<Have seen this sort, level of "aggression">
oh, why might a fiddler crab in similar tank conditions up and die for no obvious reason.
<Is a brackish water animal...>
a not too old/big male that seemed to be thriving was fine one day and upside down dead by the filter the next. he shares the tank with 2 females and one other male which doesn't currently even have its large claw. I don't suspect foul play, I am afraid there is something wrong with the water or something. the tank has been in operation for at least 6 months and has a good filter. I've heard a terrible rumor about fiddler crabs just dying after a while in fresh (not brackish) water but I've had a lot of these wonderful, mostly peaceful crabs and this is a brand new occurrence. any thoughts?  might the same thing happen to Carl?
<What is the make-up of your source water? You may have hard, alkaline water that "works" for both these species>
just one more thing, I promise. I employ a multitude of ghost shrimp as janitors and I read on your website that it was easy to breed them. that is very exciting to me, please tell me more!
I am so glad I found your website, I hope you can give me a few pointers.
thanks,
Scott
<Use your computer search tool/s... much written on Ghost Shrimp. Bob Fenner>

Re: Soapdish crab
hello again!
Carl has molted! about a week after starting the iodine treatments, Carl (Thai freshwater- Soapdish crab) molted.  could this be directly related to the addition of iodine?
<Yes>
unfortunately,  it did not go well for the big guy and he lost a leg and his larger pincher.
<Evidence of? Likely a lack of biomineral (calcium) and alkalinity... provided in foods, water...>
the next couple days were very tough for both of us, as he just sat there and twitched and I was terrified that he wasn't going to make it.  the next day I came home from work to find him on his back and motionless.  I nearly lost my mind with grief until I noticed his mouth apparatus was moving. I very gently touched the tip of his claw and to my great relief he sprung to life, trying desperately to flip over.  the poor guy just didn't have the strength! he was still very soft, so I decided to let him be rather than possibly injuring him by flipping him over.  after a couple more days he eventually started to consume his exoskeleton and move around the tank.  Carl's gonna be ok!  whew!
now for the questions: I've noticed that since the molt his carapace and claw look very strange- its a very dull tan-gray and none of his normal patterns, like the "H"  on his back, are visible. it just looks very worn, or something. I know crabs will sometimes come out of a molt a different color, but the way Carl's shell looks makes me think its related to his traumatic molt. any ideas?
<Either lack of nutrition, water quality... or will develop color, pattern in time>
Also, is it possible to over dose them on iodine?
<Oh yes>
should I add the drop only when I do a complete water change or anytime I replace water that has evaporated?
<Best to do with (weekly) water change regimens>
keep in mind I have a 10 gallon filter in about 4 gallons of water, does that make a difference as to how fast the iodine is getting used up?
<Yes>
One more thing: I really want to change my crab tanks to brackish but I have read that once crabs are in freshwater for so long, they cannot be switched to brackish. is this true?
<Not so. Bob Fenner>
thank you in advance.
Scott

Injured Red Claw Crab
Hi, firstly thanks for such a great website! The information here is comprehensive yet easy to understand. Unfortunately I have a problem with my Sesarma bidens crab. The other night whilst cleaning out the tank I did not notice the crab (Colin) burrowed under a plant, as he is almost always hiding under an ornament on the other side of the tank during the day (or breathing sitting out of the water on top of it). 
He just recently molted (about a week ago) so I thought I would leave him under the rock and clean the tank around him. Well I dumped the plant in a bucket (with Colin underneath it) and proceeded to vacuum out the gravel and remove other ornaments to the bucket. It was only when putting the ornaments back that I noticed Colin at the bottom of the bucket on his back... I immediately picked him up and put him in the tank but he didn't move, I put lots of little bits of food in front of him and left him for the night thinking the worst. 
When I came back in the morning he was on his back again but when I went to lift him out of the tank assuming he was dead he started moving his legs frantically, anyway I righted him but noticed that 5 of his legs were not working as well as one claw (I think they must have been broken in the accident) he was attempting to move around but the legs were preventing him, I left him for the day came back and he still had not moved despite attempting to with his working legs, so I amputated 3 of the legs at the base (not the claw) he is now a lot more mobile however he is unbalanced due to missing 2 back legs (resulting in him overturning and not being able to right himself frequently/a few times a day). 
I have also since noticed that one side of his mouth is not working (i.e. the exterior movable parts of his mouth that he uses to clean his eyes) he can still move it a little but cannot properly function. 
My question is: Is there anything I can do for Colin? I am aware that crabs can regenerate limbs during a molt but has he just sustained too much damage?
<I hope not>
My main concern is his mouth as I cannot see whether he is eating properly. Would it be kinder to just kill him now or try to aid his recovery? 
<I would not euthanize this animal. It may well recover>
It has been three days since the accident and he is still defending his food against the fish (a few platies) but I cannot establish if he is eating the food or whether the platies are eventually managing to take it all. In this situation could a premature molt occur or could he partially grow back before a molt?
<Not before, but might molt again sooner, shrink in body size>
I really don't want to have to kill him but equally I do not want to prolong his life if he is suffering with very little chance of recovery. He is in a 5 gallon tank with 0 ammonia, 0 nitrites, 20ppm nitrate, just over 1 tbsp. of salt per gallon and I am lifting him out of the tank daily for a few minutes to allow him access to air. pH is 6.6 (low I know but I added dolomite to the filter on the day of to raise it so hopefully that will start to take effect). Should I dose with Iodine?
<Yes, I would>
Sorry for the long question but I am very concerned about him. 
Thanks,
Chris
<Do take care to maintain good, consistent water quality, assure this animal is getting food. Could take weeks to a few months, but may well be fine. Bob Fenner> 

Odd freshwater Crab behaviour
I have a ten gallon tank with low water and rocks for crabs and other crustaceans. I bought some crabs and here's my q's.
One: Are the crabs with one large and one small claw  males, and the ones with two small claws females?
Two: Today the male??, one large one small claw, climbed out of the water onto the rock and started foaming? or bubbling from his face and doing something, like he was washing?? what is this? He the proceeded to sit then later he did this crazy claw dance, waving his arms around slowly in these rhythmic motions all the way out and then back in, what the heck? Does he have mad crab disease?
Three: I put in feeder golds but they seem to ignore them. so I feed blood worms. should I add plants for veg food, or just stay with blood worms and whatnot?
Four: The red crab I got has only one claw will his other grow back like at molting or something?
Five: What's the ratio on crabs? The same as fish or?
i tried here and all over to find good info on their behaviour and i came up empty handed!
>> Yes, crabs with one larger claw are more likely males in most species. Crabs have to get oxygen when they are out of the water they will "chew" a small amount of water to mix it with air and get oxygen from this process, that is likely why your crab is foaming. He is waving his claws to show his territory and attract females, so he is not mad. You can feed with bloodworm, but try other foods to see what else your crabs will eat, it varies from one species to another, but most are omnivores. The missing claw should be replaced in the next molt,  I would not worry. For a great website on crabs and other crustaceans check http://www.crusta10.de not sure if it is all in English, but the site owner is one of the most knowledgeable people on the subject. Good Luck, Oliver

Freshwater Invertebrates, ID?
Hey guys I am trying to ID a crab that is appearing more and more frequently in Australian stores. It has been incorrectly identified by several stores as Amarinus lacustris (Freshwater spider crab). I suspect the supplier is keeping this myth alive *lol Anyway, the crab in question is often referred to as a "brown backed crab". Orange/brown body with a chocolate brown H symbol on its shell. claws of equal size and quite heavy set, not long/slender. It seems to get to about 2" shell width. I would LOVE to know the scientific name for this little beauty, as although I am sure I could keep it happy using general crab knowledge, it would be nice to know its specifics. Sincerely, Abbey AKA Callatya
<Hey there, sorry it took me forever!  http://www.fishprofiles.net/files/~adam/tanks.htm 
Right down the bottom of that page is a front-on view of that crab. I asked a large pet store and they said they are buying them under the name Holthuisana agassizi.  I cannot for the life of me find any reference to this species online, so I thought maybe, just maybe, you guys might have more references that I have access too.
Thanks for your help!
< I have seen this crab at wholesalers referred to as "red clawed crabs" from Asia. Try looking in the internet under that name to see if you can find more info. -Chuck>

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>