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FAQs about Emerald Green, Mithrax/Mithraculus Crabs: Disease

Related Articles: Mithrax Crabs, Arrow Crabs, Crabs

FAQs on: Emerald Green Crabs 1, Emerald Green Crabs 2,
FAQs on: Mithrax ID, Mithrax Behavior, Mithrax Compatibility, Mithrax Stocking/Selection, Mithrax Systems, Mithrax Feeding, Mithrax Reproduction,

Related FAQs: Marine Crabs 1, Marine Crabs 2Marine Crabs 3, Marine Crabs 4, Marine Crab Identification, Marine Crab Selection, Marine Crab Compatibility, Marine Crab Systems, Marine Crab Feeding, Marine Crab Reproduction, Marine Crab Disease, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating Shrimp Crustacean Identification, Crustacean Selection, Crustacean Behavior, Crustacean Compatibility, Crustacean Systems, Crustacean Feeding, Crustacean Disease, Crustacean Reproduction,


Octiplegic Emerald Crab... Eat more than algae     2/21/17
I saw one of my Emerald Crab on its back with no claws.
<Oops; something/s going on here... predation, too little alkalinity, alkaline earths, iodide/ate, possibly iron>

I flipped him over in case he was alive. The next day, I saw a larger Emerald eating his legs so I thought he was dead. Three days ago I was looking at something on the substrate and I notice that his little nose feelers were moving. I immediately removed him and put him in my frag tank. I've been strategically placing him on top of food for three days now and he is eating. My question is, will he be able to molt without any limbs at all?

If not is there anything I can do for him when he is ready and, if I can help, how do I know when?
<The aforementioned necessary water chemistry>
Attached is a video of him eating.
<Nada attached. Best to post elsewhere and just send the link. Bob Fenner>

white powdery look... On Mithraculus, snail...         2/5/16
I have had 2 emerald crabs die. Both developed a white powdery looking substance on their bodies.
<Precipitation? From... supplement use likely>
I have 6 snails and a few have the same substance, 1 extreme. I have a pajama cardinal, a banded coral shrimp and a cleaner shrimp with no apparent issues. Any ideas?
<Stenopids will eat all other small crustaceans, snails.... were the bodies intact? Are you sure these weren't/aren't simply molted exoskeletons (the Mithraculus hiding?). Bob Fenner>
Thanks, Greg
Re: white powdery look         2/5/16

Thanks for the reply. No supplement use. Watched the crabs slowly die.
<Slowly? How much time; please describe their behavior. What do you feed?
Have you read on WWM re this species?
The one snail is covered with this. Would a picture help?
<Yes! As close up, highly resolved image as you can provide. B>
Thanks, Greg

Emerald crab issue.   4/18/11
Hello, thank you for taking time with this issue!
<Welcome Boo>
My system is a 125 gallon system with one Clarkii species clown, Condylactis Anemone (saved from horrible treatment at the LFS), and two damsels. I also have one Mithrax species crab.
<Mmm, some members of this genus (Mithraculus for some now) do get quite large, predaceous>
My issue is that the crab seems to have a tentacle growing from one of its lower legs!
It's known to fight my anemone for the occasional fresh piece of seafood, so I know it's come into contact with the Condylactis on occasion.
<Evidently so>
My obvious idea is that he got a tiny piece of the foot stuck in a joint of that leg and that piece is regenerating a new anemone.
However, I'm wondering if it could be an illness or parasite,
hence writing you today. In lieu of a picture (which I don't have access to) I can describe it.
It's *exactly* like a smaller version of the pink tentacles of my anemone.
It grows a few millimeters per week, and doesn't seem to be affecting the Mithrax at all.
Water parameters for nitrogen compounds are perfect, pH is 8.3, and I dose the tank with PurpleUp weekly.
Thank you!
<I either wouldn't worry, or remove the crab/tentacle together or separately... Let's see, that about covers all contingencies. Oh, yeah, read here: http://wetwebmedia.com/mithraxfaqs.htm
Bob Fenner>

emerald crab disease? 08/15/09
<Hello there>
I could not find the answer to my problem on your website (hope I didn't miss it!). I currently have 2 false percula clownfish and I recently bought an emerald crab from my LFS and did not notice it was missing two legs until I got home. I didn't think it would be a problem so I put it into my tank and it immediately hid under a rock. Later on at night, the crab walked around the tank and as I was looking at it I noticed little white "dots" crawling around his front claws. I was hoping you could tell me what they are. Are they some type of disease? Will it kill my Clownfishes?
<Mmm, likely another smaller crustacean species... not harmful to your fishes>
Please help I don't want my Clownfishes to die!!
Thanks in advance!!
<Welcome. Bob Fenner>

Pesky Red Flatworms, Injured Emerald Crab - 9/16/07 Hi, <Hi there!> I have a Mandarin in a 20 QT and I am getting ready to move him into my 180. <Good - nice big tank, hopefully mature, with lots of live rock!> Does the Mandarin eat flatworms? <If you mean the little Acoel flatworms (sometimes called "Planaria"), yes, sometimes they will eat them.> Can he help solve my flatworm problem? <He could potentially help, but if it's a large population, he might not make too much of a dent in it. The problem is that even if you're lucky enough to get a Mandarin that eats flatworms, they still don't eat them exclusively. They also eat the little pods, etc, we see in our tanks, so the flatworms will only represent a percentage of the Mandarin's diet. Please see this link (and those listed at the top of the page) for more info re: http://www.wetwebmedia.com/fltwmpredcont.htm> Also I have an emerald crab I noticed is missing an arm <claw/cheliped?> and all his legs on one side. <Yikes, poor little guy!> I think the monster emerald got him. <Is indeed possible, especially if the two are in confined quarters. These guys don't get high marks in the 'Gets along well with others' category!> Can he live like this or will he regenerate them? <The legs/cheliped will regenerate, although it will most likely take several molts. It's going to be very important during this time that he's well fed and has enough places to hide. If he can still get around (albeit awkwardly), he's got a fighting chance. What most concerns me is that whatever attacked him in the first place, may well finish him off now that he's vulnerable. The best option would be to isolate the injured crab so that he could eat/recuperate in peace. The next best option would be to make sure both are well fed and that the injured crab has sufficient hiding places. One last thing that I would add is that if it were me, I'd only keep one of these guys -- even in a big tank. Good luck - I hope everything turns out okay for the little crab, and that your Mandarin eats those pesky flatworms! --Lynn>

?Disabled? Mithrax Crab - 08/11/07 Hi guys, hope you are all well and happy! <Thank you> I contacted you a while back and got some wonderful advice from Mich, so, with my new questions I thought I'd come straight to you as I am rather concerned for my Mithrax crab. He/she, (haven't managed to work out which yet), had a molt the night before last. Unfortunately, he, (I'll use the masculine for ease!), managed to leave his main front left limb including claw, behind. I am hoping that this in time will grow back, but have been observing him since this morning and realised that his remaining, rather mean looking clawed limb appears weak and not fully operational. Because of this he does not appear to be able to feed. Poor old "crabby"... sad to say it, I am rather upset as he is quite a character. I managed to hand feed him this morning and this evening but it was rather difficult and I am not sure he has had anywhere enough to sustain him. <Mmmm> Do you have any idea if this weakness is just a passing phase and anything to do with the molt? And whether the missing limb will definitely grow back, and if so, any ideas how long this will take? <I do have such ideas... these occurrences are typically associated with either "something" deficient in the way of water quality (biomineral and/or alkaline content) and/or nutritional deficiency... Please look up these terms (the search tool likely) on WWM and test for Ca, Mg, alkalinity, provide sufficient foods... for your Mithraculus> I appreciate your time as I am sure does "crabby"! Kirsty. <Hotay! Bob Fenner>
Re: ?Disabled? Mithrax Crab   8/12/07
Hello Bob, <Kirsty> thanks for your prompt reply. <Welcome> My water parameters appear fine, including: Calcium 480mg <Is your Mg in balance?> PH 8.0 <Mmmm, not the same as alkalinity...> Since the crab has been with me, it has had a diet of natural algae from the tank, the odd bit of cockle, brine shrimp and Ocean Nutrition Formula Two flake food, so I would hope the diet wasn't a problem, but, I have only had it for approximately 2 to 3 weeks. Would you say that everything I have done is ok? Thanks again, Kirsty. <Please read here: http://www.wetwebmedia.com/marind5_5.htm The tray on Arthropods... areas on Crabs... Health, Nutrition, Systems... and the linked files you'll encounter of interest embedded t/here. BobF>

Emerald Crab Death... Sm. SW set-up mis-mixed lvstk.  -- 06/28/07 Hello, I'm Jarrid, I have a 10 gallon tank with liverock, a yellow tailed damsel, Talbot damsel, <Damsels (one) need more room than this Jarrid> 2 snails, a coral banded shrimp, <Is more than semi-predaceous... No fun for your damsels to be crowded with something that will constantly be trying to eat them...> 2 emerald crab and a curly cue anemone. <All mis-placed here...> Recently I found a Emerald crab claw floating on the surface and 3 days later found the shell completely eaten out. I can only assume my coral banded killed him <Highly likely... or that it died from some other cause... dissolved or was consumed... or that it is a molt...> but I haven't seen them fight or even pay any attention to each other. The other emerald crab is fine with no signs of a fight. The emerald that died has plenty of algae to eat and I have excellent water quality with bright colored active fish and a good colored growing anemone, I feed the animals a variety of frozen brine shrimp and squid, usually a different food each day, I make sure there is food left for the shrimp. What could have killed my crab? <Aspects of water quality (lack of biomineral and alkalinity most celebratedly), the other Mithraculus (nee Mithrax) the CBS... You have an untenable, unsustainable mis-mix of life here. Please take the time, make the effort to read re each of these species on WWM... Their Systems, Compatibility in particular... You need a much larger system, or... Bob Fenner>

Emerald Crab Injury  - 4/6/07 Hey All, <Hi George.> I have a 55 gallon reef tank with 2 Clarkii Clown fish, a ton of Hermit Crabs and 2 Emerald crabs. <Okay.> All water parameters are with in acceptable ranges. <That is good. but in he future we prefer specifics, we may see something that is overlooked by the tanks owner at times.> One on my Emerald Crabs has a damaged arm and he (the crab) is in the process of trying to remove the offending appendage. Is there anything I need or should do to help him out or should I let nature take it's course. <The latter, just feed a varied diet, include meats of a marine origin. Maintain pristine water quality and in time...with consecutive moltings the animal will heal. I would not stress/worry.> BTW you site is great and has helped me out on many occasions. <Thank you for the kind words.> Thank You <Welcome.> George <Adam J.>

Emerald Crabs Hate My Tank!  3/28/07 Hello Crew,   Thanks for the informative site, you've made my short 3 months of reef keeping much easier'¦ or at least, more understandable! <Ah... in his best Simpson's "Mr. Burns" voice impersonation, "Excellent"> My specs are: 60 gallon glass rectangle, Hagen Aquaclear 110 w/ floss and carbon only, Remora Pro skimmer, 3x Maxi-Jet 1200's, 2x Jager 150W heaters, 40lbs of medium grain Aragonite sand, 130 lbs of live rock (Fiji and Tonga). 10k and 460nm HO T5s plus 10k and 460nm regular output T5s. This tank 'cycled' in less than a week.      Steady water parameters; 78F +/- 1.5, 8.2-8.4 pH (am to pm), Calcium 400, Ammonia and Nitrites 0, S=35, dKH 9.2 to 10.4 (currently using Kent's Super dKH every two weeks). I've been battling Nitrates as I develop my feeding skills for a 60 polyp colony of Orange Sun Polyps, usually ranges from 5 to 15ppm, most often around 10. <This/these are fine... and I take it you've developed a cover/cup approach to assuring each polyp receives food...> 5% water changes 2 times per week. RO water topped off daily.   Livestock; Twinspot Hogfish, Engineer Goby, Pygmy Geometric, 2x Cleaner Shrimp, multi-colored urchin, assorted hermit crabs and 15 or so snails plus 3 Turbos, Torch Coral, Purple Oxypora, Bull's-eye Mushrooms, Pulsing Xenia, Zoos colony, Devil's Hand, Closed Brain, Spaghetti Leather and the Orange Polyps. All specimens are medium to small and spaced no closer than 8 inches at this point. <Okay>   Feeding a combination of foods'¦ TherA, Mysis and Brine Shrimp (soaked in Selcon) as well as plankton. Have restricted food in an effort to get Nitrate levels down and all livestock (except geometric) go aggressively after the food when offered. <I sense a refugium, with a DSB, Chaetomorpha... and a new Toyota in your near future...>   The issue I am having is with Emerald Crabs. The 1st was 1 ½ inches or so in diameter and lasted just two weeks, there was no trauma evident when I pulled out the carcass. Recently got two smaller ones, the 1st lasted just 4 or 5 days, the other seems to be very lethargic at 10 days. Any ideas? Other livestock appears healthy, Shrimp is full of roe, and Sun Polyps are reproducing at an alarming rate'¦   Thanks again!      Steve <Mmm, well... Mithrax/Mithraculus can/do sometimes "just die" for no apparent reason... considering the other life you have here, the measures you present... I do think these losses are anomalous. However... I do encourage you to skip trying further specimens... it may be that the Bodianus is involved here. Bob Fenner>

emeral <Bam!> crab on back... Writer in the dark  - 03/12/07 I have an emeral crab that has been on her back for about four days now, but her belly flap is open and it is an orangish color to it and it looks like there are eggs floating around in there.  Do they just lay eggs  or do they take care of them until they hatch our on their belly?   <More of this latter> If this is what it is. she is constantly fluffing her tummy and picking at it.  I am just worried that it might be something else going on with her that would need attention right away and if they are eggs that are fertile how do you take care of little baby crabs? Please help? Thanks Diane <... There is something wrong health-wise with this Mithraculus... likely aspects of water quality and/or nutrition... You need... to read: http://www.wetwebmedia.com/marind5_5.htm scroll down to marine crabs, this species... the articles, FAQs files. Bob Fenner>

Emerald Crab getting sick?  - 08/26/06 Hi, <Mornin'> I have a small (30g) marine tank that I've had running for about 4-5 months now. I fishless cycled the tank and have had fish in the tank for only 2 months now. I put an emerald crab in there one month ago and he seems to be suffering slightly. He always seems to scramble for food and has been fading his green colour to a very pale green/white. <Hard to keep in small volumes... too change-able in chemical/physical make-up> I was just wondering if this is because of poor water quality (more calcium? <Possibly this, or alkalinity, or...> I keep pH, ammonia, temp very consistent) or possibly a lack of food. There seems to be quite a bit of algae growth and I thought he would have enough food. Please help. Jamez <Please read here: http://wetwebmedia.com/mithraxfaqs.htm and the linked files above. Bob Fenner>

Mithrax crab disease or molt?   4/30/06 Hello, I have searched WWM.com and cannot find an answer to my question regarding white patches on my Mithrax crab/emerald crab.  These patches which are on her legs and carapace look like small chunks of fluffy matter or like patches of salt build-up.  I caught her having sex with the larger Mithrax crab and read on another website that she may molt soon. Could this be signs of molting or is this a disease? <Could be either, neither>   If it is a disease, <Not likely> do you know what it may be and what I can do for it or where I may search on the web to find such information. <I would do nothing outside of checking your alkalinity and biomineral content/concentrations and perhaps dosing an iodide supplement>   I really would like to save her as I have had her almost a year and she is cute and causes no problems.  Plus my larger, male emerald seems to like her as well since he chases her around the live rock and cuddles her! Thanks for any help you can give me.  I know she just a crab but she's family now.. Geri in Newton, MA <I understand... this is a good long while to husband Mithraculus... you are doing most all right. Bob Fenner>

Dead Emerald Crab...Leave In Tank? - 03/22/06 Dear Crew, <<EricR here...>> After several weeks of reduced activity and increased 'hiding' it appears that my Emerald crab has passed.  I have located him in a tiny pocket underneath lots of live rock with my flashlight. <<Ok>> His shell has turned a creamy white and it has not moved at all in several days even when food floats right in front of him (which, in the past, any amount of food in the tank would result in frantic stuffing of his mouth with sand!).  I cannot reach him without un-piling all of this rock and felt I could probably just leave him to the 'elements' where his shell would provide calcium back to the tank like when he molts. <<Indeed...and likely those "elements" have already dealt with the crabs flesh/organs.>> Is there a downside I should be aware of in this situation or is  this OK? <<A moot point by now I'm sure...nothing to worry about.  The micro-fauna, as well as other macro-fauna in your tank will have quickly dealt with any decaying matter. Mark <<Regards, EricR>>

- Emerald Crab Problems - Hope all is going good with you tonight.  <Well... it's morning now... things seem ok.>  I have a problem I can't find on your site. I have a green emerald grab that has some bugs on him. They are like a clearish red color with a white spot on the back of them. They resemble an appearance of a regular mite. They are very small, about the size of a the tip of a needle. He also has a small hole in his left claw right on top. Its not getting any wider, just deeper. He is in a QT tank although I don't know of anything to treat him. I'm sure most things would kill him, even a freshwater dip. So do I let nature take its course or what?  <Yes... is really your only option for these animals. Make sure the water quality is tip-top.>  Thanks for your help. Josh <Cheers, J -- >

Emerald-a the Mithrax I just found your site while I was searching for answers to a problem.  I have a small emerald crab in a 55 gal tank, LR filter. Bought the already running tank in Sept., and got the crab in Oct. Have run water tests with Saltwater Master test kit every week. Everything is very consistent and in normal bounds with exception of nitrates (40)... <Cherie, one thing to keep in mind about testing for nitrates...some test kits read high level and some read low level. You have to determine what kit you have.>  ... but always consistent. The crab was last seen moving and eating two days ago. This morning she was still.  I picked her up and she moved feebly. I put her back down and she flipped over on her back. I righted her and she just doesn't move anymore. Have left her alone since. She has white spots on her back which I assumed were coralline algae. But when I examined her closer, they were 3-d and swirly. Could they be some kind of worms or parasites? I've got two other emeralds in a 75 gal tank but they're all connected with a common sump. The other female also has these spots but I don't see them on the male.  Any ideas or advice would be appreciated.<It's quite possible your emerald may be in the molting stage. Keep an eye on it for a few days. James (Salty Dog)>  Thanks, Cherie
Emerald-a..?  What Happened?
The emerald crab that died had small white " 3d" swirls on her back, about 10-12 of them. Could they be a parasite? <Sorry Cherie, I really don't know without a picture of it that some members of the crew could look at. James (Salty Dog)> Thanks, Cherie 

Emerald Crab >I noticed a few weeks ago (~5) that my emerald crab's pinchers were missing. It seems to have lost them during one of its molts. My Sally lightfoot  crab didn't lose it and it molts about 2-3 times a month.   >>You have a mix of two different crabs, both known to become aggressive, are you certain they were lost *because* of the molt?  It could very well be that the Sally Lightfoot (btw, there are at least two, if not three, other species of crab called "Sally Lightfoot"--ALL aggressive) managed to catch the emerald at its most vulnerable.  With such a mix this must be expected. >It is still eating. It has learned to use it legs to get food. Will my emerald crab's pinchers ever grow back? >>Yes. >All the water parameters are zero and I add iodine to help with molting. >>All parameters, even pH, temperature?  ;) >Also what would a likely cause be for the disappearance of my peppermint shrimps? I had 3 but they slowly disappear. >>Quite easily one of these crabs, or you could even have an unknown (and most unwelcome) guest in the form of a mantis shrimp.  If you ever hear odd clicking noises from the tank (especially at night), you may have a mantis.  These animals can decimate a tank. >I have 4 mid-sized pieces of live rock, 2 pink skunk clowns, 1 humbug damsel, and 1 Nemo. Any info would be greatly appreciated. >>There you have it, you have an aggressive (far too aggressive for peppermints) mix of inverts going on there, in my honest opinion.  Marina Thanks

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