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FAQs about Marine Crab Systems 

Related Articles: Crabs, Hermit Crabs

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Crabs? Yummy!

Semi Aquatic Crab Bioload   9/11.5/11
Hello Crew!
I currently have a 55 gal land and semi aquatic crab tank. I have roughly seven to ten gallons of saltwater in the tank, with sand sloping down into the saltwater pool that is filled with live rock, heated, and filtered. I have a wide variety of crustaceans in this tank including semi aquatic crabs such as Fiddlers and odd looking wild caught shore crabs, and various land crabs such as ghost crabs and hermit crabs.
<Surprised they're not eating each other>
Anyways, I was wondering if semi aquatic crabs in general went to the bathroom on land or underwater,
<The latter>
and if their presence has any significant impact on the bioload of the saltwater portion of the tank.
I have had EXTREMELY good luck in my crab tank and experience no serious aggression from any of the potential bullies in the tank, but I am just curious as to what kind of bioload a semi aquatic crab tank would experience, and if it was any different from a tank filled with fully marine crabs.
<Mmm, about the same>
I apologize if what I wrote sounded confused and
disorganized, and I feel like I said the word crab way too much, but I am writing this at two in the morning because I can't sleep haha.
<... Ok>
Thank you very much for your time and efforts.
<Welcome. Bob Fenner>

Can a crab heal damage to its eye?... and another question. Callinectes spp. habitat, comp.   8/8/09
Hello WetWebMedia crew! A few weeks ago I received a medium sized Cardisoma guanhumi in the mail. His body (without the legs) is probably about 5 inches across and he's a lovely blue color. My only concern is that I noticed a strange brown spot on his left eye. It is the same color as the coconut fiber substrate that I have been using, so at first I was not alarmed. However, it has been a long time now and that spot is still there in the exact same spot and I have never seen him make any attempt to wipe it off. Upon further inspection the spot has a different texture than his surrounding substrate and looks like his eye is actually damaged (BTW his eyes are yellow). I do know that crabs can regenerate lost limbs, and I also know that crabs have compound eyes like that of a fly or a wasp. My question is this: Can a crab regenerate from eye damage with successive molts, or is an issue like this permanent?
<Not the eye itself, no... just the exoskeleton... Perhaps this mark is superficial, just on the external non-living matrix, and will be shed...>
My picture of the crab is over 2MB in size, far larger than what you guys said you'd like to deal with. Instead I'll post a link to a website where I asked this same question (its always good to get a second opinion.)
<... this does look like something "outside" to me... and the left eye still functional underneath>
Second Question:. The person who I bought this lovely animal from is also offering Blunt-Tooth Swimming Crabs (Callinectes bocourti). He labels them as "Barbados Freshwater Crabs". They certainly look like lovely animals. He did state to me that they'd be much happier in brackish water and that freshwater should only be a short-term arrangement for them.
<I agree... is really a marine animal>
First of all, can these animals survive in the long term in a freshwater habitat?
In spite of what he told me, I have heard of Blue Crabs (Callinectes sapidus) being kept indefinitely in fresh water and I don't find it unlikely that this closely related species can't do the same.
<A reasonable assumption... though I don't think/consider that either do "ideally" in totally freshwater settings indefinitely. For instance, I doubt that they will moult, grow t/here>
Also, in my 20 gallon tank I have a blue crayfish and a LOT of baby ghost shrimp (who's population exploded after the crayfish failed to eat the original 3 I put in there). Is there any chance that the crab and the Cray can forge a peaceful (if tedious) co-existence or is there really no hope for a good outcome if the two were to meet?
<Not likely to "get along" IMO/E>
Thank you VERY MUCH for your time.
<Welcome. Bob Fenner>

Fiddler crabs in sea water... Not  11/08/07 Hi there, I am trying to set up a fiddler crab tank for a high school research department. I've seen a lot of references to the brackish water these crabs need - <And land... most are only part-time aquatic, if then... live in/on mud and sand> but the crabs we have were taken at the beach. Should they be in pure seawater? <No... land/sand... with some water to moisten themselves> Currently the water we are using is from the same beach we found the crabs, but I'm not sure if this is an optimal condition. Any information you can provide would be greatly appreciated. Thank You!! Andrea Beatty <Andrea... "Woman of the sea"... fitting name, eh? Bob Fenner>

Cardisoma guanhumi, sys.   6/20/07 Hi folks, <Catherine> A friend just got back from Grand Cayman and her wetsuit contained what we think is a juvenile Cardisoma guanhumi. <Ah, a Blue Land Crab: http://www.google.com/search?q=Cardisoma+guanhumi&rls=com.microsoft:en-us:IE-Address&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7PCTA> She's not very excited about her new pet. However, as s/he survived a several plane flights, being in a lost suitcase, and discovered by a cat, we're going to do what we can for him/her. She's offered him/her strawberries, cooked chicken, cat food and assorted other things. S/he likes the cat food. We have an old 15 gallon tank that housed a clown fish for about 10 years. I know it's not huge, but for now, it'll have to do. We're thinking about making a hill shape out of aquarium sand and putting some salt water (we do have marine salt) in the bottom and give him/her a plate of fresh as well. Any advice would be greatly appreciated. Catherine <Need a bit of land that can/will be drier... and some mechanism, commitment to keep the water clean... Please read the above link over, and here on WWM: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/hermitcrabs.htm and the linked files above. Bob Fenner>

Mystery Hermit Crab Help - 10/20/2005 Hello.  Your website has the most in-depth info anywhere on the web!   <Hefty accusation there, Mary!  I'm glad you find the site useful.  Sabrina with you today.> You are all to be congratulated on your time, effort and expertise!   <Thank you very, very much for these kind words....> I'll try to watch my language. <Ahh, good.> That said....  I, like others, ended up bringing home a couple of hermit crabs by mistake from Dauphin Island. <Uhh, yikes.  Please, please folks - if you pick up trinkets at the beach, make sure the animals that used them are done with them!> They had survived more than 2 weeks in a tied plastic bag with other empty shells; traveling from southern Alabama up to and through the Smoky Mountains (all of those elevation and temperature changes, whew!) and finally to northern Kentucky.  So I figured the very least that I owed them was my very best efforts to help them live.  I knew absolutely nothing about them and had trouble at first figuring out that they are NOT the hermit crabs that you can readily find info for on the web and that so many kids keep as pets.  I haven't been able to exactly identify them, but here is a link to a picture of them:  http://www.touchthesea.org/hermitcrablv2.jpg <This is an aquatic or semi-aquatic animal, to be sure.  Not just a land hermit, as you correctly guessed.> I set up a mini (10 gal) salt water aquarium with:  Aragonite Reef Sand, other shells that I brought home (some of which may be suitable future homes for them), salt water made with dechlorinated tap water and Instant Ocean Sea Salt, mixed appropriately, and a thermometer. <Heater?  Filtration?  Testing supplies?  Food?> Yesterday, I thought they were goners.  After setting this 'system' up and putting them in, I gave them some food choices that I had tried previously like commercial pellets, leaf lettuce, "Sea Weed Salad, Green Marine Algae" and covered the whole sha-bang with a towel and left them undisturbed overnight. <I would try offering small bits of thawed frozen raw human-consumption shrimp....  and remove in a few tens of minutes if left untouched.> (In Kentucky, I think 'sha-bang'  is a noun, LOL)   <Can double as a verb in Kansas, spelled 'shebang'.> And, alas, they seem to be very happy crabs this morning !! SO, I will go ahead and install a water pump and filtering system, the information for which I can get from your FAQs.   <Great.> But, FINALLY, here is my question.... I have yet to see them attempt to eat anything that I have offered and I am stumped.   <These opportunistic dudes prefer meatier fare....  Try shrimp, krill, even bits of human-consumption fish.> Today, they seem to be filtering the water through their mouths and maybe eating the algae that came in the sand??.   <They'll pick through it some, sure.> But that won't last very long, will it?   <No.> What else can I offer them to eat?   <As above.> Do they maybe just need more time to acclimate to their surrounding? <Perhaps.> Minerals? <Regular water changes with saltwater of the correct salinity using a quality salt mix will help with this.  You may wish to start testing, maintaining calcium and alkalinity.> If this is successful, I think I just might invest in a new hobby.  I currently am husband to a 40 gal FW aquarium that has been very successful over the years.    <Must've been tough to get THAT marriage license!> A Marine tank would be too cool !  I had always been intimidated by the science of one, but no longer, thanks to all of the efforts y'all put into this web site. <Glad we could be of service.> ('y'all' is definitely a noun in KY !)   <That's one I could never get the hang of.> I look forward to some suggestions on food, minerals, etc.  Keep up the great work, so many of us appreciate it. <And again, thank you very much for these kind words.  It means a great deal to see comments like these.> Mary Robben <Wishing you well,  -Sabrina> Crabby Conversion? - 08/07/2005 Can saltwater crabs adapt to fresh water? <Unfortunately, no.  Thanks for writing in!  -Sabrina> Blue Claw Crab life history Hello - i believe that blue claw crabs can thrive, although not reproduce, in fresh water.  What do you think the min. salinity level from maintaining blue claw crabs can be, provided that they are not being substantially supplemented with calcium. Steve <I would keep these crabs at near seawater strength (spg of 1.025) though they do tolerate, and even engage brackish water in their life history. Please see here re: http://www.dnr.state.md.us/fisheries/education/crab/bluecrabfacts.html. Bob Fenner>

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 

Crab Legs?  Not This Crab.... - 03/12/2004 Hey friends I was wondering if you can give me some info on my blue crab I just picked up; Well I was talking with some of my friends at my local fish store, and I noticed one of them about feed the trigger. I saw it was a blue crab, and told him to save his life so I could take him home. <Mmmm, crab cakes....  Just kiddin'.  I have a soft spot for weird inverts, myself.> He's about 2-3 inches now, so I have him in a 20 long with live sand, and the whole deal (protein skimmer, etc...); <Nifty!  His own little paradise.> I was wondering what salinity rate would be good for him, because I know I've seen them in brackish before? <Mm.  Very good question.  The link I'm about to give you in in German, but you can use Google's language tools to translate (somewhat), and hopefully you can glean what salinity would be ideal for him, or at least ID the little bugger.  From there, I'm not sure what I can tell you....  Ask the fish store whether they were keeping him in fresh or salt water, look at the health of any others they have in stock and compare their health/activity level to yours, implement any changes in salinity SLOWLY, and observe carefully.  If dropping the salinity a bit makes him seem more active, that would be a good indicator that something's going right.  Try to identify him, and from there you can determine whether he needs an area to get out of the water or not.  Also do keep in mind that crabs are not wholly fish safe, and some are outright terrors to any fish (a real switch from almost being on the menu, eh?).> Also how long will he maybe live for? <Another toughie.  I would think that a couple years is likely, perhaps more.  Crabs and shrimp usually aren't as long lived as our finny friends, but should still do well with the proper care.  Wishing you and your crab well,  -Sabrina>

Dungeness crabs in a home aquarium? I live in Tacoma Washington and do a lot of fishing and crabbing. I was wondering if you had any ideas or pointers on keeping Dungeness crabs in a home aquarium for later consumption. I haven't been able to find anything on the internet on care and requirements for Dungeness. <Dungeness crabs are very tolerant of a wide range of salinities, as you know, they are often found in estuarine areas, I would recommend full salinity (33-35 ppt). Also, unless you are pumping in natural seawater for the system, I would foresee a chiller as being necessary. Being carnivorous, they could be pretty easily fed a ration of shellfish/shrimp/crabs and similar foodstuffs. Beyond these considerations, I would think normal good aquarium husbandry would be the only issue to their keeping.> Thank You, Morgan Moroni <Best, Chris>

Dungeness crab (holding facility/gear) Hi Robert, <Howdy> Our company manufactures crab and lobster traps. We're purchasing a 12' wide x 31" high wading pool to set up as a crab observation tool. We want to watch Dungeness crab, and perhaps lobster later, as they crawl into our traps and try to get out. We make some entrance devices for the traps that we would like to observe as to their effectiveness. Our web site is www.neptunemarineproducts.com. <Neat> Any advice on how extensive of a system I will need to keep the crab alive and active would be appreciated. I suspect we would only need a couple of weeks to observe the crab's behaviour in relation to our entrances. After that, a crab feed! <Take a look here: http://wetwebmedia.com/cntfiltbiz.htm re centralized filtration systems in the ornamental aquatics business... same gear, principles apply... and any/all else on our site (www.WetWebMedia.com) that is linked, is unknown to you... And make it known if I can be of further help... Am tempted to suggest a "skid unit" more for the pool industry than a more expensive "live holding system" unit here... If cost is a concern... But would like to know that I/we weren't otherwise changing the test animal/prey's behavior by neglecting good water quality. Bob Fenner> Sincerely, Ed Wyman

Dungeness crab R & D Hi Robert, Thanks for the comments and advice my previous email about observing Dungeness crab behavior in and out of our traps. We'll be able to get filter seawater from the Seattle Aquarium which is nice since it is only 3 miles away. We'll need about 3,500 gallons. <Do consider, study the need to bolster alkalinity. The facilities I help with use simple baking soda, sodium bicarbonate (Arm & Hammer) here... Inexpensive, readily available... to boost alkalinity, maintain pH at a safe level... otherwise, w/o much in the way of soluble substrate present/water flowing over... even with 3,500 gallons these values can slip dangerously, quickly...> Any idea on how much air we need aerate the pool and keep the environment good for active crab activity ?? <Not much if it's just one, a few crabs in this volume... I would use a sump (separate container, like a big Rubbermaid tote... horse/cow drinking size.) to have the water overflow from the main system (run it through a protein skimmer (will aerate here par excellence) then through some sort of biological filtration (to convert ammonia/ammonium from crab wastes (produced continuously whether you feed or not, and from your demo. baits...). Perhaps a good idea to have a few "Aquarium Service" companies come out and bid on the mechanicals, install... to get their ideas. Bob Fenner, www.WetWebMedia.com> Thanks, Ed

Sally Light Foot? Hi Bob. I was reading about the Percnon gibbesi, the Nimble Spray Crab on your site. Is this crab also known as the Sally Light Foot crab? <Mmm, maybe... perhaps sold, labeled as this by some... though the "real" Sally Lightfoot Crab is Grapsus grapsus> Does it need to be able to get out of the water periodically? <Yes> Any further tips on keeping this crab healthy? <Do use your search engines here. Not much that is practical/husbandry known about these crabs. Bob Fenner> Gracias.

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