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FAQs about Horseshoe Crabs, Systems

Related FAQs: Horseshoe Crabs 1Horseshoe Crabs 2, & FAQs on: Horseshoe Crab ID, Horseshoe Crab Behavior, Horseshoe Crab Compatibility, Horseshoe Crab Selection, Horseshoe Crab Feeding, Horseshoe Crab Disease, Horseshoe Crab Reproduction, & Crustaceans 1, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating Shrimp

Related Articles: Horseshoe Crabs: Latter Day Trilobites for Some Systems & CrustaceansMicro-Crustaceans, Amphipods, Copepods, Mysids, Isopods, Shrimps, Coral Banded Shrimp, Cleaner ShrimpP. holthuisi Pix, Mantis "Shrimp", Lobsters, Slipper Lobsters, Hermit Crabs, Squat Lobsters, Crabs, Arthropods, Pycnogonids (Sea Spiders),

Systems of size... lots of soft sand... Likely refrigerated...

Building horseshoe crab tanks      10/20/16
I can't seem to find consolidated information on ideal horseshoe crab tanks, just random spattering of information. What are ideal tanks for horseshoe crabs? Will you critique the tank I would like to build?
I would like to build a tank that is 4x4 wide and long, and 2.5 ft tall, made from non-porous cement. I'd like to line the bottom with a fine sand substrate, and keep two horseshoe crabs in it with no other fish. I plan to culture black worms and phytoplankton and feed them to the crabs, and feed them snails as well. Is this an ideal diet or is there a better way to feed them?
<Issa, that tank is definitely sufficient if you are only doing the crabs.
The fine sand will do wonders for the crabs. The crabs will sift through the sand for food, but you do need to feed occasionally. The foods you listed will work, but I would as some other meaty food to the diet as well.
Read on WetWeb re Horseshoe Crabs. Let us know if you have any further questions. Cheers, Gabe.>

horseshoe crab, fdg., sys. gen.     2/5/13
I have been reading and researching your site on horse shoe crabs and had a few things i wanted to discus with you. I have a little horse shoe crab
<The eastern seaboard species I'll assume>
 in a 10gal salt water tank. he was about 2 inch's when i got him, and now he is about 3 to 3 and a half. I have had him in the tank for about a year at this point and he has not starved to death. My salinity is between 1.024 and 1.025, ammonia and nitrites are both at 0 or close to, my nitrates are kinda hi, but they have always been high in my tank and despite anything i do i cannot get it to come back down.
<Not so important w/ these relic species>
 So far the only adverse affects to the high nitrates is a bit more red hair algae than i would like (the snails keep in under control for the most part) and my plant seems to like it as well (not sure what kind, obviously saltwater plant, its kind of  like a vine and it raises little stocks that disk shaped "leafs" grow on).
There is a very healthy bristle worm population in the tank as well as he seems to enjoy algae wafers made for Plecos and other such fish as well as high protein wafers made for catfish and other bottom feeders. He does seem to come out and eat with everything else in the tank and chasses around bits of flake food but his favorite seems to be Hikari Multi-Vitamin Enriched Brine shrimp. As for the trace elements in the tank, i use Kent Marine Nano Reef two part supplement. It is recommended for use every day, but i don't use it that way, i add that about one a week, sometimes twice if I'm feeling spunky. Tank mates include a mis-bar clown fish, a blue-green Chromis, peppermint shrimp, two Astrea snails, two dwarf blue legged hermit crabs and a group of about 9 Zoas. There was at one time a mini brittle star that came in with the Zoas, but i have not seen hide nor hair of that little guy in over 7 months so i think he died and got ate, or just got ate. There was a narsis snail and another Astrea snail, but the hermits wanted bigger shells and they didn't like any of the upgrades that i provided for them.
There is about 6 to 7 pounds of live rock, and about 20 pounds of live sand to make a sand bed of about 3 inches deep. The sand is larger grain, not fine grain, but he really does not seem to mind. I really love this little guy, he is awesome and by far the best purchase i have made. Hours of entertainment watching him walk around the sand eating, and swimming (not very well) upside down around the tank. And yes i know how big they get, i have already located tanks that he can be transferred to as he grows, including a fine grain, 6 inch deep sand bed in a 180gal tank with plenty of Spionid worms for him to break up and eat. I guess what i want to know is is there anything else i need to be doing for this little guy?
<Doesn't appear to be; no>
As i have stated he has had no problems so far, but i want to keep him this way. I have not found anything on your site with anything i really need to change so I'm just double checking that i have not over looked anything. its hard to know what your looking for when there is no problem to solve. thank you for your time and for your help! i greatly appreciate it.
<Well, the other life, fishes and invertebrates would likely appreciate lower nitrate... not easily done in the size/type setting w/ the horseshoe... All will appreciated the larger habitat. Bob Fenner>
Re: horseshoe crab    2/6/13

Thank you for the quick reply! any quick tips for lowering nitrates in a small tank other than moving them to a big tank? i would like everything to be as happy in the tank as can be.
<Read here: http://www.wetwebmedia.com/nitratesmar.htm
and the linked files above. The mechanisms, techniques of nitrate control are the same regardless of size of the system. BobF>
Re: horseshoe crab    2/6/13

thank you very much!
<Ah, welcome. B>

Horseshoe Crab... sys., sel.    2/21/11
I have spent a lot of time on your website and will not buy anything for my tank anymore without looking to see what you guys have to say about it first. I've spent a lot of time the last few days looking over all the info on Horseshoe crabs that you have, all the questions seem to be people who bought them and are now trying to figure out what to do with them, so thus I have not found all the info I am looking for. I think the horseshoe crab is an amazing animal and am very interested in setting up a tank for one. I was thinking to use a frag tank style tank, something at least 4 feet long and at least 2 feet wide, but only about 16 inches deep or so and setting up the whole thing as a sand bed for the horseshoe. I would set it up so it shared water with my reef tank
<... which is coldwater?>
so I could take advantage of the good water quality and filtration and chiller that I have on that, and add more total water volume to my system. The drawback of this is that I keep that system @ 76 degrees.
<This won't work>
I see that the commonly available Atlantic species of horseshoe prefer colder water than that, are the indo-pacific horseshoes better for warmer water,
<IF you could secure one of these it might work>
and if so are they ever available and how do i tell the difference between the species.
<Have never seen offered in the trade. ID info. you can find on the Net>
Also if I can find one that can handle my temperatures how deep of a sand bed should I set up.
<Four inches or so will likely do for the size of the specimen/s you'll be able to keep here>
And is there any other advice you would have for setting up a tank dedicated to a horseshoe?
<All I'm sure of is posted on WWM>
Lastly if this ends up happening, what quarantine recommendations do you have for horseshoes,
<Mmm, a couple weeks isolation from other systems. Do track metabolite accumulation in their quarantine system>
I am slightly paranoid about quarantine and have separate quarantine tanks for both my fish and my corals, nothing goes in without being in quarantine for a while.
Thank you,
<Welcome. Please do relate your experiences if you go forward w/ this project. Bob Fenner>

Atlantic Horseshoe Crab/Feeding/Systems 4/19/10
I have recently bought a Atlantic Horseshoe Crab and I am not sure how often to feed him. I have 4 foot tank which is 350 lt.
In my tank I have clown fish, damsels, Chromis and 2 Chocolate Chip Star fish.
<<This animal can't live here with these fishes... is NOT tropical... RMF>>
My star fish eat white bait and the other day I put half of one in the tank for the star fish and the crab eat it instead is it ok for the crab to eat that.
<Yes, will eat most anything.>
Please let me know how often to feed him I don't want to starve him but I also don't want to over feed him.
<This species is principally a sand-sifting filter feeder, though there are other horseshoe crabs that are more predatory.
Most Horseshoe crabs are short lived due to lack of nutrients, inappropriate systems. Do read FAQ's here.
Many thanks
<You're welcome. James (Salty Dog)>

Horseshoe crab arriving today, sys.  (RMF, thoughts on releasing Limulus into the wild? I'm against...)<<Am totally opposed. RMF>> 11/17/09
I read with interest your FAQ section on Horseshoe crabs.
<Fascinating animals indeed.>
Unfortunately, I did so after ordering a 2-3" crab yesterday from a website that said they are easy to raise and will do well in reef tanks.
<Good heavens no!>
I have a 125-gallon reef tank and a 55-gallon FOWLR tank.
<Not a good home for this chap.>
However, after reading your FAQ's, it is clear this new arrival will not be happy in either place due to the water temp, among other things. I want to give him the best shot at survival until I can figure out what to do with him long term.
<Very good.>
I have a 100-gallon Rubbermaid tub, 80lbs of Caribbean Live sand still in the bags, plenty of "seasoned" salt water and cured live rock, powerheads, etc. I will use whichever of these things I need to for this crab and will purchase whatever else you think I need for the next year, short of a new aquarium.
<Actually, maintaining Limulus under lab conditions isn't especially difficult, and if you Google "Limulus polyphemus" (the Latin name) as well as Horseshoe Crab alongside "maintenance" and/or "aquarium" you'll find there are fairly reliable protocols for keeping these creatures for extended periods. While not precisely white mice, they are much used lab animals, particularly for medical research. See for example, here:
In short, they're kept reasonably cool, room temperature in an unheated room usually fine, and maintained in a clean, filtered aquarium. Feeding is done separately, with the animal turned upside down, food (chunks of fish, seafood, etc.) placed in its "claws", and then the animal replaced in a tub of seawater. It's left to feed for about an hour or until its defecated, and then returned to the maintenance tank. Repeat every couple of days. In the wild these animals hunt for small organisms within the sand bed, but this really isn't viable in captivity.>
Please let me know the best way to set up these things to make a suitable environment for him until he outgrows the 100 gallon Rubbermaid (by the way, how will I know when he has outgrown it?). Also, can I release him into the Long Island Sound once he grows and if so, what size should he be before release?
<I'm not wild about releasing captive animals into the wild. For one thing, at any number of points along the chain of handling it can be exposed to parasites, bacteria and viruses that don't exist in Long Island Sound.
There's also the issue that you may not even have Limulus polyphemus, with Asian sources certainly sending out Carcinoscorpius to pet shops in Europe, and therefore possibly elsewhere. Obviously releasing non-native species is a bad thing. Since these animals do reasonably well in public aquaria, you might send a couple emails out to such places, to see if they can home your beastie. Alternatively, humanely destroy the animal (again, info on this will be in the scientific, if not hobbyist, literature).>
Lastly, would it be okay to purchase minced clams (like they use for clam sauce) and chop them even finer for him?
<A variety of seafoods is best, since by themselves seafood items tend to be lacking in one or other regard. Unshelled shrimps have calcium but too much thiaminase, shelled cockles are low in thiaminase but not enough calcium, and so on. The more variety, the less chance of problems. Lab specimens take standard fish pellets readily enough, and while there's debate about their use as a staple, as an occasional vitamin top-up they may have their place. Alternatively, your usual marine vitamin supplement could be used.>
Thank you for any advice you may offer.
<Hope this helps. Cheers, Neale.>

Re: Horseshoe crab arriving today, more re sys.   11/17/09
Thank you for your prompt response.
<You're welcome.>
I will feed him/her as you propose.
I will set up the Rubbermaid home for him/her for now. According to the seller, this is an Atlantic Limulus.
<Good to know. Telling the species apart isn't difficult, and a cursory review of the literature should help if you're interested.>
I have an extra submerged pump/filter setup from a small koi pond which I can use.
Should I leave the bioballs in there or just use the sponge filter?
<Probably won't make much difference either way. These aren't "delicate" animals provided they aren't starving or overheated (which are the prime sources of mortality in captivity).>
Will the crab be okay with the water movement that comes from the top outlet (used to be a fountain) of the pump/filter setup?
<These animals are used to very strong water currents, but that does assume they're able to "dig in" a bit. I'd see how you go. In aquaria they often get pushed onto their backs, in which case you'll need to right them.>
Should I fill the tub to the maximum level? (100gal)
<More water the better of course, but 100 gallons for a 3-inch specimen might be overkill.>
The only room I can put the tub in is heated. I will put a thermometer in the water. What is my target water temp? Should I do periodic water changes?
<Wouldn't worry too much. Unless the water temperature is above 20 degrees C, these animals aren't stressed. Do read that article I linked for you; it contains details on the established protocols.>
Lastly, should I not bother opening the two 40lb bags of Live Sand and just leave the tank with not sand?
<In labs sand is rarely used because of the risk of the sand getting dirty and causing infections. Since "clean" crabs are essential for the work being done, this is helpful. But under aquarium conditions a few cm of
coral sand and crushed coral would be very useful. Live sand is obviously helpful in terms of water quality management, but the Limulus couldn't care less either way.>
I also have Live Rock that needs a place to go. Can I put it in the crabs tub or should I put it in a separate tub?
<Limulus don't like rocks. Plus, below 25 C, your expensive Fijian live rock is soon going to die back. Would concentrate on old-school canister-type filtration, ideally supplemented with some aeration to keep
the water nicely oxygenated.>
Over the next few days I will do the research you propose so I don't have to ask you so many questions!
<I'm no great expert on these beasts, though like Bob, I've bumped into them a few times in the scientific side of my life. They're virtually never kept properly by hobbyists, hence the need to concentrate on lab reports.>
Right now, I am in a hurry to set up the crab's new home before FedEx arrives :))
<You'll be fine. These are EXTREMELY hardy animals when given essentially correct conditions. There is an Asian species sold as a freshwater horseshoe crab that manages to cling onto life for months under such
conditions, even though it's a brackish/marine beastie. Don't panic, do your reading, and enjoy.>
Thanks again,
<Cheers, Neale.>
Re: Horseshoe crab arriving today
thanks again! I will give it my best shot!!!
<Good luck! Neale.>

Horseshoe crab arriving today  11/20/09
Hi Neale,
<Hello Dennis,>
The horseshoe crab arrived healthy-looking and I set him up in the 100 gallon Rubbermaid. However, we can't keep that big tub in the house (it's in the basement) and we just realized he is so cute that we would like to watch him grow. So, I bought a cheap 14-gallon aquarium and put about 1" of sand in the bottom of it and want to move him into it temporarily until he outgrows it. The unheated water seems stabilized at 68.7 degrees.
<Sounds fine.>
Since he is only 2" in diameter, will he be okay in this aquarium for now?
At what size should we upgrade him to a larger tank (is there a size per gallon formula we can use as a guide as he grows so we know when to upgrade the size of his environment?)
<Not aware of any formula here. I'd use common sense. At its small size, a 14 gallon tank is probably fine. But once it gets too long to turn around easily (the long tail is an issue here) then it'll need a new home. I don't believe these animals grow especially fast, but they do eventually get quite big. A good size specimen will have a body around 20 cm long, with a tail about as long again. They can get bigger though.>
Lastly, this aquarium has two incandescent light bulbs. Is that ok or does he need fluorescent light?
<Couldn't care less. These animals are nocturnal, and don't particularly like bright light.>
Thanks again Neale.
<Happy to help. Good luck, and do perhaps send a photo along! I for one would be interested in seeing this beastie in his new home. Cheers, Neale.>

Re Horseshoe crab arriving today  11/20/09
Did you receive this email that I sent early this morning? Please respond at your convenience. Thank you once again.
<Hi Dennis. Read it and replied. The answer is up on today's FAQs, here:
Do check my reply didn't get thrown into your Spam folder by accident.
Cheers, Neale.>

Re: Horseshoe crab arriving today  11/20/09
wow, cool, i made the "big time"...
<As does everyone who writes... and when we tell them they're nuts keeping Seahorses and Great White Sharks in the same tank, they're not necessarily thrilled about seeing this on the Daily FAQ page!>
seriously, thanks for your prompt response...i will send you a pic in the next few days...
should i leave the light off permanently?
<Couldn't matter less. Ambient room lighting will be ample, but if you want to use lights, then by all means go ahead and do so. Under bright light, Limulus will hide, but a lower power tube like a GroLux or a moonlight tube would be fine. Cheers, Neale.>

Will my horseshoe crab eat my other livestock? (RMF, feel free to argue!) 10/15/09
Hello! I have read much of the information on this site and am very impressed. However I don't see my answer, so here we go. I just brought home a horseshoe crab from a guy that I was buying some live rock off of.
<Hope you have a large coldwater marine aquarium to keep your Limulus in; they are not tropical animals and cannot be kept in tropical reef tanks.>
I got lots of live rock, a clown fish, 2 zebra fish and an enmity.
<An enmity? Do you mean that? An enmity is a hatred. Do you mean an anemone? One of those big things with tentacles that looks like a jellyfish stuck to a rock?>
Well I got the fish and crab for nothing so I took them. The fish are doing fine tonight but the crab is all over the place, probably because of the current.
<He's looking for a way out of this tank and into a coldwater system.>
I didn't have much in the tank because I have only had it running for 2 months or so and am kinda new to all this. So I decided to come to your website and see what information you had for me! Well I panicked when I seen that horseshoe crab eat shellfish!!!
<Up to a point. But they are primarily detritivores that feed on small organisms and decaying organic matter they sift from mud. In captivity, scientists maintain them by taking them from the holding tank, putting them
upside down in a feeding tank, sticking some shellfish between their legs, and amazingly enough, they eat the shellfish. Leave in the feeding tank for an hour so they can defecate, and then return to the holding tank. They do this 2-3 times a week. While it sounds a performance, it's actually the best way to maintain Limulus for any length of time outside of a very large public aquarium. In a really big tank with a deep sandy substrate, they are to a degree "scavengers" that get by on leftover food and such, but this isn't really viable in home aquaria. We're talking tanks measured in 1000s of gallons here, which isn't what most folks have at home.!>
I Only had a few friends in the tank before tonight. They are 2 baby brittle starfish (maybe 1in. diameter) a Emerald crab, 2 blue hermit crabs, and a skunk shrimp. So immediately pulled this horseshoe guy out of my tank and put him in my sump for the night (lots of rock there with very little current and light). He's a little more calm there but, I need to know if this new guy means trouble for my other little helpers in my tank. I am trying to start slow, and do things right.
<He's actually doomed.><<I do agree. RMF>>
100gal tank
100lbs of live rock
2in of sand
<This is a weak link in the chain: you'd need a very big, very mature deep sand bed to maintain Limulus "naturally".>
1 horseshoe crab
1 skunk shrimp
2 blue hermit crabs
1 Emerald crab
2 zebra fish
1 tomato clown fish
1 enmity
1 colony of mushrooms
Dose anything above NOT belong together in a tank
<Yes, the Horseshoe crab doesn't belong. It needs a large unheated tank maintained at around 10-20 degrees C with a deep sand bed it can burrow into. If you can see the crab, it isn't being kept properly: in the wild they stay under the sand much of the time. There are tropical species, such as Carcinoscorpius, but this species is sold as a brackish-water "Mangrove Horseshoe Crab" and so far as I know not in the US, since the American trade has access to the cheaper Limulus. Even in Europe, Carcinoscorpius isn't often seen, which is a shame because it's smaller, highly euryhaline, and consequently easier to keep. Anyway, Limulus is one of those animals *not* to buy on a whim. Hope this helps, Neale.><<Well done. RMF>>

Subject: another photo, please: blue-legged hermit?   8/28/09
> Hi Bob,
> Do you have this beastie? Clibanarius tricolor, or similar?
> As a swap, I can offer a photo of Carcinoscorpius rotundicauda, a euryhaline Limulus doing the rounds as the "freshwater horseshoe crab" even though it doesn't last long in freshwater (no surprise).
> Thanks!
> Neale
Will either of the attached do? B

Re: another photo, please: blue-legged hermit?
Yes, perfectly well! Thanks Bob.
Attached, a "freshwater" horseshoe crab.
Cheers, Neale
<Will post w/ your prev. comment with credit to you. BobF>

FW Limulus, not!  8/29/2009
Hi Bob,
Here's a better caption:
"Carcinoscorpius rotundicauda, one of several Southeast Asian Limulus relatives. Basic care similar to Limulus polyphemus, except that Carcinoscorpius rotundicauda is truly euryhaline and tolerant of a broad salinity (and temperature) range. Sometimes sold as a freshwater invertebrate, as it does sometimes occur in freshwater habitats, having been recorded from the Hooghly River 90 km (56 miles) upstream.
However, it does not do well in freshwater aquaria, but can be maintained in brackish or marine aquaria from SG 1.010 upwards, assuming other factors (substrate, diet) are appropriate."
Cheers, Neale
Will append. B

Horseshoe crab and purple urchins... OPublic'sMoney... mis-stocking 1/9/08 I work in a school where we have recently (6 months) established a 1000 gallon touch tank. <Nice> We have a large variety of damsels and starfish, arrow crabs, one lemon angel, live rock, cleaner shrimp, sally lightfoot crabs, flame scallops, <Poor choice with the scallops, have a terrible survival rate.> spiny urchin, polka dotted batfish, and about a dozen purple urchins and had two horseshoe crabs, about 9" in diameter. One died about three weeks ago and the other this weekend. <Not surprising, are cold water species and would have trouble in the warm water required by the other residents. Please see here for more http://www.wetwebmedia.com/hshoesys.htm > We added the urchins about three weeks ago and wonder if they are the culprit. <Doubtful> I fed the fish one evening on a weekend and found an urchin attached over one of the horseshoe's eyes. The eye was gone and the horseshoe was dead. Don't know which came first. <The crabs death, urchin was just scavenging for a meal.> The second horseshoe would not eat for me on Sunday of this week and on Monday it was nearly dead and the urchins were attacking its eyes. <Easiest part to get to on the crab.> Are the urchins the problem or do we possibly have another issue? <Other environmental issues.> Is it absolutely important for the horseshoes to be able to bury themselves completely? <Does help them, but not the issue here.> Our sand is not that deep. We now have two very small baby horseshoes that were added before the big ones died, but we don't want the urchins to get them too! <The urchins won't but the inappropriate temperature probably will.> We were hand feeding the horseshoes squid and brine shrimp and they were eating well every day. This was advised by the supply source where we purchased them. <They should have advised you that they need different environmental parameters than the other inhabitants.> I can't find any source of complete information on their care and would LOVE to have that information if you can point us to it. They are wonderful for the tank and the kids love them, but we don't want to just add another pair to have them die again in 6 months. <The most likely outcome without a specialized cold water tank. See here for more http://www.wetwebmedia.com/horseshoecrabfaqs.htm > THANKS! <Welcome> <Chris>

Re: Horseshoe crab and purple urchins  1/10/08 What is the "ideal" tank temperature for Horseshoe crabs... <Something comparable to the wild, i.e., coastline of North America from about Delaware south to the Gulf of Mexico, but prime habitat is the warm-temperate parts. Think somewhere like the Delaware or Chesapeake Bays. So somewhat cool in winter, say 12-15 degrees C, up to the low 20s C in summer. They aren't tropical animals, and their lifespan is distinctly shortened kept under such conditions.> and what is the ideal feeding arrangement?? <Again, just as the wild. Deep sand/mud, where they process food by shoveling it past their mouth as they burrow through. If you can see a horseshoe crab clear above the sand/mud, it's an unhappy animal. They plough through the sediment, and only really feed successfully when kept thus. They don't "hunt" for food like regular crabs, sniffing out stuff and gobbling it up. They're more like earthworms on land, in the sense that burrowing = feeding.> We have our temp at 75 and had been feeding our guys by hand daily either brine shrimp or squid and the gobbled it down. <Too warm, and does need to be seasonal, with lows in winter and highs in summer. Realistically, a room temperature tank in a cool part of the building is the ideal, and anything else will only shorten the life of the animal though heat exhaustion etc.> We still have two small ones (2"). Is there any text you recommend for reading? <Nothing much published beyond the article Bob already referred you to here at WWM. In labs, where Limulus is often used, it's a short-lived animal destroyed after the experiment is done. New stock is invariably collected from the wild.> We are trying to develop a "library" for our students as well as internet sites they can research for information on our tank inhabitants. <Much written on these animals, though mostly from biochemical and physiological angles, since that's what these animals are mostly used for. Not much on ecology, nor maintenance in captivity. Quite a bit known on breeding, but mostly from field observations. Do searches using its Latin name (Limulus polyphemus) plus those of the Asian horseshoe crabs Tachypleus and Carcinoscorpius spp. Cheers, Neale.> (RMF, feel free to comment) ... the root problem/basis of many of our modern world's problems are derived, heated by their being too much government... people, money... resources stolen, mis-directed. Principally what we need is to do away with life-time civil servants... Think on this. RMF... who does see this as pertinent... the money mis-spent here...> Re: horseshoe crabs Hi I read the paragraph it seems its directed at only one species. I'm not sure what I have its light tan and about 2-3 inches in length I have about 7 inches in the back of my tank with lots of sand that he has left trails through would this be a small one that don't get big or a gigantic one? I told the pet store lady my tank was 30 gall long and she recommended him? what do you think. Thanks guys for all my question. <Most all anyone sees in the trade in the U.S. is Limulus polyphemus... they do get large. Bob Fenner>

Horseshoe crab 3/19/04 I recently bought a horseshoe crab.  I've got him in my reef tank it consist of crushed coral and sand , it is mixed about half and half.  I was just looking around the net and had read that they do not do well in captivity because they usually starve.  I also read that they will eat different frozen foods that I can feed him but my main question is that if they die do they excrete a poison like the cowfish would when it dies. because I don't want it to harm my other stuff in the tank. please help!!  thank you Angie <Don't worry about the horseshoe crab poisoning anything else when it dies.  Yes, they often starve in aquaria for lack of natural food, but the bigger issue is that they are temperate.  Normal tropical aquarium temperatures are therefore stressful to the point of being fatal.  Best Regards.  Adam>

Horseshoe crab  Dear Bob, <Michael here today, not quite as good, but I'll do in a pinch>      I live in Rockport, MA and I'm going to set up a 20 gallon, room-temperature saltwater aquarium for local species.  It will contain local seawater and sand.  Some species I'm planning on having are mummichog minnows, common periwinkles, rock gunnels, and hermit crabs. <Neat - possibly some local alga as well?>  I was wondering if a store-bought horseshoe crab could survive in such a tank.  Horseshoe crabs are occasionally found in my area, but are uncommon and usually large.  I know feeding can be a problem, but I plan to use local sand from the ocean full of living things.  I could also use native seaworms.  If you have an comments, or suggestions for other species that could survive in such a tank, please reply.  <Well horseshoe crabs aren't all that difficult to keep alive, but they grow much too large for a 20 gallon aquarium.  The carapace of a horseshoe crab can be 12" across> -Curtis  <M. Maddox>       

Re: Horseshoe crab Michael, Thank you!  I am amazed by how quickly you responded. <Thanks, thought I'm not always this vigilant>  If the horseshoe crabs got to big, I'll just release them where I've found others. <As long as they're endemic to the area, and you release them when they attain ~5" they should do fine>  Do you know any good sites with horseshoe crabs? <I would search Google for some links for you but this computer is going haywire.  I hope I can even get this email sent>  Also, do you know if tidepool Sculpins or cunner wrasse could survive at room temperature?  Do you know of any tropical species that could? <Depends what you mean by room temperature.  Most tropical fish will survive in 75-85 and do quite well> Thanks again -Curtis <M. Maddox>

Horseshoe Crabs I've recently ordered some small 1-inch horseshoe crabs for an established saltwater tank (with a few damselfish and a Hawkfish). <I do hope that your tank is quite large (~180 gallons or more), as Horseshoe Crabs are unsuitable for life in a small aquarium, even if they are purchased small (everything has the right to grow, right?)> The bottom is mostly rocky now, so I'm thinking I will need to make a sandy area for the crabs to burrow in, am I right? <Yes, your assumption is correct.> How deep should this sand ideally be for the crabs? <Depends on their size. At a small size, I would think around 3" would be plenty. At adult size, you may need a couple of feet.> Also, I've done a lot of research about diet, and have gotten quite a variety of answers. In your opinion, what works BEST with horseshoe crabs, and how often should I feed them (I know overfeeding can kill). <They are detritivores, so fish food/krill would work fine.> Thank you very much-- these are such weird creatures that it's hard to find specifics! <I'm glad I could help. Mike G> Horseshoe crab I inherited a horseshoe crab. It has developed a black "fungus?" on its back (near the tail). It is approx. 6" wide and living in a 2 gallon tank...do you think it has outgrown the tank? <Hello, the black fungus is probably algae that has grown from being in such a small tank. A horseshoe crab that size needs at least a 120 gallon tank. Good Luck MikeB.>

Crustaceans And Damsel Death - 08/12/2005 I'm wondering how my fish died; he was in a 10 g. tank.  He is a neon velvet damsel with 3 hermit crabs and horseshoe crab and a turbo snail. <Way too much life for a 10 gallon tank....  Please see here on horseshoe crabs:  http://www.wetwebmedia.com/horseshoecrabfaqs.htm .  This animal is completely unsuited to your system.> I had only had him for 24 hrs. and he was on his side. <Almost certainly environmental.  Be testing your water regularly.> When the hermit crab saw that he went over there and grabbed him so I took all the hermit crabs out in a small bucket with a bit of water and they ate that entire fish but the head. When they were done I put them back in the tank. Can you tell me if that was okay? <Probably not a problem, in any case.> My horseshoe crab has been buried for I think two or three days but has been messed with to see if he was alive. <Likely not for long in your system....> He was ,then he just buried himself again. Can you tell me the proper care for all of them? I would appreciate it. Thanks,  Drew <All you seek and more is already archived:   http://www.wetwebmedia.com/marine/index.htm .  Wishing you well,  -Sabrina>

Crustaceans And Damsel Death - II - 08/14/2005 I had read a few of your listings on horseshoe crabs would a pet store buy on from. <Might wanna proofread before you send, for future reference....  I am *guessing* you are asking if a fish store would buy back your horseshoe crab?  Possibly, or possibly would take it in trade for store credit.  You will need to check with your local fish stores; all of them vary in what they will do about livestock.> I don't know too much on the subject, I'm only 12. <Ahh, you're doing outstandingly for 12!  Keep up the research, and you're sure to learn and enjoy this hobby.> My hermit crabs are not big and neither is the horseshoe crab.   <The size of the crab is not what's in question, just the pure unsuitability of it in any warm, small, tropical reef system.  The smaller the tank, the worse for the horseshoe.> I have a little castle thingy and a little rock. I have also been cleaning the tank and doing water changes once a week. Should I keep on finding out if the crab is alive or to leave him alone. <I would not mess with him any more than it would take to get him to a fish store or someone with a suitable system.> I also don't have enough money to get a bigger aquarium. <It would take a very large, cool water aquarium to keep the little guy alive.  Were I in your shoes, I'd truck him back to the store and ask for a refund.> I haven't been able to find out about these little tiny things crawling on the glass is that bad or good and what do I do about them? <They're more than likely good.  Probably copepods and other such desirable animals.> Thank for all your help so far, you guys seem to know a lot about fish. <The more you learn, the more you realize how much more there is to learn! What a terrific hobby this is.  I'm glad you're getting into it so young. I'd like to give you a few ideas for your tank.  If you stick with just invertebrates, like your hermits, and maybe a pair of skunk cleaner shrimp, it'll probably be a very easy, very fun tank to care for.  There are a lot of neat, smallish crabs (scarlet hermits, emerald crabs) and neat shrimp that you could choose from to make your tank fun without fish.  But you've got the right idea picking a single small, hardy fish if you do want to have a fish in the tank.  You're on a great road to a great start!> Drew <Wishing you well on this adventure of learning,  -Sabrina>

Horseshoe crabs  10/5/05 I was reading on your FAQ's about horseshoe crabs that they don't  live long ..days or weeks. I had kept them before in a tank without a  heater (room temp), and they lasted for years. I fed them black worms, and I  would put a little piece of fish under their shell. The tank was fairly warm,  but most of them did ok. <Eddie, the general rule for keeping horseshoe crabs is a larger system with fine gravel/sand and preferably cool water.  As you say, they are not hard to keep provided the correct conditions are provided.  James (Salty Dog)>   Eddie V.

Horseshoe Crab selection, systems   1/17/06           Ok, first off I have to say I did not do an extensive amount of research on horseshoe crabs before I bought one (and now I regret that very much). I went to one site that said they were easy to keep and ate matter in the substrate.  With this lazy-man information I went to my local fish store and picked one up.  In my obsession with my new horseshoe crab I decided to do more research and came upon this site (which I might add is very helpful).  I feel really bad for my horseshoe crab, I fear he will starve. <Most do> I have only a 55 gallon tank, and about half the sand bed is covered with rock.  The temp is usually kept at 78 degrees Fahrenheit, I'm aiming to lower it (would 75-76 degrees be good or still too warm?). <If this is a/the (typical) coldwater species, (the Atlantic U.S....) yes>   His tank mates are one scooter blenny, one royal Gramma, two peppermint shrimp, one emerald crab, and about a dozen types of snails and maybe ten scarlet reef hermits.  As I now see I believe I cannot support one of these creatures with my sand bed alone like the site said (oh yeah, my sand is sugar fine and about 2"-3" deep, as of now the horseshoe crab is about 1.5" across and .5" tall)  I'm also worried about his health in the present, let alone starvation in the future.  When I first introduced him he had trouble getting under the sand, he would go in half way, and then come out again. <Good description> He was also very clumsy, crashing into walls and the rock and sometimes flips himself over.  I woke up this morning, watched him a bit, and he was finally able to get under the sand, but he's not moving, I can see the lump where he is and he hasn't moved for about 2 hours.  Is this normal? <Do have periods of long senescence> Any way, if he does survive *fingers crossed*, is there a way I can possibly feed him manually by putting food under his shell? <Can be tried> Any other suggestions on feeding are welcome, and what can I feed him to supplement his diet of worms other things in the sand that will be healthy? Thanks for your help! <What little I know re the captive husbandry of these ancient arthropods is posted on WWM. Bob Fenner>  

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