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FAQs on Freshwater Crab Compatibility

Related Articles: Fresh to Brackish Crabs, Freshwater Crustaceans, Invertebrates for Freshwater Aquariums by Neale Monks, Forget Crawfish Pie, Let's Make a Crawfish Tank! By Gage Harford

Related FAQs: Freshwater Crabs 1, Freshwater Crabs 2, & FAQs on: FW Crab Identification, FW Crab Behavior, FW Crab Selection, FW Crab Systems, FW Crab Feeding, FW Crab Disease, FW Crab Reproduction, & Fresh to Brackish Water Crabs, FW Crustaceans 1, FW Crustaceans 2, Terrestrial Hermit Crabs, & Marine: Hermit ID, Hermit Behavior, Hermit Compatibility, Hermit Selection, Hermit Systems, Hermit Feeding, Hermit Reproduction, Hermit Disease/Health, & Crayfish FAQs, Crayfish 2, Crayfish ID, Crayfish Behavior, Crayfish Compatibility, Crayfish Selection, Crayfish Systems, Crayfish Feeding, Crayfish Disease, Crayfish Reproduction,

"I'm going to eat you. No, I'm going to eat you"

Vampire Crab cohabitation 7/26/11
Dear WWM,
A few month ago I purchased 5 Vampire Crabs (Geosesarma Bicolor), all 5 are male. All are active and happy, and are cohabiting nicely, with little to no aggression amongst them.
<Cool. But do be aware crabs tend not to get along, and look out for signs of aggression, e.g., missing limbs.>
I am interested in expanding their paludarium with a few new species, but seem to be getting conflicting information everywhere I go. While I have gleaned that they cannot be kept with any other crab species, some sources list potential cohabiters ranging from fish to frogs to geckos and newts; though the lists do vary wildly.
<I bet. The problem is that crabs rarely live well with other animals indefinitely. Larger animals view them as food, particularly after the crabs have moulted and have softer shells, and smaller animals are often viewed as food by the crabs. One approach might be to try something inexpensive up front to see how things go, for example, cheap and cheerful "feeder" Guppies. Unlike fancy Guppies, hybrid feeder Guppies are quite robust, savvy, and fast enough to avoid casual predation. So you'll often see them thrive in public aquarium tanks with lazy predators, even Piranhas, given sufficient space and hiding places. If all goes well for a few months, and especially if you see fry surviving and growing, you can then invest in something more challenging. Do also be sensible about your water volume. If your tank is a 50/50 split, you'll realistically have something like 45% the nominal volume in water once you allow for things like gravel and rocks. So a 20 gallon vivarium would only have about 9 gallons of water, and that's barely enough for a few Endler Guppies, let alone feeder Guppies.>
I currently keep all five in a paludarium that is split 50/50 between water and various levels of land, kept at roughly 24 degrees Celsius. There is a small waterfall feature in the tank, and the entire living area is sprayed at least three times daily to ensure a humidity level of about 70%. I would be open to changing these parameters to accommodate new species, so long as the crabs stay happy - the well-being of my crabs is my primary concern, far outweighing my desire to diversify their paludarium. If you could let me know of any species that could be potentially be successful cohabiters with my crabs, I would be very grateful.
Best Regards,
<Cheers, Neale.>

FW lobsters and crabs... in/comp. 2/1/11
Hello there,
Just a few questions if you dont mind, but first a short history.
I have an Electric Blue Lobster,
<Crayfish, not a lobster.>
he has been living in brackish water for a few months and seems to be doing great.
<Surprised, to be honest. Presumably not very brackish? SG 1.002 or 1.003?>
I had a Pleco and a flounder in the tank with him as well as several small feeder fish.
<Likewise, the Plec won't be happy above SG 1.003.>
The lobster himself has grown from around 2 inches to around 3 1/2 in the time that I have had him. The Pleco was around 6 inches at the time of his demise, the flounder around 1 1/2 inches at the time of its demise. my lfs told me that the Plecos seemed to have difficulty with the water in our area!
<Least of your problems. Plecs aren't naturally found in brackish water, and while some may adapt to very low salinities -- they seem to have done so in the canals of Florida -- it isn't ideal. Flounders are a crap-shoot, and at least the sort sold widely in the US, Trinectes maculatus, is a subtropical species with a limited lifespan in tropical aquaria. It needs fairly brackish or marine conditions to do well. So let's say a water temperature of 15-18 degrees C/59-64 degrees F, with a specific gravity around SG 1.005 upwards to fully marine.>
#1: The lobster didnt bother the Pleco or the flounder for quite sometime, they seemed to tolerate each other. Is it possible that the Pleco died due to the water and the lobster made it a meal, got a taste for fish and went after the flounder next. ( he literally ate them both in a matter of a week)
<Crayfish will certainly eat anything dead. They are largely herbivorous in the wild, but they're also scavengers, with carrion being a significant part of their diet.>
#1.5 Is it safe for me to get another large Pleco to go in the same tank as the lobster?
<Crayfish are ALWAYS best kept on their own. You will never, EVER hear me recommend mixing them with anything else, certainly not fish.>
#2 I am so ashamed to say that just today I went to buy some feeders
<Do read about why feeder fish are bad:
There are almost no situations where they make your hobby better. Even putting aside cruelty issues, they introduce disease, they are too rich in fat and thiaminase, and they increase the risk of aggression.>
and came home with a Red Asian Crab,
<An amphibious, brackish water animal. Not suitable for aquaria.>
he was in an aquarium at the store and I wasnt told that his living conditions should be any different!
<Perisesarma bidens is the common species. Needs mostly land, with a pool of brackish water to bathe in. Not terribly hard to keep, but most die after a few months because of poor care. Completely unsuitable for cohabitation with crayfish.>
I am wondering how long he can survive in my aquarium? (while I set a proper one up for him)
<Hope this helps. Cheers, Neale.>
Re: FW lobsters and crabs 2/1/11
Thank you soooo much Neale,
<Glad to help.>
I will do what I can to clean up my act. And never again will I add to any of my tanks before consulting with WWM first.
<No need to go quite that far, but we are *free* and we do try to answer questions within 24 hours, so if all else fails, ask your retailer to put aside any beastie you're interested for a day or two, and drop us a line.
Do also spend some time searching the WWM site -- there are few things we haven't answered at least once before!>
<Cheers, Neale.>

Mixed crab tank 1/9/11
I currently have a thirty gallon tank set up for my five Purple Pincher hermit crabs.
<Coenobita clypeatus>
The tank is about seventy five percent land, with a large pool of fresh water and a small pool of salt water, seventy five percent humidity, and averages seventy three degrees. The highest point of the tank has about one and a half feet of substrate. Half of the tank is covered with leaves and branches, and the other half is sand sloping down towards the water, like a miniature coastline. The tank cools down to about sixty five
at night. Hermit crabs regulate their salinity requirements instinctively, therefore I don't measure the salinity of the salt water in the dish. I just add a small amount of marine sea salt to the dish after I change the
I would like to add either Fiddler or Red Clawed Crabs
<Mmm, these are all non-social animals... too likely to eat each other really>
to liven up the tank when the lights are on, and I know they require salt just like hermit crabs do. Will they regulate their salinity requirements like the hermit crabs, taking in enough salt water and fresh water from the two dishes, or will they suffer from a lack of purely brackish water in the tank?
<Can regulate to a point. I'd provide a shallow basin of both>
If the salt water dish has a salinity level that is too high, will it harm the Red Claws or Fiddlers?
<Not too likely, unless very salty>
One last question, will the main body of fresh water needed to be heated to accommodate the crabs?
Thank you very much. I have found this site to be a great help in every aspect of aquarium keeping I have
undertaken, and I wish to do the best job I can at creating a functional and comfortable habitat for my crabs.
<Again... I'd make a physical barrier to separate these species. Your tank has a sufficiently large "foot print" to do this. Perhaps a cut piece of eggcrate, or scrap acrylic... Bob Fenner>

Crab identification 11/17/10
Hello, I was wondering if you could help me identify a large crab that I recently bought from Petco. They had it labeled as a "Thai Red Devil Crab" but all my internet searching on this name has not found any results. He is about 4 1/2 to 5 inches across with a purplish red shell. His left claw is much bigger than his right, but not quite as much of a difference in claw size as Fiddler crabs. On a side note, I was wondering if crabs use their large claw for anything other than attracting the ladies. Anyways, I currently have him in a 10-gallon semi brackish tank (he will be upgraded to a 25 soon) with a cave to hid in and one of those small turtle docks to allow him to get out of the water. Is this setup ok or should I switch to a terrarium? I also included some pictures of him and one of my crayfish for your convenience. Any help would be appreciated.
<Hello Zach. You appear to have a male "Thai Devil Crab". They're periodically traded but I have no idea what their Latin name might be. In any case, they get quite large, and they are notoriously aggressive and
predatory. They do appear to be more or less aquatic in the same way as many other estuarine crab species -- i.e., by choice they stay underwater, but that can venture onto land for short periods. An arrangement of rocks above the waterline that allowed the crab to bask under the light should it choose to would be helpful, but otherwise don't worry about providing this beast with a land area. Thai Devil Crabs don't seem to be amphibious in the same way as Soapdish Crabs or Red-Claw Crabs. One clue is their rather flat body compared to the much more boxy, deeper body shape typical of amphibious and land crabs. They do require brackish conditions though, SG 1.005 is ideal, and I'd also recommend using marine aquarium Iodine supplement at about 50% the recommend dosage. Although crabs are carnivorous given the chance, their diet should be distinctly mixed with plenty of green foods alongside meaty treats such as tilapia fillet and unshelled prawns. As for differences in the size of the claws, so far as I know this species has claws of similar size, so your chap has probably lost a claw at some point, and it'll be a few moults until the new claw matches the other claw in size. Crabs do indeed use their claws for all sorts of things, from signaling to one another through to dismembering prey, snipping off vegetation, crushing snail shells, climbing up things, and of course for nipping at anything that attacks them. Crabs are fascinating animals, among the Nature's success stories, and quite a sophisticated and modern group of animals despite their sometimes archaic appearance. Cheers, Neale.>

Re: Crab identification, salt 11/17/10
Hello again and thank you for the quick reply. I don't think my crab lost his claw in a fight as all the other crabs in the tank also had one large and one small claw. He also uses his small claw to pick up food like
fiddler crabs. His large claw has roughly the same proportions to his body as a fiddler but his small claw is a little bigger proportionately. If both his claws were the same size as his left I don't think he could move them. I'm sorry if you didn't get the picture I will paste it to this message. As for the salinity, should I use marine salt or is their a salt specifically made for brackish water? Sorry if that sounds dumb I don't know much about saltwater tanks.
Thanks in advance
<Hi Zach. The claw could easily have been damaged prior to collection.
While it is not uncommon for crabs to have dissimilar sized claws through accidents and fights, Fiddler crabs are exceptional in having one claw massively overdeveloped as a signaling/fighting tool rather than one for feeding and climbing. So far as I know, crabs don't do the lobster thing of having one claw for crushing and one claw for snipping. Yes: marine salt mix is what you need, not "tonic" or "aquarium" salt used for treating freshwater fish. Around nine grammes per litre should be ample, with iodine added. Without the iodine, large crustaceans are extremely prone to moulting problems in captivity. Iodine-rich foods such as Sushi Nori make particularly good supplements to their diet for the same reason. Cheers,
Re: Crab identification, sys 11/17/10
Hi sorry for so many questions (this is the last one) but how long can these crabs live in freshwater? The salt in his tank is "aquarium" salt. I might not be able to get marine salt for a couple days will he be ok until then? I don't know how long Petco had them in freshwater but he's been in my tank 5 days. Thanks.
<Hello Zach. "Aquarium" salt will do for a few weeks, but in the longer term the lack of calcium salts as well as iodine could cause problems. If you can, add 1 teaspoon baking soda (sodium bicarbonate) and 1 tablespoon Epsom salt (magnesium sulfate) per 10 litres alongside the aquarium salt.
These will provide some of the minerals crustaceans need for their shells.
Also, add the iodine, either in the water, or through foods rich in iodine (there are some special crab pellets available from companies like JBL).
Cheers, Neale.>

crab compatibility 11/19/10
Hello, I would like to thank you again for all the info on my Thai Devil Crab. I am going to get him some marine salt this weekend. Anyway, my question is would a devil crab be compatible with a Halloween
crab(Gecarcinus sp.)? I know crabs are aggressive but I figured that since the devil crab is mainly aquatic and the Halloween crab is mainly terrestrial they would pretty much ignore each other. They would both be in a 55 gallon tank, (half water half land) about 4 ft long and 1ft wide.
<Easy one this. No. These large crabs are extremely intolerant of one another and in a small vivarium like yours cannot be reliably kept together. When one crab moults, there's a good chance the other one will
attack it. Cheers, Neale.>

FW Red Claw crab compatibility 8/12/10
Hi guys I have a 15 gallon(24"x12"x12") freshwater tank with 1 red claw crab. He's been living in it for 2-3 years now. It has sand as a substrate, driftwood a few rocks and fake grass. I was just wondering if I changed the water slowly to brackish (over a period of weeks?),
<No need for that. Just do 25% water changes, replacing the old water with water at SG 1.005 at 25 C/77 F. After the third or fourth water change you should be close enough to add any brackish water crab. Keep up with the water changes to optimise the salinity.>
could I add a fiddler crab? The RCC is about 2.5-3" full length (legs included), he's got white pincers but the rest of the claw is red.
<I would not mix them. Fiddler crabs "fight" with displays, whereas Red-claw crabs fight with violence. There's a serious risk that the poor Fiddler crab would end up battered. It's much like mixing Firemouths with Convicts; one bluffs, one punches. The outcome is usually bad for the Firemouth. Rec-claw crabs are best kept on their own, and in groups they have -- very rarely -- even been bred by some advanced hobbyists. The larvae need marine conditions to develop. Cheers, Neale.>

Crab compatibility 8/10/10
Hi fellas
I have a 15 gallon (24"x12"x12") freshwater tank that's half filled with water. The occupants are a red claw crab who I've had for 2-3 years. I'm redoing the tank with sand and some new ornaments (driftwood, rocks).
<Interesting; Perisesarma bidens is a brackish water species that tends to do poorly in freshwater tanks long term. I wonder if it really is what you think it is.>
The RRC is about 2.5" across leg-tip to leg-tip. Looks like a male because of white pincers but the rest of the claw is sort of bright red and the body dark red.
My question:
Can I add 1-2 more vampire crabs?
<Wouldn't bank on it. Geosesarma "vampire" is a near-fully terrestrial crab that spends very little time in the water. Whilst I suppose you could keep them in the same enclosure, it's hard to see how a 15 gallon tank could be spacious enough to have habitat for both. Geosesarma "vampire" is normally kept in a vivarium with coconut fibre at the bottom like that used for Arrow Frogs and the like. Plus, as with any crab, once one moults, the other will try to eat it.>
If not can I add something else if anything at all?
<Perisesarma bidens is best kept amongst its own kind, really. It's needs are quite specific. In a bigger tank it might be kept with Mudskippers, but there's always the risk of one eating the other, depending on their relative sizes.>
Thanks Connor
<Cheers, Neale.>

FW crab compatibility 07/13/09
I have 5 small vampire crabs and I am wondering if I could introduce another species of crab with them without any casualties.
<Probably not. Your Vampire Crabs -- Geosesarma spp. -- are amphibious freshwater crabs noted for their opportunistically predatory natures. Like most "freshwater" crabs, they spend 90% of their time on land, and males tend to be territorial. Best kept in groups of one male, multiple females in a reasonably spacious vivarium with a shallow freshwater pool at one end. Without sufficient space, fighting, cannibalism is likely.>
The other crabs in question are red claw crabs.
<Perisesarma bidens; a nifty amphibious brackish water species.>
Speaking of which my local fish store has "red crabs" for sale but they look just like red claw crabs. Could they be red claw or is there a small crab that is called a red crab?
<The "red claw" crabs of the trade are commonly Perisesarma bidens but may be other, closely related, brackish water species. Keep in a vivarium with a shallow pool of slightly brackish (SG 1.005) water at one end. Iodine supplements are required for all crab species; use standard marine aquarium iodine supplement, at 50% dosage; not doing this seems to cause
defects/death when moulting.>
Love the site!
<Cheers, Neale.>

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>

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>

Killer Crabs - 03/27/2004 Hello, <Hi! Sabrina here, today!> I am hoping that you can tell me if it would be possible for fresh water crabs to partially devour a human? <Please envision a huge question mark floating about my head. Er, *WHAT*?!?!> I am writing a screenplay in which such a horrible event would occur. <Ah, good! Whew! At least you're not trying to account for a body in your back yard, heh!> I would like to confirm that such a thing would at the least be somewhat plausible. <Mm, I'm afraid not. There aren't a great many species of freshwater crabs, for one, and all are pretty timid. If the person were already dead, and starting to decay, I'm sure he'd be a tasty tidbit. But a live, flailing person? No, I'm afraid not.> I know that I have seen such things in movies involving sea crabs. Pirates evidently used it as a type of torture to get people to tell them what they wanted to know. <Even these scenarios are rather unbelievable, to me.> In my story, a villainous man bales out of a plane and lands in a large Mexican lake. <Not even sure there *are* freshwater crabs in Mexico.... some shrimps of the genus Macrobrachium, yes, and these likely more aggressive than any crab! But I still don't think they'd attack a person. And somehow, being attacked by a swarm of hungry shrimp just doesn't have a very stunning quality to it ;) > He makes it to shore three quarters dead. I need him to be disfigured in some way. And this is what I have come up with! What do you think? <Um, how about drop him in drying pond, amidst a group of starving ten-foot alligator gar? http://www.fishbase.org/Country/CountrySpeciesSummary.cfm?Country=Mexico&Genus=Atractosteus&Species=spatula Or tropical gar? http://www.fishbase.org/Country/CountrySpeciesSummary.cfm?Country=Mexico&Genus=Atractosteus&Species=tropicus Fishbase reports these as gathering in large groups to spawn during the dry season - so, a large school of starving, sex-crazed gar? Still a bit fantastical, but I suppose far likelier than man-eating-crabs.> Thanks for any and all help. Martin Phillip <You bet - and thanks for sending us your extraordinary question! Certainly brought a smile to me! Wishing you and your screenplay well, -Sabrina>

Killer Krabs - II - 04/05/2004 Thanks for responding! <You bet, Martin.> It's not the answer that I'd hoped for but I do appreciate the expert information. <Flattery will get you anywhere :D > I really do not want to create an implausible scenario. I'll think of something else. <Wish I had some better ideas for you, but good luck with your screenplay, either way.> Thanks again. Martin Phillips <Any time. Wishing you well, -Sabrina>

Crab Attack - II, III - 04/09/2004 Sabrina -- thanks for your reply and suggestions. <You bet - that's why we're here.> As you asked, here's the scoop on my tank - 100 gal w/ about 65lbs live rock and live sand. Numerous "cleanup critters" -- 2 cleaner shrimp, 1 fire shrimp, 1 arrow crab (just got him, very, very small), 2 strawberry crabs, 3 emeralds, a variety of hermits from tiny blue legged, Mexicans, Scarlets, 2 peppermint shrimp, numerous snails too (obviously they're not the culprit) -- fish are as follows -- 1 blue tang, 1 yellow tang, 1 neon dotty back, 1 diamondback goby, 2 goldenhead sleeper gobies (mated pair), 2 Perc clowns (mated pair). <My vote is on one of the Mithrax/emerald crabs, or one of the strawberries.> You mentioned treating the tank with iodine -- is it safe for everyone else in there? <Oh, goodness, YES! I had been given the original question, and answered, under the impression that we were talking about a "freshwater" (brackish) fiddler - I would *definitely* recommend dosing iodine for your inverts.> If yes, I would appreciate dosage info. <Please take a look at our Iodine FAQs: http://www.wetwebmedia.com/iodfaqs.htm and the various articles on supplementation and testing: http://www.wetwebmedia.com/marine/maintenance/index.htm > THANKS SOOOOOOO MUCH!!!! Jennefer <Any time.> ----------------------------------- Sabrina -- I know this may sound totally nuts, but I'm thinking the culprit(s) may have been 2 (vicious) yellow tangs I got rid of (had 3). <Er, yeah, multiple tangs in one tank is most often a pretty bad idea, especially of the same species. I've seen multiple yellow tangs slice each other to ribbons when housed together, even in large tanks.> If I didn't see it for my own eyes, I wouldn't believe either that they actually went after my cleaner shrimps, ending up killing one of them, ripping half of the legs off the other one <WOW.> (he's much happier since getting rid of the 2 Satan tangs and growing his legs and antennae back and back to climbing on the rocks instead of cowering in a corner). I never saw them go after the fiddler, but I don't know. What do you think? <Well, with the behaviour that you observed, I'm sure it's possible.> I was (pleasantly) surprised to still see the fiddler crab even though he's just a body with 1 lonesome leg and his 2 nippers. <Poor fellah! I'm glad he's holding on.> It makes me sooooo sad every time I see poor "stumpy". <Hah! I like that. 'Course, I have named a Sturisoma cat "Stick", and an L-260 Plec "Suckhead". Go figure ;)> Anyway, would appreciate any and all suggestions. <I would definitely test/dose iodine. Testing is a pain, but you get used to it.... or numb from it.... or something. Also look into calcium - er, and check out those links to find out more about what you can/should dose, and how to go about it.> Oh, as far as treating with iodine, just to give you the full scoop on my tank, I have a wet/dry filter, w/skimmer and U.V light. THANKS AGAIN! Jennefer <You're quite welcome. Wishing your crab a swift recovery, -Sabrina>

Crustacean for a Community Tank - 05/21/2006 Hello folks, <Hello, Doug.> I've been reading your articles with interest but I still am unsure about what I should do with regard to finding a suitable crustacean for my community tank. <Someday we'll have a shrimp article up.... just (finally) wrote the thing.> This is a freshwater tank, 20 Gallons, 2+ years old, nice and stable. Right now I have 5 Rasbora tetras, 6 cardinal tetra's and one fairly large Chinese golden algae eater (5" long). We added the Cardinals a month or so back and they are doing fine. We wanted to get some kind of crustacean to complete our community but are not sure what would be best after reading about predation of tank mates. What do you think might work in this situation? <LOTS and LOTS of options.... Any shrimp from genera Atya, Atyopsis, Caridina, or Neocaridina....> I had thought of a Hammers cobalt blue lobster but after reading more about it realized that it would probably be the sole tank occupant in short order. <It would. Stay away from any crayfish/"lobsters". If you want something big and beefy, for a 20g tank, maybe look for Atyopsis moluccensis, the "bamboo" or "wood" shrimp. A 20g tank is suitable for a male and a few females. Or if you want something bright and tiny, look for "cherry" shrimp (Neocaridina denticulata sinensis v. red), "Rudolph"/"red-fronted" shrimp (Caridina gracilirostrus), or maybe "crystal red" shrimp, (Caridina sp.). There are plenty of other small shrimp species that are less colorful, and most any would be of use here. I do hope you are able to find a fun and pleasing pet to add!> Thanks for your advice. -Doug <Glad to be of service! Wishing you well, -Sabrina>

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>

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!>

Just a quick question, missing livebearers post holiday 7/14/07 Hi, I currently own a ten gallon tank with a few platies and a guppy inside it, along with a few platies that are small. I went on vacation and notice that a few are missing. <Sorry to hear that. Be sure and figure out *why* before adding anything new. Check water chemistry and quality, for example, and double check you're using the right food, i.e., something vegetable/algae based rather than generic flake food.> I think they might be dead, and I just want to know your suggestions on what might have happened... <No idea without more details. Water chemistry, water quality, number of each species, how long you were gone, what foods used, etc....> ...and what kind of crabs and shrimps are compatible with them. <None. Crabs are [a] amphibious so need somewhere to walk on land and [b] predatory. Shrimps can work with small fish but they are generally delicate and if you can't keep guppies alive then you're probably not at the stage in your hobby where buying shrimps would be worthwhile. That is, unless you don't mind the shrimps being dead in 4 weeks. Seriously, they need excellent water quality, the correct diet, and safe places for moulting where they can't be molested.> I usually leave fry in the tank instead of separating them and I want a few to live, are these good to add to the tank? <Don't understand this. Do you mean the crabs and shrimps are good to add to the tank? If so, no.> Or are they bad like Albino Aquatic Frogs? (I had bad experiences with them) <Not "bad" but just wrong for you and your aquarium. Crabs need their own vivarium a bit like something used for newts or frogs, with some water for bathing but also some dry land for social behaviour and feeding. Shrimps are really something for the semi-advanced hobbyist. Most of the ones sold end up dying within a few weeks when thrown into generic community tanks. Cheers, Neale>

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