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FAQs on Freshwater Crab Compatibility

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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