FAQs on Freshwater, Terrestrial
Related Articles: Fresh to Brackish
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 Compatibility, FW Crab Selection, FW Crab Systems, 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, &
2, Crayfish ID, Crayfish Behavior, Crayfish Compatibility, Crayfish Selection, Crayfish Systems, Crayfish Feeding, Crayfish Disease, Crayfish Reproduction,
Calcium in Crab & Shrimp Tanks 6/2/16
I keep a few crustaceans (Panther crabs, Rainbows crabs, Geosesarma
crabs, Crayfish and Cherry Shrimp). I know that calcium is important for
the proper development of their shells. I have looked all over the net
and can't find any definitive information on how much calcium and how
often it's needed, so I'm hoping you can help.
I bought some small calcium tablets (1" long by .5" wide), but I haven't
put them in the tanks yet. I need to know how often I should be giving
my crustaceans calcium and how much. So far they've been doing good but
I want to make sure they have the best care possible.
Any help is much appreciated. Thank you.
<As with humans, it's the "bio-available" Ca that is important; and for
freshwater organisms this takes the form of both dissolved and
macro-sources. Unless you have a Calcium concentration test assay, I'd
rely on "hardness" as a measure here; and aim for "medium hardness"
(measured in various ways:
AND I would use the small calcium tablets you mention (or softer sea
shells, cuttle bone) as an exogenous source these animals can/may pick
Re: Calcium Supplements for Panther Crabs?
I know you told me about the cooked unshelled shrimp commonly used for
human consumption, but wanted to know a couple things. I've heard you
can also feed egg shells and cuttlebones to crustaceans to help them get
the calcium they need. Is this true?
<Potentially, but it depends if your crab will eat them. By themselves
they don't sound very appetizing!>
Which type of cuttlebone should I use, if any? Also, how can I help ease
the moulting process to help ensure proper moulting and survival?
<Use marine aquarium iodine supplement, at 50% the dose stated on the
How long does this normally take (moulting and hardening of new shell)?
<Varies dramatically with age. Young crabs may moult once a month, while
older specimens may essentially stop moulting altogether, and their
shells often look very tatty and encrusted with algae.>
Thanks for everything!
<Real good, Neale.>
Re: Calcium Supplements for Panther Crabs?
Okay. One more question. After a crab moults, how long does it take for
their new shell to harden?
<Hours, couple days, depending on species, temperature, diet, calcium
Essentially, how long should I wait until I start worrying about if the
crab is alive or not?
<Anything more than a week would be worrying. But keep crabs singly,
give them iodine, let them eat calcium-rich foods, and moulting should
happen without problems. It's when people either ignore their mineral
nutrition and/or keep them in groups (or with fish) that moults fail.
Re: Calcium Supplements for Panther Crabs?
I'm getting a male and a female Panther Crab and am planning on housing
them together because I heard the male impregnates the females when she
moults. Is this true?
<Yes; or at least, is standard for crabs generally.>
Should I separate them when they moult just in case or when she isn't
I am going to put them in a 20 gallon long which I've heard is able to
house two female and one male Panther Crabs.
<Hmm… I wouldn't bank on this, but I don't know for sure it won't work.
It's a case of "suck it and see".>
Re: unknown crab, fdg., sys., beh.
I was mistaken when I said that the crab had eaten a nice piece of
<Banana! Land crabs seem to love banana, the softer the better! Also
try small pieces of white fish, ideally lancefish, which you can buy in
pet shops. These have bones in them, and the calcium there is excellent
for the crabs. Unshelled prawns, perhaps sliced along the middle to
make things easier, are also a good source of calcium. Crabs are
scavengers, and generally eat anything that's soft or
My wife had removed it as it was getting a bit smelly. The crab has not
eaten anything since we got her and has seemingly become very weak.
<Review air temperature and humidity; these are essentially like
frogs in terms of care, and cold, dry air does them no good at all.
Turning the heater up in the water side of the tank can create more
conditions in the land side of the tank. Likewise, keeping the lid more
firmly secured will help, too.>
She has not moved much in the past 2 days. Maybe she's getting
ready to molt.
<You can actually check this: before they moult, crustaceans absorb
extra water. When picked up, you may notice they've both bulked up
and yet the shell is softer than normal, and may even yield a bit to
the touch. They feel less heavy for their size that you'd expect (a
tip you using when buying edible crabs, by the way). While the
following link refers to Land Hermits, in terms of generalities, it
would hold true for Land Crabs too:
So, prior to moulting, the crab will puff up, become softer, tend to
hide away from light, and generally become inactive. Moulting starts
with the exoskeleton unzipping, and the crab sort of backs out of its
I hope so. We would not feel like very good stewards if she dies.
Already lost one pet this week :-( One of our Fischer's lovebirds
had a seizure and died in my hands.
<Oh, sorry to hear that.>
Of course, I have zero history on the crab. Have tried feeding her a
variety of foods to no avail. Any suggestions? Thanks.
Soapdish Crabs, Fiddlers, Ghost Shrimp hello:
please, I was wondering if y'all could help me. I
have what was sold to me as a Soapdish crab in a 2' x1'
6" tank with about 4 or 5 inches of fresh
water. Carl, as he is called, has a 2" wide body
and is probably about 6" across including
legs. he has relatively short (compared to my fiddler
crabs) eye stalks and is a reddish brown color with orange legs
and claws that have reddish brown
"designs". the tips of his claws are
whitish gray. he has easy land access but hardly ever
comes out of the water. is that weird? <Mmm, not
necessarily> he eats live minnows and frozen
peas. anything else I could feed him for a little more
variety? <Other meaty foods> please don't
say crabs eat anything, he won't eat carrots or
broccoli. is it safe to feed him hot dog?
<Mmm, no... too fatty> he'll eat it and
seems to like it but I took it away because I'm wondering if
it could be harmful with all that sodium. should I
remove any left over fish parts from the water?
<Yes, I would> sometimes he just eats half a minnow and the
other half just floats around in the filter
current. will it muck up the water or make it unsafe
for him in any way? <Could. I'd remove
all uneaten food> I have had him for probably 8 months and he
seems to be doing well. I just want to know if
you guys and girls have any tips to make him happier and/or
healthier. I read something on your site about iodine
supplementation for crustaceans? anything else? <You could
monitor, adjust biomineral (mainly calcium) and alkalinity... has
this animal molted while in your care?> what is krill, where
do I get it and how do I "soak it in vitamins"?
<Euphausiids... liquid vitamins... just putting a few drops on
for ten, fifteen minutes before offering...> I love my soap
dish crab(s) and would really appreciate any help y'all could
give as there is virtually zip on the web about them. also, for
anyone wondering, Carl (as with all Soapdish crabs, in my
experience: I have 2 males, I lost a female when she wondered
into Carl's territory) is extremely aggressive and will
decimate anything it can catch, including other Soapdish crabs of
equal or greater size. does not play well with others.
I've even heard of one wasting an Oscar. <Have seen this
sort, level of "aggression"> oh, why might a fiddler
crab in similar tank conditions up and die for no obvious reason.
<Is a brackish water animal...> a not too old/big male that
seemed to be thriving was fine one day and upside down dead by
the filter the next. he shares the tank with 2 females and one
other male which doesn't currently even have its large claw.
I don't suspect foul play, I am afraid there is something
wrong with the water or something. the tank has been in operation
for at least 6 months and has a good filter. I've heard a
terrible rumor about fiddler crabs just dying after a while in
fresh (not brackish) water but I've had a lot of these
wonderful, mostly peaceful crabs and this is a brand new
occurrence. any thoughts? might the same thing happen
to Carl? <What is the make-up of your source water? You may
have hard, alkaline water that "works" for both these
species> just one more thing, I promise. I employ a multitude
of ghost shrimp as janitors and I read on your website that it
was easy to breed them. that is very exciting to me, please tell
me more! I am so glad I found your website, I hope you can give
me a few pointers. thanks, Scott <Use your computer search
tool/s... much written on Ghost Shrimp. Bob Fenner>
Re: Soapdish crab hello again! Carl has
molted! about a week after starting the iodine treatments, Carl
(Thai freshwater- Soapdish crab) molted. could this be
directly related to the addition of iodine? <Yes>
unfortunately, it did not go well for the big guy and
he lost a leg and his larger pincher. <Evidence of? Likely a
lack of biomineral (calcium) and alkalinity... provided in foods,
water...> the next couple days were very tough for both of us,
as he just sat there and twitched and I was terrified that he
wasn't going to make it. the next day I came home
from work to find him on his back and motionless. I
nearly lost my mind with grief until I noticed his mouth
apparatus was moving. I very gently touched the tip of his claw
and to my great relief he sprung to life, trying desperately to
flip over. the poor guy just didn't have the
strength! he was still very soft, so I decided to let him be
rather than possibly injuring him by flipping him
over. after a couple more days he eventually started
to consume his exoskeleton and move around the
tank. Carl's gonna be ok! whew! now for
the questions: I've noticed that since the molt his carapace
and claw look very strange- its a very dull tan-gray and none of
his normal patterns, like the "H" on his
back, are visible. it just looks very worn, or something. I know
crabs will sometimes come out of a molt a different color, but
the way Carl's shell looks makes me think its related to his
traumatic molt. any ideas? <Either lack of nutrition, water
quality... or will develop color, pattern in time> Also, is it
possible to over dose them on iodine? <Oh yes> should I add
the drop only when I do a complete water change or anytime I
replace water that has evaporated? <Best to do with (weekly)
water change regimens> keep in mind I have a 10 gallon filter
in about 4 gallons of water, does that make a difference as to
how fast the iodine is getting used up? <Yes> One more
thing: I really want to change my crab tanks to brackish but I
have read that once crabs are in freshwater for so long, they
cannot be switched to brackish. is this true? <Not so. Bob
Fenner> thank you in advance. Scott
Halloween Land Crab 03/17/07 Hi, thank you for
taking the time to read this. I have what the pet store
called a Halloween Land Crab. <Gercarcinus sp., maybe G.
lateralis.> He is not set up in some amazing aquarium, he is just in
a plastic cage. I have a water dish for him that's 2
inches deep that he climbs in and out of. The bottom of the
cage is filled with calcium sand and aquarium pebbles.
<Ideally, he needs a sand substrate deep enough and just damp enough
to burrow into, and needs enough saltwater and enough freshwater, each
in separate containers, deep enough to fully submerge himself - though
the land area is by far the most important.> He has been doing
really well eating bits of fruit such as apples, oranges, pineapple and
also an occasional guppy. <Needs more meaty foods, preferably things
like human-consumption shrimp (raw, frozen and then thawed) and fish;
krill, meaty fish foods, and also Nori (seaweed) would be other
important foods.> But recently three of his legs fell off on his
right side! What is going on? <Likely he is very
deficient in something that he needs - saltwater, perhaps, or
iodine.... Feeding the foods mentioned above, especially
shrimp, krill, and Nori which are rich in iodine, will be very
important. Supplementing the food with a reptile calcium
supplement will be helpful, as well.> He was not in a fight with
another crab and I've never experienced him going through the
"shedding process"! Is he unhappy or sick? How can I tell
what's going on? <sounds like a state of disease, not a normal
molting situation at all.... I would urge you to improve
this critter's living space and food.> If this is below what you
guys do, then I'm sorry to waste your time, <A question is never
a waste of time.> I just need simple answers and can't seem to
find them anywhere. <Thank you very much for searching for your
answers, and for asking questions.> Nick <All the best to