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FAQs on Freshwater, Terrestrial Crab Foods/Feeding/Nutrition

Related Articles: Fresh to Brackish Crabs Freshwater CrustaceansInvertebrates 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 1FW 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,


Red Claw Crab not Eating 12/29/19
Hello! Hardly anyone knows anything about red claw crabs, as I cannot find any answers as to why my red claw crab has stopped eating!
<Let's see if we can help.>
He is kept in brackish water conditions, has filtered water, and water that is always about 74 degrees Fahrenheit.
<Right. Let's review first. By "brackish", how salty are we talking about? The first thing you do when brackish water animals misbehave is change the salinity. Many if not most come from places where the salinity varies, so just making a change can have a positive effect. But the bigger issue is that you need to be using a substantial amount of salt, not the teaspoon per gallon amounts often mentioned. I'd suggest one teaspoon per litre (i.e., a salt concentration of about 6 gram/litre) to produce about one-sixth normal seawater salinity. If that didn't do the trick, feel free to double that amount, which would get you around one-third normal seawater salinity. Either of these would be much closer to real world situations for Perisesarma bidens. Next up, review air temperature. 23 C/74 F is very much towards the low end for a tropical animal, and I'd crank the water heater up to 25 C/ 77 F. In cold conditions tropical animals will slowly lose vigour, and loss of appetite is an extremely common symptom of that. Death invariably follows soon after, though it may take weeks to happen.>
He is able to climb to get air or be in water when he wants. I have sand substrate. When I first got him, he would eat his food fine, but now, he won’t eat at all. I noticed he wouldn’t eat, so I ended up putting his food right in front of him, and he still won’t eat that food.
<Loss of appetite in crabs is almost always a symptom of environmental problems. Review as stated above.>
I don’t think he’s molting, because he’s been acting this way for about 2 weeks and I was told molting should only take about a day.
<Correct, and moulting crabs tend to hide away. They do need a source of iodine to moult successfully, for which purpose either offer regular portions iodine-rich foods (Sushi Nori is ideal) or else specific iodine-enriched crustacean foods sold for use in marine aquaria.>
Also, I don’t think it’s a calcium problem, as I give him special vitamins that help provide him calcium every 3 weeks. I’m really worried about him, and I have no idea why he is not eating.
<Hope this helps. Cheers, Neale.>
Re: Red Claw Crab not Eating       1/1/2020

Thank you very much for this help! Right after I added more salt, he molted the next day.
Does he absolutely need to eat his exoskeleton? If so, he is not eating it.
<No, he doesn't need to eat it, but most crabs do, simply to recycle the calcium. If he doesn't, that's fine, but do add some suitable replacement, like a small shell-on prawn that he can pick apart and consume. Failing that, just dusting whatever he likes to eat (fish meat, banana, etc.) with crushed cuttlebone or even fragments of edible snail shells (escargot) will have the same usefulness. Some crab foods are calcium-enriched and may be good enough on their own, but personally, I'd make a point of offering
extra calcium immediately after moulting. Cheers, Neale.>
Re: Red Claw Crab not Eating   1/11/20

I’d like to thank you for helping me with my red claw crab. Unfortunately, he has passed away even after adding a proper amount of salt and turning up the temperature, as he just did not eat at all.
<I'm sorry to hear that.>
I don’t know the reason for his refusal to eat, but after taking your advice, he seemed to have more energy and would actually approach the food (but still didn’t eat it). Maybe he was sick?
<Indeed, or perhaps, he'd been away from salty water for too long. These are tricky animals to keep well -- they need brackish water, high humidity (cold or dry air quickly kills them), and food that contains all the nutrients including iodine and calcium. So while inexpensive in themselves, and not demanding in terms of space, they are tricky.>
I don’t know, but I’m glad I found your website and got some help. You are very knowledgeable about these creatures, and people who are having trouble with their pet crabs are fortunate enough to be able to contact you for help. Again, thank you very much.
<You are most welcome, and thanks for these kind words. Good luck with your next pet! Cheers, Neale.>

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.
Kind Regards,
<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: https://en.wikipedia.org/wiki/Hard_water
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 on.
Bob Fenner>

Re: Calcium Supplements for Panther Crabs?     11/1/12
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 bottle.>
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?      11/2/12

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 availability.>
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. Cheers, Neale.>
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 mature?
<Sounds wise.>
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".>
<Welcome, Neale.>

Re: unknown crab, fdg., sys., beh.   4/22/09
I was mistaken when I said that the crab had eaten a nice piece of cantaloupe.
<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 meaty.>
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 warm, humid
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 shell,
tail-end first.>
I hope so. We would not feel like very good stewards if she dies.
<I understand!>
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.
<Cheers, Neale.>

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 you,  -Sabrina>

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