Like all crustaceans, crayfish have external exoskeletons (shells) that limit their growth. Therefore, to grow in size, they have to shed their old shells. It may sound like a simple process but it is not!
Actually, it would be no exaggeration to say that molting is the most stressful and important time in a crayfish’s life. This is the time when they are the most vulnerable and are prone to die. That is why it is absolutely critical that crayfish keepers have the correct information on what is happening with their pets.
In this article, I will answer the most popular questions regarding crayfish molting. You will know about the crayfish molting cycle and their molting behavior. How to tell if your crayfish is about to molt? How can water parameters affect the molting process?
Molting Cycle
Molting cycle in crayfish is a highly complex, asynchronous process and consists of 4 stages:
- Proecdysis(Pre-molting Stage)
- Ecdysis (Molting Process)
- Metecdysis (Post-molting Stage)
- Anecdysis(Inter-molting Stage)
Interesting facts: The molting process is controlled by environmental and endocrine hormones, which are located in their eyestalks.
1. Pre-molting Stage (Proecdysis)
This is a preparation stage right before the upcoming molt. During this stage crayfish start:
- intensively absorb calcium from the food and environment,
- reabsorbing calcium from the old skeleton.
At first, calcium enters skin cells and then goes to the hemolymph and transported to the stomach for storage in the form of gastroliths (little stones located on both sides of the stomach wall). As the molt cycle progresses toward ecdysis, the gastroliths increase in size.
Note: Calcium is super important for any crustacean because this is the main component of their shell. For example, crayfish exoskeleton comprises 50% of dry weight and is mineralized with calcium carbonates and magnesium.
As the crayfish approaches the pre-molt stage, the exoskeleton undergoes partial degradation, with the calcium ions being dissolved out of the mineralized matrix and transferred through the integumentary epithelium to the hemolymph.
Simply put, the pre-molt reabsorption of calcium serves primarily to weaken the current exoskeleton in preparation for shedding. Otherwise, crayfish may have some problems with breaking the shell at all!
In addition, according to the studies, another indication of the beginning pre-molting stage is the regeneration of lost limbs. Any lost appendages will begin to regenerate as limb buds that will unfold at the time of molting.
2. Ecdysis (Molting Process)
The pre-molt stage terminates with ecdysis, the shedding of the old shell. To achieve this, crayfish start pumping up its body with water. According to some studies, water enters the body both by ingestion and by absorption through the external surface.
The water uptake starts about 1 hour before shedding, increases rapidly during the molting process itself, and stops about 1 – 2 hours after ecdysis. To increase the hydrostatic pressure crayfish also stops urinating.
The water uptake should hit a critical number, so the old exoskeleton can crack at the breaking point so that crayfish could withdraw from it. The breaking point is located in the ‘neck’ area of the crayfish, more precisely in the skin fold between the carapace and the abdomen.
At the same time, the gastroliths (calcium stones) fall into the stomach, where they are rapidly digested in the stomach releasing calcium, which is mobilized through the hemolymph to harden the new exoskeleton.
Note: Ecdysis or molting process is the shortest stage out of four. Depending on the crayfish species and how old it is, it usually lasts from a few minutes to several hours.
3. Metecdysis (Post-molting Stage)
The post-molting stage is one of the most dangerous stages for crayfish because they become extremely vulnerable not just to physical injuries but to some diseases and parasites as well. They are too soft and weak to protect themselves. It makes them easy prey for any predators.
During post-molting stage crayfish need to hide and recuperate from the previous molting.
Note: I have heard stories when even dwarf shrimp managed to kill crayfish (unintentionally, of course) during this stage. It is not a surprise because they can barely move their legs. During post-molting stage crayfish need to hide and recuperate from the previous molting. There are two main goals at this stage:
- As I have already mentioned, crayfish continue to absorb a significant amount of water in order to stretch its body and increase in size.
- The soft shell must be urgently remineralized for support and protection. Crayfish start producing a substance called chitin synthetase, which is essential to creating and hardening the new exoskeleton. In addition, calcium originating from the gastrolith provides an immediate source for the calcification of essential body parts such as mouthparts (for the resumption of feeding) and walking legs (to hide). After that calcium is reabsorbed and redistributed throughout the newly formed exoskeleton.
How long does the post-molt stage last?
The post-molt stage can be identified by increasing degrees of the rigidity of the different parts of the body. Since different parts of different crayfish species become rigid at different times after the molt, there is no uniformity from species to species in the meaning of the different stages based on rigidity.
The amount of time it takes a crayfish to molt is also determined by its size. The smaller the crayfish the less time it takes to molt. In most cases, it usually lasts from 24 hours (for small and your crayfish) to 3 – 5 days for adults and big ones.
Tip: Do not remove the old shell, crayfish will consume their entire exoskeleton to recycle necessary minerals and salts to aid in the calcification process. That is why it is also advisable not to feed crayfish for a few days after the molt.
4. Anecdysis (Inter-molting Stage)
The inter-molting stage is the last and the longest stage during which most of the calcium is stored in the cuticle. Basically, it is a period of rest between the end of one molt and the beginning of the next.
As the crayfish grows, this phase gradually increases in length. A small growing crayfish will molt more frequently than a larger crayfish.
| After molting, the metabolic demand (to harden the exoskeleton) for calcium is particularly great. Crayfish use calcium to produce a new and healthy shell. I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”. |
Crayfish and Molting Signs
How can we tell if the crayfish is about to molt? There are different signs that might help you out if you pay attention.
1. The difference in crayfish behavior
Every crayfish has a unique personality. They prefer to eat a certain amount of food or sleep a certain amount of time. All in all, they act a certain way. So, when they are about to molt their behavior will change. For example:
- Eating
At first, you may notice that your crayfish start eating more than usual. Then it will be a completely opposite, they start eating less until completely stop a few days before molting. - Lethargic Behavior
Crayfish will be less active before molting. They get very lethargic and lazy. It is like nothing interests them. - Hiding Spots
Crayfish start spending more time It will try to find a secluded area away from its tank mates.
2. Difference in appearance
- The color of the exoskeleton
The earliest sign that pre-molt has begun is the detachment of the epidermis from the cuticle (separation of new shell and old one sometimes can be better seen where the joints meet). When it happens the color of the crayfish becomes dimmer or duller.
- Cloudy eyes
Another molting sign is cloudy eyes. The crayfish will have whitish, cloudy, or hazy looking eyes.
3. Limb regeneration
It can be hard to notice but if your crayfish does not have a leg, claw, etc., it will begin the process of regenerating it. At first, it looks like a small nub. However, as the time for molting grows near, it will swell and become more defined.
Keep in mind that all of these signs not always occur and sometimes none of them do.
How often do Crayfish Molt?
It depends on the species, size, age of your crayfish, and their environment. For example, newly-hatched Procarambus Clarkii will usually molt in a few days. Juvenile crayfish may molt every 7 – 10 days.
Adult crayfish molt less frequently, it can be 30 – 40 days or even more. The point is that fully grown crayfish do not grow, they molt only to regenerate lost limbs.
As long as you are providing a good environment and a variety of food, your crayfish will molt regularly.
Crayfish, pH, and GH
It is very important to know that decreased pH and GH have profound negative effects on crayfish. It affects the inter-molt duration and increases the mortality rate.
General Hardness (GH) is the measurement of the level of dissolved minerals in the water. It is predominantly represented by calcium and magnesium, therefore, “responsible” for exoskeleton mineralization.
The power of hydrogen (pH) also affects the metabolic investment in calcification. At low pH levels, the crayfish exoskeleton becomes too flex and malleable.
This is because their shells are composed of calcium carbonate which reacts with acid. As a result, crayfish will have trouble breaking their shells when it is time to molt. It will stress them a lot and can lead to death.
Although most crayfish species are pretty tolerant to hardness, it would be better to avoid extreme water parameters anyway. For example, too hard water may also be a problem for a crayfish. Hard water can make crayfish shell too rigid to break as well.
Generally, crayfish will thrive best in water hardness between the ranges of 6 – 14 GH and pH 7.0 or 8.0. Even though they can tolerate acidic water, it is not good for them in the long run.
Crayfish Molting and Hiding Places
The problem is that in this phase, crayfish are soft, weak, and cannot fight back. In the wild, they are known to be vulnerable to predation and cannibalism during molting. In the aquariums, it happens pretty commonly as well.
Therefore, if your crayfish is living in a community tank with fish or other crayfish, you will have to provide them with lots and lots of hiding places.
That is why, driftwood, rock, PVC pipes, and decorations are crucial to a successful crayfish tank. Otherwise, they can fall prey not only to other crayfish but even to small fish!
You can read my article “Driftwood in Shrimp Tank”.
Crayfish Molting Problems
Unfortunately, sometimes crayfish can fail at molting (they cannot get out of their old shell or cannot even break the shell). They lie on the side and periodically try to bend the shell. In some cases, it may last hours and days.
Unfortunately, once the molt starts to go bad, we cannot do anything to help them. All we can do is wait and hope for the best.
In Conclusion
The growth process in crayfish demands periodic shedding of the old exoskeleton. Therefore, if you see that your pet has lost some coloration and does not eat much, do not panic, this is a completely normal behavior before molting. Just do not forget to provide them with lots of hiding places in the tank, so they can molt safely.
Related article:
- Introduction to the Crayfish Care – Setup, Diet, and Facts
- How to Set Up a Crayfish Tank
- What Do Crayfish Eat?
- Breeding and Life Cycle of Crayfish
References:
- Water uptake at ecdysis in the western rock lobster. Journal of Experimental Marine Biology and Ecology. Volume 35, Issue 2, November 1978, Pages 165-176.
- Reproduction and molt in previously spawned and first-time spawning red-claw crayfish Cherax quadricarinatus females following eyestalk ablation during the winter reproductive-arrest period. Aquaculture. 156 (1997) 101-111.
- Changing Activities of the Crustacean Epidermis during the Molting Cycle. J. Ross STEVENSON. A.M. ZOOLOCIST, 12:373-380 (1972).
- Calcium Transport Mechanism in Molting Crayfish Revealed by Microanalysis. The Journal of Histochemistry and Cytochemistry. Vol. 31, No. IA, pp. 214-218, 1983.
- Ion Regulation in Crayfish: Freshwater Adaptations and the Problem of Molting. AMER. ZOOL., 35:49-59 (1995).
- Search for hepatopancreatic ecdysteroid-responsive genes during the crayfish molt cycle: from a single gene to multigenicity. The Journal of Experimental Biology 210, 3525-3537. 2007 doi:10.1242/jeb.006791.
- Growth rate, life span and molting cycle of the crayfish Orconectes Sanborni. The Department of Zoology, The Ohio State University. 76(2): 73, 1976.
- Reciprocal Changes in Calcification of the Gastrolith and Cuticle During the Molt Cycle of the Red Claw Crayfish Cherax quadricarinatus. Marine Biological Laboratory. Biol. Bull. 214: 122–134. 2008.
- The growth process in crayfish. Aquatic Science, 6(3,4):335-381. 1992
Thank you keep up the great work I greatly appreciate it! The article is very helpful as I have recently took on the care of two crayfish for my 12 year old step son for we only have him half the time he nor myself have a clue about crayfish
Hi Sara,
Thank you so much for the lovely feedback. I am glad I was able to help 🙂
Best regards,
Michael
My crayfish claws and limbs came off while molting. What I’m I supposed to do ?
Hi Imi,
Sorry to hear that but it happens. Crayfish can lose claws during molting.
Don’t panic, it will regrow back in a couple of molts.
Best regards,
Michael
i have a blue lobster that molted but now he drags his claws behind him what can i do
Hi Michael Contri,
There are two options:
1. It is just too weak yet. So, give it some time. Depending on the size of your crayfish it may take several days.
2. Something went really wrong during molting. In this case, you can only hope for the best. Sorry.
Best regards,
Michael
Hi Michael, our son’s crayfish molted a week ago. He has been laying on his back, and barely moving since then. At times it appears he is trying to right himself. I’m very concerned. Is this natural? Is he still just recovering from the molting process?
Hi Teniel Sherman,
Sorry, I could not answer earlier.
Well, this is definitely not a good sign. It seems like molting was not successful for the crayfish.
Unfortunately, you cannot do anything for them. Just hope for the better.
Let me know how it goes.
Best regards,
Michael
I would like to ask can my lobster survive? I did a mistake by throwing the molted shell can my lobster survive without the molted shell thank you
Hi Mark Bryan,
It is not a big problem if your lobster has some other ways (calcium-rich products, cuttlefish bones, etc.) to restore calcium in its body.
The molted shell is just one of these sources.
Best regards,
Michael
how long does the crayfish hide after molting, my cf is 3 inchs long but now i dnt know cause he moulted 2 days ago
Hi Marco,
In my experience, it can be from 1 to 5 days.
Best regards,
Michael
Our blue crayfish molted about 2 weeks ago. Her tail is still tucked under. Her color is a redish blue. After a week, she’s even more lethargic, falling over on her side. Now she’s on her back in a “hiding spot”. Sometimes she appears dead. Her legs will move every once in awhile so we know she is still alive. Is she dieing? Is she getting ready to molt again?
Hi Kerrie Bryan,
How old is it?
There is a very slight hope that your crayfish is just very old, therefore, it takes so much time for the exoskeleton to harden.
Generally, it should not be like that.
I am sorry.
Best regards,
Michael
Hi i have a blue crayfish and we’ve had him for about a year he has never shed i have 2 others that do all the time can you tell me why he has not
Hi Tiffany,
How old is your crayfish?
Fully grown crayfish can molt once in 6-8 months or even more.
The point is that they molt to grow or regenerate lost limbs. So, if there are already full-grown and they did not lose any limb – why molt?
Best regards,
Michael
Hi, I just bought a Orange Dwarf Mexican Crayfish, so I don’t know they’re age, its about an inch long. It is currently trying to molt, but its been 2 days. They are on their side or back with its tail curled up. I thought it was dead but its still moving its legs and kind of moving spots in the log it’s hiding in. It is suppose to take this long for them to molt? Or could there be something else wrong?
Hi Sadie M Peisel,
It should not be that long.
I am afraid something went wrong. You can only hope for the best. Sorry.
Best regards,
Michael
hi my crayfish who is around 1 year was not able to moult properly.the old claw portion was not able to come out and my crayfish presently has a longer appendage due to this reason.he is able to sit but moving around with difficulty.its been almost 24 hours or a little more since it started shedding its moult.is there any chances of it getting rectified in this or subsequent moults.if not what are the precaution i should take.
Hi Mukta Roy,
Crayfish can regenerate lost limbs. It can take them 1 or 2 molts but, eventually, they will restore everything.
So, I would not worry about it.
Best regards,
Michael
Thanku for the wonderful article Michael
It is very informative 👍🏻
Hi Agnel,
Thank you! I do appreciate your kind words 🙂
Best regards,
Michael
Hi I have a Australian red claw crayfish (Cherax quadricarinatus) that I bought for my autistic son. I had him in my community tank to start with as where I got him from said he was fine to live with my Mollies and Endlers. As you can imagine it did not go well so I bought him his own tank and put one of my large pleco’s (he is about 4 inches long) in to help with algae control. Craig the Cray was doing well in there for a few weeks, eating well and doing laps of the tank, which my son will sit for hours just watching him go.
For the last week or so he has become inactive and lethargic occasionally falling over. So much so I can pick him up by hand when usually he is virtually impossible to catch with a net. He has stopped moving around the tank. I check him every morning and he is in the exact same place as he was the night before.
I’ve only had him a couple of months and he was about an inch long and bright blue when he arrived, now he is a good 3-4 inches however his color is changing. The blue is going quite dark and he is starting to turn red on his sides. I’ve seen him molt once maybe twice since I’ve had him but not in the last 2-3 weeks. I’ve checked all my water levels, filter, heater etc and all are fine and within range.
Do you think he is about to molt, having trouble with the molt or something worse. I’ve upped his Bloodworm and got him extra mysis shrimp which he doesn’t seem to interested in and I’ve turned up the heater from 22c to 24c. I don’t know what else to do.
I hope I’m not losing him as my son will be devastated. any advice would be greatly received as the only info I can find on the web are about how to cook him or scientific reports on how they are invasive and what ammonia levels they can survive in before it kills them. (not a nice read by the way)
Thankyou in advance.
Hi Fiona Brumpton,
Frankly saying, I wouldn’t keep even large plecos with these crayfish. Eventually, they will outgrow them.
Inactivity, lethargic behavior, falling over, decreased appetite (stop eating) – generally, these are signs of upcoming molt.
Do not change anything, it may disrupt the molting process.
Provide cover. Let him hide. It will reduce stress levels and improve molting chances.
Do not touch him. This is the most vulnerable process in his life.
In my article, I have a link describing the molting process in detail.
I hope that everything will be OK. Please keep me posted.
Best regards,
Michael
Hi Fiona Brumpton, my crayfish that i have for a couple of weeks now just started molting. and is now out of his shell.
although I panicked, and couldn’t find anything about the process until it was to late. when I came across your article. I threw out the shell, cause I thought he didn’t needed it anymore, although his been laying on his back, and was hardly moving, (looking like he was dead.) so my mother hide him in the corner between the stones. Cause of his Tank mates, which means that she touched him. the cray fish haven’t been moving since, and I am scared that he is dead now. how do you identify a dead crayfish. I really hope that he is okay, and that it is not to late. please enlighten me, if there is a slight chance that I can safe him.
best regards Christina
Hi Christina,
It is stronly not recommended to touch crayfish after molt. They can be easily crushed. Nonetheless, leaving them in the open also makes them vulnerable for tank mates.
As for you question, the easiest way to identify a dead crayfish is the smell they release as they decompose. However, before that I would leave him for a day and remember his position.
I hope it will be OK.
Best regards,
Michael
OBS!
So I just realized I wrote Fiona Brumpton. I Meant Michael. sorry it’s late and been a long day, hope to hear from you soon. 🙂
Best regard Christina
HI Michael
a little update, thanks for the quick answer.
so he died, the tank mates started eating him, and I woke up to a half eaten crayfish. A fallen soldier.
best regards Christina
Hello, my white spector cray molted and did not eat her shell. This was 3 days ago. She appears to have lost both antennae and is now very lethargic. One claw has what appears to be algae & black spots on her tail. Complete water change 3 wks ago. Water tests came back appropriate. I.I’m worried!
Hi Lynelle Hengen,
It seems like somethinng went wrong during molting.
I am sorry, but you can only hope for the best.
Try not to disturb her. Cover the tank to provide more darkness and keep giving her food, in case she decides to eat.
Please keep me posted how it goes.
Best regards,
Michael
Hi Michael,
I bought a crayfish from Petco in January 2022. Sold under the name Blue Quad Lobster, Procambarus paeninsulanus. He is actually Cherax quadricarinatus, a male, as he has the bright red patches on his front claws. His name is Steve. Since I bought him, Steve averaged one molt every month until June when he went from June to October. He hasn’t had a problem molting, just has the usual behavioral changes, eating less, hiding more. For the past week, Steve hasn’t been eating really and the past couple of days he has been laying on his side. I thought ok, he’s probably going to molt even though it’s been less than 2 months. I came home today and found that his WHOLE ARM CAME OFF! Like the arm with big claw. So off course I’m panicking. I test the tank 0 ammonia, 0 nitrite, 40-80 nitrate, KH 6, GH 12, pH 7.6-7.8. These values have been pretty steady over the year. Then, I kid you not, his other arm falls off this evening. Steve is in a 40 gallon breeder with 5 white clouds and many female endlers. Tank temp varies between 73-75F. I am at a loss. Have you ever heard of this? Losing arms before a molt? He did break out of his tank in August but was only out of the tank for about an hour and he had a normal molt in October. Do you have any advice or thoughts?
Thanks,
Mandy
Hi Mandy,
Sorry to hear that.
Your water parameters are OK for these crayfish.
Did you change anything in the tank recently? What are you feeding him?
How is he doing right now?
It is really hard to pinpoint the problem without knowing more about our setup and situation in general.
If it is possible, I would move him to a quarantine tank.
Best regards,
Michael
Hi Michael,
I have not changed anything in the tank. The most recent water change was 9 days before his arms fell off. It was about a 40% water change. I did gravel vac and I used Prime with the new water. I didn’t clean the filters (Tidal 55 and Tidal 35) or any of the decor inside the tank. The substrate is CaribSea Super Naturals Peace River gravel mixed with Petco white sand. The plants are fake but there is some duckweed from my other tanks that I added a few weeks ago. There is a log that is open on both ends (big enough for him to go into), a cave, a lava rock and a driftwood log. When Steve started laying on his side, I put in a quarter of a wondershell, hoping that some extra calcium and minerals would help him out.
I feed a variety of foods. Hikari crab cuisine, sinking pellets, and carnivore pellets; Sera shrimp food and crustacean food; Bug Bites algae crisps; frozen bloodwoms, brine shrimp and beef heart; peas, carrots and zucchini. I rotate through all of these of course, I don’t put all of this food in at one feeding. Also, if I find MTS in my other tanks, I put those in there. Steve loves them.
The only thing abnormal that has happened is a couple of nerite snails died and I didn’t take them out right away. If I see a snail not moving, I usually leave them a few days to make sure they are really dead. When I saw they were both dead, I took them out. Could that have caused an ammonia spike that I missed? Would that have caused an arm issue? I would think a 40 gallon with an established cycle could handle a couple of dead nerite snails but I can’t say for sure.
Steve is mostly on his side but he does move around the tank a little bit. I would say his eyes look a little bit hazy. I dropped a carnivore pellet right in front of his face this evening and he didn’t show any interest. He is usually all about the food.
I unfortunately don’t have another tank to move him to for quarantine.
I feel like if he was going to molt he would have done it by now but I’m really not sure how long the process takes. Does it take longer as they get bigger? He just has never had a problem, his molt always looks perfect, no broken off limbs or anything. I’m at a loss.
Thank you,
Mandy
Steve passed this morning 🙁
Hi Mandy,
Sorry to hear that.
Sometimes things may go wrong even when we do everything right.
Best regards,
Michael
Hi Michael, where can I learn more about my cray ? I have a Cherax Quadricarinatus and I want to make sure she is getting the best possible care
Hi Dani,
Check out my article about this species.
If you have any questions, let me know.
Best regards,
Michael
Hi, for some reason I can’t tell how recently your last response was posted on here but I hope its still active and you are available also. Thanks so much for all of your informative content here!
To cut to it, what would you suggest as a potentially helpful treatment process for an open sore on a crayfish’s claw?
He just recently molted and it concerns me that the single tankmate, a rosy red minnow (put in as food / company weeks ago) may have nibbled at him while still soft and at his most vulnerable. The only information I find for first aid for crayfish online is about shell rot which I don’t specifically think is the issue I don’t see any rusty looking areas, he is an east coast coldwater native species and has a rusty ish color naturally. This sore showed up overnight and I can see the red underneath. I’m worried he will get a bacterial infection or maybe it’s caused by a bacterial infection or he could have gotten it from the fish. I’m really not sure where to begin to help him but I would like to. He’s a beloved family member, we have been through many molts together. I am guessing he is probably 3 years old, we have had him about 2.5 years. I say ” he” because of the significantly larger claws than the other cray( of the same species who was caught at the same time – “she” is housed separately due to a more aggressive nature). They are both the same size otherwise.
I have started treatment with em erythromycin API. It says it’s not a problem for inverts but I don’t know how effective it will be either. The only other thought is maybe treating it with iodine or maybe I should do a salt bath? Do you think anything would help more than another? Should I allow his wounds to air out, decrease the water and have a land area? Right now and he’s always been in a filled aquarium with aeration and filter. Anything you can advise is appreciated, truly thanks🧐!
Hi Abigail,
Thank you for your kind words. I continue to do my best to answer questions.
Erythromycin is a potent antibacterial medication used for treating fish (and eliminating cyanobacteria). I haven’t personally used it for crustaceans, so I can’t say how effective it would be for them. In theory, it should work because it affects the external bacterial membrane, breaking down and destroying them.
If that doesn’t work, I would suggest trying hydrogen peroxide. You can refer to the article on Rust disease in shrimp for a detailed guide on how to do this.
Could you deand me pictures of the damages claw, check your email, please?
Best regards,
Michael