Crayfish and Molting Process

Crayfish and Molting Process

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:

  1. Proecdysis(Pre-molting Stage)
  2. Ecdysis (Molting Process)
  3. Metecdysis (Post-molting Stage)
  4. 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:

  1. As I have already mentioned, crayfish continue to absorb a significant amount of water in order to stretch its body and increase in size.
  2. 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?

crayfish eats old exoskeletonThe 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 less. 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

Crayfish and Molting ProcessIt 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, 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

References:

  1. 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.
  2. 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.
  3. Changing Activities of the Crustacean Epidermis during the Molting Cycle. J. Ross STEVENSON. A.M. ZOOLOCIST, 12:373-380 (1972).
  4. Calcium Transport Mechanism in Molting Crayfish Revealed by Microanalysis. The Journal of Histochemistry and Cytochemistry. Vol. 31, No. IA, pp. 214-218, 1983.
  5. Ion Regulation in Crayfish: Freshwater Adaptations and the Problem of Molting. AMER. ZOOL., 35:49-59 (1995).
  6. 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.
  7. Growth rate, life span and molting cycle of the crayfish Orconectes Sanborni. The Department of Zoology, The Ohio State University. 76(2): 73, 1976.
  8. 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.
  9. The growth process in crayfish. Aquatic Science, 6(3,4):335-381. 1992

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Content