Dwarf shrimp shedded exoskeleton

Aquarium: Molting Process and Metabolism of the Dwarf Shrimp

by Michael

Molting is one of the most important physiological processes for shrimp growth. It is a very complex procedure in which complicated metabolic processes take place. Since increasing body size occurs in a series of steps associated with the casting of old exoskeleton.

In this article, you will know why, how, when dwarf shrimp molt. The same as any other crustaceans, shrimp have external shell (which is often called an exoskeleton or cuticle) that limit the size of shrimp growth. Due to the fact, that the development rate is not linear as with fish but it is stepwise, the only way to grow for the shrimp is to replace its exoskeleton.

Thus, in order to breed shrimp successfully in your aquarium, it is better to know and understand this process.

Molting cycle in dwarf shrimp

In dwarf shrimp, as in other crustaceans, the rate of growth is a function of both the frequency with which they molt and the size increase per molt.
Unfortunately, there is not much information in the literature regarding, this important biological aspect of shrimp life. I have tried my best to gather everything here to share it with you.

Without further ado let’s start.

What is Exoskeleton?

 According to the researches the shrimp shell consists of the three main components and additional elements such as:

  1. Chitin (20-30 %). It is a linear polymer of amino sugars.
  2. Proteins (30-40%)
  3. Calcium carbonate (30-50%). A bone-like mineral called.
  4. Pigments (astaxanthin, canthaxanthin, lutein or β-carotene)

All these components are arranged in a layered structure that looks like a spiral staircase. Combination of calcified chitin and protein makes the exoskeleton firm.

There are Four Stages in Dwarf Shrimp Life

These are pre-molting, molting, post-molting, inter-molting. Let’s take a look at each of them.

1. Pre-molting Stage

The shrimp is preparing for the next molt.
Before an upcoming molt, a new skin (the hypodermis) develops under the old exoskeleton.  The hypodermis also absorbs many particles and chemical components from the old exoskeleton. Therefore, after molting, the new exoskeleton can gain hardness faster.

Interesting fact: the shrimp starts eating significantly less and less the closer is the moment of molting.  During this period of time, approximately 20 to 25% of the total body-calcium will be absorbed from the old shell, along with other important minerals.

Shrimp Molting How To TellAt this stage, the new shell becomes visible to the naked eye. Also, aquarists noticed that some type of dwarf shrimp starts looking really strange, they get muddy color. In addition, shrimp start scratching or “itching” their back a lot. They do that to reduce the strength of the exoskeleton in the breaking point.

2. Molting Process

predetermined breaking pointWhen it is time to molt, the shrimp start slowly pumping up its body with water until the old exoskeleton bursts at the breaking point. This predetermined breaking point is located in the neck area, more precisely in the skin fold between the head and the armor of the abdomen.

Then the shrimp jump out of their old shell in fractions of a second at the breaking point.

Note: In some rare cases the berried females molt. Unless you save the eggs, they will not survive. You can read an article “Save the Eggs from a Dead Shrimp. Artificial Hatching” right here.

3. Post-molting Stage

It is the shortest stage. It usually lasts from 12 to 36 hours for an adult shrimp. This is the time when the shrimp recuperates from the previous molting. There are two goals at this stage:

  1. Shrimp continues to absorb a significant amount of water in order to stretch its body. The new shell is inflated with water to develop
  2. It needs to consolidate its shell and in addition to adjusting it to its new extent. It takes some time for the new shell to become firm. During this time, the adult shrimp start producing a substance called chitin synthetase, which is essential to creating and hardening the new shell.

Shrimp start curling their tails right under themselves so that their whole body forms a tight “U” shape. By doing so they stretch and loosen their old shell.

The process of shedding off the shell has a huge stress effect to the shrimp’s body. As a result, its body, which is formed by the exoskeleton, cannot function at its full capacity yet. Therefore, the shrimp have to activate all its inner body reserves so it can harden and mineralize its weak exoskeleton.

During this stage, the shrimp become extremely vulnerable not just to physical effects but to some diseases and parasites as well. If you look at shrimp right after molting, you will see that they can barely move their pleopods. They have a sort of dull appearance right after a molt. They are too weak and soft. Which makes them easy prey for predators.

In addition, absorption of huge volumes of water leads to the osmotic shock. Which in its turn negatively affects the shrimp’s internal organs by rupturing or bursting the cells due to big and abrupt changes.

Shrimp molt failNote: If you see that your shrimp lies on the side in the “U” shape for hours, it means that something went wrong during the shedding. Unfortunately, in most cases, it will be too late to help. They will become too stressed and simply die. Some of my friends aquarists tried manually to free the shrimp from its shell. I have never heard that any of their tries were successful. In the best case scenario, they broke all shrimp’s legs. This is not worth doing. As a matter of fact, but shrimp will have better chances of surviving if you do not try to safe them.

In order to help, it would be better to create all the conditions for a favorable outcome of molting. It is advisable to use osmoregulators to help shrimp to survive.

You can read more about “Dwarf shrimp and Molting problems. The White Ring of Death” right here.

dwarf shrimp molting stages

4. Inter-molting Stage

This is the stage where the shrimp’s exoskeleton and body functions without any limitation. The shrimp eat as much as it is possible, and actively gains the weight.

Molting and Growth Rate. How often Shrimp Molt

Growth rate correlated with the percent gain per molt. The highest growth rate resulting in the highest percentage gain per molt.

  1. Larva stage. During this period shrimplets can molt almost every day. In my article “Breeding and Life Cycle of Red Cherry shrimp” you can find more information about larva stages and how fast shrimplets grow.
  2. Post-larvae stage – 20% (every 3-4 days).
  3. Juvenile (Subadults) -7% (every 4-10 days).
  4. Adult dwarf shrimp (In general every 1-1,5 month). Adult specimens molt only to regenerate lost limbs.

The exoskeleton weight about 5% of the shrimp body weight.

There was an observed weight change during the pre-molt and post-molt state. A sharp increase in weight began about 2 to 3 days before molting and about 2 to 4 days following molting. It was suggested that this was due to water absorption, firstly for the removal of the old exoskeleton and also to expand the soft new cuticle.

Tip: Sometimes the female can molt while wearing her eggs. Most likely, this is a consequence of deviations in the habitat. Check your water parameters ASAP. You can manually try to save the eggs and incubate them.

You can read more about “Save the Eggs from a Dead Shrimp” right here.

Factors Affect Molt Frequency in your Aquarium. What can Promote Molting?

According to studies, there are several factors, which play an important role in molting:

  1. Nutrition. This is one of the most important factors. Like any living being, they simply cannot grow without it. If they do not grow or grow very slowly, basically, there is no reason to molt. For example, the molt cycle period varied with the type of diet fed and averaged between 4 and 10 days for the subadult shrimp.
  2. Water quality (kH, NH3/4, NO2, pH, GH, TDS).

Usually molting is affected by the hardness and TDS of the water. If your water has a high parameter of hardness, the shell of the shrimp can be overly built up. Therefore preventing the shrimp to break and shed it.

Note: if you transfer the shrimp in the tank where the hardness is a lot harder than what they were used to, it can make their exoskeleton very rigid. As a result, it makes it very difficult to crack in the breaking point where they need to open up their exoskeleton to molt.
On the other hand, if you put them in the tank that has much softer water than what they are used to their exoskeleton becomes too malleable and it will not crack as well.

  1. Water temperature. Sudden and abrupt changes of the temperature can cause the molting. We are not talking about 1-3C difference because these changes do not affect shrimp (By the why, it also affects sex ration of Shrimp).

Tip: In addition, Some researchers believe that in warm water (25-26 °C) shedding is easier for the shrimp. Maybe because in this case it increases their metabolism and gives them more energy and strength.

  1. Shrimp age (size). It was also observed that the molting frequency declined as the shrimp increased in size. I have covered this moment a little bit earlier.
  2. Shrimp sex. The intermolt period varied between sexes. Male had a slightly longer intermolt period than females. Which related to the slightly higher growth rate obtained with female shrimp.

All these factors affect molt frequency to a varying degree. The dwarf shrimp molting process is highly susceptible to environmental factors, particularly temperature and food availability, which affect growth by altering molt frequency and molt increment. While the relationships between temperature, food, and growth are consistent, the response to CO2-induced pH reduction is variable.

Note: water changes for newly molted shrimp can be very dangerous if replaced water contains higher concentration of salt compared to that the shrimp has right now.

In this case, shrimp’s sell will absorb the salt (because of Osmosis). In its turn, in order to adjust the saline concentration, the cells will have no intake more water to compensate. As a result, there will be a Cell Hypertrophy. It causes to cell death and eventually shrimp death.

What Dwarf Shrimp Need to Molt

The required salts for an upcoming molting are absorbed mainly from the water and apart from the diet, transferred to the bloodstream and mobilized for use. Therefore, eating the old exoskeleton after the molt, as often assumed, is not necessary.

The calcium intake itself depends on the concentration in the body.

Tip: use Indian Almond Leaves (Catappa leaves), Mulberry leaves etc. their components help the molting process, (reduces mortality rate during this stage). You can also solve the problem of lacking some minerals (like calcium) by adding mineral rocks to your aquarium.

Personally, I think that Almond leaves and mineral rocks should be enough for any shrimp breeder. But if you are interested in over products, take a look at JBL Nano-Crusta. It gives the shrimp the clay mineral montmorillonite, which shrimp need for molting or GENCHEM BETA-G 50G.

Is It a Dead Shrimp or Molting?

Having seen the discarded exoskeleton for the first time, the novice aquarist can take it as a dead one. Some people think that molt is always transparent and (or) clear white. This is not so. Especially, if the old exoskeleton belonged to a more intensely colored female. It is very interesting but exoskeletons of the females often retain traces of pigmentation. Thus it is very easy to confuse it with the really dead shrimp.

To be sure you need to take a closer look at the shell. If there is no pigmentation, most likely in it is an empty shell. Also, the molt will have a very identifiable split in the middle (breaking point) of the shell.

What Should I Do With Shrimp Exoskeletons

Nothing. Do not remove them from your aquarium. These shells contain a lot of minerals and shrimp will eat them gladly. Do not worry. Your tank will not become a mess.  The only reason to remove the exoskeletons if your shrimp are sick or there is a parasite in the tank like, for example, Scutariella Japonica.

Conclusion

During the life cycle of shrimp, the succession of molts is more frequent in the early stages of life, decreasing or ceasing in adults.

Smaller shrimp molt more frequently than larger shrimp, the body size and sexual state also affect the length of the inter-molt cycle. Adult shrimp shed every four to six weeks depending on feeding and water changes. The older they get, the slower dwarf shrimp grow and the less often they molt. Adult specimens molt only to regenerate lost limbs.

 

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