The Marmorkrebs Crayfish (Procambarus fallax f. virginalis or Procambarus virginalis sp. nov.) is not only known as Marbled crayfish but also regarded as the self-cloning crayfish that has surely stunned the imaginations of many people. In case you didn’t catch the last part of that sentence, it simply means that this crayfish can reproduce itself with natural cloning techniques.
Populations of the Marbled crayfish are exclusively composed of females. This species is easy to keep and breed. They mature early, reproduce asexually and rapidly. In addition, Marbled crayfish have high fecundity and short generation time. This means, that a single individual can establish a whole population of female clones.
But beyond its self-cloning capabilities, is there anything interesting that you should know about the Marmorkrebs crayfish? Well, if you have questions, then you have come to the right place. On this post, you will learn everything you need about this amazing crayfish, from the way it feeds to the way it breeds as well as much other useful information.
Quick Notes about Marmorkrebs Crayfish
|Common Names||Marmorkrebs, Self-cloning crayfish|
|Scientific Name||Not established yet. There are two main versions:
– Procambarus fallax virginalis
– Procambarus virginalis sp. nov.
|Tank size (optimal)||20 gallons (~90 liters)|
|Size||up to 7 – 12 cm (~ 3 – 5 inches)|
|Optimal Temperature||18 – 25°C (~64°F – 77°F)|
|Optimal PH||7.0 – 8.0 (6.0 – 9.0)|
|Optimal GH||3 – 18|
|Optimal KH||3 – 15|
|Optimal TDS||150 – 300 (100 – 500)|
|Nitrate||Less than 40 ppm|
|Diet||Detritivore / omnivore|
|Temperament||Conditionally Peaceful / Slightly aggressive|
|Life span||up to 3 years|
|Color Form||Highly variable, from tan to dark olive-brown|
Taxonomy problems of Marbled Crayfish
This species was first described in the German aquarium trade in the late 1990s and became widely distributed in subsequent years under their German name “Marmorkrebs”. While its identity was unknown it was dubbed Marmorkrebs (Marbled crayfish) for its marbled carapace.
In 2003, Gerhard Scholtz confirmed that an unidentified crayfish in Germany was reproducing parthenogenetically (without males) in an aquarium. This was the first record of a parthenogenetic decapod crustacean.
Using morphological characters and molecular markers, scientists identified the sexually reproducing slough crayfish Procambarus fallax from Florida as the closest relative of Marbled crayfish and suggested the provisional name Procambarus fallax forma virginalis.
However, the International Code of Zoological Nomenclature (ICZN, 1999) excludes “forma” for names published after 1960 (Article 15.2). Consequently, the provisional name for Marbled crayfish was also considered “unavailable” in a recent taxonomic summary of freshwater crayfish.
It created another problem. Nobody knew how to call it because different fitness traits, reproductive incompatibility, and substantial genetic differences suggest that the Marbled crayfish should be considered an independent species. Therefore, some biologists suggested using a new scientific name, Procambarus virginalis sp. nov. for the time being.
Note: The native geographical distribution of this form, if at all present in the wild, is still unknown. Basically, nobody knows even how this species was created. Although it cannot be excluded that the origin of this crayfish could have been a hybridization between Procambarus fallax and some other species of the genus Procambarus.
One of the problems is that biologists use male pleopods and gonopods to identify crayfish species. It is absolutely not possible with the Marbled crayfish, they are all females.
Important Facts about Marbled Crayfish:
The Marbled crayfish has become one of the potentially most dangerous nonindigenous crayfish species spreading in European countries and elsewhere.
Before about 25 years ago, the species simply did not exist. Nowadays, this crayfish has been recorded in the wild in several European countries, including Croatia, Germany, Hungary, Italy, the Netherlands, the Czech Republic, Slovakia, Sweden, and Ukraine.
Due to its invasion potential, Marbled crayfish has been recently included, together with four other invasive crayfish of North American origin, in the list of 37 Invasive Alien Species of European Union Concern (EU Regulation No. 1143/2014; Commission Implementing Regulation No. 2016/1141).
NEVER release Marbled crayfish into the wild. Check your state laws before purchasing. This is a restricted (banned) species in some US states and European countries.
Description of Marbled Crayfish
The Marmorkrebs is a medium-sized crayfish. The marmorated coloration of the carapace (pigmented), which prompted the informal names “Marbled crayfish” or “Marmorkrebs”, is particularly prominent in aquarium stocks. It is often less pronounced in wild animals. The color greatly depends on the diet. The basic color of the carapace is usually dark brown to olive but can vary from tan to reddish-brown or blue, and even green.
Interesting fact: Although, the Marbled crayfish are genetically identical. They show a surprisingly broad range of coloration, growth, lifespan, reproduction, behavior and fluctuating asymmetry of sense organs even when reared under identical conditions.
The Marbled crayfish can live up to 2 – 3 years.In their adulthood, they grow up to 3 – 5 inches or even more.
Behavior of Marbled Crayfish
There are several facts about them that you need to know if you decide to keep them.
1. First of all, Marbled crayfish are very destructive. Therefore, keeping them in a planted tank can be a challenge.
2. Keep in mind that they can cause water turbidity by disturbing fine sediment particles while burrowing for shelter or searching for food.
3. They are very good escape artists. It is good to have your tanks covered as much as you can. In addition, keep the water level slightly below the surface.
4. They are not that peaceful as people think. It is not recommended to keep them with fish and shrimp. Unless you are ready to lose a few here and there.
5.They are territorial and very competitive. They can behave aggressively towards anybody on their territory.
The Marbled crayfish can spend much of their time hiding. According to the study, activity peak starts shortly before lights off and continues for several minutes, a shorter and less intense burst of activity occurs at the beginning of the light phase.
Interesting fact: In one of the experiments, biologists put Marmorkrebs and Louisiana red swamp crayfish in the same tank. As a result, fights between them began significantly faster than contests between two Marmorkrebs. In addition, Marbled crayfish initiated fights more often!
Feeding Marbled Crayfish
They are an omnivore and utilize a wide range of food sources. However, according to the scientific studies and experience of many aquarists, detritus and algae are the most important food sources in the diet of the Marbled crayfish.
Another fact that you have to keep in mind is that they also feed on plants. So you will need to watch out when you are putting them inside any tanks that have live plants because they are going to eat them up.
Note: Only floating plants can be relatively safe with the Marbled crayfish.
This species has a very good appetite for vegetables – cucumbers, zucchinis, spinach, cabbages. Whatever you give them they will eat it. You can read more in my article “How to Blanch Сucumbers, and Zucchini for Shrimp, Snails and Fish the Right Way”.
Nonetheless, they are not vegetarians. Once or twice a week they need to eat organic food. They enjoy blackworms, earthworms, brine shrimp and … snails. Actually, Marbled crayfish are a great fan when it comes to feasting on aquarium snails. They will gladly control the population of snails in your tank.
As we can see, they will eat basically anything you throw in the tank.
Tip: I have already mentioned that you can alter the Marmorkrebs color by simply changing what they eat. According to the experiment, they can get:
- Darker gray, grayish brown and light gray color if you give them carp feed (carotenoid-free food).
- Dark blue color if you give them discus feed (carotenoid-rich food).
Different levels of astaxanthin and protein in feed have a significant effect on carapace coloration, growth rate, maturation in Marbled crayfish. They grow faster and mature earlier.
Keeping Marbled Crayfish
Keeping Marble crayfish is easy. They are very hardy animals and can live in a wide range of water parameters. They feel excellent in the range of pH 7.0 – 8.0. Although, they were also found in pools, rivers, lakes, swamps, and even drainage ditches, where pH values from 6.0 to 9.0.
In addition, they have a higher nitrate tolerance threshold. For example, they were found in the lake with high TDS and Nitrates (20 ppm).
Optimum temperatures for the growth of the Marble crayfish range from 18 – 25°C (64 – 77 F). However, the growth rate is not drastically reduced until the temperature falls below 15°C (59F) or rises above 30°C (86F). For example, at 25°C, their length and total weight increased by 17.5 mm (0,7 inches) and 1700 mg, respectively over 150 days, whereas at 15°C these parameters increased by 7 mm (0,28 inches) and 100 mg, respectively during the same period of time.
Basically, they do not care about water parameters and can live even in dirty water. This is one of the reasons why they have become an invasive species and banned in many countries worldwide. They have only one weakness. According to the study, Marbled crayfish have a lower salinity tolerance than other crayfish species.
Extreme Temperature and Marbled Crayfish
Marbled crayfish are very tolerant and can survive under extreme conditions. For instance, experiments with outdoor tanks indicated that Marble crayfish survive temperatures below 6°C (43F) for 6 months and tolerate temperatures below 2°C (36F) at least one week. Its overwintering ability, with successful survival at 3°C (37F) for three months and above 30°C (86F) for many weeks, was also confirmed experimentally.
Note: Although mortality increases under such conditions and reproduction stops. Marbled crayfish were active and ate at a temperature above 10°C (50F). They become less active when the water temperature decreased and stopped eating below 10°C. Most crayfish hid in shelters at temperatures below 5°C. At temperatures below 2°C, some marble crayfish came out of the shelters and lay motionless on the bottom of tanks like dead animals, but the movement could be seen when they were observed closely. When the water temperature was increased above 4°C (39F), crayfish became more active and shelters were used less often.
In general, low-temperature water tolerance depends on the body size of the Marble crayfish. Larger crayfish are more tolerant of very low temperatures.
Temperature and Molts
The growth pattern in all crustaceans is a discontinuous process with successive molts. (To learn more read my article “Aquarium: Molting Process and Metabolism of the Dwarf Shrimp”).
Temperature is the most important environmental factor influencing crayfish growth because it directly affects the metabolic rate. The Marble crayfish can sometimes molt even at temperatures below 10°C (50F) and reproduce after surviving extreme environmental conditions. Although they are extremely tolerant, higher temperatures shorten the molt cycle and lead to faster growth, but only within a suitable range.
Note: Adult Marbled crayfish molt only 2 – 3 times a year. After molts, they can lose some color. Do not worry. This is a normal process and the bright color will return in 7 – 10 days. They can regenerate lost appendages within 1 to 2 molts.
Tip: You can add cuttlebone, blanched kale or eggshell to the aquarium to supplement calcium, which will aid in exoskeleton formation. You can read more about calcium in my article “Dwarf shrimp and Molting problems. The White Ring of Death”.
Marbled crayfish and Filtration
They are not picky. However, I would recommend sponge filters or Matten filters. This species follows the same principles as shrimp. Therefore, these filters will be more beneficial for the Marble crayfish.
Marbled Crayfish and Shelters
They are very much similar to other crayfishes in this regard since they equally need crevices or hiding places for protection and healthy growth. Therefore, it will be better to add some rocks, driftwood, PVC tubes, etc.
Actually, this is absolutely crucial when housing multiple crayfish in the same tank. The point is that shelters also play a significant role when it comes to fighting. For example, according to the experiments, large Marbled crayfish usually defeat small opponents but they are frequently beaten by small opponents that are shelter owners. More than 2 hours of residency in a shelter is sufficient for small owners to defeat large intruders!
In addition, the quality of shelter also plays a huge role here. Small owners of low-quality shelters were frequently beaten by large owners with the shelters of same or better quality.
So, now you can ask – what is the high-quality shelter for Marbled crayfish? Well, there were also other experiments about it. In short, they prefer big, long PVC pipes with multiple entrances.
Breeding Marbled Crayfish
Breeding Marbled crayfish is super easy because they do not even have to mate! Due to its asexual mode of reproduction, even a single marbled crayfish can overpopulate a home aquarium in a short time.
It takes them between 5 and 7 months (depends on the temperature) to mature enough to have their own babies. The typical size at maturity of this species is about 35mm (~1,5 inches). Female fecundity increases with body size and brood sizes even for very small females usually exceed 45 eggs and may reach up to 700 of eggs! For example, under the laboratory conditions, the maximum observed fecundity per female reached 647 juveniles (on average 420) eggs per female.
The eggs are normally incubated within a time span of 22 and 42 days. Interclutch periods are varied between 50 and 85 days.
Note: They start reproducing when the water temperature reached 15.8°C. Marbled crayfish can reproduce approximately every 3 months (up to 7 – 8 reproduction cycles during its lifespan of 2 to 3 years). Multiply it by 420 eggs – every year one female can have up to 1500 babies! Absolutely astonishing.
Note #2: The Marmorkrebs crayfish can be aggressive to their young. So think beforehand what you are going to do with them.
Marbled Crayfish and Crossbreeding
I would like to share another interesting fact about this species. In crossbreeding experiments, Marbled crayfish females and Procambarus fallax males showed typical courtship behavior and mating. However, offspring of marbled crayfish females that had been mated with Procambarus fallax males were exclusively female and exclusively showed only the genetics of the marbled crayfish mother. These findings are in agreement with the notion that the Procambarus fallax male did not contribute to the genome of the offspring and that the progeny is the product of asexual reproduction in the marbled crayfish mother.
Marbled Crayfish and Tankmates
Marbled Crayfish and Fish
I would like to start off by busting the myth that Marble crayfish are peaceful and exceptionally efficient when it comes to living with fish and shrimp. Well, they are not!
Of course, they are not super aggressive and will not hunt down relentlessly every single fish or shrimp in your tank. Nonetheless, they are opportunistic feeders. It means that if they can catch it (shrimp or small fish), it will be eaten.
Therefore, if you are still planning to keep them in a community tank you need to follow these rules:
1. DO NOT keep them with bottom-dweller fish.
2. DO NOT keep them with fish with big and fluffy fins.
3. Give them organic food from time to time. They need protein.
4. They should not be hungry.
I would like to repeat that keeping any crayfish in a community tank can become a disaster. Of course, you might get lucky and your Marbled crayfish will not show any interests in others. Frankly saying, I would not count on that. That is why it surprises me that some guides write about this species as fish safe. There will be loses and injuries.
Note: Do not keep Marbled crayfish with cichlids and puffer fish. It will not end well for the crayfish.
Marbled Crayfish and Shrimp
Basically, the same situation is with all dwarf shrimp. The good news is that, in most cases, healthy shrimp are simply too fast for the Marbled crayfish. Therefore, if they caught a shrimp, you can tell yourself that they did culling for you. Read more about “Culling Shrimp. Selective Breeding.”
Note: DO NOT keep them the Bamboo shrimp. Due to the unique food intake technique (Bamboo shrimp stay motionless), they can be an easy target for any crayfish.
Marbled Crayfish and Snails
Marbled crayfish are active predators of the freshwater snails. They are not compatible with any type of snails. So, do not put them in the tank with decorative snails like (Nerite Snail, Rabbit Snail, Mystery snail, etc).
Marbled crayfish are widely available, undemanding pets. Due to its asexual mode of reproduction, fast growth, early maturation, high fecundity, short intervals between reproductive cycles, marbled crayfish can overpopulate a home aquarium in a short time.
This, together with the substantial ability of the Marbled crayfish to withstand extreme environmental conditions, make them an attractive choice for the beginner aquarist.