The Marbled Crayfish (Procambarus virginalis), aka Marmorkrebs wouldn’t have received much attention if it wasn’t for its self cloning ability. While they’re cool (like all crayfish), there’s nothing striking about a Marmorkreb’s appearance–olive or brown with a marbled pattern, hence their name. Sometimes they can be blue or red, or change color in response to diet or other factors, such as water quality.
A Marmorkrebs (Catherine):
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/cat.jpg?w=1024)
No one knows for sure how the first Marmorkrebs came to be. Genetic studies of the Krebs confirmed that Marbled Crayfish originated in the German aquarium trade sometime in the mid 90’s, and from then on spread to Madagascar, Europe and elsewhere.
Marmorkrebs are close relatives of the Slough crayfish, Procambarus fallax, but unlike these “regular” crays, they’re triploid animals, with 276 chromosomes (3 sets of 92 each) instead of the usual 184. Triploidy occurs when 2 sets of chromosomes come from the mother and 1 set from the father, or 2 from the father and 1 from the mother.
Each of the 3 sets seems to be a variation of the Procambarus fallax chromosomes. 2 are nearly identical, but the 3rd one is distinct enough to indicate that the two original parent Slough crayfish must have come from very different geographical regions.
Just a few of Catherine’s many clones:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/some-of-cat-ch.jpg?w=768)
Marbled Crays aren’t the only triploid animals. Goldfish, Oysters, Salmon, Trout and even some humans can have 3 sets of chromosomes. However, humans with 3 sets don’t survive for very long, and many commercially farmed animals such as salmon and oysters that are created purposely to be tripoloids are infertile. On the other hand, Marmorkrebs is the only known decapod crustacean to reproduce asexually, with no apparent negative effects on the clones.
Incidentally, Marmorkrebs and Slough crayfish recognize each other as mates, but the Marbled crayfish will still just produce clones of herself after mating with a male Slough crayfish. Possibly, mating triggers the Marmorkrebs to go into breeding mode, similar to the Amazon Molly (Poecilia formosa), but the Krebs will breed anyway, regardless of whether other crayfish are present.
Claws of the Marmorkrebs (first two sets from below, taken from different molts, and possibly different crayfish). At the top are molt-claws belonging to a Procambarus Clarkii, aka White Specter Crayfish.
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_8744.jpg?w=768)
The self cloning process is kind of magical. One day a Marmorkrebs is sitting alone under a log or in a cave, the only creature in the tank. The next time you see her, she has a “berry” of eggs under her tail and then they hatch and pretty soon you have 300 tiny copies of this crayfish walking around. They climb off her tail, crawl about in her “whiskers” and generally use her as a jungle gym, and she doesn’t bat an eye. They’re all 100% identical clones of the mother, and each in turn will grow up and clone herself into hundreds of more crayfish.
If you look closely at Catherine’s tail section, you’ll see baby crayfish clones about to hatch! She runs around the tank a lot as the fry start leaving her tail, one by one. Goodbye, safety of mother’s pleopods!
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_4204.png?w=638)
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![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_4203.png?w=634)
Unlike some other cray species, Mama-krebs does not try to snack on her young, so they have an increased chance of survival. And they are very successful at that. They’re hardy, eat literally everything, and their marbled shells provide them with excellent camouflage from predators.
The only thing Marmorkrebs don’t appreciate is salinity. They tend to avoid marshy areas or otherwise salty water, which keeps them from spreading even further than they already have. They can live pretty much anywhere – rivers (both fast and slow), lakes, rice paddies, swamps, brick pits, drainage ditches, and of course, home aquariums and fish ponds. In short, they’re really good at adapting to different conditions and not only surviving, but flourishing and out-competing native species.
For this reason, they’ve been outlawed in the EU, Japan, and the Canadian province of Saskatchewan, as well as in several US states—as of 2022, they are prohibited in Idaho, Missouri, Tennessee, Michigan, Maryland, and more recently, in Ohio under the Lacey Act.
However, I think that picking on one individual does not solve the bigger problem—crayfish don’t have any concept of state lines, so a cray that’s released into the wild either by chance or by an uninformed or careless aquarist in one state has no problems finding its way into another state where it may be an illegal species. The only real solution is to outlaw the Marbled Crayfish in all of the United States.
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/1_wanted.jpg?w=600)
But (while they’re still legal to keep), they make excellent freshwater pets!
Here’s Catherine the Marbled Crayfish again
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/cat-1.jpg?w=1024)
And here’s Betty, her daughter
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/betty.jpg?w=1024)
One of Catherine’s many clones:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/one-of-cat-many-children.jpg?w=768)
Some of Betty’s many clones (having a go at each other by claw-parrying):
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_8724.jpg?w=1024)
Fathead Minnows
If you don’t want all the crayfish fry, there’s a solution: Fathead Minnows. This common North American fish is sometimes sold in silver form, as well as the popular Rosy Red or “Tuffy” Minnow variety. They will readily and happily snack on crayfish fry, especially small hatchlings. If you decide to keep some of the crayfish fry, just move them into a refugium or a separate tank of their own.
They are the only fish I trust around crayfish. Minnows are very strong swimmers and are lightning fast, and I have never seen any crayfish induced injuries after over a year of keeping both species in the same tank.
Actually, Minnows are more likely to attack crayfish. They do this by head butting them. I’ve seen it a few times. The Minnows mostly do this while protecting their nests or “egg lairs”, so if a crayfish strays into their territory it will be speedily butted out. After a few attempts, a Marmorkrebs will learn that it’s a no-go and will tend to avoid the Minnow’s cave in the future.
A Minnow “bull” protecting his cave:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/minnow.png?w=1024)
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As food
I’ve never tried a Marmorkrebs but people say they don’t taste very good. Nevertheless they’re an excellent (and continuously self-renewing) source of protein.
The Blue color variety
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/blue.jpg?w=1024)
Sometimes Marmorkrebs can be blue or can turn blue in response to diet or some other factors, although there is a “true blue” variety of the Krebs. The above crayfish (image courtesy of a customer) was brown to start with but something made it turn blue. Some Astaxanthin rich foods in a Marmorkreb’s diet can cause it to change color.
I’ve kept Marmorkrebs for a few years now and none of them have ever turned blue except one time. By accident, a few very small crayfish got stranded in a waste water bucket after I cleaned the tank. The water quality in that bucket wasn’t very good—it was the tank’s waste water. The next morning, I noticed a group of these small fry at the bottom of the pail. They were quite blue in color. Upon returning to their tank, they changed back to brown within a few days.
Aside from self-cloning, Marmorkrebs do what any crayfish usually do.
They eat:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_8730.jpg?w=1024)
Molt:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/molt.jpg?w=768)
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Explore their habitat:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/exploring.jpg?w=768)
Take naps:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/napsincaves.jpg?w=1024)
Groom themselves:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/groom.jpg?w=1024)
Uproot and eat aquarium vegetation (in this case, Betty is eating duckweed):
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/duckweed_eating.png?w=691)
Occasionally get into fights with each other over a piece of zucchini or other matters:
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_8723.jpg?w=1024)
Most of the time they don’t lose any claws… but sometimes they do.
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_4120.jpg?w=1024)
Some fun facts about crayfish (goes for all crayfish, not just the Marmorkrebs):
- Crayfish have taste receptors on their feet. When they walk over something delectable like a piece of rotten fish or a sweet pea, their feet instantly tell them it’s time to chow down. A convenient adaptation!
- They pee from ducts located at the base of their antennae, just above their mouths. Male crayfish spray each other when they fight, and female crayfish signal potential mates with pheromone laced urine. Another convenient adaptation! (No, just kidding).
- Right after molting, if a crayfish crawls into some tight or awkward space, its claws or other parts may harden in a deformed way. Which is why molting and newly molted crayfish should never be disturbed!
- Crayfish like to groom themselves. A lot. They sometimes take small rocks or sand grains and use those to rub and polish their shells.
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/cat-baby.jpg?w=1024)
Sand grains lying on top of Catherine’s head. This was one of the first pictures of her that I ever took. Note how small her right claw is in comparison to her left claw–she’d lost it, most likely in a crayfish fight. Every time a crayfish molts, any lost limbs or other parts grow a little bigger.
- They like to keep a clean house. Every once in a while, a crayfish will scoop up any dirt or debris that had accumulated in its den and use its claws to carry the garbage outside. They also like to rearrange things, like shells or other objects. They carry these around and deposit them where they see fit.
- They block entrances to their caves (these can be logs, pvc pipes, etc) with vegetation that they routinely uproot in the aquarium. Luffy moss balls are a huge favorite with crayfish as they can be fitted snugly into almost any type of cave opening. They plug up the entrances against invaders, such as fellow crayfish.
- Crayfish are more aggressive toward other species of crayfish than to their own species. They are also cannibals by nature. If they can catch another crayfish, of the same species or not, they will eat it. Guess which part is their favorite? The tail, of course! Marbled Crayfish are known to be the most peaceful of any larger crayfish species. They tend to avoid serious, claw ripping fights if they can. Under normal conditions (enough space, food, etc) cannibalism among them is virtually non-existent.
- Surprisingly, some of the most feisty crayfish are also the smallest. For example, the hyper aggressive CPO or Dwarf Crayfish (Cambarellus patzcuarensis). These tiny monsters grow to only about 2″ at the most, but their attitude makes up plenty for their small size!
![](https://fishzombie.wordpress.com/wp-content/uploads/2022/06/img_6434.jpg?w=1024)
- Crayfish can breathe atmospheric air.
- They can drown if the water is too low in oxygen. They can run out of air just like fish.
- Crayfish can come of the water and trek across dry land to find a better home, moving from one lake or pond to another. They can also sometimes climb out of their tanks, which is why it’s a good idea to keep all crayfish tanks fully covered and weighted. Crayfish are strong animals. They can pop up a tank lid and climb out easily. They can survive on dry land (or in your room) for a few days, depending on the humidity and temperature, but eventually their gills will dry out and they will die. Betty once escaped from her tank. Luckily, I found her in time.
- Crayfish seem to have two modes of feeding–one when they pretty much dig their faces into something tasty, using just their mandibles to chomp down. They do this either when they’re really hungry or when the food is irresistibly delicious. The second mode of feeding is when they pick at food with their claws at leisure, taking little bits at a time and carrying them slowly to their mouths. This is a more relaxed or “lazy” mode of feeding.
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- When a crayfish sees you approach, it will often stay completely motionless as it flicks one or both of its antennae in your direction. Underwater, the antennae would tell the crayfish a bit about who or what you are, but of course that’s impossible through the glass wall of a tank.
- Crayfish can get drunk and high.
- Drunk Crayfish behave a lot like humans. They do some stupid shit, then totally lose their motor coordination and pass out. Also, crayfish tend to get drunk more quickly in groups as opposed to when they’re alone.
Hey, how about getting crayfish drunk off their tails before cooking them?