Text: Monika Rademacher
Photos: Oliver Mengedoht
Translation: Ulrike Bauer
In the course of manifold additions to hobby aquaristics during the last years, more and more inverts have found their way to private tanks, among them the crayfish this article is about.
Procambarus sp, known under the trivial name of marble crayfish, has acquired a rather bad reputation since the first beginnings.
This results firstly from its pronounced reproductivity, which is performed by the females without any help from male marble crays and secondly from the fact that this species cannot only be found inside aquariums but unfortunately all too often outside of them, too. Due to some keepers' inconsideration time and again some individuals have escaped to nature, and just as often they are deliberately set free, for example when formerly enthusiastic craykeepers are overwhelmed with the continuous glut of cray offspring and cannot find any takers for their tanks' inhabitants that have suddenly become so bothersome.
Once in freedom, marble crayfish cannot only survive in the most adverse conditions, but they also reproduce in great numbers.
One effect of this unwanted colonization not only in our region of the world is on the one hand that the marble crayfish outpopulates native crays, and on the other hand that they carry a spore (Aphanomyces astaci) that causes crayfish plague, a spore, by the way, that all American crays are potentially carrying. As a rule they have become immune against this pathogen and don't get sick themselves, but for European crays an infection signifies the outbreak of a fatal disease, which can eradicate the crayfish population of entire regions in no time.
So why are we dedicating an entire article to a crayfish species whose keeping can bring about such negative consequences?
Well, there are some good reasons for this.
Marble crayfish are pretty often given to people who have only started to keep crustaceans and simply do not have any background information on the subject by pet shops or private keepers. They have maybe bought such a cray because they simply liked it and moreover, because they tend to be sold at really low prices. The consultation regarding the "right" keeping of marble crays is only too often scanty at best or even outright wrong, and it so happens that future keepers just take these crays home without being informed about them beforehand in an adequate way.
A further reason is that this is indeed a crayfish species that has its charms, may it be because it looks good or because it's a reliable live-food producer, e.g. for turtles or cichlids.
So the marble crayfish might be an animal whose keeping is rightfully debatable, but it seems legitimate to me if the keeper knows already beforehand how to deal with a possibly huge crop of offspring and if he or she is willing to deal responsibly with this sensitive subject. A part of this is of course making absolutely sure that these crays can in no case escape from the tanks and that none of them are given to future keepers without alerting those to the possible troube with this crustacrean. Even if this crayfish species is still praised as easy-to-keep "beginner's cray" time and again, the problems we called attention to above show that especially new beginners can feel overwhelmed pretty soon. This is why marble crayfish should in no case be passed on as "newcomer's crays".
Maybe this article will also bring about some awareness of this subject.
The marble crayfish
This is a still undenominated North-American crayfish species; however, scientists are pretty sure that it belongs to the genus Procambarus. Undenominated because a well-founded denomination can only be done on male crustaceans, and never has a male marble cray been found. Its natural habitat could not be defined either, it is assumed that it originates from the South of the United States.
Optically striking is the marbled coloring of these crays' carapace, which was the name-giving criterium. The basic color is mostly brown, but there are also blue specimens or ones that display a mixture of brown, blue and reddish colors; these different color variants probably show up depending on the water hardness.
When hatching, Procambarus sp. is only 0.5 cm in size and grows over time to a total length of up to 12 cm without the claws; even larger individuals have been reported sporadically.
Basics about keeping marble crays
The marble cray's habitat is the water, thus they are kept in an aquarium. It is not advisable to keep them in ponds, even though, regrettably, these crustas are repeatedly sold in pond supply departments in the trade.
As for all crayfish the tank is not chosen according to the volume but according to the available ground area. They are bottom-dwellers who need enough room to satisfy their urge to move. Thus the height of the tank is only secondary, however, it should be so high that the cray cannot reach the tank's upper rim when standing upright. 30 cm should be enough for this purpose, you should be aware though that decoration or plants close to the glass panes could be used as a "ladder". As minimum ground surface for a single cray we recommend an area of 80 x 30 cm. One could also use a tank with a ground area of 60 x 30 cm, but then its set-up ought to be structured in a way that brings about more ground surface by using e.g. flat stone plateaus or a low second level.
The water parameters only play a role insofar as there mustn't be any poisons or heavy metals in the water. Marble crays are also very tolerant towards various water temperatures, however, keeping them at lower temperatures is preferrable to warm-water tanks.
Of course you can plant the tank, in many cases the keepers will learn though that a lovingly created green environment is only short-lived as the crustas are quick to find out they're partial to eating aquatic plants and to shredding those plants that don't taste so good.
Moss balls (marimos) are relatively long-lived, they also keep growing after being shredded. Small floating plants are also very suitable for greening the cray's home. The tank inhabitants only reach them with great difficulty, and luckily they often lack the motivation to do so.
Feeding them has proven not to be a problem at all. Marble crays are to be counted among the omnivores, they devour vegetables and fruit as enthusiastically as frozen food, earthworms or conventional crayfish and fish food. If you keep these crays together with fish they won't despise eating one or the other of these cohabitants from time to time. Socializing them with bottom-dwelling fish generally cannot be recommended due to this. It's possible with livebearers like guppies if the keeper can live with some possible losses.
Socializing these crays with amphibians is not possible. Frogs and newts could get badly hurt when coming in contact with the claws. Turtles might put those crays on their live foods list rather quickly. Considering all this the most sensible thing to do seems to be keeping them in a dedicate tank or socializing them with dwarf shrimp. These seem to be able to live side by side with the crayfish unharmed. Trying to socialize them with snails tends to end in a very protein-rich crayfish diet; we could watch them cracking open very diligently even large apple snails and eating them.
The one thing that really distinguishes the marble crayfish from the other crays is their ability to reproduce through parthenogenesis. One animal kept single thus is a complete breeding group that may well exasperate its keeper's patience rather quickly. An adult female can "produce" about 200 young crays every 8 to 10 weeks when kept at a temperature above 16 °C (60 °F). So how do you deal with that much offspring when you don't want to explicitly breed marble crayfish?
Well, there are basically two possibilities. Either you feed the young breed to predators – if you have the pertinent predators at hand or takers for this kind of live food, or you prevent the young crays from hatching.
During the time we granted a marble crayfish asylum we resorted to both methods. When we had takers who wanted and were able to use the offspring as live food we let the cray lady carry her eggs to term, if we didn't have any potential takers we removed the eggs at an early stage by washing the entire egg package off.
This method has proved totally positive for us, however, it requires watching the cray daily in order to catch the gestation at an early stage. Within the first four days after the eggs have been attached to the pleopods (swimming legs) they can be removed without harming the mother crayfish. In order to wash off the eggs of a berried marble cray you best proceed as follows:
First you have to take the female out of the tank und put it into a small bowl or bucket filled with tank water so that the water level is about 15 to 20 cm above the cray. Then you take the animal in your hand from above so that you have a safe grip on the carapace with your thumb on one side and the fore, middle and ring fingers on the other; don't squeeze too hard.
In the following you turn the cray around under water so that you can see the underside and thus the eggs. The cray will try to protect the eggs with the tail fan, that's why you have to carefully stretch out the tail and hold it, leaving your thumb and forefinger free if possible so you can use those to wipe off the eggs.
Then you gently rub the eggs off the pleopods with thumb and forefinger of the hand holding the tail. Be careful here so you don't hurt the animal. The crayfish has to remain in the water for the entire procedure. If the eggs adhere too strongly you cannot do a thing, unfortunately, and have to let the litter hatch. Please deep-freeze the washed-off eggs before disposal or else fertile eggs might be released into nature and the already existent bastardization of fauna will be made even more pressing. When all the eggs have been washed off you can put the cray back into its tank and offer it some food. As marble crays tend to stop eating completely when they're berried the food might not be paid attention to right away. However, the cray will soon become aware that there are no more eggs to protect and will start taking food again. This can take a few hours or even some days.
However, if you decide to let the litter hatch you will get some interesting insights when watching the development from egg to mini cray.
Depending on the tank temperature this can be a pretty rapid development. We have been able to witness that eggs ripened to young crays within 14 to 17 days. Even after hatching the young crays live in close contact with their mother, as this species cares actively for its brood. The mother carries the young on her swimming legs for about 8 to 10 days after hatching. From there the young crays start exploring their habitat and at the beginning always return to their mother's swimming feet.
When they feel endangered the adult cray is their hiding place during the first days. If you take a marble cray that's just gathered all its young on the pleopods out of the aquarium it will throw off its entire brood at the moment of air contact, probably in order to get them out of danger as fast as possible. This is something you can make use of if you want to take a hatched litter out of the tank, thus avoiding complicated capturing activities.
The decision for or against keeping this crayfish species is up to you. Anyway, it would be desirable if all those people inclined to housing this cray did so rationally and responsibly.