Over the few years that I started keeping Marbled Crayfish, I did a few experiments for my own edification. I am not a degreed biologist, but have been in the aquarium hobby for 50 years and have had a wide range of experience. Take this information for what it is worth.
Since I live in North Texas, we have a wide range of temperature extremes. In 2008, I set up a ten gallon and 20 gallon tank in our garage, and added some marbled crays to each tank. These tanks had filtration but no heater, and were on the same regular feeding schedule as my indoor tanks. This experiment was to take course over the period of a year.
That summer, as usual, all thermometers outdoors peaked (at 120 degrees, the tip top of all mercury based themometers). This included the thermometers in the shade. The garage was even hotter, from heat buildup day after day. The water thermometer reached over 100 degrees for each day for several weeks. To my surprise, all crays survived! They did not reproduce, and activity slowed quite a bit, but extreme heat did not kill them.
When fall and spring came, reproduction resumed and activity increased in general.
The winter of the same year, we had freezes, snow and ice. Without a heater in the tanks, we lost a couple of crays, but the majority lived. Again, activity slowed (movement, feeding) and reproduction stopped. The water temperature dropped to the 30’s and once even had ice crystals on the top of the water in the 10 gallon. But the animals survived.
So from that year, I must gather that marbled crays could certainly survive temperatures in lakes, if they could survive in a relatively shallow 10 gallon tank. However, in the same period, I noted that shipping the live animals (from inside aquariums) had a 50/50 survival rate, particularly in summer. During shipping, the crays are in sealed plastic bags, and put in a standard 8x8x8 box with a few packing peanuts as shock absorbers. The issues of shipping included warehouses and trucks which are always unregulated for temperature, and basically can boil in the bag which contains limited water and limited oxygen. Only a Texas based shipping company took the trouble to put the box in a refrigerator when not in transit, and the crays in those shipments survived. Shipment to colder states usually fared well, but in the coldest days of winter, the shipping process again had a 50/50 success rate. Warehouses and trucks are often unheated in transit. This is why I always tried to get overnight shipping to be chosen, but the cost of overnight shipping skyrocketed with increasing gas prices. Many people who wanted the animals could simply not afford overnight shipping. This is why I decided to limit the selling of crays to local individuals who could pick them up in person.
The Blue Marbled Crayfish
Many people have advertised blue marbled crayfish. Since I started selling from the original batch, to people who in turn sold offspring from their stock, I have seen Blue Marbled Crayfish advertised for sale. All Marbled Crayfish are clones, meaning they are identical in DNA. And all Marbled Crayfish contain blue and green colors, particularly as they age, and particularly in claws and legs, of the natural brown colored crays. However, like many species of miniature shrimp, it is the food which can cause a TEMPORARY color change. Color enhancing fish foods which contain astaxanthin and spirulina will alter the color (of some individuals – not all) to a very pleasing blue. It can range from a baby blue to a sapphire blue, to blue-green. The true blue Marmorekrebs crayfish are Marbled Crays, , and specially bred to retain the blue gene.
The Oscar Trial
In one aquarium, I decided to try and simulate what might happen in a natural lake situation. In a 55 gallon tank with a substrate of large white marble (from a garden shop, found in the bagged rock section) I had a colony of Marbled crays that was 4 years and ongoing with old, young, baby and pregnant members. This tank had the PVC tubes for pregnant crays. It was overrun, which happens in most Marbled Cray colonies. I had a beautiful tiger oscar (astronotus ocellatus, a cichlid) from another aquarium, who I raised from a baby to feed on Marbled Crays. In fact, it refused to eat goldfish and minnows, only wanting Marbled Crays. I moved this oscar into the Marbled Cray tank.
It took about 6 weeks for this Oscar to eat all the Marbled Crayfish. I then kept the oscar in the tank for 3 months, and would occasionally see the oscar “bite” and move the large marble gravel to get to any crays living in the substrate. Finally, there was nothing left. I stirred the substrate twice a week, along with regular water changes, until I could see no crays of any size, not even tiny babies. The tank was scrutinized by me as well as the fish, on a daily basis.
After I was satisfied the tank was devoid of Marbled Crays, I gave away the beautiful Oscar to a good person with a very large tank. I carefully watched the cray tank, and after a week, saw no activity of any kind. But at about 2-1/2 weeks after the oscar was gone, sure enough, tiny, tiny cray babies emerged from under the substrate. At first, they were very careful to poke out and look for danger (and food). Apparently, they were eating the gunk under the substrate, even though I was careful to stir up the tank and remove all detrius while the oscar was in the tank. What little there was left, served as food for newborn crays. Anything larger than newborn was eaten by the oscar, and he ate as many newborn crays as possible.
Now, that same tank is completely repopulated, some 6-8 weeks later, with full grown adults, young and babies, and of course pregnant crays. This tells me that these crays are survivors in the harshest of conditions. A side note here: we have all seen the horror stories about Marbled Crays ruining the ecosystem of waters in Europe. The Procambarus species and sub-species is based in North America. This means that while the Marbled Crayfish can essentially come back from being wiped out, it also means that it has to compete with other similar Procambarus species crays, if found in the wild. In the bigger picture, they would provide a huge resource of food to lake fishes, turtles, and other animals in the ecosystem. And at the same time, they would have to compete with their cousins for food and shelter.
This is why I feel that the Marbled Crayfish might just be “the” perfect feeder animal for use in aquariums, as well as in Aquaponics systems where tialpia and bass are at the top of the food chain. I personally feel that this animals would simply join in the balance in ecosystems of lakes and streams in North America, and not be a hazard, any more than other Procambarus species crayfish. I believe that wildlife divisions of government do over-react to the tainted threat word of “invasive species”. After all, many (if not most) of the animal kingdom is in place because it migrated from another place, making practically everything an “invasive species”. Fish, snails and crustaceans are naturally carried from one place to another by birds and by other means. The words “invasive species” are a knee-jerk term which allow politicians to react, but man is never going to stop the migration and evolution put in place by nature.