These are an interesting breed, sort of a frankenfish. No one knows where they came from, but the conventional wisdom is that they came from an accidental hybridization between two different species of north American crayfish.
Marmorkrebs are the only known species of crayfish that are all female. Each female is identical to the mother and she produces fertile eggs without mating.
Here is what they look like:
They are non-aggressive for crayfish. Mom does not eat her young and the babies do not cannibalize each other. They are cold hearty and can live under ice. When a female berries, she can have upwards to 300 babies and can do so about every 3 months. Mine seem to live about 2 years. They start reproduction at around 4 months.
They don't get big, maybe 4" but are probably more than big enough to eat. Match that with being able to pack them together without a lot of trouble and these may be a winning combo. I'm thinking a screened bottom to keep the fish and crays apart would work well to co-crop them.