I highly recommend that you take them out of the pond ASAP as the Marmorkrebs is a highly invasive species and should NEVER be placed outside where may escape into the local eco system and cause the destruction of native species and disruptions on a major scale. Please scour the pond bottom to make sure they did not reproduce as they reproduce asexually--even missing one crayfish is a bad thing.
They do fine in home aquariums and are generally not aggressive to fish. They often become food for aggressive fish. The marmorkrebs are opportunistic feeders though and will eat fish if they can get them. They go great in goldfish tanks and can live in tanks with heaters or without. The marmorkrebs can adapt to many different environments and this is one reason that they are such an invasive species. They also eat many plants--they are lawnmowers IMO.
