Hmm, lots of conflicting on here, however.......
The advice from the lfs was that mine would be okay with my fish, as long as they were quick swimmers, my fish started disappearing fast.
Your crayfish is a scavenger and will eat anything it can find/grab so please dont put it into a community tank.
Live plants make a very tasty meal too so I've now switched to artificial ones.
My crayfish tends to be nocturnal and "sneaks up" on any fish which is resting/sleeping on the bottom, hence the loss of fish.
He now has his own 40l tank accompanied by half a dozen inexpensive neons which no doubt will make a nice meal if he catches them.
Feeding next, they will eat anything and everything.. flake, worms, snails and even fish poo. I tend to drop in some cucumber and carrot (weighted down), the odd bit of cooked chicken and raw red meat.
Please fit a tight lid, mine climbs the plants, heater, air hose but hasn't managed to escape yet.
He has grown in the last few months, but I haven't managed to catch him shedding his shell yet.
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Phil
Very much the beginner.