Rule of thumb is that fins and claws don't mix.
I was once in a LFS who had put a lovely halfmoon Siamese Fighter in with an electric blue lobster (a type of crayfish). The Fighter had lost 3/4 of its tail. I went back to the same LFS the next day, and the Fighter was no longer there. I'm sure you can draw your own conclusions.....
Yeah that's what I heard of too so far.It must not be a fish that sleep or stays at the bottom / needs to be a non-agressive fish ( when the cray molts it is at risk), It needs to be quick and agile to stay away easily from the crayfish and similar water settings.
There's a lot to look for
The whole crayfish thing sprouted in my head after a few months of wanting a fishtank but no real idea what fish I wanted. So my parents were having lobsters for diner (lol Yeah...) and I wondered if it was possible to keep some in a fishtank and when I found out yes (different species though lol) That was the signal in my head, a cool little creature like that would be perfect for me!
I still hope I'll find a blue Clarkii since they keep a relatively small size for a crayfish compared to the Alleni or other species that can reach 30-40cm long but they're hard to find. Otherwise I'll go for a white one, they're really nice too and will look awesome in my tank.