I have 2 large (5-6" length) crayfish in a 125g tank with 2 florida gar, 1 shortnose gar, an indo datnoid, a venezualan pike, an albino channel cat, and a red snook. They seem to get along fine. The crayfish hang out on/under the driftwood (although sometimes they venture around on the substrate), the fish don't bother them, and they don't bother the fish. If a fish gets too close, they might reach up and tap the fish with a claw, but they've never (that I've seen) snapped at a fish. The fish nosed them around for a few minutes when I first put them in the tank, but now they pretty much ignore them.
I think it helps that the crayfish are larger, and that all my fish (including the crayfish) are well fed. I make sure to target feed the crayfish every couple of days to make sure they're eating.
Edit: I also had one of them with some green sunfish and a bluegill, and they ignored each other as well. That cray was eventually transferred to my 125g, which is the one I talked about above.
I think it helps that the crayfish are larger, and that all my fish (including the crayfish) are well fed. I make sure to target feed the crayfish every couple of days to make sure they're eating.
Edit: I also had one of them with some green sunfish and a bluegill, and they ignored each other as well. That cray was eventually transferred to my 125g, which is the one I talked about above.
