I have had a couple of wild caught crayfish in the past couple of months...
I had one that was about two inches long in a 10g w/ some feeder guppies. He did snag a few of them over time, but not many. One recommendation is that you make sure the tank lid is on securely and there are no smaller holes in the top. The lid on my 10g was cut out for a larger filter and had an airline fed through it. After a weekend away, I found it laying on the floor, dried out. He must have climbed up the air line. So again, make sure he has no way of getting out, or it will.
The other one is my 55g with a few large rock caves and lots of rocks everywhere else with my sev & BP. If your crayfish is anything like either of mine, get used to not seeing it very much. The cray in my 55g spends a lot of time digging tunnels under rocks and pots for places to hide. I can go three or four days without seeing him roam the tank. I usually target feed mine algae discs and presoaked krill. From what I've witnessed, they appear to like low light levels. The one in my 55g is a lot more active with the lights off, actually.
..just the other day I was watching one of my BP's fight with him - the crayfish actually latched on to the fishes gills and got drug around the tank for a few seconds.
Good luck keepng it! -hopefully there'll be no problems
BobRoss
