When I was researching these guys, the information I got was that they are better off in a species tank. Small fish are potential prey and large and aggressive fish may attack the crayfish.

They will eat anything at all, from flakes to plants to worms to pieces of fish, and are opportunistic feeders, grabbing anything that passes close enough. Don't keep more than one, unless you have a very large tank. They are territorial and a larger one may kill a smaller specimen. The North American kind are coldwater so no heater necessary.

They come in all kinds of beautiful colours (I think the blue is most beautiful), and I think if you have a spare 20 gal tank, you might enjoy one of these creatures. They're interesting and like to totally rearrange their tanks to suit their taste! Just make sure you have a well fitting lid with no openings, or you may find the crayfish wandering around your house!