No fish are completely crayfish safe, a crayfish will attack and atleast hurt most fish as they are pretty tough little creatures. Crayfish are also very hardy and you probably wouldn't find any problems catching one and putting it in a tank as far as surivavability goes. They will eat live plants vigorously and, like pretty much any aquatic creature it's best to keep it in extremely clean filtered water. They should be kept alone unless there is adequate space, probably at least 10 gallons each, and adequate terratorial claims, 1-2 caves per crayfish and even then crayfish will battle, if one is molting, the other will probably kill it. The same thing must be watched when keeping fish, when a crayfish molts it can end up as lunch for some larger fish. Hope this info helps.