I've kept crays in my tanks for a few months, and they seem to be scavengers first, hunters second. Keep them well fed with a variety of foods and they should be happy. One of my more aggressive ones would often share accommodations with my 2.5" striped raph. I don't have any crays at the moment as one got eaten, and the other went on a sojourn to the basement where he met his untimely demise with the "dry". But I did put a nasty looking Yabbi on hold today and will be picking him up just as soon as the green tank is clear again now that the sharkies are feeling better.
One thing to remember though, is that there are thousands of species of crays, all with different behaviors, and I can only speak for the ones I procure at the local bait shop - this yabbi may be a recipe for disaster. But time will tell.
A bigger problem is that most tropical fish prefer temps around 78-80+. I know the crayfish we have in the wild here live in cold water environments, closer to 60-70 in the streams and rivers in hte summer. I don't know how they'd fare living in an 80 degree habitat.
the high temp makes their metabolism faster and they need an abundan source of food.. tahts not good.. i guess thats why a handfull of people say high temps equal an aggressive crawfish
Two comments about crayfish and tank temp. Firstly, one day my son was playing with the control on the heater in one of the smaller tanks. The temp hit around 95 overnight. The cichlids were doing backflips, but the crays were just chilling. They don't seem to be affected greatly by excess of heat.
As for heat feeding their hunger, it's actually proven to be the inverse in my experience. I kept one in an 80 degree tank for months, and then when I needed to treat the tank, I moved her to a cold water tank with a goldfish. Her hunger was insatiable and eventually led to her demise when she decided to look outside the tank for food.