i wish i had a 200g tank. but i don't think i'd put oscars and crayfish in it. besides, my crayfish is evolving lungs. he'll soon be sitting beside me at the other computer with a cup of coffee, ripping off credit card companies and buying stock...biding his time and waiting for his chance to bring down the man!
info...let's see...temp effects metabolism to a more visible level than with fish. will eat ANYTHING. in warmer waters, they are capable of catching fish as fast as zebras. they molt frequently when they're small, but this slows down as they get larger. mine is now 5-6 inches, only molted twice since may, both times were after i moved and his water was a bit warmer. during this time they are sensitive to attacks from fish, other crayfish, etc. this is the best argument for keeping only one, unless the tank is 20+ gallons and you have plenty of hiding spaces for them. i think they prefer sand or small gravel, as they can dig around. bitey used to have a favorite rock he would dig under, which was cool to see.
now i have him in a temporary rubbermaid tank while i set him up in a 10g of his own, the water is lower, so he can stand up and reach to the top of the water with his claws! he follows a trail of pellets / flakes / whatever around as i deposit it in the tank, waving his claws at me! that's a lot of fun...as crayfish go. i wouldn't recommend getting pinched, i've had a couple close encounters but have been lucky. with his current size, i think it would hurt. i generally try to corral bitey into a cup when i have to move him. he would just wreck a net anyway.
anything else you want to know? i might be able to answer.