Thanks both of you.
Well, i don't really believe in "required tank sizes" per say. In my opinion, a tank where i can keep nitrates at 0-5, and the fish can move comfortably around, is a big enough tank.
Other people will have different opinions and stick to a wikipedia type recommendation.
But they can get 20"+, and can be real killers. So you will need a bigger tank for one than your standard firemouthe's tanks.
Don't think i helped much, but it's the best i can do for an answer.