I'm not sure who said you couldn't keep smaller fish with a lionfish. Lionfish, while quite capable of handling themselves, are very non-aggressive. They mark out a small section of the tank for themselves and then hang out there. Currently, I have two lionfish.
My fuzzy dwarf lion is in a 72 gallon bowfront tank with a small valentini puffer, a jawfish, a gobi, a koran angel, three cleaner shrimp, a small clown (can't remember type offhand, starts with an O), about 75ish or so of both snails and crabs and he does wonderfully. My one complaint actually is he hides so much that I can't see him as often as I like! (He sleeps during the day and finds himself a nice hole to sit in).
My other lion is a full size and sits in a 440 double bowfront with a school of nassau tangs. The first day he went to each one and brushed up on them. I thought he killed them all, but before I had a chance to clean the corpses out, they were all swimming around again, albeit on one side of the tank. He was basically just letting them know where his territory was. That tank has a full compliment of smaller fish too, with a couple gobis, jawfish and the like to keep it clean.
Lionfish are just simply beautiful fish, and despite their formidable looks, they're rather timid. They lay on rocks to guard their bellies and simply refuse to move in fear of making themselves vunderable. They're also active only at night, so if you do daylight cycles with your lights (that's where you have a set of blue lights come on before and go off after your white lights to simulate sunup/sundown), you're gonna see them primarily during the "sundown" phase.
Also, they don't NEED live food. My lions both eat frozen food just fine. Perhaps that helps with keeping him from eating my other fish, but after about 4 weeks they were both perfectly happy eating it as opposed to live food. While live food is more entertaining to watch, it's also a hassle for me as I can't see myself keeping a tank just to store live food in.
Hope this helps some!
-Ryan
