LionFish says......
Avoid live foods. They are bad in nutrition and if you feed too much live food they can die. Well, try to get the lion to eat by using a feeder stick. Get a small clear tube or string and tie a piece of food to it and move it around to make it look alive. After awhile you won't have to do this. A lions diet should be varied and should consist of small meaty foods such as: krill, shrimp, choppe squid, mussel or clam meat, and silversides. By doing this it will greatly increase your lion's health. Also, what was your fish store feeding it when you bought it? If you feed what they fed it, it usually works best.